Week 9 - Tissue Compatibility Flashcards
Is there a completely inert biomaterial?
No - all elicit a non specific inflammatory response around foreign matter
How long after implantation does cellular invasion occur?
24 hours - layer of tissue is formed
What is the difference between implant response and regular wounds?
- An implant never gets better
- No matter how hard the body tries, it cannot heal the implant
What actions does the body take to remove the implant?
When it cannot be digested, the body tries to extrude the object or surround it with a dense fibrous sheath
If the object is not chemically and physically inert, what cells are primary involved in the implant response?
Macrophages and giant cells
What is the generalised response to metal implants?
- Most pure metals tend to evoke very strong immune response
- Certain antibodies are produced to help destroy
Are there any exceptions to the metal implant response?
Gold and platinum
What happens to metals in the body with regard to oxidation?
- The body corrodes and forms oxides
- Dense oxide layer may passivate the metal
- Ti the best because of this
What happens when metal ions are leached from the implant and why does it happen?
What: they can further leach into the blood and cause toxicity
Why: not specifically antigens but they form metalloprotein complexes which are antigens
Are ceramics antigens within the body?
No - the only biomaterial to not be recognised as antigens, meaning the body loves them
Are ceramics bioinert/bioactive?
At the very least bioinert, at the best bioactive
What types of ceramics are mostly used?
Oxides - often in their highest oxidation state
Why are bioglass based and calcium phosphates used?
They are both bioactive and can either bond to bone directly or enhance bone formation (bioglass even bond to soft tissues)
What are the systemic effects of implants?
Immune diseases, cancer, changes in blood pressure, particles being transported, wear particles and toxic buildup
What are the requirements for blood compatibility of biomaterials?
- Cannot allow blood coagulation
- Must not cause hemolysis
- Should be smooth
- Should be compatible with endothelial cells
What are the factors affecting blood compatibility?
Surface roughness, surface wettability, electrical properties and chemical properties
Why surface roughness for blood compatibility?
The rougher the surface, the higher the contact surfaces area available for clotting
Why surface wettability for blood compatibility?
Hydrophobic was thought to be better but not strong correlation
Why electrical properties for blood compatibility?
Relates to the amount of potential built up by blood flow over the surface - a negatively charged surface tends to reduce clotting
Why chemical properties for blood compatibility?
Related to electrical properties but highly reactive chemical elements = bad blood compatibility
What are carcinogens?
Substances causing the onset of cancerous disease
Why is the form of the implant important for carcinogenicity?
Physical form is often important but so is surface chemistry - e.g. when polymers are in sheet form they create cancer but less in fibre form
What are some examples of known or suspected carcinogens?
Nickel and cobalt
What are examples of systemic and host responses to implants?
Hypertension, blood composition changes, metabolic or enzymatic changes due to metal ion content and metal allergy causing loosening of implants
