prof. dr. pedro bertemes -filho · 09/10/2016 ibme (chapter03) - dr. pedro bertemes-filho 1. ......

STATE UNIVERSITY OF SANTA CATARINA

CENTER FOR TECHNOLOGICAL SCIENCES

POSTGRADUATE PROGRAM ON ELECTRICAL ENGINEERING

RESEARCH GROUP ON BIOMEDICAL ENGINEERING

INTRODUCTION ON BIOMEDICAL ENGINEERING - IBME

Prof. Dr. Pedro Bertemes-FilhoProf. Dr. Pedro Bertemes-Filho

[email protected]@gmail.com+55 (47) 34817848

09/10/2016 IBME (chapter 03) - Dr. Pedro Bertemes-Filho 1

Chapter 04 – Biomaterial and Tissue Eng.

� MATERIALS IN MEDICINE

� Aseptic surgical technique by Dr. Joseph Lister in the 1860s;

� End of 1890s - metal devices to fix bone fractures;

� 1938 - total hip replacement prosthesis;

� 1950s and 1960s - polymers for cornea and blood vessel replacements;

INTRODUCTION ON BIOMEDICAL ENGINEERING

� 1950s and 1960s - polymers for cornea and blood vessel replacements;

� USA numbers for 2002:

� Total hip joint replacements: 448,000

� & Knee joint replacements: 452,000

� & Shoulder joint replacements: 24,000

� & Dental implants: 854,000

� Coronary stents: 1,204,000

� & Coronary catheters: 1,328,000

� DEFINITION: biomaterial is nonviable material used in a medical device, intended to

interact with biological systems (Williams, 1987)




� Impact of biomaterials:





� Biomaterials are expected to be “bioactive”;

� Bioactive: capability to initiate a biological response after implantation;


� Biomaterials are guided by design, selection, synthesis, and fabrication;

� Biomimetics: involves imitating aspects of natural materials or living tissues such as

their chemistry, microstructure, or fabrication method.



� BIOMATERIALS: PROPERTIES, TYPES, AND APPLICATIONS

� Mechanical Properties and Testing

� The most common way to determine mechanical properties is to pull a specimen

apart and measure the force and deformation;

� Force is measured in Newtons & deformation in millimeters, then Stress is

calculated as: σ(N/m2) = force/cross-sectional area



Measuring the stiffness of the material, which is called the elastic modulus (E=σ/ε) or Young’s modulus



� Mechanical Properties and Testing

� Summary of mechanical properties of cortical bone and biomaterial:


MaterialTensile strength

(MPa)Compressive

strength (MPa)Elastic modulus

(GPa)Fracture toughness

(MPa. m-1/2)


Bioglass 42 500 35 2

Cortical Bone 50-151 100-230 7-30 2-12

Titanium 345 250-600 102.7 58-66

Stainless steel 465-950 1000 200 55-95

Ti-Alloys 596-1100 450-1850 55-114 40-92

Alumina 270-500 3000-5000 380-410 5-6

Hydroxyapatites 40-300 500-1000 80-120 0.6-



� Metals

� Used as biomaterials have high strength and resistance to fracture and are

designed to resist corrosion





� Metals





� Metals: examples


Metal plates and screws used to

hold fractured bone segments


total hip joint

replacement

artificial

knee joint

hold fractured bone segments

together during healing



� Metals:

� Advantages of metals over other materials such as ceramics and polymers are

that they are strong, tough, and ductile (or deformable);

� Disadvantages include: susceptibility to corrosion due to the nature of the

metallic bond (free electrons);


metallic bond (free electrons);

� In the 1900s, steels used for hip implants had corrosion in the body THEN they

changed to alloys of titanium or cobalt-chrome for hip, knee, and dental

implants;

� Metals are also applied in eye glasses and coronary artery stents that are

inserted through a catheter (i.e., nitinol – a shape memory alloys).




� Ceramics and Glasses

� The advantages of the ceramics are that they are biocompatible, are inert, have

low wear rates, are resistant to microbial attack, and are strong in compression;

� Some disadvantages include: fragility, and being difficult to machine;

� Ceramics do not conduct heat or electricity, but Ceramics have very high melting

points, generally above 10008C, and are brittle;


points, generally above 10008C, and are brittle;

� Bioactive ceramics (i.e., compositions of ceramics, glasses, glass-ceramics, and

composites) are used stimulate direct bone bonding for securing orthopedic

medical devices


synthetic bone graft

substitutes: made of

calcium phosphate or

calcium sulfate



� Polymers

� Advantages: flexibility , stiffness, low/high strength, resistant or not to protein

attachment, biodegradable or permanent, and fabricated into complex shapes by

many methods;

� Disadvantages: they tend to have lower strengths than metals or ceramics,

deform with time, may deteriorate during sterilization, and may degrade in the


deform with time, may deteriorate during sterilization, and may degrade in the

body by releasing toxic products;

� Fillers, plasticizers, stabilizers, and colorants typically are used in polymer

synthesis to enhance the mechanical, chemical, and physical properties;

� Polymers can be classified as thermoplastic or thermosetting;

� Thermoplastic polymers can be heated, melted, molded, and recycled;

� Thermosetting is a three-dimensional cross-linked structure, then it cannot be

heated and reused (i.e., Hydrogels);

� Applications of hydrogels: contact lenses, drug delivery vehicles, wound healing

adhesives, sexual organ reconstruction materials, artificial kidney membranes,

and vocal chord replacement materials.




