Metals, Ceramics and Polymers Flashcards
*List the metals (8), ceramics (5) and polymers (7) currently used in medical implants
Metals: Stainless steel, Cobalt-Chromium alloys (cast), Titanium alloys (Ti-6Al-4V), Gold, Nickel-titanium alloys, Dental amalgam, Tantalum, Magnesium
Ceramics: Calcium phosphate, aluminium oxide, glass ceramics, carbon, titanium oxide.
Polymers: Polyamides, polyethylene, polypropylene, polyacrylates, rubber, proteins, polysaccharides.
What are the main diseases of the joint leading to total joint replacement?
Inflammatory arthritis
- Rheumatoid arthritis
- Crystal synovitus
- Psoriatic arthritis
Damage to articular cartilage and subchrondral bone
Non-infammatory arthritis
- primary generalised osteoarthritis
- Isolated osteoarthritis
- Pseudogout
- Mechanical abnormalities
Outline the differences between inflammatory and non-inflammatory arthritis.
Inflammatory arthritis is caused by inflammation of synovium (soft tissue membrane), damage to articular cartilage and subchondral bone.
Noninflammatory arthritis is caused by focal cartilage loss, subchondral bone reaction (becomes thinner and more porous) and osteophyte (bony spurs) formation.
*What are the requirements of a total joint replacement prothesis?
An articulating surface (low friction)
Anchorage at the implant site
Elasticity of implant material matching that of implant site
Biocompatibility
*Define what an articulating surface is and how different materials can act as one.
An articulating surface is the connection made between bones in a joint. A hip joint has a coefficient of friction of 0.003-0.015.
Ceramic/polymers 0.05
PTFE/PTFE 0.07
Metal/ polymers 0.25
Nylon/steel has 0.3.
*Define anchorage at implant site, and the 2 types of fixation.
Anchorage describes how an implant is secured in place in the body.
For some implants, they are designed to have a porous surface such that bone growth adheres to the surface, known as biological fixation.
Bioactive fixation describes a direct chemical bonding between the implant and bone.
e.g. bone cement is used for implants that attach directly to bone.
*Why is elasticity important in implant material?
If the elastic modulus of a material is different to that of, for example, bone, it can lead to stress shielding. This is where the implant takes most of the stress and the bone weakens over time.
It can also lead to bone resorption (destruction of bone tissues) and poor osseointegration.
What are the current directions for implant materials?
There is an increased interest in surface modification. This includes coatings, which may increase hardness of surfaces and limit ion release for metals. Plasma assisted coatings exist.
There are also monolithic structures which are multilayer and have a ‘columnar’ structure, but these can crack which leads to particle release.
A new generation of nanoscale multilayer coatings are being investigated to address this.
What are the 4 classes of ceramics? State their type of attachment to the body and give an example for each.
1) Morphological fixation - dense nonporous nearly inert ceramics which attach using bone growth into their irregularities (press fitting). Single crystal or polycrystalline alumina.
2) Biological fixation - Porous inert ceramics, mechanically attach the bone to the material. Porous polycrystalline alumina, HA coated metals.
3) Bioactive fixation - Dense, nonporous ceramics and glasses which attach directly by chemical bonding. Bioactive glasses/ glass ceramics, HA.
4) Degradable/ resorbable - Dense, nonporous or porous resorbable ceramics designed to be slowly replaced by bone. Calcium sulphate, calcium phosphate salts.
