1. Overview of Biomaterials
By:
Dr. Murtaza Najabat Ali (CEng MIMechE P.E.)

2. Types of Biomaterials Biomaterials Metals Natural Ceramics Composites
Biomaterials can be divided into four major classes of materials
Biomaterials
Polymers
Metals
Natural
Ceramics
Composites
Fifth Class of Biomaterials

3. Types of Biomaterials contd..

4. Types of Biomaterials contd..

5. Types of Biomaterials contd..
Polymers
Consists of repeating units strung together in long chains
Represent the largest class of biomaterials
Natural
Synthetic
Hydrophobic
Hydrophilic
Water swelling materials (Hydrogels)
Biostable
Biodegradable

6. Types of Biomaterials contd..
Application of Polymers as Biomaterials
The hip joint is the largest load bearing joint. A hip joint is lined with a layer of cartilage that reduces friction and acts as a shock absorber. When the bone is exposed to arthritis and injury, this protective layer is damaged, causing extreme pain.
Polymers used as femoral head and acetabular cup in total hip replacement

7. Types of Biomaterials contd..
Polymers
By using a Polymethyl-methacrylate (PMMA) cement to adhere the metal to the bone
By using a porous metal surface to create a bone ingrowth interface
The acetabulam and the proximal femur ca be also replaced, where the femoral side is completely metal. The acetabular side is composed of the polyethylene bearing surface

8. Bonding Time: Cemented Vs. Cementless
Types of Biomaterials contd..
Polymers
Bonding Time: Cemented Vs. Cementless
Cemented
Approximately 10min
Cementless
One year or more for good ingrowth
Healing Time
Cemented
Cementless
Weight bearing
Next day with crutches
Next day depending on stability
Walk (crutches)
2 day after surgery
6-12 weeks depending on surgeon
Pain Free
5 days in some cases
Depends on stability
Normal Walk
2 weeks (6 weeks with crutches is recommended)
Couple of months to 1 year depending on ingrowth rate
Everything good
Around six months for a knee replacement
2 years onward

9. Types of Biomaterials contd..
Polymers
PMMA and silicone elastomers are used as Intraocular lenses to treat cataract
Hard contact lenses for clear vision

10. Types of Biomaterials contd..
Polymers
Ultra high molecular weight Polyethylene, as Femoral head, acetabular cup or insert
Polyethylene, Polytetrafluoroethylene (PTFE) and silicone used as medical tubing for drains and catheters

11. Types of Biomaterials contd..
Polymers
The healthy human knee joint is also lined with articular cartilage. Arthritis and injury can similarly damage this protective layer of cartilage causing extreme pain
Hyaluronic Acid (HA) Injections restores lubrication and fluid in the joint and creates a shock absorber between the bones

12. Types of Biomaterials contd..
Polymers
Pacemakers leads are insulated by silicone
PTFE and Polyurethane used as Vascular and non-vascular grafts
Polyvinylchloride (PVC) and silicone used as Tubing, blood storage bags, in blood transfusion, feeding and dialysis

13. Types of Biomaterials contd..
Metals
Load bearing implants and internal fixation devices;
When processed suitably contribute high tensile, high fatigue and high yield strengths;
Properties depend on the processing method and purity of the metal.
When metallic biomaterials were first used in biomedical applications, the only requirement was to achieve a suitable combination of physical properties to match those of the replaced tissue with a minimal toxic response of the host
Few concepts were gradually introduced with time as requirements for metallic biomaterials in the design of implantable devices, such as
Foreign body reaction (particularly due to wear debris)
Stress shielding
Biocompatibility
Bioactivity, and
Osteoinduction

14. Types of Biomaterials contd..
Metals
Although many metals and alloys are used for medical device applications, the most commonly employed are
Stainless steels
Cobalt-base alloys
Commercially pure Titanium and Titanium alloys
Nickel- Titanium alloys, and some
Noble metals (Au, Pt, Pd)

15. Types of Biomaterials contd..
Metals

16. Types of Biomaterials contd..
Metals

17. Types of Biomaterials contd..
Metals
Ti alloy Pacemaker case and metallic leads encapsulated in silicone tubing
Metal electrodes
In Phrenic stimulator for respiratory control

18. Types of Biomaterials contd..
Metals
Tooth metal crown
For securing removable denture
Ti alloy single teeth replacement
Metal wires and braces

19. Types of Biomaterials contd..
Metals

20. Types of Biomaterials contd..
Ceramics
Bone bonds well to them
Exhibit minimum foreign body reaction
High stiffness
Low friction and wear coefficients
But
Low fracture toughness
Low impact resistance
Owing to its Brittle nature

21. Calcium Phosphates (CaPs) Bioactive Glasses (BGs)
Types of Biomaterials contd..
Ceramics
Alumina (Al2O3)
Zirconia
Several porous ceramics (CaCO3)
The most common ceramic materials can be classified (both as cements and ceramics) as ;
Calcium Phosphates (CaPs)
Bioactive Glasses (BGs)
Glass Ceramics
Hydroxyapatite Ca10(PO4)6(OH)2
A range of suitable CaPs (amorphous CaP (ACP), dicalcium phosphate (DCP), tricalcium phosphate (α-TCP, β-TCP), tetracalcium phosphate (TTCP) e.t.c.)
Several BGs formulations containing e.g. SiO2 as network former and Na2O, CaO and P2O5 as
modifying oxides (Bioglass 45S5)

