Annual Conference Abstracts //

MeDe Innovation

28.01.16 //

2 3

Session A: Manufacturing at the point of need - Chaired by Professors Kenny Dalgarno and Phil Coates

A1 - Regenerative strategies in orthopaedics; right patient, right treatment, right time - Prof Andrew McCaskie

A2 - Manufacture and assembly of biopolymer-bioceramic hybrid composites - Miss Natacha Rodrigues

A3 - Shape memory soft tissue fixations for arthroscopic delivery - Dr Fin Caton-Rose

A4 - Development of materials for arthroscopic delivery - Mr Simon Partridge

A5 - Design and fabrication of 3D printed POSS-nanocomposite-based lumbar cage for spinal fusion - Dr Tiziano Serra

A6 - Droplet based deposition for in clinic bioprinting - Dr Matthew Benning

Registration and networking (tea and coffee available)

Welcome and introduction – Prof John Fisher

Poster elevator pitches – Chaired by Professor John Fisher

Session A: A7 - A14

Session B: B14 - B21

Session C: C4 - C11

MeDe Innovation Network Update - Rowan Grant

Lunch and poster viewing

Poster presenters available from A7-B17

Poster presenters available from B18-C11

Session B: Manufacturing regenerative devices, biological and biomimetic scaffolds – Chaired by Professors Paul Hatton and David Grant

Nanoparticles and medical devices

B1 - Continuous hydrothermal synthesis of new nanoscale hydroxyapatite morphologies - Prof Ed Lester

B2 - Integrated molecular design of melt-processable bioresorbable engineering nanocomposites for health-care - Miss Kirsty Walton

B3 - Rapid mix preparation of biomimetic nanoscale hydroxyapatite for biomedical applications - Dr Caroline Wilcock

B4 - Biomimetic nano-structured materials for bone repair and regeneration – Industrial perspective - Dr Becci Goodchild

9.30

9.55

10.00

10.15

10.30

10.45

11.00

11.15

11.30

11.55

12.00 12.30

13.00

13.30

13.35

13.40

13.45

13.50

13.55

14.07

14.15

14.23

14.30

14.37

14.44

14.51

15.00

15.30

15.35

15.45

15.55

16.05

16.20

Page No.

Page No.

7

8

9

10

11

12

13-20

35-42

47-54

22

23

24

25

B5 - Continuous hydrothermal synthesis of nanoparticles – Scaling up - Dr Selina Tang

Resorbable composite research

B6 - Bioresorbable composites for bone fracture repair applications - Dr Ifty Ahmed

B7 - Development of bio-active glass products and production processes - Dr Malcolm Gledenning

Spinal medical devices

B8 - Trabecular directionality in three dimensional remodelling of bone graft substitute in cervical fusions - Dr Donal McNally

B9 - Porosity measurements in three dimensional remodelling of bone graft substitute in cervical fusions- Dr Scott Johnson

Surface modification and scaffolds

B10 - Layer-by-layer: a bioengineered tool to enhance specific biological activities at nanoscale - Dr Piergiorgio Gentile

B11 - Hydroxyapatite functionalised using a coupled heparin-binding peptide - Mr Joss Atkinson

B12 - Development of 3D polymer scaffolds for biomedical applications; degradation and compression properties - Dr Reda Felfel

B13 - The JRI approach to innovation in Med Tech- Dr Sarrawat Rehman

Break and poster viewing

Session C: Stratified design and manufacture of orthopaedic implants – Chaired by Professors John Fisher and Ruth Wilcox

Overview of Challenge 1: Stratified design and manufacture of orthopaedic implants- Prof John Fisher

C1 - Computational modelling of patient variation in the spine: a route to stratified device design and testing - Prof Ruth Wilcox and Prof Philippe Young

C2 - Application of a computational and experimental wear simulation approach to new product development - Dr Louise Jennings and Dr Adam Briscoe

C3 - Effect of surgical variations on the function and tribological performance of hip joint replacement - Dr Mazen Al Hajjar and Dr Jonathan Thompson

Panel discussion

Closing comments - Prof John Fisher

26

27

28

29

30

31

32

33

34

44

45

46

4 5

MeDe Innovation (The EPSRC Centre for Innovative Manufacturing in Medical Devices) is addressing the future opportunities and challenges in the design and manufacture of medical devices.

Our innovative design and manufacturing advances centres around three research focus areas: implants, biomaterials, and regenerative devices for the treatment of musculoskeletal disease; where there is a growing demand for increased precision to deliver improved reliability and outcomes of medical devices.The centre activities are addressing two grand challenges:• Manufacturing at the point of need• Stratified design and manufacture

The global market for medical technologies is set to exceed $500bn per year by 2018, with a UK industry base valued at £18bn per year. Musculoskeletal implants, biomaterials and the emerging field of regenerative devices are major strengths in the UK, addressing a global market estimated to grow to $75bn by 2020.

The needs of an ageing population, the expectations of fifty active years after fifty® and the growth in healthcare markets in developing economies provide a real opportunity for growth in this part of the medical device technology sector.

However there are increased expectations and demands for enhanced lifetimes, cost effectiveness, more consistent patient outcomes and improved reliability. Stratification and increased precision, leading to improved reliability, is a key challenge in all areas of medicine and future opportunity for medical devices.

As we approach the mid-term of MeDe Innovation, the conference will report on progress and advances in research, innovation, and translation of its three focus areas:• New approaches to manufacturing at the point of need• Manufacturing regenerative devices, biological and biomimetic scaffolds• Stratified design and manufacture of orthopaedic implants

The conference will include presentations and posters from industry, regulators clinicians and academic researchers, panel discussions, poster pitches and networking opportunities.

Showcasing the success of our Centre to date is an exciting opportunity for all involved in our research, and MeDe Innovation will use the event to accelerate plans, increase the profile of innovative manufacturing approaches, and motivate more organisations and individuals to become involved in the Centre.

Prof John Fisher CBECentre Director

Foreword from the Director Acknowledgements

It is our pleasure to present the 2016 abstracts of oral and poster presentations from the MeDe Innovation Annual Conference 2016. We would like to take this opportunity to thank once again all of the participants in the conference – invited speakers, presenters, and audience alike.

We would also like to extend our gratitude to our External Advisory Board who have generously shared their time and expertise to help us shape our research and Centre activities over the past two years. It is at the 2016 annual meeting that we say a final thank you to Mr Brian Jones, Chairman of JRI Orthopaedics Ltd. We would like to gratefully acknowledge the dedication from Mr Jones in leading the External Advisory Board for MeDe Innovation since its first meeting in 2013.Finally, we would like to thank our colleagues at each of the MeDe Innovation academic partner centres for their responsiveness and contributions; and support of participants and collaborators; and our administrative colleagues who contributed vastly to the organisation and success of the conference.

6 7

Osteoarthritis causes joint destruction and sufferers can experience debilitating pain and restricted movement. In this talk, key challenges will be considered and how advances in orthopaedic surgery can address them by repairing or regenerating bone and joint tissues – often called tissue engineering or regenerative medicine. The talk will highlight strategies using advanced materials, molecules and cells can encourage repair in the body.

The talk will also indicate how a bench to bedside research programme, building up clinical evidence, is key to successful adoption into healthcare. In particular, it will discuss the importance of patient stratification and experimental medicine approaches.

REGENERATIVE STRATEGIES IN ORTHOPAEDICS; RIGHT PATIENT, RIGHT TREATMENT, RIGHT TIME

#A1

Prof. Andrew McCaskieawm41@cam.ac.uk

University of Cambridge

Session A // Contents

Regenerative strategies in orthopaedics; right patient, right treatment, right time

Manufacture and assembly of biopolymer-bioceramic hybrid composites

Shape memory soft tissue fixations for arthroscopic delivery

Development of materials for arthroscopic delivery

Design and fabrication of 3D printed POSS-nanocomposite-based lumbar cage for spinal fusion

Droplet based deposition for in clinic bioprinting

Harnessing micro-injection moulding and Poly-ether-ether-ketone (PEEK) to manufacture orthopaedic trauma implants that resist microbial colonisation

Processing and characterisation of novel bioceramic formulations using indirect powder-based 3D printing technology

Cell encapsulation for bio-ink formulation

Compression screws for the fixation of small bones and bone fragments using biocompatible, bioresorbable, body-temperature reverting, plasticised shape memory polymers

Session A // ContentsApatite-Wollastonite glass ceramic scaffolds for osteochondral tissue engineering applications

Polyether ether ketone (PEEK) crystallisation phases analysis in microinjection moulding for anterior cervical decompression and fusion

Viscoelastic mechanical optimisation of functionally graded cell-conducting materials for osteochondral implants

Synthesis of tendon tissue-like grafts using a hybrid PHBV-Collagen material

7

8

9

10

11

12

13

14

15

16

17

18

19

20

8 9

Introduction: One of the major challenges in orthopaedic surgery is the repair of osteochondral lesions, which affect both articular cartilage and the underlying subchondral bone. Among the possible therapies, tissue engineering of osteochondral scaffolds has shown as a potential method for the treatment of such defects. One of the current approaches for matching the biomechanical and biological properties of osteochondral tissue relies on the development of an osteochondral construct in a single integrated scaffold. The use of Additive Manufacturing (AM) has been growing in recent years due to its ability to directly print 3D porous scaffolds with patient customized geometry, solvent-free, controlled and interconnected porosity. Aims/Objectives: This works aims at developing an innovative manufacturing process for the fabrication of a biomimetic biphasic osteochondral scaffold. This consisted in three steps: 1) fabrication and characterisation of a porous polylactic acid (PLA) scaffold for the trabecular bony phase; 2) fabrication and characterisation of a porous apatite wollastonite glass-ceramic (AW) scaffold for the cortical bony phase; 3) assembly of the fabricated parts to obtain a hybrid composite structure.Methods: The three step manufacturing route consisted of: 1) laser cutting of a PLA scaffold from a 3D printed porous PLA bar previously prepared with a fused filament fabrication commercial machine (Ultimaker2); 2) AW porous discs were produced by a Z310 Plus 3D printer (Z-Corp, USA) using prepared AW and Maltodextrin powder, followed by a sintering process at 1150ºC for 2 hours. 3) assembly of the hybrid biopolymer-bioceramic composite structure with two different approaches: i) ultrasonic welding and ii) thermal fusion. Mechanical properties, an in vitro degradation study, and SEM were used to characterise the materials. Results: 1) The laser cut PLA scaffold obtained in step one presented a well-defined and interconnected structure with a uniform open pores distribution with a PS in XYZ-axes of 550-620 µm and 60% porosity. The average compressive strength and modulus of the PLA scaffolds was approximately 13 MPa and 280 MPa, respectively. After 10 weeks immersion in PBS, the PLA scaffolds scaffold dry weight, Mw and compressive properties values did not show any significant decrease. 2) The 3D printed A-W scaffolds were charaterised by an interconnected porosity of ~56%. Shrinkage of 20% was observed after sintering of the A-W discs. 3) SEM characterisation of the hybrid composite interface, suggests a good integration of the polymer and ceramic parts for both bonding approaches used. Conclusions: Overall the laser cut PLA scaffolds fabricated in step one presented well-defined and open architectures, with potential for trabecular bone replacement applications. When 3D printing the A-W discs in step two, compensating for shrinkage is key. Ongoing work is focussing on studying the interface shear strength and the in vitro degradation behaviour of the assembled hybrid composite structure. Future work will focus in the validation of fabrication of customised scaffolds for large osteochondral defects with the 3-step manufacturing route described here.

MANUFACTURE AND ASSEMBLY OF BIOPOLYMER-BIOCERAMIC HYBRID COMPOSITES

#A2

Miss Natacha Rodrigues n.rodrigues2@ncl.ac.uk

Newcastle University

Professor Kenny Dalgarno (Newcastle University) Matthew Benning (Newcastle University) Javier Munguia (Newcastle University) and Naif Alharbi (Newcastle University)

Solid phase orientation of polymers is well known for imparting significant property improvements. It is also an attractive route to making ‘shape memory’ products which have potential for applications such as cementless soft tissue fixations. We have extensive research into a range of polymers; the focus here is on bioresorbable polymers (PLAs and modified PLAs). We describe the die drawing process to make oriented PLA samples. Choice of draw ratio fixes the recovery behaviour, so providing a route to ‘tailored’ property products, for example, matching the stiffness of bone.

It is increasingly recognised that the properties of polymers depend on their chemical nature, and the structure which is imparted during processing. Solid phase orientation processing of polymers at temperatures above Tg but below their melting point, provides the major route to imparting a wide range of polymer molecular orientation. It unlocks the potential of molecular orientation for the achievement of a range of enhanced physical properties, including enhanced stiffness, yield strength and creep resistance, anisotropy of thermal conductivity, barrier properties and even drug elution. Fibre or tape drawing, solid phase extrusion and die drawing are the major routes for the manufacture of oriented products, with a range of draw ratios (strains) from low (around 2) up to very high (>20) levels, depending on the polymer selected.

The die drawing process has been utilized to create devices which change shape in-situ on exposure to temperature or, potentially, body fluid, allowing the device to adapt to the surrounding bone topology. Prototype devices have been manufactured from resorbable (modified PLAs) or inert polymers, with inorganic particles and suitable plasticisers, all having known clinical history. The devices may be programmed to mechanically function (e.g. expand to form a fixation in bone) and then degrade to expose known inorganic salts/scaffolds which can be used to promote osteogenesis. In the case of medical implants such as tissue fixations, the shape recovery typically needs to take place at an appropriate temperature to avoid tissue damage (less than ~50C), or - more challenging (but part of our research) - be driven by exposure to body fluids, and to occur in an acceptable timescale to the operating clinicians (e.g. less than 15s), and to retain fixation strength over required timescales (months for bioresorbables, permanent for non-resorbables).

In a further class of medical devices, the die drawing process has been further developed in our laboratories to produce precision small diameter biaxially oriented tubes with wall thicknesses less than 150 microns for application in arterial stents.

Full experimental optical and thermal imaging is used along with computer modelling to help optimise the manufacturing process. We also have interest in drug eluting implants, and are exploring the effects of orientation on anisotropic drug elution. Other manufacturing technologies, including micromoulding, are being investigated for imparting orientation to achieve shape memory properties in part of a net shape product.

SHAPE MEMORY SOFT TISSUE FIXATIONS FOR ARTHROSCOPIC DELIVERY

#A3

Dr Fin Caton-Rosep.caton-rose@bradford.ac.uk

University of Bradford

Prof Phil Coates (University of Bradford), Dr David Farrar (Smith and Nephew), Dr Dimitrios Vgenopoulos (University of Bradford), Glen Thompson (University of Bradford)

10 11

Biomaterials refers to an assortment of materials designed to repair, replace or enhance tissue function. Bone tissue repair requires load bearing materials which encourage implant integration with the surrounding tissue to contravene stress shielding. Transient replacement of bone using bioresorbable ceramics or polymers is also beneficial allowing the tissue to remodel and avoids the risk of excessive fibrosis. Minimally invasive arthroscopic surgical techniques are limited by tube diameter. Consequently injectable materials are ideal for an arthroscopic treatment approach. Solidification systems can often contain toxic components in its liquid form. One route to mitigate this is to use a degradable membrane to segregate potentially toxic components of the injectable from the implant site.

2-hydroxyethyl methacrylate (HEMA) monomer (viscous liquid) was used to optimise photo-polymerisation solidification system. Camphorquinone (CQ) was used as a photoinitiator, ethyl 4-(dimethylamino) benzoate (DMAB) as a co-initiator and triethylene glycol dimethacrylate (TEGDMA) as a cross-linker. Samples were cured in an in house PTFE mould and shielded with nitrogen. 1mm HEMA disks and 6mm multi-layered plugs were fabricated. Degree of conversion (DOC %) was calculated from ATR-FTIR spectra of uncured and cured samples. Equilibrium water content (EWC) was performed to determine crosslinking density. Cytotoxicity of monomers were assessed using an MTT viability assay with human telomerase reverse transcriptase modified mesenchymal stem cells.

Results demonstrated an adequate DOC of 60% following 60 seconds of exposure to 1000 mW / cm2 with 1% wt / v CQ and 1% wt / v DMAB. EWC was similar for all compositions at ~39%. Cytotoxicity revealed <50% cell viability with <1% v/v HEMA monomer concentration. This has demonstrated that the processing route can produce devices with appropriate volumes of material in clinically relevant timescales. Work is continuing with novel photocurable material formulations based on methacrylate terminated poly (L-lactide) 2-hydroxyethyl, which will be investigated using a printed array to optimise compositions and curing parameters. In addition poly glycerol sebacate (PGS) biodegradable elastomer is being investigated as a resorbable exclusion membrane.

