characterization and corrosion behavior of poly(ɛ-caprolactone)/hydroxyapatite composite coating...
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Characterization and Corrosion Behavior of Poly(ɛ-caprolactone)/Hydroxyapatite Composite Coating on Ti6Al4V Fabricated by Dip - Coating TechniqueTRANSCRIPT
Characterization and Corrosion Behavior of Poly(ɛ-caprolactone)/Hydroxyapatite Composite Coating on
Ti6Al4V Fabricated by Dip - Coating Technique
By :Mohd Faiz Mohd Yusoff
MW103004Main-Supervisor :
Prof. Ir. Dr. Mohammed Rafiq
Co-Supervisor :Dr. Rafaqat Hussain
GARDEN OF KNWOLEGDE AND VIRTUEGARDEN OF KNWOLEGDE AND VIRTUE
INSPRING CREATIVE AND INNOVATIVE MINDSINSPRING CREATIVE AND INNOVATIVE MINDS
:: IN THE NAME OF ALLAH, MOST GRACIOUS, MOST MERCIFUL :::: IN THE NAME OF ALLAH, MOST GRACIOUS, MOST MERCIFUL ::
Presentation Outlines
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1.0 INTRODUCTION1.0 INTRODUCTION
2.0 MATERIALS & METHODS2.0 MATERIALS & METHODS
1.1 Project Background1.2 Problem Statement1.3 Objectives1.4 Scope of Study1.5 Significance of study
3.0 RESULTS & DISCUSSIONS3.0 RESULTS & DISCUSSIONS
4.0 CONCLUSIONS4.0 CONCLUSIONS
5.0 RECOMMENDATION5.0 RECOMMENDATION
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Biomaterial
Biocompatibility
Bio-degradable Bio-inert
Natural or synthetic material that aims to replace part of living tissue or to restore a normal function in biological
environment
Does not initiate a positive response when introduced
to the living tissue
The acceptance of the implant material by the surrounding tissues without producing any undesirable
response from the body and vice versa [1,2]
Induce positive interaction with
surrounding tissue
Metal Polymer Ceramic Composite
Bio-activeThe ability of material to
dissolve in biological environment and gradually substituted by new tissue
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Metals in Biomedical Applications
Metallic biomaterials are most commonly used for load bearing implant and internal fixation device due to its featured characteristics such as :i.Excellent mechanical properties :
High tensile strength High yield strength Resistance to cyclic loading (fatigue) Resistance to time dependent deformation (creep)
ii.Biocompatibility (low cyto-toxicity)iii.High corrosion resistance
The most commonly used metals and alloys for medical devices application include :i.Ti and Ti6Al4Vii.316L Stainless Steels iii.Co-Cr-based alloys
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DentistryOrthopedic
Craniofacial Cardiovascular
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Limitations of Metallic Implants
Bio-inert :Do not promote the formation of apatite layer on its surface [3]
Release metallic ions :May combine with biomolecules and
cause adverse biological reaction [4,5]
Solution
Surface modification:Coating with bioactive material
• Accelerate bone healing and bonding of the coatings with bone [6,7,8]• Enhance the corrosion resistance of metallic implant where coating layer
will reduce the release of metallic ions by acting a barrier• Combine the mechanical benefits of metal alloys with bioactivity of bioactive
materials
Advantages
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Coating materials
Hydroxyapatite (HA)Hydroxyapatite (HA)
Chemical Formula : Ca10(PO4)6(OH)2
The most important calcium phosphate compounds found in natural hard tissues as mineral phase
Ca/P ratio : 1.67 (similar to the bone)
Act as reinforcement in hard tissue and responsible for the stiffness of bone, dentine, and enamel.
Osteconductive : Promote osteointegration & accelerate implant fixation
Bioactive ceramic materials
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Deposition Technique
Plasma Spray
CVD
EBDPVD
Dip-Coating
PLD Sol-Gel
Sputter Coater
Biomimetic
Advantages Disadvantages
Rapid deposition rateHigh processing temperature
induces decomposition of HA[9,10]
Non-uniform coating with cracks[11]
Good adhesion High cost equipment and demand elaborate setup
Commercial Technique
What is potential alternative technique
to fabricate HA coating?
What is potential alternative technique
to fabricate HA coating?