22. Types of Biomaterials contd..
Ceramics
Alumina Femoral head and Acetabular liner

23. Types of Biomaterials contd..
Ceramics
Zirconia dental crown and bridges
Hydroxyapatite coated metallic implants
Zirconia artificial tooth root

24. Calcium Phosphate Scaffold
Types of Biomaterials contd..
Ceramics
Calcium Phosphate Scaffold
All-carbon mono-leaflet mechanical heart valves consist of a rotatable housing ring within a compliant suture ring
HA scaffold (light purple colour) with bone (yellow colour) that has grown in the scaffold

25. Types of Biomaterials contd..
Example 6 :
Which of the following classes of biomaterials would be most appropriate for use to fabricate an artificial tendon, a tissue that must sustain substantial deformation at low forces and return rapidly to its original dimensions upon release of the stress ? WHY ?
(a) Metals (b) Ceramics (c) Polymers

26. Important Characteristics
The selection of the biomaterial and selection of the appropriate processing techniques for a given application is determined primarily by
Surface
Bulk, and
Degradative properties of the material

27. An interface is the boundary region between two adjacent layers
Important Characteristics contd..
Surface Properties of Biomaterials
What constitutes a surface?
An interface is the boundary region between two adjacent layers L V G S
L = Liquid
G = Gas
S = Solid
V = Vapor
We recognize (S/G), (S/L), and (L/V) as surfaces

28. Important Characteristics contd..
Surface Properties of Biomaterials
Biomaterial surface Protein adsorption
The effect of protein size on interaction with a surface. Notice that the larger protein composed of more amino acids is capable of making more interactions
Proteins (red) adsorb differently to the different materials and are depicted as elongated on metal and globular on polymer. Cells (blue) interact with the materials via the adsorbed proteins and conformation of the adsorbed proteins dictates how the cells will respond (adhere, proliferate, differentiate, etc.).

29. Important Characteristics contd..
Surface Properties of Biomaterials
The surface of a material is defined to be the few atomic layers on the exterior of the object
Surface properties can be different from the bulk properties
Surface properties include both chemical and physical characteristics

30. Important Characteristics contd..
Surface Properties of Biomaterials
Surface Chemical Property
Contact Angle
The contact angle is the angle at which a liquid-vapor interface meets the solid-liquid interface
The contact angle is determined by the resultant between Adhesive and Cohesive forces
As the tendency of a drop to spread out over a flat solid surface increases, the contact angle decreases
A shows a fluid with very little wetting, while C shows a fluid with more wetting. A has a large contact angle, and C has a small contact angle.
Wetting
Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together
Water bead on a fabric that has been made hydrophobic
Thus, the Contact angle provides an inverse measure of Wettability

31. Important Characteristics contd..
Surface Properties of Biomaterials
Surface Tension
Surface tension is a measurement of the cohesive energy present at an interface
This forms a surface “Film” which makes it more difficult to move an object through the surface
Hydrophilicity
If the liquid is very strongly attracted to the solid surface
The droplet will completely spread out on the solid surface
Hydrophobicity
If the solid surface is hydrophobic, the contact angle will be larger than 900C

32. Important Characteristics contd..
Surface Properties of Biomaterials
Surface Physical Property
Surface Roughness

33. Important Characteristics contd..
Surface Properties of Biomaterials
Example 2.1:
Would a hydrophobic or hydrophilic polymer be a more appropriate choice for a Contact lens application? WHY ? Would a melting temperature (Tm) of the polymer above 37oC or below 370C be more appropriate for this application ? WHY ?
Example 2.2:
A 1ml droplet of distilled water is dropped onto each material “A” and “B” as shown below. Which material is more hydrophilic ? Justify your answer.
Example 2.3:
Why do atoms at the surface of a crystalline material generally possess higher energy than those inside of the crystal and what is the term for this heightened energy ?

34. Important Characteristics contd..
Bulk Properties of Biomaterials
Most important parameter
They may play a less significant role in initial biological interaction/response, but they have a large long-term impact
They can be altered to allow the biomaterial to mimic the physicochemical properties of the biological system
Bulk characteristic of biomaterials include
Mechanical Properties
Physical Properties
Chemical composition

35. Important Characteristics contd..
Bulk Properties of Biomaterials
Mechanical Properties
Such as,
Strength
Stiffness
Anisotropy
Fatigue properties/strength
Mechanical properties of materials are highly affected by their physical and chemical characteristics

36. Important Characteristics contd..
Bulk Properties of Biomaterials
Physical Properties
Such as,
Crystallinity
Thermal Transition Points
Melting Point (Tm)
Glass Transition Point (Tg)
Chemical Composition
SEM Micrograph of steel showing grain boundaries
It varies when chemicals are added or subtracted, and when the ratio of substances changes
It determines the (bulk) properties of the substance
It also dictates other properties such as chemistry at the surface

37. Important Characteristics contd..
Degradative Properties of Biomaterials
Factors that affect biomaterials’ degradation in vivo
The size and shape of the implant
Its location in the body
Chemical, physical and mechanical (both bulk and surface) properties
Although the temperature and pH of body environment/fluids are relatively mild, BUT !
Degradation can be undesired or desired
The biocompatibility of degradation by-products is as important as the biocompatibility of the intact material