Biomaterials

Question 1

What is meant by the term biomaterial?

Answer 1

A biomaterial is defined as any substance that has been engineered to interact with biological systems for an intended therapeutic or diagnostic purpose

Question 2

What is biocompatibility a measure of?

Answer 2

Degree to which a biomaterial interacts with particular tissue type = biocompatibility (ability to perform with an appropriate host response, in a specific situation without eliciting any undesirable effects in the recipient

Question 3

What tests should biomaterials be subject to?

Answer 3

1. Sensitisation and tissue irritation
2. Systemic toxicity
3. Genotoxicity (including DNA damage)
4. Carcinogenicity (propensity for tumour induction with exposure)
5. Teratogenicity (embryonic effects and effect on reproduction functions)
6. Biodegradation (degradation characteristics and nature of degradation products)

Question 4

What is an example of a tissue adhesive and how do they work?

Answer 4

Cyanoacrylates (adhesives rapidly polymerise in presence of moisture on skin or wound edges - resulting in a strong flexible bond)

Question 5

What is a problem with using using these adhesives in contaminated or infected tissues?

Answer 5

May cause fistulation

Question 6

What is an example of a biomaterial mechanical haemostat?

Answer 6

gelatin sponges (Gelfoam or surgifoam). These materials absorb blood, providing a mechanical barrier that facilitates haemostasis and provide a scaffold on which the body is able to mount a haemostatic response

Question 7

Why are some advantages of silicon rubber in implants and provide an example?

Answer 7

Non-absorbable, heat resistant , biocompatibility and durability (although relatively inert they do induce an inflammatory response and increase tissue susceptibility to infection)

Examples of these include: foley urinary catheters, closed suction drain systems)

Question 8

When is surgical mesh used and what is an example of an absorbable and non-absorbable type?

Answer 8

Surgical mesh - used in restoration of excessive tissue defects - thoracic wall and hernia repair

Absorbable mesh - polyglycolic acid

Non-absorbable mesh - polyester

Question 9

What is an advantage of using porcine small intestinal submucosa in bioscaffolds?

Answer 9

Acts as a scaffold for tissue ingrowth

Question 10

What is an example of a material that can be used to elicit a fibrotic response?

Answer 10

cellophane and ameroid constrictions

Question 11

What is the composition of 316 steel and why does this make it a favourable material for orthopedic work?

Answer 11

low carbon content and a high chromium and nickel content for promoting corrosion resistance

Question 12

Why are chromium and cobalt alloys used?

Answer 12

Higher corrosion resistance, high abrasion resistance and high fatigue strength

Question 13

Why is titanium used used in bone plates?

Answer 13

Highly corrosion resistant and has a high fatigue life

Question 14

What are ceramics and what is it designed to mimic? What is an advantage and disadvantage of this type of material?

Answer 14

Made from calcium phosphates and are designed to resemble bone - very high resistance to compression however they are brittle

Question 15

What is a use of ligafibre and monofilament nylon and what are some advantages of these types of materials?

Answer 15

ligafibre is very high molecular weight polyethylene - material is 2.5 x stronger than nylon - has much better abrasion resistance, impact strength and a lower co-efficient of friction

Question 16

What is polymethyl methacrylate used for?

Answer 16

PMMA available as two monomers that when combined polymerise to form a rigid structure used a bone cement in orthopedic surgery. Can also be formed with beads and anitbomicrobials to make a slow release antimicrobial system in the tissue

Question 17

What are the four stages involved in the tissue response continuation of implantation?

Answer 17

1. Injury caused by implantation
2. Biomaterial-blood interaction
3. Inflammation and propagation of wound healing
4. Foreign body reaction

Question 18

Briefly explain what is meant by the Vroman Effect and explain how the response differs if albumin or fibronectin arrive first ?

Answer 18

More mobile serum proteins such as albumin and globulin arrive first and then are eventually replaced by less mobile proteins with greater affinity such as fibronectin.

Albumin - predominant then process called surface pacification occurs where absorbed cells remain minimally adherent covered by a thin layer of collagen

Fibronectin arrives first - greater reaction occurs with significant fibrosis and thickening of the soft tissue

Question 19

What factors influence interface conversion?

Answer 19

1. Host signalment
2. Site of implantation
3. Mechanical properties of the material
4. Chemical and degradation properties of the material

Question 20

How long does it normally take to see proliferation of fibroblasts and the formation of granulation tissue?

Answer 20

Fibroblasts and the formulation of granulation tissue is typically 3-5 days following implantation.

Question 21

What are the two ways in which biomaterials may be absorbed into the body?

Answer 21

Phagocytosis - by foreign body giant cells

Hydrolysis - following reaction with water, results in the cleavage of susceptible molecular functional groups

Question 22

Briefly explain the problem with bacterial biofilms:

Answer 22

Bacteria are bonded to the implant and are relatively ‘safe’ from destruction due to the physical and chemical properties of the biofilm.

Question 23

What are the four stages that are involved in the formation of a biofilm?

Answer 23

1. Reversible attachment - initial attachment depends on biomaterial surface characteristics, bacterial cell surface characteristics and extracellular fluid
2. Irreversible attachement - bacteria becomes less susceptible to detachment following glycocalyx “slime” layer
3. Differentiation - glycocalyx provides protection of sessile bacteria and concentrates nutrients allowing for bacterial survival and
4. Detachment - dissemination or dispersion of the bacteria from a sessile state to a planktonic (mobile state) - results in formation of a new biofilm or reinfection of local tissues at the biomaterial: tissue interface