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Deposition Technique
Dip-Coating
Advantages Disadvantages
Inexpensive equipment & simple setup
Poor adhesion between the coatings and metallic substrates
Uniformity of deposition [12]
Low processing temperature
Ability to coat complex substrate [13]
Ability to control coating amount and thickess
Alternative Technique
Solution: Post heat treatment (sintering)
i.Improve the coating adhesionii.Densify coating layeriii.Eliminate porosity
Solution: Post heat treatment (sintering)
i.Improve the coating adhesionii.Densify coating layeriii.Eliminate porosity
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Effect of high sintering temperature during heat treatment :
Problem Statement
Sintered in air at 600°C for 1h
Cracks
Sintered in vacuum at 800°C for 1h
i. The formation of cracks on the surface due to the thermal expansion coefficient mismatch between the coatings and substrate during sintering and cooling [14,15]
Substrate expose to the high temperature
iii. Oxidation and impaired mechanical properties [17]
ii. Catalyze the decomposition of HA into non-crystalline which increased the in-vitro dissolution rate [16]
HOW TO SOLVE ?Electrochemical study of HA coatings on stainless steel substrate (Quihua Yuan, 2009)
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• Poly (ɛ-caprolactone) [PCL; (C6H10O2)n] is a semi crystalline aliphatic polyester that can be synthesised by ROP of monomeric unit "ɛ-caprolactone” with good biocompatibility, sustained biodegradability, and remarkable mechanical properties [18,19,20].
• The use of PCL as polymeric binder can help to improve HA coating and eliminate the need of sintering process to densify the coating layer.
Polymer Binder : Poly (ɛ-caprolactone) (PCL)
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i. To develop a polymer-ceramic composite coating for Ti6Al4V alloy substrate by using dip coating technique
ii. To study the effect of PCL concentration in HA coating on deposition technique parameters.
iii. To study the anti-corrosion properties of the PCL/HA coated Ti6Al4V alloy substrate.
Objectives
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Significance of Study
i. An alternative coating technique which is simple, cost effective yet gives clinically acceptable results will be developed.
ii. The problem related to the dip coating technique (poor bonding adhesion) is solved by using polymeric binder.
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Parameter Description
Metallic Substrate Ti6Al4V (Dimension : 10 mm x 10 mm x 10 mm)
Deposition Technique Dip Coating ( HTWL-01 Destop Dip Coater (MTI Cooperation, USA)
HA precursor Ca Precursor : Ca(NO3)2.4H2OP precursor : (NH4)2HPO4
Polymeric Binder Poly (ɛ-caprolactone) (PCL)
Characterization Analyses XRD, FTIR, SEM
Electrochemical test Potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) test(VersaSTAT 3, Priceton Applied Research)
Scope of Study
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Materials
Name Formula Brand MW (g/mol)
Calcium nitrate tetra hydrate Ca(NO3)2.4H2O QRëCTM, AR grade 236.18
Diammonium hydrogen phosphate
(NH4)2HPO4 QRëCTM, AR grade 132.06
Ammonium hydroxide NH4OH QRëCTM, AR grade 35.04
Chloroform CH3Cl QRëCTM, AR grade 119.38
Poly (ɛ-caprolactone) pallets [C6H10O2]n Sigma Aldrich, UK -
Sodium chloride NaCl Sigma Aldrich, UK 58.44
Sodium bicarbonate NaHCO3 Sigma Aldrich, UK 84.00
Calcium chloride CaCl2 Sigma Aldrich, UK 110.98
Potassium chloride KCl Sigma Aldrich, UK 74.55
Dipotassium phosphate anhydrate
K2HPO4.3H2O Sigma Aldrich, UK 174.18
Magnesium chloride hexahydrate
MgCl2.6H2O Sigma Aldrich, UK 203.30
Sodium sulphate Na2SO4 Sigma Aldrich, UK 142.04
Table 2.1 List of reagent used in the experiment
Substrate Preparation
Grinding 150 - 1000 grit sized silicon
carbide (SiC) paper
CleaningUltrasonically clean in acetone for
15 min
DryingIn oven at 40 °C for 30 min
4 mm
12 mm
12 mm
Cutting
StorageDesiccator
Synthesis of HA powder : Microwave assisted co-precipitation method
Ca – Precursor[Ca] = 1.0 M
P - Precursor[P] = 0.6 M
Ca - P MixtureCa/P : 1.67
Precipitation pH above 10
Drop wise
RefluxingMicrowave oven
30 min ( 20 s ON and 20 s OFF)
Filtration & Washing
Drying 24 h (80°C)
Heat TreatmentMuffle Furnace
900 °C for 3h (heating rate 5°C)
CharacterizationXRD & FTIR
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Preparation of PCL/HA Suspension
Sample code
HA PCL Solvent Total volume
(ml)Weight
(g)% Weight
(g)%
i 1.35 90 0.15 10
Chloroform
10ii 1.20 80 0.30 20iii 1.05 70 0.45 30
iv 0.90 60 0.60 40v 0.75 50 0.75 50
1. PCL pallets were dissolved in chloroform at room temperature for 15 min followed by the addition HA powder (sieved to 71 µm) as shown in Table 2.2.
