Week 9 - Tissue Compatibility

Question 1

Is there a completely inert biomaterial?

Answer 1

No - all elicit a non specific inflammatory response around foreign matter

Question 2

How long after implantation does cellular invasion occur?

Answer 2

24 hours - layer of tissue is formed

Question 3

What is the difference between implant response and regular wounds?

Answer 3

• An implant never gets better

- No matter how hard the body tries, it cannot heal the implant

Question 4

What actions does the body take to remove the implant?

Answer 4

When it cannot be digested, the body tries to extrude the object or surround it with a dense fibrous sheath

Question 5

If the object is not chemically and physically inert, what cells are primary involved in the implant response?

Answer 5

Macrophages and giant cells

Question 6

What is the generalised response to metal implants?

Answer 6

• Most pure metals tend to evoke very strong immune response

- Certain antibodies are produced to help destroy

Question 7

Are there any exceptions to the metal implant response?

Answer 7

Gold and platinum

Question 8

What happens to metals in the body with regard to oxidation?

Answer 8

• The body corrodes and forms oxides
• Dense oxide layer may passivate the metal
• Ti the best because of this

Question 9

What happens when metal ions are leached from the implant and why does it happen?

Answer 9

What: they can further leach into the blood and cause toxicity
Why: not specifically antigens but they form metalloprotein complexes which are antigens

Question 10

Are ceramics antigens within the body?

Answer 10

No - the only biomaterial to not be recognised as antigens, meaning the body loves them

Question 11

Are ceramics bioinert/bioactive?

Answer 11

At the very least bioinert, at the best bioactive

Question 12

What types of ceramics are mostly used?

Answer 12

Oxides - often in their highest oxidation state

Question 13

Why are bioglass based and calcium phosphates used?

Answer 13

They are both bioactive and can either bond to bone directly or enhance bone formation (bioglass even bond to soft tissues)

Question 14

What are the systemic effects of implants?

Answer 14

Immune diseases, cancer, changes in blood pressure, particles being transported, wear particles and toxic buildup

Question 15

What are the requirements for blood compatibility of biomaterials?

Answer 15

• Cannot allow blood coagulation
• Must not cause hemolysis
• Should be smooth
• Should be compatible with endothelial cells

Question 16

What are the factors affecting blood compatibility?

Answer 16

Surface roughness, surface wettability, electrical properties and chemical properties

Question 17

Why surface roughness for blood compatibility?

Answer 17

The rougher the surface, the higher the contact surfaces area available for clotting

Question 18

Why surface wettability for blood compatibility?

Answer 18

Hydrophobic was thought to be better but not strong correlation

Question 19

Why electrical properties for blood compatibility?

Answer 19

Relates to the amount of potential built up by blood flow over the surface - a negatively charged surface tends to reduce clotting

Question 20

Why chemical properties for blood compatibility?

Answer 20

Related to electrical properties but highly reactive chemical elements = bad blood compatibility

Question 21

What are carcinogens?

Answer 21

Substances causing the onset of cancerous disease

Question 22

Why is the form of the implant important for carcinogenicity?

Answer 22

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

Question 23

What are some examples of known or suspected carcinogens?

Answer 23

Nickel and cobalt

Question 24

What are examples of systemic and host responses to implants?

Answer 24

Hypertension, blood composition changes, metabolic or enzymatic changes due to metal ion content and metal allergy causing loosening of implants

Question 25

What factors affect the risk to patients following implantation?

Answer 25

Increasing periods of implantation and increased surface area

Question 26

Why synthetic biomaterials?

Answer 26

Immune responses are caused between autografts, allografts and xenografts

Question 27

What is the relevance of protein adsorption?

Answer 27

Protein adsorbed on the surface of the biomaterial is what is seen by cells - makes it the key determinant to controlling bioreaction to implants