DEVELOPMENT OF MATERIALS FOR ARTHROSCOPIC DELIVERY

#A4

Mr Simon PartridgeSimon.partridge@ncl.ac.uk

Newcastle University

Kenny Dalgarno (Newcastle University)

Introduction: Spinal fusion is the gold standard surgical procedure for degenerative spinal conditions when conservative therapies have been unsuccessful in rehabilitation of patients. Current techniques and instruments for lumbar cage fusion can be invasive and disruptive to the surrounding tissues. New strategies are required to improve biocompatibility and osseointegration of traditionally used materials for lumbar cages. Furthermore, new design and technologies are needed to bridge the gap due to the shortage of optimal implant sizes to fill the IVD defect. Within this context, additive manufacturing represents a breakthrough for the capacity to fabricate anatomically-shaped medical devices.

Aim: The goal of this study is to design and manufacture a 3D printed lumbar cage based on POSS-nanocomposite biomaterial for lumbar interbody fusion. ObjectivesThe process of fabrication and testing of a novel, anatomically shaped, cage was divided into three stages: first, optimization of cage design and 3D-manufacturing process; second, morphological -structural analysis and mechanical characterization of the developed cage; and, thirdly, in vitro biological evaluation.

Methods: Optimizations of the design via in silico analysis and cage’s printing parameters were opportunely settled. A commercial polycarbonate (PC) filament was used to print anatomically shaped cage. Coating procedure with thin film of nano hydroxyapatite (nHAp) / POSS-PCU was conducted. The achieved construct was characterized via SEM, contact angle, µCT, AFM and compressive test in order to examine its surface morphology, wettability, architecture, and mechanical properties. Finally, an in vitro biological evaluation of the developed cage by seeding adipose derived stem cells (ADSCs) was carried-out combining metabolic activity and immunofluorescence assays.

Results: In silico analysis, was a powerful method to preliminary test cage design and to find an optimal value of filling density, which was also confirmed by µCT analysis. Morphological examination by SEM of the cage’ surface coating showed homogeneously dispersed nHAp particles embedded in a biocompatible POSS-PCU matrix. Addition of hydrophilic nHAp strongly increased the surface wettability of the cage. Mechanical evaluation showed comparison between mechanical properties of trabecular bone and cage analysed. Similar behaviour was observed in term of metabolic activity and cell morphology for materials analysed demonstrating that the addition of nHAp was not cytotoxic for ADSCs so that can be used for coming studies.

Conclusion: Design optimization based on computational and experimental analysis combined with the 3D printing technique and using POSS-nanocomposite is a promising method for the development of biocompatible lumbar cages, with sufficient mechanical properties to support lumbar interbody loads. Finally, the described methodology represents a scalable, faster and inexpensive way to fabricate customizable anatomically shaped intervertebral cages.

DESIGN AND FABRICATION OF 3D PRINTED POSS-NANOCOMPOSITE-BASED LUMBAR CAGE FOR SPINAL FUSION

#A5

Dr Tiziano Serrat.serra@ucl.ac.uk; d.kalaskar@ucl.ac.uk

University College London

Dr Claudio Capelli (University College London), Dr Julian Leong (University College London), Prof Kenneth Dalgarno (University of Newcastle), Dr Deepak Kalaskar (University College London).

12 13

The ability to construct mechanically functional tissue scaffolds, containing a plurality of cell types within a well-defined 3D architecture is a significant and currently unrealised goal for tissue engineering. The problem is twofold; creating bioinks which allow for reliable printing while maintaining cell viability; and the formation of three dimensional (3D) structures consisting of both structural and cell based materials.

Bioinks: A piezoelectrically actuated drop-on-demand (DOD) printing system has been used to deposit electrostatically stabilised cells from a human osteosarcoma cell line (U-2 OS), and the effectiveness of a polyelectrolyte cell encapsulant to maintain cell dispersion within a bio ink was assessed. Results indicated the dispersion and printability of PLL coated cells was significantly better than that of uncoated cells, leading to printing with good repeatability

Structural Materials: Photo-curable methacrylate based polymers have been deposited using the same DOD printing system used during bioink printing experiments, but adapted to provide blue light curing. Simple three dimensional structures consisting of stacked ‘log pile’ type filaments were successfully deposited and photo cured. Electromagnetically operated micro valves arranged in ‘V’ formation have been used to impinge mix two low viscosity droplet streams resulting in a third higher viscosity material. Alginate hydrogels were formed using two microvalves mounted left and right actuated at between 0.5 kHz and 1kHz producing an impinging droplet stream of alginic acid sodium salt solution and calcium chloride solution respectively. Early trials of the impingement mixing of hydrogels have shown that suitable mixing for gelation occurs and simple 3D deposition is possible.

This range of new processing methods gives a set of processing tools which can process cells, soft materials and hard materials, and which will be integrated to rapidly create, at the point of need, a wide array of complex biocomposites for musculoskeletal applications.

DROPLET BASED DEPOSITION FOR IN CLINIC BIOPRINTING

#A6

Dr Matthew BenningMatthew.Benning@NCL.AC.UK

Newcastle University

Kenny Dalgarno, Ana Ferreira-Duarte, Ricardo Ribeiro, Sarah Upson, Matt German, Sotiria Toumpaniari (all Newcastle University)

Introduction: More than 2 million people/year in the UK suffer a bone fracture that is addressed using mainly metal implants. These attract microorganisms representing niches for medical device associated infections. In the case of trauma and external fixators, pin-track infections have an overall incidence of approximately 30% and serious complications may follow failure of the bone-pin interface including pin loosening, non-union fracture and chronic osteomyelitis. Antimicrobial strategies supplemental to systemically administered antibiotics often focus on modifying the surface of the medical device. In this direction, the aim of this study was to evaluate the feasibility of engineered surface manufacturing, through micro-injection moulding of Poly-ether-ether-ketone (PEEK), for the preparation of orthopaedic trauma implants that prevent microbial colonisation. Materials and Methods: VICTREX® PEEK 150G, without reinforcement, and 30% carbon or glass fibre reinforced; PEEK 150CA30 and PEEK 150GL30 respectively, were micro-injection moulded using a Wittman Battenfeld Micropower 15 moulding system and flat or nanostructured mould inserts. The moulding process parameters were determined using a dedicated data acquisition system. The moulded structures were assessed in terms of geometric uniformity using surface measurement techniques including Confocal Laser Scanning Microscopy (CLSM) and an Asylum Atomic Force Microscopy (AFM). The mechanical properties of the moulded components were measured using a Hysitron nanoindentation system. Contact Angle Measurements (CAM) were used for the evaluation of the materials surface energy. The wear performance of the moulded components was evaluated using a Biomomentum system and abrasive materials. The non-fouling and antimicrobial performance of the moulded components, before and after wear testing, was assessed against initial bacterial adhesion and subsequent biofilm formation of both Gram-positive and Gram-negative bacterial strains, using the Colony Forming Units (CFUs) counting method and a number of microscopies; AFM, CLSC after live/dead staining and Scanning Electron (SEM). Results: Geometric characterisation of the moulded PEEK surfaces showed excellent replication of the mould inserts at the nanoscale. The mechanical properties of carbon reinforced PEEK match those of cortical bone and this was not affected by the presence of nanostructuring. The CAM showed higher wettability of the structured surfaces in comparison to the flat. In terms of the antimicrobial performance, it was shown that the flat surfaces retained more bacteria that were accumulated, while the structured ones prevented bacterial adhesion and biofilm formation. Worn samples slightly increased bacterial adhesion in comparison to the non-worn, showing the resistance of PEEK to wear. Discussion: These preliminary data suggest that micro-injection moulding can be successfully employed as a surface modification technology of composites at the nanolevel. Nanostructuring PEEK and substituting some of the metallic implants that are currently used appear as promising strategies for the manufacture of orthopaedic trauma implants that resist microbial colonisation, without the use of antibiotics. Acknowledgments: Professor Peter Giannoudis is acknowledged for valuable discussions in the area of orthopaedic implant associated infections and Dr Pete Twigg for his help with the wear testing. This work was funded by MeDe Innovation, the EPSRC Centre for Innovative Manufacturing in Medical Devices, under a “Fresh Ideas” Feasibility Study Funding Award.

HARNESSING MICRO-INJECTION MOULDING AND POLY-ETHER-ETHER-KETONE (PEEK) TO MANUFACTURE ORTHOPAEDIC TRAUMA IMPLANTS THAT RESIST MICROBIAL COLONISATION

#A7

Dr Maria G. Katsikogiannipcatonro@bradford.ac.uk

Advanced Materials Engineering, Faculty of Engineering and Informatics, University of Bradford

Dr Anna M. Snelling (School of Medical Sciences, Faculty of Life Sciences, University of Bradford), Dr Colin A. Grant (Department of Medical Engineering, Faculty of Engineering and Informatics, University of Bradford), Dr Ben R. Whiteside (Advanced Materials Engineering, Faculty of Engineering and Informatics, University of Bradford)

14 15

Annually, more than 3 million bone graft procedures are performed worldwide to repair bone defects stemming from either a disease or a traumatic event (Henkel, J., et al., Bone Research, 2013). In 2013 the global market for joint reconstruction and replacement was worth nearly $13.2 billion. The market in Europe is projected to increase from $3.8 billion in 2013 to $4.5 billion by 2018 (www.bccresearch.com). In this scenario bioactive glasses have gained much interest as promising materials for repair and reconstruction of bone tissue defects.

The use of porous bioceramic substitutes to support bone tissue growth and regeneration is a longstanding area of interest (Stevens M, Materials Today, 2008). More recently, additive manufacturing techniques along with doped bioactive glasses have been employed to produce 3D porous scaffolds with designed structure and controlled chemistry to replicate the native bone architecture as well as to restore and repair bone tissue functions. This research aimed to fabricate and characterise 3D porous scaffolds for bone tissue engineering applications, using novel bioceramic compositions, via indirect powder-based 3D printing technology.

Two silicate-based glasses (NCL2 and NCL7) containing different elemental combinations: Al and Fe (to improve the mechanical properties), Cu and Zn (for maintaining the bone matrix and density), and also Ca, Na, K, Mg and Mn (essential elements for all living organisms) were provided by GTS Ltd (Sheffield), along with apatite-wollastonite (AW), which was used as control. The glass frits were ground and sieved to obtain particle sizes under 53 µm. Each powder formulation was then processed to “green” parts using a ZPrinter® 310 Plus 3D printer and, then, sintered according to the data derived from the hot stage microscopy analysis, to obtain consolidated 3D porous structures. Flexural strength and modulus were evaluated by a 3 point bending test. The level of sintering of the obtained scaffolds was investigated by scanning electron microscope (SEM) and the scaffold microarchitecture by micro-CT analysis. Volumetric shrinkage and porosity after sintering were also measured, and finally cell-materials interaction was tested in vitro using MC3T3 cell line.

The scaffolds exhibited porosity values (~35%) comparable to those of natural bone and a high interconnected structure as demonstrated by SEM and micro-CT investigations. Both the new compositions showed mechanical properties comparable to commercial available AW. Moreover, the in vitro biocompatibility indicated positive responses with a cell viability of ~ 70% after 7 days similarly to AW. Also, the cytoskeletal staining (by FITC), detected by confocal microscopy, indicated a biological active response by the novel bioceramic scaffolds supporting cell adhesion.

Finally, the 3D printed silicate-based scaffolds exhibited suitable architecture as well as porosity, and good mechanical properties with respect to the commercial AW. Furthermore, no detrimental effects on the cell viability were detected, revealing the potential of the new materials for bone reconstruction applications. Future work will focus on the optimisation of the powder blend formulation and also to the possible use of the novel bioceramics as inorganic phase of biocomposite materials for bone tissue substitutes.

PROCESSING AND CHARACTERISATION OF NOVEL BIOCERAMIC FORMULATIONS USING INDIRECT POWDER-BASED 3D PRINTING TECHNOLOGY

#A8

Ms Elena Mancuso elena.mancuso@ncl.ac.uk

Newcastle University

Prof. K. Dalgarno (Newcastle University), Dr. O. Bretcanu (Newcastle University) Dr. M. Birch (Cambridge University) Mr M. Marshall (GTS, Sheffield)

Aim: Single cell encapsulation with a semi-permeable biodegradable shell is an attractive procedure for a range of biomedical applications [1]. Nozzle clogging is one limitation of inkjet bioprinting, which makes the process unreliable [2]. This work explored the use of poly-L-lysine (PLL) to encapsulate single osteosarcoma cells (U2OS), evaluating the effect of different PLL concentrations on the viability and morphology of the cells.

Methods: Single osteosarcoma cells were encapsulated into PLL shells using three concentrations: 100, 50 and 10 µg/ml. Cell viability was evaluated by MTT and Live-Dead assays, fluorescence-activated cell sorting (FACS) and image flow cytometry, with the latter two techniques also used to assess the encapsulation efficiency. The mechanism of capsule release was studied using Transmission Electron Microscopy (TEM), and cell morphology by fluorescence and confocal microscopy.

Results: Over 99% of cells were encapsulated. A viability increase with polymer concentration decrease was demonstrated, with 94.1% healthy cells with the lowest concentration immediately after encapsulation. At higher concentrations cells were found to still be encapsulated 4 hours after coating and undergoing necrosis. The cytotoxic effect of the higher polymer concentrations was confirmed by TEM, where highly vacuolated cells and polymer uptake was observed.

Conclusions: Cell encapsulation can be used as a mechanism to stabilise bio-inks in order to achieve consistent printing yields over extended time periods of up to an hour. The mechanism of degradation involves both dissolution of the shell and ingestion of the polymer by the cells, and for encapsulation using a 10 µg/ml concentration of PLL occurs over a timeframe of a few days.

References: [1] Germain (2006) Biosensors and Bioelectronics 21:1566-73; [2] Murphy (2014) Nature Biotechnology 32:773-785.

CELL ENCAPSULATION FOR BIO-INK FORMULATION

#A9

Mr. Ricardo RibeiroR.Da-Conceicao-Ribeiro1@newcastle.ac.uk

Newcastle University

Mr. Ricardo Ribeiro (Newcastle University), Dr. Ana Ferreira-Duarte (Newcastle University), Dr. Matthew Benning (Newcastle University), Dr. Deepali Pal (Newcastle University), Dr. David Jamieson (Newcastle University), Dr. Kenneth Rankin (Newcastle University), Professor Kenneth Dalgarno (Newcastle University).

16 17

Orthopaedic compression screws promote fracture healing by drawing-together and stabilising adjacent bone fragments (e.g. Herbert screws in scaphoid repair).Shape memory polymers are materials that switch from one macroscopic shape to another following the application of external ‘triggering’ stimuli (e.g. by shrinking in length when heated). A shape memory compression screw could therefore potentially be used to pull bone fragments together. The shape memory phenomenon occurs because when polymers solidify from a melt (or dry from solutions), the molecules form tangled networks in which individual molecules adopt conformations with the lowest available energies. If a solid polymer is (i) heated to a temperature above the point where the polymer chains are able to begin to move relative to one another (called Tg) but below its melting point; (ii) stretched; and then (iii) rapidly cooled below Tg without releasing the tension, then the polymer’s chains become ‘locked’ into energetically unfavourable conformations, (analogous to frozen, stretched rubber bands). As long as the polymer remains below Tg then its molecules remain locked in these energetically unfavourable conformations. However, if the polymer is heated above Tg, then molecules will move relative to one another and revert to their original energetically favourable conformations (e.g. re-heating a stretched shape memory polymer above Tg will cause it to shrink in length).The biocompatible, bioresorbable polymer polylactic acid can show shape memory properties and could therefore potentially be used to make a shape memory compression screw. Unfortunately, the triggering temperature required to initiate shape reversion in unmodified PLA is too high to be conveniently incorporated into routine clinical practice. The value for Tg for a particular polymer can be reduced by adding plasticisers, low molecular weight compounds that facilitate the movement of molecular chains within solid polymers. To identify plasticisers that can reduce the Tg of PLA to 37C (i.e. physiological temperatures), standardised mixtures of PLA, plasticiser and solvent were added to moulds and dried in a computer controlled oven to produce plasticiser-polymer films. The Tg of these materials was determined using an identiPol machine. The films’ shape memory properties were assessed by (i) heating 10 mm long pieces of film to 85C in water; (ii) stretching them to 20mm long; (iii) rapidly cooling them to 5C without releasing the tension; and then (iv) attempting to trigger shape memory reversion by brief immersion in water at 10C – 60C or more prolonged immersion in saline at 37C.Results showed that two reportedly biocompatible plasticisers, Triacetin and Tributyl O-acetylcitrate reduced PLA’s Tg in a dose dependant manner and that shape memory reversion could occur at 37C in saline. Such materials could potentially be used to form compression screws that shrink in length post-implantation and pull bone fragments together.Ongoing work aims to optimise the conditions required to produce the shape memory plasticised PLA. Future work will use the manufacturing and characterisation equipment available at Bradford (e.g. injection moulding, extrusion and machining) to produce compression screws from these shape memory materials.