2. The ratio of final concentration was 15 % (w/v).
3. Finally, the mixture was stirred at room temperature for 72 h.
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Dip – coating process
To investigate the effect of dip coating parameter on coating efficiency :
i.Withdrawal speed (mm/min): 40, 80, 120, 160, 200
ii.Number of dips: (1 -5)
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Characterization
Viscosity of the suspension :• Brookfield DV-II Pro Viscometer
Coating thickness :• Hitachi Tabletop Microscope, TM3000
Phase composition : • XRD (Bruker D-8 Advance diffractometer)
Functional group :• FTIR (ALPHA-T, Brucher)
Surface morphology : • SEM (JOEL JSM-6390 LV)
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Electrochemical Test
Parameter Description
Equipment Potentiodynamic/galvanostat (VersaSTAT 3, Priceton Applied Research)
Cell electrode Counter : Graphite Reference : Ag/AgClWorking : Ti4Al4V
Artificial body fluid Simulated body fluid (SBF)
Exposed surface area of working electrode
0.5 cm2
Potentiodynamic polarization test
Scan rate : 1 mV/sPotential range : -400 mV to +900 mV
Electrochemical Impedance Spectroscopy (EIS) test
Perturbation amplitude : 10 mVFrequency range : 105 Hz to 10-3 Hz
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Electrochemical Test
Tafel extrapolation method
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The effect of PCL concentration on coating properties
Deposition amount
Coating Thickness
PCL Concentration
(wt. %)
Viscosity,ƞ
(N.s.m-2)
0 0.03328
10 0.07274
20 0.09628
30 0.10716
40 0.13416
50 0.27122
No. of dips : 5; Withdrawal speed : 200 mm/min
SEM : Surface Morphology
The surface is not fully covered by HA coating
HAHA
10 % PCL/HA10 % PCL/HA
30 % PCL/HA30 % PCL/HA
50 % PCL/HA50 % PCL/HA
Surface level pores
Free cracks
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SEM : Cross Section
HAHA 10 % PCL/HA
10 % PCL/HA
30 % PCL/HA30 % PCL/HA 50 % PCL/HA
50 % PCL/HA
Coating layer Coating layer
Coating layer
Coating layer
Ti6Al4v Ti6Al4v
Ti6Al4v
Ti6Al4v
Thin and loosely packed coating
Thick and densely packed
coating
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30 % PCL/HA composite coating
SMSM
CSCS
For further investigationFor further
investigation
Surface level pores
Important for promoting osteointegration & nutrient diffusion
Important for promoting osteointegration & nutrient diffusion
Densely packed and intact coating
Indicate the bonding between coating and Ti6Al4V is enough to
resist the force during implantation process
Indicate the bonding between coating and Ti6Al4V is enough to
resist the force during implantation process
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The Effect of Withdrawal Speed and Number of Dips on Deposition Amount
30 % HA/PCL
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The Effect of Withdrawal Speed and Number of Dips on Coating Thickness
30 % HA/PCL
Landau-Levish equation :Landau-Levish equation :
h : thicknessȠ : viscosityv : withdrawal speedγ : liquid-vapour surface tensionρ : densityg : gravitational acceleration
The coating thickness increases as the withdrawal speed
increases
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XRD
HA
TCP
PCL
HA
30 % HA/PCL
Confirm the presence of PCL
Confirm the presence of PCL
Scherrer’s EquationCrystallite size of HA : 18 nm
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FTIR
HA
30 % HA/PCL
Confirm the presence of PCL Confirm the presence of PCL
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Sample Ecorr (mVSCE) icorr ( µA/cm2) Rp (MΩcm2)
Ti6Al4V -372.4 2.6827 x 10-7 0.9110
HA -229.1 6.2560 x 10-8 6.9498
30 % PCL/HA -79.24 7.6862 x10-9 15.0987
PPT
Noble direction
Lower current density
4 x
35 x
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EIS
Higher Z modulus at lower frequency displays a better corrosion resistance
on metal substrate
1.5 orders
2 orders
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Conclusion
I. In this study, we have demonstrated that dip coating technique can be used to obtained homogeneous crack-free coating of PCL/HA composite coating on Ti6Al4V.
II. Process parameters and polymer concentration were successfully manipulated to control the deposition amount and coating thickness.
III. The addition of 30 % PCL to HA considerably improved the adhesion of HA and resulted in densely packed coating which provide better corrosion protection when compared with HA coating making this combination a potential candidate for biomedical application.
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RECOMMENDATIONS
In vitro study : cell adhesion, proliferation and differentiation
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