� Polymers: synthetic polymer scaffolds for tissue engineering:





� Natural Materials

� Proteins and polysaccharides are nature’s form of polymers and are used in

medical devices;

� Types: Nylon, silk, calcium phosphate bone crystals or calcium carbonate coral

or sea shells, collagen, biopolymers;

It also encompasses donor tissue such as bone or skin which may be patient


� It also encompasses donor tissue such as bone or skin which may be patient

derived (autograft), from another human (allograft), or from a different species

such as bovine or porcine (xenograft);

� Advantages: lower incidence of toxicity and inflammation as compared to

synthetic materials;

� Disadvantages: expensive to produce or isolate natural materials; variability

between lots of natural materials;




� Composites

� The term composite is reserved for materials consisting of two of more chemically

distinct constituents that are separated by a distinct interface;

� Composites are made by mixing two components and molding, compacting, or

chemically reacting them together;

Advantages: the properties can be tailored to fit nearly any application;


� Advantages: the properties can be tailored to fit nearly any application;

� Disadvantages: difficult to make a composite with an ideal structure;




� Composites





� Other examples




� TISSUE–BIOMATERIAL INTERACTIONS





� Interactions with Blood and Proteins

� It makes first contact with the implanted biomaterial;

� Proteins play an important role in determining the final nature of the tissue–

implant interface: immunoglobulins, fibrinogen;


� The Wound Healing Response after Biomaterial Implantation


(a) Protein attachment to the biomaterial

surface guides cellular interactions;

(b) Hemostasis is accomplished by clot

formation;

(c) Cells found in blood and other

inflammatory cells attempt to process the

foreign biomaterial and repair adjacent

material;

(d) The host protects itself from the foreign

biomaterial through encapsulation with

fibrous tissue.



� Metallic Corrosion:

� Corrosion resistance is one of the most important properties of metals used for

implants: galvanic (or mixed metal) corrosion, crevice corrosion, and fretting

corrosion;

WHY? - when two dissimilar metals are connected in an electrochemical cell, one


� WHY? - when two dissimilar metals are connected in an electrochemical cell, one

will act as an anode while the other will be the cathode;




� Biomaterial Degradation and Resorption:

� Biomaterials may be permanent or degradable;

� Bioresorbable implants are designed to degrade gradually over time in the

biological environment and be replaced with natural tissues;


� Collagen and the lactic acid and/or glycolic acid polymers are the most

commonly used for resorbable applications;

� Immunogenicity

� It is the tendency for an object to stimulate the immune response;

� Examples: bacteria, pollen from grass or trees, small or absorbable biomaterials,

and proteins in food that lead to allergies or inflammation;

� Corrosion of metallic implants releases metal ions that can cause metal sensitivity

or allergic reactions in some individuals. Allergic reactions can lead to slow or

inadequate bone fusion or skin dermatitis.



� WHAT IS TISSUE ENGINEERING?

� Tissue engineering is a biomedical engineering discipline integrating biology with

engineering to create tissues or cellular products outside the body (ex vivo) or to make

use of gained knowledge to better manage the repair of tissues within the body (in

vivo).

� It also requires knowledge of many engineering fields, including biochemical and

mechanical engineering, polymer sciences, bioreactor design and application, mass


mechanical engineering, polymer sciences, bioreactor design and application, mass

transfer analysis of gas and liquid metabolites, and biomaterials.

� Clinical trials with cell therapies or extracorporeal organs: cartilage, bone, skin,

neural, and liver tissues;




� Challenges Facing the Tissue Engineer

� The four principal size scales in

tissue engineering and cellular

therapies---------------------------�





� Cellular Therapies, Grafts, and Extracorporeal Bioartificial Organs

� It requires organized culture control and exploitation of cell metabolites;

� Bioengineering challenges: i) cell therapies include injection needle design and

procedure protocols; ii) bioreactors — the function, choice, manufacturing, and

treatment of biomaterials for cell growth and device construction;


� Human Cells and Grafts as Therapeutic Agents

� Cell therapies use human cells as therapeutic agents to alleviate a pathological

condition (i.e., blood transfusion, platelets, bone marrow, hematopoietic stem

cells);




� Mechanisms Governing Tissues

� The number of cells required to replace the physiological functions defines the

overall dimension of an engineered product.





� Resume:



prof. dr. pedro bertemes -filho · 09/10/2016 ibme (chapter03) - dr. pedro bertemes-filho 1. ......

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