COMPRESSION SCREWS FOR THE FIXATION OF SMALL BONES AND BONE FRAGMENTS USING BIOCOMPATIBLE, BIORESORBABLE, BODY-TEMPERATURE REVERTING, PLASTICISED SHAPE MEMORY POLYMERS

#A10

Dr B.M.Thomsonb.thomson@bradford.ac.uk

University of Bradford

B.M. Thomson (Bradford University), G. Thompson (Bradford University), D. Vgenopoulos (Bradford University), K. Nair (Bradford University), J. Duncan (Lacerta Technology), K. Howell (Bradford University), M. Martyn (Bradford University) and P. Coates (Bradford University)

In bone tissue engineering, creating scaffolds that promote and support osseous formation remains a challenge. In this work, Apatite- Wollastonite (A-W) was used a material for the scaffold fabrication. A-W is biocompatible, bioactive, osteoconductive, bioresorbable in vivo and has good mechanical properties.

Two different scaffold fabrication techniques were used, both based on initially processing powder to create a pre-form for subsequent sintering. One group was prepared by mixing A-W with water to form a slurry that was cast in a mould to produce microporous scaffolds. Different particle size ranges (20-53 µm and 80:20 54-90 µm: <20 µm) were used to vary the topography, surface area and pore size without significantly influencing the porosity. The second group was prepared by the addition of A-W powder (20-53 µm) in a pre-warmed polymer: solvent solution (PLA: dioxane). The slurry was cast, frozen down and freeze-dried to produce scaffolds according to thermally induced phase separation (TIPS) methodology before sintering. The sintered TIPS scaffolds were highly porous and interconnected.

The main goal of this work was to identify whether changing structural parameters would have an effect on biodegradation and bioactivity of these A-W scaffolds. A secondary aim was to characterise how these scaffold characteristics could influence human mesenchymal stem cell fate and in particular osteogenesis.

Scaffolds were imaged using SEM. The surface of the microporous scaffolds was characterised using light profilometry and the interconnected structure of the porous scaffolds was imaged using µCT. Samples were incubated in simulated body fluid (SBF) for 21 days. EDX and ICP were used to identify precipitated elements on the scaffold and ions released in the SBF respectively. PicoGreen was used to measure cell viability. Alamar blue and p-NPP substrates were used to measure metabolic and alkaline phosphatase activity. Gene expression was assessed using RT-PCR. A combination of Von Kossa and Toluidine Blue staining were used to identify calcium deposits in the mineralised tissue and the acidic sulphated mucosubstances respectively on the same sample.

It is concluded that the surface area of A-W scaffolds affects their bioactivity, degradation and mechanical properties. Increased surface area of A-W results in higher Ca/P precipitation that produces increased scaffold mass; whereas a decreased surface area of A-W allowed more nucleation points causing slower Ca/P precipitation that promotes scaffold degradation. Cell viability, proliferation and alkaline phosphatase activity are influenced by the surface area and porosity. Gene expression in combination with histological staining indicate that microporous scaffolds with smaller pores allow cell-cell interaction and promote osteogenesis. Scaffolds with increased surface area demonstrate signs of chondrogenesis. Highly porous A-W scaffolds allow cell infiltration, migration and exhibit signs of osteochondral lineage differentiation.

APATITE-WOLLASTONITE GLASS CERAMIC SCAFFOLDS FOR OSTEOCHONDRAL TISSUE ENGINEERING APPLICATIONS

#A11

Miss Sotiria Toumpaniariria.toumpaniari@ncl.ac.uk

Newcastle University

Dr Mark Birch (Cambridge University), Prof Andrew McCaskie (Cambridge University), Prof Kenny Dalgarno (Newcastle University)

18 19

Anterior cervical decompression and fusion (ACDF) is the standard surgical treatment for spinal stenosis, radiculopathy and myelopathy. Due to its mechanical properties polyether ether ketone (PEEK) appears well suited for use as the implant in ACDF procedures. What makes PEEK special is its unusually high plasticity, its toughness, and its ability to experience cold drawing at temperatures considerably below its Tg. Not only amorphous, but also semi-crystalline PEEK samples are capable of undergoing sufficiently large plastic deformation even at 100°C. Our project will focus to produce layers of different crystallinity to mimic better the cartilage/bone structure of the spinal discs. The aim of our research is the improvement of spinal spacer’s quality and design using PEEK crystallisation behaviour. In order to control the mechanical properties of PEEK and to refine the general knowledge about orientation and crystallisation processes in polymers, further investigation is required, especial for the case of microinjection moulding. This poster presents data on the change in crystallinity upon micro-injection moulding of PEEK at various mould temperatures, injection speeds and hold pressures. The samples were analysed using X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Small-angle X-ray scattering (SAXS), Raman spectroscopy and Differential Scanning Calorimetry (DSC).

POLYETHER ETHER KETONE (PEEK) CRYSTALLISATION PHASES ANALYSIS IN MICROINJECTION MOULDING FOR ANTERIOR CERVICAL DECOMPRESSION AND FUSION

#A12

Dr Cristina Tuinea-Bobec.tuinea-bobe@bradford.ac.uk

University of Bradford

H. Xia (Sichuan University), Y. Liu (Sichuan University), B.R. Whiteside (University of Bradford), P.D. Coates (University of Bradford), Y. Ryabenkova (University of Bradford), P. Twigg (University of Bradford), G. Fei (Sichuan University)

Osteochrondral implants replace damaged cartilage and bone and are used in the treatment of osteoarthritis and traumatic lesions of articular cartilage. Osteochondral implants based on traditional composites are homogeneous mixtures and so must be a compromise between the requirements of the cartilage and bone. Implants that employ bilayers of two different compositions to mimic these two tissues suffer from large interfacial shear stresses and potentially adhesive failure. By varying the composition and cross-linking of the composite through the thickness of the implant the mechanical properties can be matched to the surrounding tissue, avoiding both these problems.

This study produced cell-conducting materials using well established freeze-thaw techniques for poly(vinyl alcohol) (PVA) and either ß-tricalcium (ß-TCP) or hydroxyapatite (HA) as a particle filler component. Functional gradients were introduced during the processing of the implants by a number of mechanisms. Initial biocompatibility testing has yielded promising results.

The composite produced here is a viscoelastic material and both storage (E’) and loss (E’’) moduli are investigated at macro (dynamic compression), micro (nanoindentation) and nano (AFM) scales using dynamic mechanical analysis. This multi-scalar approach is necessary to understand the behaviour of this structured material. The sinusoidal loading frequency was varied across a physiologically relevant range (0.1-10Hz).

The results demonstrate the importance of matching local mechanical properties of the implant to the surrounding tissue. Further development of this approach is discussed with reference to collaborative work at partner institutions on structured PVA (Sichuan University) and biomineral particle design (Beijing Institute of Chemistry, Chinese Academy of Sciences).

VISCOELASTIC MECHANICAL OPTIMISATION OF FUNCTIONALLY GRADED CELL-CONDUCTING MATERIALS FOR OSTEOCHONDRAL IMPLANTS

#A13

Andrew D. PattinsonA.D.Pattinson@bradford.ac.uk

Advanced Materials Engineering RKT Centre; Faculty of Engineering and Informatics, University of Bradford, Bradford BD7 1DP, UK

Yulia Ryabenkova (University of Bradford), Colin A. Grant (University of Bradford) and Peter C. Twigg (University of Bradford)

20 21

Rotator cuff tears are estimated to affect 40% of those aged 60, and up to 70% of the population aged 80 (JBJS, 2006, 88(A): 2294). In order for the arm to function fully, integration of the rotator cuff tendons to bone is compulsory. Surgery to repair a torn rotator cuff involves reattaching the tendon to the bone with sutures. In this procedure, a degradable anchor is used to hold the stitches in place until the repair has taken place. High failure rates have been reported for the repair of large tears and some are deemed irreparable by this method requiring musculotendinous transfers and patch grafts using biological or synthetic materials. Repair of rotator cuff tears remains a significant clinical challenge with failure rates of 20% to 70%. In order to address this challenge this project aims to develop a nanofiber based construct

for the repair of rotator cuff tears using a tendon tissue-like “graft”. The final construct will mimic tendon structure and mechanical properties in the rotator cuff tissue.

The tendon graft is based on polyhydroxyalkanoate-type polymer (poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV) conjugated to collagen (PHBV-Col). The “grafting-to” approach has been utilised by coupling amines from the collagen with activated carboxylic acid groups on the PHBV using traditional carbodiimide coupling chemistry. Characterisation of the PHBV-col will include evaluation of its physico-chemical, thermal and mechanical properties. Novel nanofibre-based constructs made of PHBV-col will be obtained by centrifugal spinning. The centrifugal spinning parameters and device configurations will be optimised in collaboration with the University of Leeds.

Development of this novel material and nanofiber-based construct has the potential to improve the structural and physical properties of injured rotator cuff tendons. As a result, the quality of life of rotator cuff tear suffers will be improved.

SYNTHESIS OF TENDON TISSUE-LIKE GRAFTS USING A HYBRID PHBV-COLLAGEN MATERIAL

#A14

Dr Sarah Upson Sarah.upson@ncl.ac.uk

Newcastle University

Dr. Ana Ferreira-Duarte (Newcastle University), Prof. Kenny Dalgarno (Newcastle University)

Session B // ContentsContinuous hydrothermal synthesis of new nanoscale hydroxyapatite morphologies

Integrated molecular design of melt-processable bioresorbable engineering nanocomposites for health-care

Rapid mix preparation of biomimetic nanoscale hydroxyapatite for biomedical applications

Biomimetic nano-structured materials for bone repair and regeneration – Industrial perspective

Continuous hydrothermal synthesis of nanoparticles – Scaling up

Bioresorbable composites for bone fracture repair applications

Development of bio-active glass products and production processes

Trabecular directionality in three dimensional remodelling of bone graft substitute in cervical fusions

Porosity measurements in three dimensional remodelling of bone graft substitute in cervical fusions

Layer-by-layer: a bioengineered tool to enhance specific biological activities at nanoscale

Hydroxyapatite functionalised using a coupled heparin-binding peptide

30

22

31

23

32

24

36

28

38

39

40

41

42

35

27

34

26

33

25

37

29

Development of 3D polymer scaffolds for biomedical applications; degradation and compression properties

The JRI approach to innovation in Med Tech

Controlled release of antibacterial drugs through in-situ crosslinked wet-spun collagen triple helices

The development of stratified acellular biological scaffolds for osteochondral repair

Pre-clinical biomechanical evaluation of acellular biological scaffolds for tissue repair and replacement in the knee joint

Novel porous structures with internally-coated surfaces

Development of 3D artificial niches for regenerative medicine

Fabrication of electrospun poly(caprolactone)/strontium-substituted bioactive glass composite membranes for bone tissue regeneration

Resorbable, therapeutic ion leaching thin films for implant osseointegration

Design of bespoke collagen hydrogels for chronic wound care

22 23

This presentation will describe the production of a number of novel morphologies of nano-hydroxyapatite, including crystalline sheets and tubes that lend themselves to new multifunctional purposes. The process uses continuous hydrothermal synthesis to mix a preheated aqueous solution of (NH4)2HPO4 into a flow of cold aqueous calcium nitrate at temperatures between 200 and 400°C. Altering the pH of the (NH4)2HPO4 flow from 8 to 10 changes the morphology of the HA sheets to tubes. Initial experiments showed how nanotubes can be produced in combination with nanomaterials or polymers. These morphologies of hydroxyapatite have potential for use as scaffolds, allowing new structures to be made e.g. nano-rods composed of a controlled sequence of different nanomaterials or biological molecules or drugs.

Whilst batch hydrothermal processing can be used to manufacture HA, scaling up production is generally preferable through continuous production in order to avoid batch to batch variability and the scalability of continuous systems. The continuous hydrothermal synthesis of nanomaterials was first described by Adschiri[17] in 1992 but the development of this process was hampered by the need for an optimised reactor design. The fluid mechanics involved in mixing the superheated water flow with the cold aqueous metal salt flow is critical in determining product quality and avoiding blockages. In respect of this issue, we developed a symmetrical counter current nozzle reactor as a proposed ‘optimised’ design for producing high quality materials. This presentation will describe an innovative approach whereby the aqueous (NH4)2HPO4 precursor solution forms the superheated stream and the Ca(NO3)2.4H2O is the cold metal salt flowing upwards. This approach appears to alter the kinetics of formation resulting in the formation of interesting morphologies that could have potential applications as scaffolds or containers for other functionalised nanomaterials.

CONTINUOUS HYDROTHERMAL SYNTHESIS OF NEW NANOSCALE HYDROXYAPATITE MORPHOLOGIES

#B1

Prof Ed LesterEdward.lester@nottinghama.ac.uk

University of Leeds

Dr Selina Tang, (Promethean Particles), Dr Miguel Gimeno-Fabra, Professor David Grant (University of Nottingham)

In this work we are focused on producing low molecular weight (Mw) polymers capable of dispersing novel nanoparticles in a biodegradable polymer (Poly(lactic acid) or PLA) for medical applications. The dispersants are primarily PLA based to maximise the interactions between the matrix polymer and the surface of the coated nanoparticles to prevent aggregation and are introduced into a high pressure hydrothermal flow reactor as reported previously by Edward Lester et al (2006). The reactor is capable of both successfully synthesising and coating hydroxyapatite nanoparticles with the desired dispersant. We have shown that the degree of coating is subject to the length of the polymeric dispersant, its morphology, the polymer ‘head group’ and the location in the reactor that the dispersant is introduced.

INTEGRATED MOLECULAR DESIGN OF MELT-PROCESSABLE BIORESORBABLE ENGINEERING NANOCOMPOSITES FOR HEALTH-CARE

#B2

Miss Kirsty Waltonenxkw1@nottingham.ac.uk

University of Nottingham

Dr Alec Ilchev(University of Nottingham), Associate Professor Derek Irvine (University of Nottingham)

24 25

Hydroxyapatite has been widely used as a medical ceramic due to its good biocompatibility and its similarity to the mineral found naturally in bone and tooth enamel. Specifically, the nanoscale hydroxyapatite (nHA) found in bone tissue is calcium-deficient. Recently there has been increased interest regarding the use of nHA in biomaterials to encourage bone tissue regeneration. There are several methods which can be used to prepare nHA including hydrothermal and sol-gel methods. For this project the wet precipitation method was used due to its relative ease and low cost of production. The aim of this project was to investigate the preparation of high quality biomimetic nHA suitable for biomedical applications using the wet precipitation method.

In this study, the wet precipitation of nHA was investigated utilising the acid-base reaction involving calcium hydroxide and phosphoric acid. In detail, a phosphoric acid solution was poured into a calcium hydroxide suspension. The prepared nHA suspension was washed using distilled water and dried in an oven at 80 °C. The sample was then ground and half of each sample was sintered at 1000 °C for 2 h to investigate the high temperature stability of the prepared product. Material characterisation techniques including x-ray diffraction (XRD), transmission electron microscopy (TEM), x-ray fluorescence (XRF) and Fourier-transform infrared spectroscopy (FTIR) were used to analyse the material produced.

The characterisation results demonstrated the successful formation of nHA. XRD patterns showed the precipitation of phase pure hydroxyapatite with a relatively small crystallite size. The sharpening of the XRD peaks after sintering showed an increase in the crystallite size of the sample. TEM micrographs displayed that the particle size was approximately 50 x 30 nm, with a particle aspect ratio of approximately 1.7. After high temperature sintering treatment a minor phase of β-TCP was detected which indicated that the precipitated nHA was calcium-deficient. This was in agreement with XRF results which showed a calcium: phosphorus ratio (1.63) lower than the stoichiometric ratio (1.67). Furthermore, XRF results showed the high purity of the nHA produced with only trace amounts of other elements detected.

