Composites Flashcards
*Define a composite.
A physical combination of two or more materials with different physical or chemical properties, where the individual components remain separate (not an alloy for instance)
In such materials the structure has been to maximise the benefits of each component
*What is the rationale for the development of composite biomaterials?
- It has the ability to provide material properties that either material alone cannot.
- Many tissues are natural composites.
*List, with examples, applications of composite biomaterials
- Dental fillings
- Orthopaedic repair and replacement devices
- Spinal devices
- Vascular grafts
- Tendon/ ligament prostheses
- Abdominal wall prostheses
- Cartilage replacement
Define matrices and reinforcing phases of composite biomaterials, and list materials that serve in these roles.
The reinforcing material, also known as the discontinuous phase, is the added material in the form of fibres or particulates.it can be: Carbon fibre - polymer fibre etc.
The matrix, also known as the continuous phase, is the material that houses the reinforcing material. Can be non degradable (UHMWPE or PTFE), or degradable (PLA or PGA)
*Describe the main parameters that determine the mechanical properties of composites.
Mechanical properties of composite materials are strongly related to the nature of the discontinuous phase, and changing the parameters of the discontinuous phase can change the mechanical properties of the composite.
Particles, fibres, and platelet reinforcing phases have increasing effectiveness for creating stiff composites.
*Give examples of composite biomaterials and their applications, and comment on their success in those applications.
1. Dental fillings
Resin based composites are more desirable than amalgam or gold for cosmetic reasons.
They are typically composed of a polymer matrix (dimethacrylate) with stiff inorganic inclusions such as barium Glass or silica
They have high stiffness and wear resistance as well as being translucent and have an index of refraction similar to tooth enamel
Dimethacrylate-based composites undergo shrinkage which may result in crack formation
Glass ionomer cement are used as liners to reduce shrinkage stress and interfaces
*Give examples of composite biomaterials and their applications, and comment on their success in those applications.
2. Orthopaedic devices
Carbon fibre reinforced PEEK used in total hip prostheses, intramedullary nails, and fracture fixation plates.
Discontinuous phase of fibre sheets, long fibres, or chopped fibres.
The mechanical properties are determined by volume fraction, length, and alignment of carbon fibre
Has better mechanical properties than biometals, lower wear debris compared to titanium
Cannot be contoured during surgery.
*Give examples of composite biomaterials and their applications, and comment on their success in those applications.
3. Hapex
Hydroxyapatite in HDPE designed with load-bearing applications in mind
HA provides the stiffness and PE the toughness
HA is in isotropic distribution 40% by volume
The composite has a superior fracture toughness to that of bone but it’s not as strong
The mechanical properties of this composite restrict it to non-loadbearing applications such as orbital floor replacement.
Also used for customised intervertebral disc substitution
Device mimics intervertebral disc structure has softer more hydrophilic nucleus with stiffer plus hydrophilic fibre reinforced ring
*Give examples of composite biomaterials and their applications, and comment on their success in those applications.
4. Calcium sulphate composite
Calcium sulphate is a successful non-weight-bearing fast resorbing bony defect filler
Hydroxyapatite is a bioactive osteo conductive slow resorbing material
Composite produced from these two materials may be expected to demonstrate favourable results when used as a bone graft substitute
*Describe interfacial bonding within a composite and the different types.
This is how a composite holds itself together, due to intermolecular forces. There are 4 main types:
* Interdiffusion and chemical reaction
* Electrostatic attraction
* Mechanical keying
* Residual stresses (stresses that remain even after after absence of external loading)
*Discuss 5 critical factors to be considered for composite biomaterial development.
These are:
* The effects of in vivo environment
* Using improved testing methods
* Effects of wear debris from composites, and leached or resorbed products
* Using improved manufacturing methods and effects of sterilisation
* Effects of using surface coatings