It was likely that the rapid addition of the phosphoric acid solution lowered the pH of the calcium hydroxide suspension which may have contributed to the precipitation of calcium-deficient nHA. In conclusion, this method was successful and convenient for the preparation of biomimetic nanoscale hydroxyapatite, which is of great interest for the manufacture of the next generation of advanced biomaterials.

The authors would like to acknowledge the EPSRC and Ceramisys Ltd. for funding this work.

RAPID MIX PREPARATION OF BIOMIMETIC NANOSCALE HYDROXYAPATITE FOR BIOMEDICAL APPLICATIONS

#B3

Dr Caroline Wilcockmta07cw@shef.ac.uk

University of Sheffield

Prof Paul Hatton (University of Sheffield), Dr Cheryl Miller (University of Sheffield), Dr Piergiorgio Gentile* (University of Sheffield) *Present address is University of Newcastle.

Biomaterials based on nano-structured calcium phosphates have demonstrated great potential for the repair and regeneration of bone in orthopaedic and spinal surgery due to their biomimetic nature and bioactivity. In recent years growing confidence in the clinical performance and safety of this type of biomaterial has led to a rise in products which contain biomimetic nano-structured materials being launched onto the market. One example commercial product is ReproBone® novo, a bone graft paste manufactured by Ceramisys Ltd., which can be directly injected into the defect site, offers a reliable alternative to autologous bone and provides excellent clinical outcomes.

As a result of the success of current commercial biomimetic biomaterials there is a growing interest from the academic, clinical and industrial communities which is driving forward research and innovation in this area. Nano-structured calcium phosphates, in particular, have a firm foothold in basic science and therefore offer significant potential for further development in order to address the clinical challenges associated with bone repair in compromised and ageing patients. The MeDe Innovation network has a vast research capacity and through industrial and clinical collaboration has great potential to support the innovation necessary to address these significant clinical challenges therefore improving patient outcomes and strengthening UK medical manufacturing in the future.

BIOMIMETIC NANO-STRUCTURED MATERIALS FOR BONE REPAIR AND REGENERATION – INDUSTRIAL PERSPECTIVE

#B4

Dr Becci Goodchildr.goodchild@ceramisys.com

Ceramisys Limited

26 27

Promethean Particles (PROM) uses continuous-flow hydrothermal synthesis for the manufacture of inorganic nanomaterials. Their bench-scale facilities allow for the rapid screening of reaction parameters in order to optimise their bespoke products, tailored for each application. Their pilot-scale plant is then capable of producing kilograms per day (dry weight equivalent) of nanomaterials, with high reproducibility demonstrated between each scale.

As part of the European Commission-funded FP7 project SHYMAN (Sustainable Hydrothermal Manufacture of Nanomaterials), PROM is working with The University of Nottingham to build a full-scale industrial plant capable of manufacturing up to 1000 tonnes of nanomaterials per year, which will be operational in 2016. Also within this project, PROM is working with several industrial partners on individual case studies to develop functional nanomaterials for a wide range of products and applications - ranging from architectural coatings to precious metals for medical imaging. For one of these case studies, PROM is working with MeDe partner Ceramisys on hydroxyapatite for use in artificial bone scaffold and cements.

The scale of manufacture would make this industrial plant the largest in the world for nanomaterial production, allowing several markets to be accessed.

CONTINUOUS HYDROTHERMAL SYNTHESIS OF NANOPARTICLES – SCALING UP

#B5

Dr Selina Tangselina.tang@proparticles.co.uk

Promethean Particles Ltd.

Dr Pete Gooden (Promethean Particles Ltd.), Prof. Edward Lester (University of Nottingham)

Introduction: The use of composites based on poly(lactic) acid ‘PLA’ and phosphate glass fibres ‘PGF’ for bone fracture repair has been deemed as highly beneficial due to their excellent biocompatibility and biodegradability. However, difficulties in achieving thorough melt impregnation whilst limiting polymer degradation has been one of the main issues hampering their implementation. Therefore, innovative manufacturing techniques, with reduced cycle times that manage to achieve optimum fibre wet-out will pave the way for product adoption. Materials and Methods: Melt drawn polyphosphate glass fibres were embedded into a PLA matrix using a purpose built compression moulding tool and two pressure schemes: i) static pressure ‘SP’ (pressure held constant at 40 bar) and, ii) cyclical pressure ‘CP’ (pressure cycled for 1.5 min towards the end of the consolidation stage). Two series of unidirectional composites plates of four volume fractions ‘vf’ 0.15, 0.25, 0.35 and 0.45 were fabricated. The composite plates were then machined into rectangular bars and reshaped into cylindrical rods through hot forging using two deformation profiles: i) plain strain ‘PS’ and ii) uniaxial compression ‘UC’. Results: The flexural strengths of the CP composites were approximately 30% higher than the SP samples due to the CP influence on fibre network permeability through relaxation and reapplication of pressure, leading to improved impregnation. CP could also alter the melt viscosity and capillary pressure. The CP composites mechanical properties were found to be the highest hitherto reported for this composite system (ca. 480 MPa and 23 GPa for flexural strength and modulus respectively for the 0.45 vf) and even greater to cases were coupling agents in previous studies. Differences in the dynamic crystallisation behaviour between the CP and SP composite plates suggested transcrystallinity formation in the CP composites, probably as a result of locally induced chain alignment. The PLA molecular weight showed a maximum reduction of 20% in the case of the 0.45 vf composite due to the moisture absorbed by the hydrophilic glass surface. However, the extent of degradation did not deleteriously affect the PLA mechanical properties in the composites.The mechanical properties of the UC-rods were found to be significantly lower than those of the parent plates due preferential crack propagation through the sinusoidal fibre breakage pattern under loading. The flexural properties of the 0.15 and 0.25 vf PS composite rods were found comparable (and even higher) to those of both plates series. However, the 0.35 and 0.45 vf samples were found to prematurely fail due to interlaminar flaws (induced by through-thickness stresses experienced in SP) whose development into cracks was more likely in the higher fibre volume fraction composites. Conclusions and Future work: Cyclical pressure implementation during composite consolidation led to enhanced fibre impregnation with limited PLA thermal degradation. Additionally, cyclical pressure promoted the development of transcrystallinity which may further enhance mechanical properties upon annealing. The occurrence of fibre breakage and/or the inducement of interlaminar flaws highlight the inadequacy of forging to process laminated fibre reinforced products. Ongoing work is focused on the manufacture of continuously reinforced products through crosshead extrusion.

BIORESORBABLE COMPOSITES FOR BONE FRACTURE REPAIR APPLICATIONS

#B6

Associate Prof Ifty AhmedIfty.ahmed@nottingham.ac.uk

University of Nottingham

Fernando Barrera Betanzos (University of Nottingham), Joel Segal (University of Nottingham) and David Grant (University of Nottingham).

28 29

Glass Technology Services (GTS) has been involved in the development of bio-active, bio-soluble and bio-inert glasses for a number of years. Over the past 3-4 years this activity has increased considerably.

Alongside the MeDe project GTS is actively involved in the development of bio-materials. GTS has been working on additive manufacturing of bio-active glasses with the University of Sheffield and JRI Orthopaedics for acetabular cups, and on bio-active glass based implants for knee defects with Newcastle University and JRI Orthopeadics. Further work on additive manufacture, with laser sintering, for complex implant revision has been carried out with the University of Leeds and JRI Orthopeadics, while GTS is also involved with projects on resurfacing of teeth with the University of Leeds.

The results of a project carried out with the University of Nottingham will be described. In this project GTS aimed to produce multiple tows of 20 micron glass fibres which can then be woven into fabrics for biomedical applications. As a result of this work GTS now has new routes for production of the next generation bio materials. It has also been demonstrated that woven fabric can be produced in innovative new bio-reactive glass formulations. The fibre production has been demonstrated for glass compositions where fibre has previously been unavailable. As a result GTS has in place a 10 tip platinum bushing for fibre production.

A follow on project will provide production technologies to scale up the process of phosphate fibre manufacture for use within three industrial textile environments (woven, braided, knitted). The textiles will be processed further into composite materials using compression, liquid transfer and pultrusion moulding to create high strength, synthetic, fibre-based materials for use in medical devices.

At the same time GTS in developing manufacturing capability for these glasses in a spin out company Vitritech. Vitritech has recently acquired the assets and business of another company (Giltech) and is now setting up to manufacturing of bio-soluble and bio-active glasses in a facility near Sheffield. This includes further fibre drawing capability producing 50-500 fibres simultaneously as well as producing glass in other formats. The capability will be briefly described. Products will be used in a variety of medical applications including implants and wound care.

DEVELOPMENT OF BIO-ACTIVE GLASS PRODUCTS AND PRODUCTION PROCESSES

#B7

Dr Malcolm Glendenningm.d.glendenning@glass-ts.com

Glass Technology Services Ltd

Chris Sorsby (Vitritech Ltd)

Introduction: Numerous bone graft materials are available to surgeons as alternatives to iliac crest autograft. Fusion success is defined by the presence of bridging bone between vertebrae at the operative site. The number of fused segments is often quoted as a measure of clinical performance for bone graft materials; however, it does not provide any information regarding the ‘quality’ of bone that resides within the cage or whether this bone develops characteristics similar to normal bone in response to mechanical load.

Normal bone will remodel along the principal axis of strain. Therefore by analysing the direction of the individual trabeculae an understanding of the loading patterns within the graft can be obtained and compared to normal bone.

Materials and Methods: Anterior cervical discectomy and fusion for single and multi-level symptomatic cervical radiculopathy was completed in 13 patients (20 spinal levels) using a PEEK interbody cage. Each cage was filled with i-FACTOR™ Peptide Enhanced Bone Graft. Post-operative radiographic follow-up was conducted at 3 and 6 months using Cone Beam CT. The graft region containing i-FACTOR™ was segmented by hand, then a multistage algorithm was applied to segment out the bone in the region of interest while compensating for both beam hardening and x-ray scattering (Performed in the software Mimics). The models of fusions (determined by the operating surgeon), were subjected to raytracing to identify the directions of their internal trabeculae. These directions were related to the position of the cage via the cage markers. The directions were represented via a “3D Histogram Rose plot” using 10 degree bins. Eight remote sites of healthy bone in the sample set were taken from vertebra which had not been part of the surgery but had also been scanned.

Results: The trabecular analysis in 3D of the healthy remote bone sites showed not only distinct major directions of the trabeculae which theoretically would relate to the major axis of strain in the bone, but also an array of supportive directions. The trabeculae of the fused bones at 3 months show similar major directions but not the supportive directions that are seen in the healthy trabeculae. The trabeculae of the fused bones at 6 months show a smaller proportion of major directions than the 3 month sample but more supportive trabecular directions, much like the healthy bone.

Conclusion: The study shows that the structure of the bone that i-FACTOR™ forms at 3 and 6 months is being actively remodelled with the resulting bone developing characteristics similar to healthy mature bone at 6 months. The structures of these fusions show a relationship to the external forces as normal bone does. This provides a new type of measurement to determine how a graft has remodelled in relationship to healthy trabecular bone and thus give a measure for quality of fusion.

TRABECULAR DIRECTIONALITY IN THREE DIMENSIONAL REMODELLING OF BONE GRAFT SUBSTITUTE IN CERVICAL FUSIONS

#B8

Dr Donal McNallydonal.mcnally@nottingham.ac.uk

University of Nottingham

A.J.B.Parish.1, G.Kesteloot.2, S.Johnson.3, 1Dept Biomechanics, University of Nottingham, Nottingham, England; 2Dept Neurosurgery, Azdelta, Roeselare, Belgium; 3Cerapedics Inc. Denver, USA

30 31

Introduction:Numerous bone graft materials are available to surgeons as alternatives to iliac crest autograft. Fusion success is defined by the presence of bridging bone between vertebrae at the operative site. The number of fused segments is often quoted as a measure of clinical performance for bone graft materials; however, it does not provide any information regarding the ‘quality’ of bone that resides within the cage or whether this bone develops characteristics similar to normal bone.

As bone is a naturally porous structure, a measurement for how well a bone graft substitute remodels during fusion would be to track how the porosity changes over the time of the fusion and compare it to a healthy sample of bone.

Materials and Methods:Anterior cervical discectomy and fusion (ACDF) for single and multi-level symptomatic cervical radiculopathy was completed in 13 patients (20 spinal levels) using a PEEK interbody cage. Each cage was filled with i-FACTOR™ Peptide Enhanced Bone Graft. Post-operative radiographic follow-up was conducted at 3 and 6 months using Cone Beam CT.

The region of implantation of the i-FACTOR™ was first segmented by hand, then a multistage segmentation algorithm was applied to segment out the bone in the region of interest while compensating for both beam hardening and x-ray scattering. This was all performed in the software Mimics (Materialise). The 3D models of the remodelled i FACTOR™ were measured in cages which had been deemed fused by the operating surgeon. These were then ‘wrapped’ and the volume of the wrapped models compared to the unwrapped to measure the porosity in each sample. Remote sites of healthy bone were taken from 8 sites in the sample set where vertebra which had not been part of the surgery had also been scanned by the Cone Beam CT.

Results: The change in porosity of the bone formed from the i-FACTOR™ from 3 to 6 months for the two different types of cage (single and double) was shown to be 15%±8% (n=5) at 3 months to 22%±6% (n=6) for the single level cages and 12%±9% (n=9) at 3 months to 22%±10% (n=11) at 6 months for the double level. The remote healthy bone samples were shown to have a porosity of 20%±8% (n=8).

Conclusion: The change in porosity shows that there is a trend towards increasing porosity and closer to the porosity seen in mature and healthy bone. This measurement provides another method to track how the graft remodels into bone and clearly shows how the bone’s structure is changing over time and is in fact not just losing volume from the outside of the graft site.

POROSITY MEASUREMENTS IN THREE DIMENSIONAL REMODELLING OF BONE GRAFT SUBSTITUTE IN CERVICAL FUSIONS

#B9

Dr Scott Johnsonsjohnson@cerapedics.com

Cerapedics

A.J.B.Parish.1, G.Kesteloot.2, D.S.McNally.1

1Dept Biomechanics, University of Nottingham, Nottingham, England; 2Dept Neurosurgery, Azdelta, Roeselare, Belgium;

Guided bone regeneration (GBR) is employed in dental implantology and the treatment of periodontal bone loss. It is based on the surgical placement of a barrier membrane that excludes soft tissue growth that would otherwise prevent bone healing [1-2].Unfortunately, non-resorbable membranes require a second operation for their removal while resorbable collagen membranes have an associated risk of disease transmission, and also existing commercial systems do not promote tissue regeneration beyond their barrier function. The aim was therefore to develop a functionalised, bilayered resorbable membrane with a dense layer to contact soft tissues, and a porous layer to promote bone healing.

Compact films of poly(D,L-lactide-co-glycolide) (PLGA, 75:25) were prepared by solvent casting from acetone. Porous membranes were prepared by dissolving PLGA (22% w/v) and nano-hydroxyapatite powder (20% w/w) [3] in acetone prior to electrospinning. Both layers were subjected to plasma polymerisation for acrylic acid grafting, and were modified by layer-by-layer (LbL) technique to generate functional polyelectrolyte (poly (styrene sulfonate) /poly(allyl amine) (PSS/ PAH); Sigma) to obtain 20 nanolayers to incorporate (1) an antibiotic drug (Metronidazole; Sigma) to provide antibacterial activity for the compact layer, and (2) specific bone matrix peptides (KRSR and FHRRIKA; GenScript) to promote bone healing at the porous surface. The layers were assembled using fibrin glue. Drug release from the compact layer was evaluated by UV-Vis, while in vitro biocompatibility was investigated using L292 mouse fibroblasts (compact layer) and rat mesenchymal stromal cells (porous layer).

FTIR-ATR showed that the typical absorption bands of PAH and PSS increased with layer number (i.e. SO3- stretching vibrations at 1130 cm-1 for PSS, and NH scissoring vibrations at 1580 cm-1 for PAH). The contact angle values had an alternate behaviour from the 9th and from 11th nanolayer for the compact and porous layer respectively. XPS spectra showed a N1s peak at 399.5 eV and S2p peak at 168 eV, indicating PAH and PSS had been introduced. Preliminary study of biocompatibiity demonstrated that all membrane components supported cell growth.

The advantages of the low temperature fabrication technology described here are evident, providing an opportunity to prepare structures with predictable physico-chemical and biological properties. The bilayered membrane described is ideally suited to GBR in terms of its integrity, biodegradability, and biocompatibility including directed cell–membrane interaction.

References1. Gentile P et al. Biotechnol J 6, 1187, 2011.2. Bottino MC et al. Dent Mater 28, 703, 2012.3. Prakash KH et al. Langmuir 22, 11002, 2006.

LAYER-BY-LAYER: A BIOENGINEERED TOOL TO ENHANCE SPECIFIC BIOLOGICAL ACTIVITIES AT NANOSCALE

#B10

Dr Piergiorgio Gentilepiergiorgio.gentile@ncl.ac.uk

Newcastle University

Dr Cheryl Miller (University of Sheffield), Prof K Dalgarno (Newcastle University), Prof PV Hatton (University of Sheffield).

32 33

Introduction: Bone tissue loss often results in reduced quality of life, pain, poor aesthetics and impaired functionality for millions of people throughout the world. Therefore, in order to restore health and function surgeons use a variety of alloplastic biomaterials as bone graft substitutes. Calcium phosphates such as hydroxyapatite (HAP) are arguably the most successful group of bone graft substitutes, but clinical performance is often limited in ageing or compromised patients1. While some progress has been reported in the field of orthobiologics (e.g. the use of bone morphogenic proteinstissue loss often results in reduced quality of life, pain, poor aesthetics and impaired functionality for millions of people throughout the world. Therefore, in order to restore health and function surgeons use a variety of alloplastic), this approach is both expensive and faces a more complex regulatory pathway2. New strategies are therefore being considered to enhance bone tissue regeneration without the costs and risks associated with orthobiologic substances, one promising route is the coupling of bio-functional peptides to implant surfaces.

Methods: Sintered HAP discs were produced via gelcasting and sintering at 1160°C. The surface was then functionalised using acrylic acid plasma polymerisation. The carboxyl groups generated at the surface were then activated for peptide attachment using carbodiimide hydrochloride and n-hydroxysuccinimide (EDC/NHS). Finally the HAP discs were exposed to a heparin binding peptide KRSR3. X-ray photoelectron spectroscopy (XPS) was used for surface characterisation at each stage of treatment. The release profile of the KRSR peptide was studied in water and analysed using reverse-phase high performance liquid chromatography (HPLC).

Results, Discussion and Conclusion: The sintered gelcast HAP discs showed a calcium/phosphate ratio very similar to that of stoichiometric HAP when analysed using a XPS survey scans. After full treatment XPS survey scans detected ~7 at% nitrogen at the HAP surface indicating the presence of peptides and successful functionalisation. Release studies showed peptide retention was significantly improved on a fully treated HAP samples when compared to controls. It was therefore concluded that peptide coupling provides a highly promising route to produce bio-functional modifications to calcium phosphate biomaterials.

References1. Bach T et al. J. Cranio. Maxill. Surg. 42: 552-559, 2014.2. Roberts T et al. Organogenesis. 8: 114-124, 2012.3. Dhara S et al. Bull. Mater. Sci. 25: 565-568, 2002.

Acknowledgments: The authors would like to thank JRI Orthopaedics Ltd, Ceramisys Ltd and the EPSRC for providing financial support for this project. In addition the authors would also like to thank the National EPSRC XPS User’s Service at Newcastle University.

HYDROXYAPATITE FUNCTIONALISED USING A COUPLED HEPARIN-BINDING PEPTIDE

#B11

Mr Joss AtkinsonJoss.Atkinson@Sheffield.ac.uk

University of Sheffield

Piergiorgio Gentile, Paul Hatton & Cheryl Miller(University of Sheffield)

Various types of 3D polymer scaffolds have been developed and investigated at the University of Nottingham. Multilayer functional chitosan scaffold with controlled pore sizes has been developed with guidance from JRI Orthopaedic Ltd for the regeneration of osteochondral lesion. We have also recently completed FP7 project (Innovabone) which aimed to develop a biomimetic product that consists of a bespoke scaffold and a bioactive self-setting gel, which will provide a microenvironment that contains active elements such as growth factors and CaP nanoparticles to promote bone repair. 3D scaffolds were manufactured with specific controlled porous architecture, defined microstructure and an adjustable degradation profile was achieved using two-photon polymerization (TPP) with a maximal size of 2x2x4 mm³. Scaffolds made from poly(D,L-lactide-co-ε-caprolactone) copolymer with varying lactic acid (LA) and ε -caprolactone (CL) ratios (16:4, 18:2 and 9:1) were generated via ring-opening-polymerization and photoactivation and coded LC16:4, 18:2 and 9:1. All materials were suitable for defined microstructuring of reproducible porous scaffolds. The pore sizes for all LC scaffolds were ca. 300 µm and throat sizes varied from 152 to 177 µm.

In vitro degradation was conducted at body and elevated temperatures; 37, 50 and 65°C and activation energies for the scaffold materials were determined using an Arrhenius equation. Change in compressive properties immersed at 37°C over time was also measured. Rates of mass loss for the LC16:4 scaffolds at all temperatures were significantly lower than that for LC18:2 and 9:1. A prediction for degradation time was applied through a correlation between long-term degradation studies at 37oC and short-term studies at elevated temperatures (50 and 65°C) using the half-life of mass loss (Time (M1/2)) parameter. However, the initial compressive moduli for LC18:2 and 9:1 scaffolds were 7 to 14 times higher than LC16:4 (ca. 0.27) which was suggested to be due to its higher CL content (20%). All scaffolds showed a gradual loss in their compressive strength and modulus over time as a result of progressive degradation of scaffold materials over time.

Cytocompatibility of the scaffolds was assessed using human mesenchymal stem cells (MSCs). All three types of scaffold were capable of supporting cell proliferation and osteogenic differentiation of human MSCs over 21 days and LC18:2 showed the best bone cytocompatibility response.

In vitro degradation studies at 37oC and were also conducted to LC scaffolds-ELR hydrogel hybrids. No significant differences in degradation and mechanical properties were seen between LC scaffold alone and combination of LC scaffold and ELR +/- CaP nanoparticles. Weight of the wet scaffolds increased gradually to reach ca. 180% at the end of the study (112 d) due to water uptake and swelling. Compressive strength and modulus for all specimens were approximately 0.07 and 0.45 MPa until day 35 and started afterwards to decrease gradually to be 0.008 and 0.04 MPa respectively at day 112 due progressive degradation of the scaffold material.

The manufacturing process utilized and the scaffolds produced have vast potential for use in tissue engineering and regenerative medicine applications.

DEVELOPMENT OF 3D POLYMER SCAFFOLDS FOR BIOMEDICAL APPLICATIONS; DEGRADATION AND COMPRESSION PROPERTIES

#B12

Dr Reda FelfelReda.felfel@nottingham.ac.uk

University of Nottingham

Dr Miquel Gimeno-Fabra (University of Nottingham) , Dr Amy Prosser (University of Nottingham), Dr Ifty Ahmed (University of Nottingham), Dr Colin Scotchford (University of Nottingham), Dr Virginie Sottile (University of Nottingham), and Prof David Grant (University of Nottingham).

34 35

JRI Orthopaedics Limited (JRI) is a privately owned British manufacturer of innovative and quality orthopaedic solutions for healthcare providers and patients worldwide. Established in 1970, JRI has been a specialist in the field of orthopaedics with its own Design, Manufacturing and Regulatory teams. Its revenue generating activities are predominantly through the sale of its implant products which include hip, shoulder and knee replacement systems and orthobiologics throughout the UK, Europe and the rest of the world.

With the company’s long standing history of innovation, JRI continually strives to improve the lives of patients through advancing treatments of joint disease. JRI have committed investment in developing novel bioactive materials, advanced manufacturing processes, new approaches to treatment and regenerative medicine.

JRI has a collaborative approach to developing new cutting-edge technologies and it works across Europe with leading clinical and non-clinical academics on the underpinning science and engineering. JRI’s academic partners include the top universities with world-class research equipment and facilities. The Company also works alongside other industry partners with additional manufacturing and technical expertise to ensure successful commercialisation and the new technologies reach patients. These industrial partners often form part of the future supply chains.

The Company ensures its research activity is commercially-sustainable through grant funding and investment, future revenue arising from protected intellectual property and future direct sales from advanced products.

JRI is wholly owned by the charity Orthopaedic Research UK to which it donates all profits. These profits are redistributed by the Charity to further orthopaedic research.

THE JRI APPROACH TO INNOVATION IN MED TECH

#B13

Dr Sarrawat Rehmansarrawat.rehman@jri-ltd.co.uk

JRI Orthopaedics Ltd

Bacterial infection is one of the most common complications associated with implants for fracture fixation, joint replacement and spine surgery. Although advances in sterilization techniques have greatly reduced the possibility of bacterial infection in hospital settings, pathogenic micro-organisms are still found at the site of approximately 90% implants [1], potentially leading to bone infection such as osteomyelitis. In this regard, implantable matrices, capable of delivering antibacterial drugs in a sustained and localised manner are a promising strategy to minimise the risk of infection and failure of medical devices in vivo. As an implantable matrix collagen fibre has the potential to offer excellent biological and physiological features, and flexibility to be assembled into nonwoven fabric. However, avoiding denaturation of the native triple helical structure of collagen still remains essential in order to manufacture robust fibres. Here, collagen triple helices were manufactured into stiff (tensile modulus: 2200 MPa) microfibres through an in-house developed wet-spinning technology [2] and investigated as potential vehicle for the controlled delivery of ciprofloxacin (Cfx) as an antibacterial drug. We have hypothesised that incorporation of an aromatic ring during crosslinking could effectively control the rate of Cfx release through collagen fibre (CF). To evaluate the hypothesis Cfx loaded wet-spun collagen fibres (CFs-Cfx) were covalently in-situ crosslinked via (i) state-of-the-art 1-ethyl-3-(3-dimehylaminopropyl) carbodiimide hydrochloride (EDC), (ii) reaction with activated 1,3 phenylenediacetic acid (Ph) in the presence of carbodiimide and (iii) reaction with activated Ph only, where ß-mercaptoethanol (ßME) were added following Ph activation and prior to the crosslinking reaction, in order to deactivate EDC/N-hydroxysuccinimide (NHS). The NHS-activated Ph in the presence of EDC/NHS (Ph*) and NHS-activated Ph (Ph) collagen fibres showed higher tensile modulus and strength compared to EDC crosslinked CF-Cfx, likely due to the capability of Ph to crosslink distant collagen molecules [3]. The drug loaded crosslinked fibres showed slightly lower tensile modulus and strength compared to the respective non-drug loaded crosslinked fibres. The degree of crosslinking for the in-situ crosslinked fibres ranges from 50 – 67%, with the highest value achieved with the group activated with the Ph only. Besides the tensile mechanical properties, Cfx release kinetics were also improved in both Ph crosslinked CF-Cfx groups either in the presence of EDC/NHS or even just NHS-activated, suggesting the establishment of pi-pi interactions between the aromatic groups of Ph and Cfx. Thus, Ph crosslinked CF-Cfx could be a promising material for medical implants to minimise the risk of implant failure due to bacterial contamination.

[1] Nablo BJ, Rothrock AR, Schoenfisch MH. Nitric oxide-releasing sol–gels as antibacterial coatings for orthopedic implants. Biomaterials 2005;26:917-24.[2] Arafat MT, Tronci G, Yin J, Wood DJ, Russell SJ, Biomimetic wet-stable fibres via wet spinning and diacid-based crosslinking of collagen triple helices. Polymer 2015; 77:102-12.[3] Tronci G, Doyle A, Russell SJ, Wood DJ. Triple-helical collagen hydrogels via covalent aromatic functionalisation with 1,3-phenylenediacetic acid. Journal of Materials Chemistry B 2013;1:5478-88.

CONTROLLED RELEASE OF ANTIBACTERIAL DRUGS THROUGH IN-SITU CROSSLINKED WET-SPUN COLLAGEN TRIPLE HELICES

#B14

Dr Tarik Arafatm.t.arafat@leeds.ac.uk

University of Leeds

Giuseppe Tronci (University of Leeds), David J. Wood (University of Leeds), Stephen J. Russell (University of Leeds)

36 37

Introduction: Early intervention to repair cartilage defects has the potential to prevent or delay degeneration of joint tissues to osteoarthritis. Current surgical therapies have limitations and this has led to the development of novel tissue engineering approaches. We propose the use of acellular composite xenogeneic osteochondral scaffolds for cartilage regeneration. Initially, research has focussed on the development of a decellularisation bioprocess for porcine subchondral bone and proof of concept of osteointegration of the acellular bone in sheep. Methods: Porcine bone plugs (distal femur; 6 mm diameter, 10 mm long; n=6) were decellularised using low concentration sodium dodecyl sulphate (SDS) with protease inhibitors. Decellularisation was assessed by histology. DNA was extracted from tissues and quantified by spectrophotometry. In vitro biocompatibility tests were carried out using BHK and L929 cells, cell viability was determined by quantification of cellular ATP. In vivo biocompatibility of the acellular bone was assessed by subcutaneous implantation in mice (4 and 12 weeks; n=3 native and n=3 acellular porcine bone). Explanted tissues were assessed by histology. The acellular porcine and control allograft ovine bone plugs (6 mm diameter, 10 mm long; n=6) were implanted into the femoral condyle of skeletally mature sheep for 4 and 12 weeks. Sheep received oxytetracycline injections to fluorescently label newly formed bone. Explants were assessed by histology and semi-quantitatively graded.Results: Decellularised porcine bone plugs were devoid of cell nuclei. The mineralized bone matrix appeared intact, isolated traces of residual material were present in trabecular spaces. Decellularised bone had residual total DNA content of 20.2 ± 8.5 ng.mg-1 per tissue dry weight compared to 546.5 ± 216.8 ng.mg-1 in native porcine bone (p<0.05; Student`s t-test). No contact cytotoxicity was observed with BHK or L929 cells. The ATP content of cells grown with acellular bone extracts was not significantly different from cells grown in culture medium alone (p<0.05; ANOVA). Assessment of tissues explanted from mice showed no adverse host response to the decellularised porcine bone.Following in situ implantation in sheep both acellular porcine and allograft ovine bone weree well integrated after 4 weeks. Histologically, decellularised porcine bone showed a higher density of new bone deposition after 12 weeks compared to allograft bone, however new bone formation was not homogeneous. At 4 weeks decellularised porcine bone grafts contained a fibromesenchymal infiltrate, and some areas showed a marked focal lymphocytic response, a lesser response was observed in the allografts. After 12 weeks the lymphocytic reaction was greatly reduced in the acellular porcine bone grafts and was no longer present in allografts. Both grafts demonstrated new marrow formation and were fully osteointegrated. Discussion: Decellularised porcine bone fully osteointegrated when implanted into an ovine femur, with the level of integration comparable to that of allograft bone. An initial lymphocytic response was observed although this was greatly reduced after 12 weeks. The integration and biological acceptance of acellular porcine bone supports the inclusion of bony attachment sites in composite osteochondral scaffolds. The successful decellularisation bioprocess is now being applied to porcine condyles to produce an acellular osteochondral scaffold.

THE DEVELOPMENT OF STRATIFIED ACELLULAR BIOLOGICAL SCAFFOLDS FOR OSTEOCHONDRAL REPAIR

#B15

Dr Hazel Fermorh.l.fermor@leeds.ac.uk

University of Leeds

Dr Gemma Jones (University of Leeds), Prof John Fisher (University of Leeds) & Prof Eileen Ingham (University of Leeds)

The growth in the popularity of tissue engineering principles in the treatment of musculoskeletal disorders has been complemented greatly with research investment into tissue specific scaffolds. Biological scaffolds produced by means of decellularising native tissues have the advantage of providing the natural complex hierarchical matrix and, in doing so, replicating the specific biomechanical and biological functions of the tissue in question.

Decellularisation treatments are multi-faceted, vary considerably between different processes and may involve many lengthy treatment steps. Some of these bio-processes may cause undesirable structural changes to the extracellular matrix of tissues and, by association, their mechanical properties. Thus, it is of paramount importance to ensure that the properties of the scaffolds are not affected to the extent of reducing their integration, biomechanical performance and longevity.The work presented here comprises of the pre-clinical biomechanical evaluation of a range of acellular biological scaffolds for tissue repair and replacement in the knee joint. Specifically, this includes studies investigating the acellular porcine super flexor tendon and human patellar tendon as candidates for anterior cruciate ligament replacement and acellular porcine bone which forms substrate of decellularised osteochondral tissue.

Decellularised porcine and human tendons were subjected to uniaxial tensile testing at low strain rates until failure occurred, while decellularised porcine bone underwent compressive testing at low strain rates in an aqueous environment until failure occurred. The biomechanics of the porcine super flexor tendon were found to have been altered only in the toe region of loading, with all other material properties including strength and Young’s modulus remaining unchanged compared to native controls. The human patellar tendon was found not to have been biomechanically affected by decellularisation for any of the material parameters investigated. Lastly, in the case of decellularised porcine bone, the strength and Young’s modulus were found to have reduced significantly compared to native controls.

The changes in the toe region biomechanics of the acellular porcine super flexor tendon were not sufficient to reduce overall function and no biomechanical changes were observed in the human patellar tendon following decellularisation, indicating both scaffolds can be used as possible grafts for the replacement of the ACL. The changes in the mechanical properties of porcine bone following decellularisation may stimulate new bone formation with the host environment due to the increased deformability of the material, providing sufficient initial strength still remains to ensure the survival of the scaffold until integration occurs. Further work investigating the in-vivo performance of these acellular ACL and bone scaffolds is currently underway.

PRE-CLINICAL BIOMECHANICAL EVALUATION OF ACELLULAR BIOLOGICAL SCAFFOLDS FOR TISSUE REPAIR AND REPLACEMENT IN THE KNEE JOINT

#B16

Dr Anthony HerbertA.Herbert@leeds.ac.uk

University of Leeds

Dr Gemma Jones (University of Leeds), Dr Jennifer Edwards (University of Leeds), Dr Christopher Brown (University of Leeds), Dr Hazel Fermor (University of Leeds), Prof Eileen Ingham (University of Leeds), Prof John Fisher (University of Leeds).

38 39

A novel process has been developed to produce porous polymers with coated pores. The method is adapted from a compression moulding process, using NaCl beads as a porogen. The size of the porosity is, of course, dictated by the size of the porogen (for this study in the range of 0.5 to 3 mm), the size and number of connecting windows between the pores is governed by the shape and packing of the porogen as well as the moulding pressure. Parts with diameters of 180 mm and thicknesses of 15 mm have been produced (limited only by the size of the current tooling) and with the salt porogen in place, these mouldings can be machined into smaller, more intricate pieces before the salt is removed by dissolution in water. Owing to the good interconnectivity of the structure, dissolution of the salt is rapid (typically in a few hours) and residual salt levels, as measured by the electrical conductivity of the water in which they are soaked, are very low.

By a simple pre-treatment of the NaCl beads, the internal surfaces of the pores can be coated with powders of another material type. The type is only limited by the requirement that the powder isn’t soluble in water and that it is available in a suitable size for pre-treatment of the beads. In the context of materials that might be suitable for medical devices, porous polymers have been coated with Ti, Ag, HA and bioglass-type powders. By treating the beads, issues of inaccessibility or “clogging” in thick, porous samples, as is the case with most other coating processes, is avoided. The coatings are uniform and the level of coverage can be varied. A unique aspect is that mixed material coatings are also possible (so both Ti and a bioglass for example) with either both materials within the coating on each pore or each material coating different pores or regions within the porous component.

Mechanical testing has shown the structures to perform as expected based on their high (circa 80%) porosity levels, that the coating process is not detrimental to the stiffness or strength and that the coating remains attached to the pores even after significant pore deformation. At the time of writing, cell testing is underway, seeking to clarify the effect of coating of bioactive metals on “inert” polymer surfaces.

NOVEL POROUS STRUCTURES WITH INTERNALLY-COATED SURFACES

#B17

Dr Andrew Kennedyandrew.kennedy@nottingham.ac.uk

University of Nottingham

The use of stem cells offers great potential in the fields of biomedicine and tissue engineering, ranging from the development of in vitro disease and drug screening models to the creation of bespoke implants for tissue regeneration. Stem cells present unique self-renewal features and they are known to be fundamental for repairing and maintaining tissue along life; their behaviour is complex and is regulated both by intrinsic cellular programs and by extrinsic signals dictated by the surrounding environment (niche). Stem cell niches can be described as intricate microenvironments that play an important role in stem cell renewal and differentiation. Understanding the stem cell niche instructive behaviour is nowadays an important challenge and there is a need for the development of new in vitro approaches to reproduce closely the physical space where stem cells reside. The aim of this research is to create and evaluate 3D-niche models for the control of stem cells fate to ultimately translate these models to current and future stem cell therapies and biomaterial devices with potential use in the regeneration of musculoskeletal tissue. For this purpose microfabricated membranes have been computer-designed and manufactured via a combination of novel 3D-printing techniques and conventional electrospinning. The additive manufacturing part of the fabrication allows the creation of intricate structures which will simulate to a certain extent aspects of the native stem cell niche; on the other hand, the use of electrospinning allows the creation of biodegradable membranes and the use of FDA approved polymers (polycaprolactone has been used in this work). Initial studies have shown that the shape and morphology of the underlying 3D patterns seem to affect cell responses. The development of this platform technology sets the basis for the creation of artificial 3D microfabricated membranes for controlling stem cell fate which could be ultimately translated to a biomaterial device with potential use in the regeneration of musculoskeletal tissue.

DEVELOPMENT OF 3D ARTIFICIAL NICHES FOR REGENERATIVE MEDICINE

#B18

Dr. Ilida Ortega Asencioi.ortega@sheffield.ac.uk

The University of Sheffield

Martin E Santocildes-Romero (University of Sheffield), Paul V. Hatton (University of Sheffield)

40 41

Membranes are frequently used in oral and dental to treat bone tissue defects caused by periodontal disease in a procedure known as guided bone regeneration. In this therapy, membranes are used as a barrier to prevent the migration of tissues originating from surrounding tissues into the defect site, creating a relatively isolated environment where osteogenic cell populations will better proliferate and produce new bone matrix leading to better healing. Biodegradable materials such as collagen or bioresorbable polymers are preferred for this purpose, as they do not require a second surgical intervention in order to remove the implant. However, membranes made with these biomaterials lack the ability to encourage the formation of new bone tissue beyond their physical barrier function. In order to improve bone healing, barrier membranes should also be able to stimulate osteogenesis, a property that may be enhanced through the addition of an osteogenic component during the manufacturing process. Therefore, the aim of this study was to investigate the development of composite membranes with greater osteogenic properties made of bioresorbable polymers and bioactive glasses using the solution-electrospinning technique. Electrospun composite membranes were fabricated using poly(caprolactone) (PCL) and particles of strontium-substituted bioactive glasses based on the 45S5 composition. For the substitution, calcium was partially (50%) or fully (100%) replaced with strontium on a molar basis. The effects of the substitution on density, solubility, and in vitro metabolic activity of mesenchymal stromal cells (MSCs) were studied. Stimulation of osteogenic differentiation on MSCs was investigated using RT-qPCR. Additional particles were added to the surface of the electrospun fibres using two methods developed internally. All electrospun materials were characterised using scanning electron microscopy and energy dispersive x-ray spectroscopy, and particle dissolution was evaluated in water. In vitro material cytotoxicity was investigated using a rat osteosarcoma cell line.Strontium substitution resulted in increased glass density and solubility. MSCs metabolic activity was inhibited in the presence of 45S5 and fully-substituted glass, although it was enhanced in the presence of <20 mg of partially-substituted glass (Santocildes-Romero ME, et al. J. Tissue Eng Regen Med. 2015 9(5):619-31. The osteogenic response of mesenchymal stromal cells to strontium-substituted bioactive glasses). All composite materials were made of fibres exhibiting regions of increased diameter where the particles accumulated. The embedded particles dissolved after immersion in water, increasing the local pH. Further evidence suggested accelerated polymer degradation due to interactions between PCL and the glass. All materials generally exhibited good levels of in vitro biocompatibility, except those with >0.5 mg of additional surface glass particles.In conclusion, strontium-substituted bioactive glasses promoted osteogenesis in a differentiating MSC culture model and, therefore, are promising compositions for bone tissue regeneration. This is supported by the potential shown by electrospun PCL/strontium-substituted bioactive glass composites for bone regeneration applications including barrier membranes with enhanced osteogenic properties (e.g. for guided bone regeneration) or scaffolds for musculoskeletal tissue engineering.

Acknowledgements: The authors would like to acknowledge the EPSRC for support.

FABRICATION OF ELECTROSPUN POLY(CAPROLACTONE)/STRONTIUM-SUBSTITUTED BIOACTIVE GLASS COMPOSITE MEMBRANES FOR BONE TISSUE REGENERATION

#B19

Dr Martin Eduardo Santocildes Romerom.e.santocildes-romero@sheffield.ac.uk

University of Sheffield

Dr Rebecca Goodchild (University of Sheffield), Prof Paul Hatton (University of Sheffield), Dr Aileen Crawford (University of Sheffield), Prof Ian Reaney (University of Sheffield), Dr Cheryl Miller (University of Sheffield)

Introduction: Resorbable phosphate based glasses (PBG) can be tailored to deliver ions over different dissolution periods and this can be controlled further and applied via thin film coatings for orthopaedic implants. PBG compositions such as the P2O5-40 MgO-24 CaO-16 Na2O-16 Fe2O3-4 mol% are cytocompatible whilst others such as P2O5-30 CaO-60 Na2O-7 TiO2-3 mol% have exhibited bioactive behaviour in vitro. Experimental Methods: Quinternary PBG targets were produced by melt-quenching. These were then used as targets for RF magnetron sputtering onto Ti6Al4V discs. FIB-SEM cross sectional milling was used to observe interfacial characteristics. FTIR, XRD, EDX, XPS and NMR have been employed to make a structural comparisons between melt quenched glasses (MQG) and sputtered coatings (SC). Static contact angle with distilled water was examined. The coated samples and MQG rods were weighed and submerged in distilled water (dH2O) or phosphate buffer saline (PBS) and measured at time points up to 2 days and 28 days to determine the mass loss due to degradation. Results and Discussion: Cross sectional FIB-SEM micrographs suggested that the (SC) followed the topographical features of their substrates, whilst forming an adherent featureless interface. Of significant interest SC and MQG phosphate based glasses of similar chemical composition were found to be structural dissimilar. This was attributed to thermal history and coating surface etching. Coatings of 2.67 µm were found to fully degrade in dH2O, showing a t1/2 degradation profile in the first 2 hours, followed by a linear dependence from 2-24 hours until the coating was entirely degraded by the 48 h time point. The enhanced hydration ability of the SC was confirmed by contact angle <1° with dH2O in comparison to 25° for MQG. XPS results suggested an increased ratio of (P-O-P) to (PO- /P=O) and mostly (PO3)- Q

2 species, in comparison to the MQG counterpart which contained mostly (PO4)3- Q0 species and (P2O7)

4- Q1 species, which may be responsible for the early t1/2 dissolution profile. Following 16 h of degradation in dH2O milling through a dissolution pit revealed that dissolution had preferentially occurred in locations and consequently extended through to the Ti6Al4V substrate prior to lateral spreading. In contrast dissolution of the SC in PBS was halted by 48 hours as an X-Ray amorphous Na/Fe/Phosphate precipitation barrier had formed and showed no further signs of dissolution over a 28 d test period. NMR comparison of a second composition indicated variation in Q structure such that SC glasses were composed of 9.4% Q0, 45.2% Q1 and 45.4% Q2, compared to 0.8, 67.3 and 31.9% respectively for MQG.Industrial Application: Sputtering of thin films (PBG) is a promising method for delivering a controlled release of therapeutic ions to an implant site. The method is the most suitable for the deposition of adherent glass coatings. PBG’s have shown the ability to facilitate cellular activity, leading to the development of an extracellular matrix, and eventual osseointegration. The coatings may be the next generation of coating implants to complement or replace plasma sprayed hydroxyapatite on implant devices such as hip stems, and dental implants. Its low temperature operation allows for coating onto medical polymers such as PEEK. The tailorability of glass formations makes these coatings desirable in the development for stratified medical devices. This project has been followed by MeDe’s industrial collaborators, JRI Orthopaedics and DePuy Synthes. The current focus is on the scale up of the technique for coating of full scale implant devices.

RESORBABLE, THERAPEUTIC ION LEACHING THIN FILMS FOR IMPLANT OSSEOINTEGRATION

#B20

Mr. Bryan StuartEpxbs4@nottingham.ac.uk

University of Nottingham

Bryan Stuart, Miquel Gimeno-Fabra, Joel Segal, Ifty Ahmed and David M. Grant

42 43

Chronic wound care is a major cost to national health systems worldwide [1]. Improved exudate management via the use of wound dressings is a recognized route to decreased healing times. Hydrogels have been widely investigated aiming at the design of exudate-swollen dressing material, although (1) the narrow trade-off between hydrated mechanical properties and swelling ration, (2) the lack of biomimetic features potentially enabling modulation of hyperactive proteases at the wound site, and (3) the limited customisation of hydrogel architecture critically impair the successful translation of these materials in to the clinic [2]. To address these challenges, collagen was selected as a biomimetic building block for the formation of highly-swollen hydrogels with remarkable hydrated mechanical properties and enzymatically cleavable peptide sequences [3]. Type I rat tail collagen was covalently functionalised with either methacrylic or aromatic monomers, resulting in crosslinking segment of varied backbone rigidity. The type of collagen functionalization at the molecular level proved to impart adjusted compression properties to resulting hydrogels from the nano- up to the macroscopic scale, whilst the degree of collagen functionalisation enabled hydrogels with tunable and remarkably high swelling ratio (SR: 707±51–1996±182 wt.-%). Further to the hydrogel design, comparable wet-spun fibres could also be accomplished via wet-spinning of collagen polypeptides with varied secondary protein conformation [4, 5], enabling an additional dimension for the adjustment of macroscopic properties and material architecture. Non-toxic hydrogels were successfully prepared from a GMP collagen source and investigated in a wound healing model in diabetic mice along with two leading wound dressing products. The large absorbency of wound exudate by and remarkable hydrated compression moduli of GMP collagen hydrogels successfully enabled wound closure of a 10×10 mm wound following 20 d, whereby no sign of toxic response was observed at and around the hydrogel application site. Hydrogel wound closure profile was observed to be comparable to the wound closure profiles of the two leading dressing products, whilst dressing-free wounds proved to be unable to self-heal in the same conditions. In light of these results, the presented collagen technology offers great promise for the formulation of competitive dressing materials for applications in chronic wound care, whereby the tunability of macroscopic properties, hydrogel architecture and protease activity is expected to play a major role. [1] C.J. Phillips, I. Humphreys, J. Fletcher, K. Harding, G. Chamberlain, S. Macey (2015). “Estimating the costs associated with the management of patients with chronic wounds using linked routine data”, Int. Wound J., DOI: 10.1111/iwj.12443. [2] J.J. Schmidt, J.H. Jeong, V. Chan, C. Cha, K. Baek, M.-H. Lai, R. Bashir, H. Kong (2013). “Tailoring the dependency between rigidity and water uptake of a microfabricated hydrogel with the conformational rigidity of a polymer cross-linker”, Biomacromol. (14) 1361. [3] G. Tronci, C.A. Grant, N.H. Thomson, S.J. Russell, D.J. Wood (2015). “Multi-scale mechanical characterization of highly swollen photo-activated collagen hydrogels”, J. R. Soc. Interface (12) 20141079.[4] G. Tronci, R. Kanuparti, M.T. Arafat, J. Yin, D.J. Wood, S.J. Russell, Wet-spinnability and crosslinked fibre properties of two collagen polypeptides with varied molecular weight (2015). Int. J. Biol. Macromol. (81) 112. [5] M.T. Arafat, G. Tronci, J. Yin, D.J. Wood, S. Russell, Biomimetic wet-stable fibres via wet spinning and diacid-based crosslinking of collagen triple helices (2015). Polymer (77) 102.

DESIGN OF BESPOKE COLLAGEN HYDROGELS FOR CHRONIC WOUND CARE

#B21

Dr Giuseppe TronciG.tronci@leeds.ac.uk

University of Leeds

Dr M. Tarik Arafat, Roisin A. Holmes, Prof David J. Wood, Prof Stephen J. Russell (all University of Leeds)

Session A // Contents

Session C // ContentsComputational modelling of patient variation in the spine: a route to stratified device design and testing

Application of a computational and experimental wear simulation approach to new product development

Effect of surgical variations on the function and tribological performance of hip joint replacement

The next generation of simulators for stratified pre-clinical wear simulation of total knee replacements

Enhanced preclinical testing of hip joint replacements

Manufacturing phosphate-glass fibre reinforced composite rods as bioresorbable intramedullary nails

PEEK Optima® as an Alternative Bearing Material to Cobalt Chrome in Total Knee Replacements

The determination of acetabular orientation: measured in different coordinate systems

Subject-specific multi-validation of a Finite Element model of cervical functional spinal units

44

45

46

47

48

49

50

51

52

The combined effect of head and cup centres mismatch and different cup inclination angles on the occurrence and severity of edge loading and wear in hip replacement

Wear of a total ankle replacement

53

54

44 45

Introduction: Physical devices and therapies for treatment of spinal musculoskeletal disorders have generally had lower levels of success than corresponding interventions for other joints such as the hip or knee. There are many reasons for this, but a major factor has been the lack of realistic pre-clinical testing to aid in device design. In particular, tests do not currently take account of the large variation in patient population in terms of the anatomy and functional performance. This has prevented devices being designed to match the requirements of a functionally stratified patient population. The aim of our research is to develop improved preclinical testing tools for the design and manufacture of spinal devices. A particular focus is to develop finite element (FE) models in which patient variation can be incorporated in a controllable way. Methods: We have developed approaches to generate finite element models from microCT scans of vertebrae which have been extensively validated against corresponding experimental specimens (e.g. [1], [2], [3]). A bespoke principal component analysis (PCA) tool has been developed by our Project Partners Simpleware that can determine the principal modes of variation of vertebral image data and morph new FE models representing variations of each component. To validate the tool, a series of scans of 30 human vertebrae were imaged using microCT. FE models of each scan were generated using ScanIP (Simpleware Ltd, Exeter, UK) such that the material properties were assigned on an element-by-element basis based on the bone volume fraction [4]. The downsampled scans were then also used as input data for the PCA tool. The tool was used to ‘morph’ new FE models representing the mean and up to three standard deviations away from the mean for the major principal components. The FE models were analysed under axial load and under the simulated incorporation of a total disc replacement (TDR). Comparisons were made between the gross geometrical measurements and the predicted FE stiffness of the models generated from the input image dataset and those generated by the PCA tool. Results: Good agreement was found in terms of the mean and spread of geometrical data between the models generated directly from the input scan dataset and those generated using the PCA tool. The stiffness and stress distributions predicted by the two sets of FE models were also very comparable. Finally, there was almost identical variation in FE-predicted compressive stiffness as a function of TDR component sizing for both Input and PCA model sets. Conclusion: The results suggest that the PCA tool is able to generate models that not only ‘look like’ but also behave like those developed directly from image datasets. The example of the TDR used here illustrates that the PCA modelling approach provides a much more rapid and systematic method of evaluating performance of a device across a population. The approach could now be extended for a larger input dataset and developed for more complex models, for example of the functional spinal unit, enabling a route to virtual stratified modelling during pre-clinical testing.

[1] Jones & Wilcox, J. Biomech Eng, 2007. [2] Wijayathunga et al, J. Eng. Med. 2008 [3] Tarsuslugil et al, Ann Biomed. Eng, 2014; [4] Robson Brown et al, RS Interface 2014.

COMPUTATIONAL MODELLING OF PATIENT VARIATION IN THE SPINE: A ROUTE TO STRATIFIED DEVICE DESIGN AND TESTING

#C1

Ruth WilcoxR.k.Wilcox@leeds.ac.uk

University of Leeds

Dr Sebastien Sikora (University of Leeds), Dr Philippe Young (Simpleware Ltd), Dr David Raymont (Simpleware Ltd)

Wear of joint replacements remains a major factor determining their reliability and lifetime. The pre-clinical determination and prediction of wear is currently undertaken experimentally by joint simulators under a limited set of conditions, which do not take into account the wide variation of clinical conditions in the patient.

Our Stratified Approach For Enhanced Reliability (SAFER®) approach takes into account variations in surgical delivery, variations in kinematics, variations in the patient population and degradation of the biomaterials technology, and indeed combinations of all these different conditions. Testing under such a wide portfolio of stratified conditions cannot be achieved using experimental simulation alone, as too many experimental simulations are needed. Hence a new computational modelling approach has recently been developed, which can be combined with the experimental approach.

Invibio’s PEEK Optima® polymers are used in 5 million implanted devices worldwide. Their revolutionary polymers, unsurpassed manufacturing support and deep device knowledge have allowed device companies around the world to advance the medical device market for 15 years. A new joint replacement product, an all-polymer knee, is currently under development. This product consists of a PEEK Optima® femoral component coupled with an all-polyethylene tibial insert. PEEK is attractive in this application due to its favourable mechanical properties, low weight, biocompatibility and clearance for clinical use and lower cost compared to conventional materials.

In this collaboration with Invibio our unique combined computational and experimental approach has been applied to advance the development of this new product. Examples of variables under our SAFER® approach that have been studied include variations in kinematics through investigation of two levels of patient activity; variations in the patient population through investigation of the influence of size on wear; and degradation of the biomaterials technology through third body wear simulation.

APPLICATION OF A COMPUTATIONAL AND EXPERIMENTAL WEAR SIMULATION APPROACH TO NEW PRODUCT DEVELOPMENT

#C2

Dr Louise Jennings & Dr Adam Briscoel.m.jennings@leeds.ac.uk

University of Leeds & Invibio

46 47

Introduction: Although hip joint replacement surgery is considered one of the most successful orthopaedic surgeries, failures do occur. Failures can occur due to many reasons including infection, loosening, dislocation or adverse biological reaction to wear debris and can happen at different lengths of time post-surgery in different patients. One of the driving reasons for failure is related to how the implant is positioned in the body during surgery. Variations in surgical positioning can in some cases lead to edge loading where the contact area between the head and the cup during an activity intersects with the rim of the acetabular cup. This condition can lead to adverse contact mechanics and tribological conditions that may lead to early failure of the implant. So it is crucial that the optimum implant position can be defined for each particular patient and that the surgeons have the tools for implanting the different components of the hip replacement system in their intended optimum position.

The aim of this research study is to determine the effect of different surgical variables such as cup orientation, joint laxity and soft tissue tension, and mismatch between the centre of rotation of the head and the cup on the occurrence and severity of edge loading and assess the tribology and function of the hip replacement bearing.

An advanced physiological in vitro simulator method, that can predict the occurrence and severity of edge loading and the wear of different hip bearing materials and designs due to variations in surgical positioning, can be used as a preclinical testing technique to better predict the efficacy and reliability of new hip replacement bearings.

Current results have shown that the severity of edge loading increases with increased mismatch between the centre of rotation of the head and the cup. This severity increases further when the acetabular cup was positioned at a steeper inclination angles. Variations in joint centre mismatch and rotational positioning has been shown to influence both the mechanical and tribological function of hip replacement bearing.

The occurrence and severity of the resulting edge loading causing increased wear and contact stresses in hip bearings will depend on the combinations of surgical variations, such as steep inclination angle, excessive version and tilt angles, cup medialisation, head offset deficiencies, stem subsidence, and joint laxity and future work will include investigating these variables.

EFFECT OF SURGICAL VARIATIONS ON THE FUNCTION AND TRIBOLOGICAL PERFORMANCE OF HIP JOINT REPLACEMENT

#C3

Dr Mazen Al-Hajjar/ Dr Jonathan Thompsonm.al-hajjar@leeds.ac.uk

University of Leeds/ DePuy Synthes

Mr Oscar O’Dwyer Lancaster-Jones, Dr Murat Ali, Dr Sophie Williams, Dr Louise M Jennings, Prof John Fisher (University of Leeds) Prof Graham H Isaac (DePuy Synthes)

Introduction: A new six station electromechanically driven simulator with 5 fully independently controlled axes of articulation for each station, capable of replicating deep knee bending as well as other adverse conditions, which can be operated in either force or displacement control has been developed (SimSol, UK). This study investigated the wear of a fixed bearing total knee replacement using this electromechanically driven knee simulator, and compared it to previous data from a predominantly pneumatically controlled simulator that was not fully independently controlled.Materials/Methods: The wear of six Sigma CR fixed bearing TKRs (DePuy, UK) with curved moderately cross-linked polyethylene inserts (XLK) was determined in the six station electromechanically driven Prosim knee simulator. Displacement controlled kinematics were used, with a maximum anterior-posterior (AP) displacement of either 10mm (high kinematics) or 5mm (intermediate kinematics). A six-axis load cell and displacement sensors on every controlled axis and station allowed the full range of output loading and kinematic profiles from the second generation simulator to be obtained and compared to the demand inputs. The lubricant used was 25% new-born calf serum and wear determined gravimetrically. The study was run for 3 million cycles (MC) each of high and intermediate kinematics. The results were compared to previous data obtained for the same type of TKR under the same test conditions in a previous generation (predominantly pneumatically controlled) simulator [1]. Statistical analysis was performed using the one-way ANOVA with 95% confidence interval (CI) and significance was taken at p<0.05. Results: The electromechanical knee simulator achieved the demanded maximum axial load and initial peak at heel strike. The maximum delivered AP displacements under high kinematic conditions were 2.8mm (3.5mm input) and 9.6mm (10mm input) during the stance and the swing phases respectively. The corresponding values for the internal-external (IE) rotation angle were ±4.9º (±5º input). After 3MC of each of intermediate and high kinematic conditions, the mean wear rates were 2.7±0.9 and 5.6±2.3 [mm3/MC] (mean ± 95%CI) respectively. Discussion: The mean wear rates from the electromechanical simulator were similar to the predominantly pneumatic simulators at 2.6±0.9 (p=0.99) and 6.7±1.5 (p=0.69) [mm3/MC] under intermediate and high kinematics respectively [1]. The actual delivered loading and kinematic profiles followed the input profiles more closely on the electromechanical simulator. For example, the pneumatic simulator did not achieve the initial peak on heel strike. The maximum AP displacements and IE rotation were lower than those achieved by the electromechanical simulator (1.7 and 9.2 [mm] for AP displacement and ±4.1º for IE rotation from the pneumatic simulator). However, despite the closer following of the input profiles, inter-station variability in terms of varying wear rates still existed in the electromechanical simulator, suggesting other factors such as alignment of the TKRs and station set up played a role.Significance: The second generation electromechanically driven fully independent knee simulator showed improved performance and capability compared to the previous generation of predominantly pneumatically driven knee simulator, and can therefore better meet higher current and future simulation demands. The wear rates from the two simulators were similar under standard gait conditions.

References: [1] Brockett et al. ORS, 2014.

THE NEXT GENERATION OF SIMULATORS FOR STRATIFIED PRE-CLINICAL WEAR SIMULATION OF TOTAL KNEE REPLACEMENTS

#C4

Dr Abdellatif Abdelgaied A.Abdelgaied@leeds.ac.uk

University of Leeds

Prof John Fisher (University of Leeds), Dr Louise Jennings (University of Leeds)

48 49

Introduction: There is an increasing demand to produce safer and more reliable hip joint replacements. Advanced preclinical testing methods are being developed to test joint replacements under a wide range of conditions [1,2]. Translational surgical mismatch in the centres of rotation of the acetabular cup and femoral head in hip joint replacements can lead to dynamic separation resulting in edge loading contact, [3] and may lead to increased wear in ceramic-on-ceramic bearings [4]. Recently developed electromechanical simulators have been designed to comply with the latest international standards, which include three axes of rotation [5]. Previous simulators applied microseparation conditions with two axes of rotations conditions [6]. The aim of this study was to compare the wear of ceramic-on-ceramic bearings obtained under edge loading due to microseparation conditions during gait using an electromechanical hip joint simulator with two axes of rotation and three axes of rotation conditions.Methods: A six-station electromechanical hip joint simulator (ProSim EM13, Simulation Solutions, UK) was set up with 36mm diameter ceramic-on-ceramic (BIOLOX®delta, PINNACLE®, DePuy Synthes, UK) hip replacements under standard conditions (n=6) [7] and microseparation conditions under two axes [7] (n=6) and three axes [5] (n=6) of rotation conditions. Under two axes of rotation conditions, flexion/extension and internal/external rotation was applied with 90° out of phase to compensate for no adduction/abduction motion. The loading profiles comprised of 3kN twin peak loads and 300N swing phase load under standard conditions [5,7]. The swing phase load was reduced to approximately 70N under microseparation conditions. Approximately 0.5mm of fixed dynamic microseparation between the head and the cup was applied in the medial/lateral direction. The lubricant used was 25% new-born calf serum supplemented with 0.03% sodium azide to minimise bacterial growth. The gravimetric wear rates were determined using a microbalance (XP205, Mettler Toledo, UK) and compared over two million cycles for each test. The mean wear rates of the acetabular cup and femoral head, and 95% confidence limits were calculated and statistical analysis was carried out (independent samples t-test) with significance levels taken at p<0.05. Results: The mean wear rate of BIOLOX® delta ceramic-on-ceramic bearings under standard conditions was 0.03±0.01 mm3/million cycles. Under microseparation conditions, the mean wear rates for two axes and three axes of rotation conditions were 0.14±0.01 mm3/million cycles and 0.14±0.03 mm3/million cycles respectively. There was no statistically significant difference between the wear rates using two axes and three axes of rotation conditions under fixed level of microseparation conditions (p=0.86).Conclusion: Higher wear rates were observed under microseparation conditions compared with standard conditions, as reported in a previous study using a different hip joint simulator [6]. Similar wear rates were obtained under microseparation conditions with two axes and three axes of rotation conditions using the same simulator.References: [1] Fisher, J., Semin Arthroplasty, 2012 [2] Jennings, L.M., Orthop Trauma, 2012 [3] Fisher, J., JBJS, 2011. [4] Nevelos, J.E., et al., Biomaterials, 1999. [5] ISO14242-1:2014. [6] Al-Hajjar, M., et al., Biomed Mater Res-B, 2010. [7] Barbour, P.S.M., et al., Proc. Inst. Mech. Eng. H J. Eng. Med., 1999.

ENHANCED PRECLINICAL TESTING OF HIP JOINT REPLACEMENTS

#C5

Dr Murat Alim.e.ali@leeds.ac.uk

Institute of Medical and Biological Engineering, School of Mechanical Engineering, University of Leeds, Leeds, UK.

Dr Mazen Al-Hajjar (University of Leeds), Dr Louise M Jennings (University of Leeds) and Professor John Fisher (University of Leeds).

Current bone repair implants for use within the body are made from metals, which can suffer from disadvantages such as stress shielding and can remain in the body permanently. In addition, fractured bones fixated using metals plate can undergo re-fracture upon removal of the implant. This is because the bone does not carry sufficient load during the healing process.

More recently, a move towards degradable composite materials for bone repair applications (to replace metal equivalents) has been viewed as extremely favourable [1]. The main objective of these resorbable biocomposites would be to degrade in vivo and to also take an active part in the tissue regeneration process. The main advantage of a material that degrades is so that an implant would not necessitate a second surgical event for removal. In addition, biodegradation may offer other advantages and implants prepared from bioresorbable materials can be engineered to degrade at a rate that could transfer load slowly to the healing bone.

In this project, fully resorbable composite bone repair rods manufactured utilising polylactic acid (PLA) as matrix reinforced with phosphate glass fibres (PGF) were investigated.

References:[1] I. Ahmed, I.A. Jones, A.J. Parsons, J. Bernard, J, Farmer, C.A. Scotchford, G.S. Walker and C.D. Rudd. Composites for Bone Repair: Phosphate Glass Fibre Reinforced PLA with Varying Fibre Architecture. Journal of Materials Science: Materials in Medicine: 2011, Vol 22, pp 1825 - 1834.

MANUFACTURING PHOSPHATE-GLASS FIBRE REINFORCED COMPOSITE RODS AS BIORESORBABLE INTRAMEDULLARY NAILS

#C6

Mr Fernando Barrera Betanzosemxfb@nottingham.ac.uk

University of Nottingham

Miquel Gimeno-Fabra (University of Nottingham), Joel Segal (University of Nottingham), David Grant (University of Nottingham) and Ifty Ahmed (University of Nottingham)

50 51

Introduction: In this study, the potential to use PEEK Optima® as an alternative bearing material to cobalt chrome in the femoral component of a total knee replacement was investigated. An all-polymer implant as proposed in this study would be lighter weight and lower cost than conventional materials and PEEK is of interest in this application due to its favourable mechanical properties, biocompatibility and clearance for clinical use [1]. Experimental wear simulation under different tribological and environmental conditions has been used to assess the wear performance of the all-polymer implant with conventional metal-on-polyethylene knee implants of similar surface topography and geometry being tested in parallel. Methods: Six mid-size cruciate retaining PEEK Optima (Invibio Biomaterials Solutions, UK) and six cobalt chrome femorals of similar initial surface topography and geometry were tested against GUR 1020 UHMWPE tibials (conventional, EO sterilised) in two six station ProSim knee simulators (Simulation Solutions, UK). N=3 of each material type was tested under room temperature conditions as per standard practice at Leeds and n=3 under elevated temperature conditions where the bulk lubricant temperature was maintained at approximately 33°C. All tests were carried out under Leeds High kinematic conditions [2] with a maximum anterior-posterior displacement of 10mm and 25% bovine serum supplimented with 0.03% sodium azide was used as a lubricant. 5 million cycles (MC) of simulation was carried out at room temperature and 10MC under elevated temperature. The wear of the UHMWPE tibials was assessed by their loss in mass by gravimetric analysis. Significance was taken at p<0.05. Results: When tested under room temperature conditions, the wear of the metal-on-polyethylene implant was 2.6±1.6mm3/MC and the wear of the PEEK-on-polyethylene implant was 4.2±5.4mm3/MC, there was no significant difference in the wear of the UHMWPE tibial against the different materials, p>0.05. Under elevated temperature conditions, the wear was lower for both the conventional and all-polymer implants at 0.2±0.7mm3/MC and 1.8±0.9mm3/MC respectively. A high density of linear scratches was observed on the surface of the PEEK implants but this did not influence the wear of the UHMWPE which remained constant over the duration of the study. Conclusion: The wear rates measured in this study were considered to be low, <5mm3/MC for all test conditions [3] and the different femoral materials did not influence the wear rate. Testing at elevated temperature led to a reduction in wear of the UHMWPE against both materials, potentially due to the higher temperature causing increased protein precipitation which when deposited on the articulating surfaces of the implants may have a protective effect [4]. It is likely that testing at an elevated temperature led to a test artefact which would not be seen in vivo or in room temperature tests. This study shows a comparable wear performance between the all-polymer knee and conventional materials, environmental conditions such as the lubricant temperature can lead to test artefacts which influence wear.

[1] Kurtz, S.M. 2007, Biomaterials 28(32):4845-69[2] McEwen, H.M.J. 2005, J Biomechanics. 38(2):357-365[3] Fisher, J. 2010, CORR. 468(1):12-18[4] Lu, Z. 1997, Proc IMech E. 211(1):101-108

PEEK OPTIMA® AS AN ALTERNATIVE BEARING MATERIAL TO COBALT CHROME IN TOTAL KNEE REPLACEMENTS

#C7

Dr Raelene Cowier.cowie@leeds.ac.uk

University of Leeds

Dr Adam Briscoe (Invibio Biomaterials Solutions), Prof John Fisher (University of Leeds), Dr Louise Jennings (University of Leeds)

Introduction/Aims/Objectives: Mal-positioning of the acetabular component in total hip replacement (THR) could lead to unexpected complications. In order to provide guidelines on proper THR component positioning, the determination and assessment of the acetabular orientation relative to different coordinate systems from a large cohort of subjects is important. The aim of the present study was therefore to assess the orientation of acetabulum in a local pelvis coordinate system and a new global body coordinate system from a large cohort of subjects.

Methods: Three-dimensional computed tomographic (CT) images of fifty-six subjects (27 males and 29 females) in supine position were obtained from a public image archive. 3D solid models were generated from the CT images. Two coordinate systems, pelvis and global body coordinate systems, were established using a custom-written MATLAB program. For the pelvis coordinate system, the coronal plane was generated using bilateral anterior superior iliac spine (ASIS) and midpoint between bilateral pubic tubercle (MPT). The sagittal plane was established as the plane containing the MPT and perpendicular to the line connecting bilateral ASIS points. The axial plane was defined as normal to both the coronal and sagittal planes. For the global body coordinate system, the geometric centres of five lumbar vertebrae bodies were determined and fitted to a spatial line. The axial plane was then established as vertical to this spatial line. The sagittal plane was defined as the plane that contained the spatial line and to which the total distances of the geometric centres of five spinous processes was minimum. The coronal plane was established as perpendicular to the sagittal and axial planes. The acetabular rim plane and its corresponding unit vector were obtained in the two coordinate systems based on the points taken along the acetabular rim using least squares fitting technique.

Results: The three components (x-, y-, z-) of the acetabular unit vector were measured as 0.75±0.05 (SD), 0.30±0.09 (SD) and 0.58±0.07 (SD) respectively in pelvis coordinate system and 0.74±0.06 (SD), 0.25±0.12 (SD) and 0.60±0.07 (SD) respectively in global body coordinate system. There was significant correlation between the two x- components (r=0.83) with a best-fit line that did not differ significantly from the line y=x (R2=0.68). Statistically significant differences of y- and z- components between the two coordinate system measurements were observed (p<0.01).

Conclusion: The present study showed that different variations of acetabular orientation were measured in different coordinate systems. The significant differences of y- and z- components of the acetabular unit vector indicated that the tilt of the pelvis in sagittal plane was the primary factor causing the different variations. The study also showed that there was a larger variance of the acetabular orientation in the global body coordinate system compared to that in the pelvis coordinate system, indicating that there is a large range of variations in the load vectors relative to the acetabulum/acetabular components when the subject is in an upright position. Therefore, a global body coordinate system considering the tilt of pelvis is necessarily required to define the acetabular orientation in order to achieve a correct positioning of THR component in clinical practice.

THE DETERMINATION OF ACETABULAR ORIENTATION: MEASURED IN DIFFERENT COORDINATE SYSTEMS

#C8

Dr Xijin Huax.hua@leeds.ac.uk

University of Leeds

Professor Ruth K. Wilcox (University of Leeds), Professor John Fisher (University of Leeds), Dr Alison C. Jones (University of Leeds)

52 53

Introduction: The complex motion and geometry of the spine in the cervical region makes it difficult to determine how loads are distributed through adjacent vertebrae or between the facet joints and the intervertebral disc. This distribution mechanism is an important biomechanical consideration in the investigation of surgical interventions and performance of medical devices. Whilst finite element (FE) models allow these distributions to be investigated, they need validation for the results to be meaningful. This validation process is recognised as an important step [1], but direct, subject-specific, validations of Functional Spinal Units (FSU’s) in-silico models are sparse in the published literature.The aim of this contribution was to produce direct validation of subject-specific finite element models of FSU’s and to evaluate the importance of including fibre directionality in the mechanical description of the annulus fibrosus.Methods: Eight specimens of cervical FSU’s were prepared from five ovine spines and mechanically tested in axial compression monitoring overall load and displacements as well as local facet joints pressure and displacement. Subject-specific finite element models were produced from microCT image data, using scanIP (Simpeware Ltd, Exeter UK) and Abaqus (Simulia, Providence USA), reproducing the experimental setup and measuring global axial force and displacement as well as local facet joints displacement and contact forces. Bone elasticity was computed from the greyscale of the microCT images [2,3]. Other material models and parameters were taken from the literature, testing isotropic and anisotropic materials for the annulus fibrosus [4,5].Results: The produced models showed good to excellent concordance correlation coefficients for all measured outputs (CCC from 0.70 to 0.95), suggesting the models can be considered as valid in axial compression. The load transferred through the facet joints was always accurate, irrespective of the annulus material model, while the predicted facet displacement was larger than the measured one but not significantly. The load ratio through the facet joints does not depend on the choice of model for the annulus. The validated models showed that adding the direction of the fibres to their non-linear behaviour in the description of the annulus fibrosus improves the predictions at large strain values but not at low strain values.Conclusion: This is, to the authors’ knowledge, the first subject-specific direct validation study on a group of specimens, accounting for inter-subject variability. This study provided evidence on the level of detail required to reproduce an in-vitro axial compression protocol, accounting for inter-subject variability. The FSU models and methodologies developed can be used to assess the direct mechanical effects of interventions such as vertebroplasty or nucleus augmentation where the disc-facet load share may be compromised.

References:[1] Jones A.C., Wilcox R.K. (2008) MEP, vol. 30, pp. 1287-1304[2] Wijayathunga V.N. et al. (2008) iMechE/H, vol. 222 (2), pp. 221-228[3] Mengoni et al. (2016) In-silico models of trabecular bone: a sensitivity analysis perspective, in Uncertainty in Biology: a computational modelling approach, Springer International Publishing[4] Reutlinger et al, (2014) JMBBM. vol. 17 pp 229-241[5] Abd Latif et al. (2012) JBiomech vol. 45 (8) pp 1346-1352

SUBJECT-SPECIFIC MULTI-VALIDATION OF A FINITE ELEMENT MODEL OF CERVICAL FUNCTIONAL SPINAL UNITS

#C9

Dr Marlène Mengonim.mengoni@leeds.ac.uk

Institute of Medical and Biological Engineering, University of Leeds

Ms Ksenija Vasiljeva (Institute of Medical and Biological Engineering, University of Leeds)Dr Alison C. Jones (Institute of Medical and Biological Engineering, University of Leeds)Dr Sami M. Tarsuslugil (Institute of Medical and Biological Engineering, University of Leeds)Prof Ruth K. Wilcox (Institute of Medical and Biological Engineering, University of Leeds)

Introduction: Clinically, increased wear and deformation of hip replacement bearings have been associated with edge loading and its effects have been assessed in vitro. Factors that influence the occurrence of edge loading in total hip replacement include surgical translational and rotational positioning of the femoral head and the acetabular cup.Aim: The aim of this study was to determine how the level of medial-lateral surgical translational mismatch between the head and cup centre under different cup inclination angles for ceramic-on-ceramic bearings, affect the; 1) magnitude of dynamic separation, 2) the magnitude of the forces acting under edge loading, 3) the time during the cycle the head spends on the rim of the cup (duration of edge loading), and 4) component wear.Methods: Ceramic-on-ceramic hip replacement bearings (BIOLOX® delta, Pinnacle®, DePuy Synthes, UK) were tested in a hip joint simulator under a standard walking cycle. The study was split into two parts; a biomechanical study where the occurrence and severity of edge loading was assessed, and a wear test, where the tribological performance was assessed under edge loading. For the biomechanical study, a mismatch of the centres of rotations was applied between the femoral head and the acetabular cup in the medial-lateral axis. Four different levels of translational surgical mismatch between the head and the cup were applied; 1, 2, 3 and 4 (mm). Each level of mismatch was coupled with a cup inclination angle equivalent in vivo to 45°, 55° and 65° (n = 3 for each condition). Wear tests were performed on six selected conditions with three different level of surgical translational mismatches between the centre of the head and cup of 2, 3, and 4 (mm) and two cup inclination angles of 45° and 65° (n = 6 for each condition). Mean values and 95% confidence limits were determined, and student t-test and ANOVA analysis were completed with significance taken at p<0.05.Results: The magnitude of separation and the maximum axial force, measured before the head and cup relocated, increased as the level of translational mismatch between the femoral head and acetabular cup increased from 1 to 4mm (p<0.01 and p<0.01, respectively) for all cup conditions. Under a large mismatch of 4mm, the percentage of the cycle where edge loading occurred increased from 54% to 65% to 99% with increasing inclination angle (from 45° to 55° to 65°, respectively). The mean wear rates for the 2, 3 and 4mm translational mismatch conditions with the cup inclination angle at 45° were 0.07±0.04, 0.11±0.02 and 0.32±0.04mm³/million cycles respectively. The mean wear rates for the 2, 3 and 4mm conditions with the cup inclination angle at 65° were 0.14±0.05, 0.30±0.16 and 1.01±0.17mm³/million cycles respectively. Increasing the mismatch from 2 to 3 to 4mm resulted in an increased wear rate for both inclinations, with the 65° cup having significantly higher wear rate than the cup of 45° (p=0.02, p=0.02, and p<0.01 respectively). The wear rate was found to correlate positively (R²=0.99) with the level of dynamic separation under 2, 3 and 4mm mismatch for the 45° and 65° cups.Conclusion: This study demonstrated how rotational and translational surgical positioning affects the occurrence and severity of edge loading under a set of kinematic conditions. It provides an indication which supports the rationale for aligning the head and cup centres and correctly positioning the cup inclination angle during total hip joint replacement.

THE COMBINED EFFECT OF HEAD AND CUP CENTRES MISMATCH AND DIFFERENT CUP INCLINATION ANGLES ON THE OCCURRENCE AND SEVERITY OF EDGE LOADING AND WEAR IN HIP REPLACEMENT

#C10

Mr Oscar O’Dwyer Lancaster-Jonesmnoghl@leeds.ac.uk

University of Leeds

Mazen Al-Hajjar (University of Leeds), Sophie Williams (University of Leeds), Louise M. Jennings (University of Leeds), Jonathan Thompson (DePuy Synthes), Graham H. Isaac (DePuy Synthes), John Fisher (University of Leeds)

54 55

Introduction: Total ankle replacement (TAR) is an alternative to ankle fusion, replacing the natural joint with a motion preserving bearing. Current designs typically consist of three components; a dual condyle talus articulating on a conforming surface of an unconstrained polyethylene insert, the other flat insert surface slides against a similarly flat tibial surface aiming to facilitate any ankle rotation or displacement. As class II devices very little pre-clinical testing has been carried out on TARs and no wear testing standards exist. Ankle gait is complex and difficult to measure accurately therefore the aim of this study was to understand the wear effects of a range of ankle gait conditions.

Methods: Five Zenith (Corin Group PLC) unconstrained TARs consisting of Titanium Nitride coated bulk titanium tibial and talar components separated by mobile bearing conventional polyethylene inserts were tested in an adapted knee simulator (Simulator Solutions, UK) for twelve million cycles (MC). The input gait parameters were taken from available literature. The range of motion included 30degrees plantar/dorsiflexion, 10degrees rotation and a peak load of 3.15kN. A parametric study with five different kinematic conditions and six stages was conducted to understand the impact of kinematic inputs on the polyethylene wear rat. The first condition aimed to understand the effect of linear wear with isolated flexion in contrast stage two included multidirectional motion by implementing a rotational input with a maximum 9mm anterior/posterior (AP) displacement. The third stage removed the displacement, fourth reinstated it and removed rotation and the fifth ran with a 4mm AP displacement. Finally stage two was repeated. Each condition was run for two MC lubricated with 25% bovine serum solution. The wear was measured gravimetrically every MC and converted into a wear rate for each stage. A one way anova defined the significance between the wear rates. Surface measurements were taken at the end of each stage with a contacting profilometer.

Results: Post testing the tibial components showed a visual imprint of the insert contact area on the titanium nitride coating, the polyethylene inserts showed multidirectional scratches on the flat tibial articulating surface while the curved surface and talus showed fine unidirectional scratches. Stages one and four, the conditions without rotation, resulted in low polyethylene wear rates less than 2mm3/MC with no significant difference between the gait conditions with AP displacement or without. Initially the rotation and 9mm displacement of stage two caused a significant increase in wear rate to 25.8±3.1mm3/MC but this may be a wearing in period as the flat polyethylene insert surface roughness decreased from 1.343µm to 0.140µm. Three different levels of AP were tested with rotation after this polishing; 0mm, 4mm and 9mm and no significant difference was found between their wear rates ranging between 11 and 15mm3/MC. During these latter stages any changes in surface roughness were minimal.

Conclusion: The variation in the wear results showed the linear kinematic conditions compared to multidirectional had the most effect on wear. After the initial wearing in period, the displacement conditions tested had no effect on the wear rate.

WEAR OF A TOTAL ANKLE REPLACEMENT#C11

Ms Alexandra SmythMn08as@leeds.ac.uk

University of Leeds

Dr Claire Brockett (University of Leeds), Professor John Fisher (University of Leeds), Dr Silvia Suñer (Corin Group PLC)

Founding Partners

Ceramisys Ltd

Corinthian Surgical Ltd

DePuy Synthes Companies of Johnson & Johnson

Eminate Ltd

Fripp Design Ltd

Glass Technology Services Ltd

JRI Orthopaedics Ltd Materialise NV

NetComposites Ltd

NIHR LMBRU

Promethean Particles Ltd

Simpleware Ltd

Simulation Solutions Ltd

Surgical Innovations Ltd

56

NOTES

Published by MeDe Innovation, University of Leeds

ISBN 978 0 85316 347 3