Biomaterials Flashcards
What is meant by the term biomaterial?
A biomaterial is defined as any substance that has been engineered to interact with biological systems for an intended therapeutic or diagnostic purpose
What is biocompatibility a measure of?
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
What tests should biomaterials be subject to?
- Sensitisation and tissue irritation
- Systemic toxicity
- Genotoxicity (including DNA damage)
- Carcinogenicity (propensity for tumour induction with exposure)
- Teratogenicity (embryonic effects and effect on reproduction functions)
- Biodegradation (degradation characteristics and nature of degradation products)
What is an example of a tissue adhesive and how do they work?
Cyanoacrylates (adhesives rapidly polymerise in presence of moisture on skin or wound edges - resulting in a strong flexible bond)
What is a problem with using using these adhesives in contaminated or infected tissues?
May cause fistulation
What is an example of a biomaterial mechanical haemostat?
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
Why are some advantages of silicon rubber in implants and provide an example?
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)
When is surgical mesh used and what is an example of an absorbable and non-absorbable type?
Surgical mesh - used in restoration of excessive tissue defects - thoracic wall and hernia repair
Absorbable mesh - polyglycolic acid
Non-absorbable mesh - polyester
What is an advantage of using porcine small intestinal submucosa in bioscaffolds?
Acts as a scaffold for tissue ingrowth
What is an example of a material that can be used to elicit a fibrotic response?
cellophane and ameroid constrictions
What is the composition of 316 steel and why does this make it a favourable material for orthopedic work?
low carbon content and a high chromium and nickel content for promoting corrosion resistance
Why are chromium and cobalt alloys used?
Higher corrosion resistance, high abrasion resistance and high fatigue strength
Why is titanium used used in bone plates?
Highly corrosion resistant and has a high fatigue life
What are ceramics and what is it designed to mimic? What is an advantage and disadvantage of this type of material?
Made from calcium phosphates and are designed to resemble bone - very high resistance to compression however they are brittle
What is a use of ligafibre and monofilament nylon and what are some advantages of these types of materials?
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
What is polymethyl methacrylate used for?
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
What are the four stages involved in the tissue response continuation of implantation?
- Injury caused by implantation
- Biomaterial-blood interaction
- Inflammation and propagation of wound healing
- Foreign body reaction
Briefly explain what is meant by the Vroman Effect and explain how the response differs if albumin or fibronectin arrive first ?
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
What factors influence interface conversion?
- Host signalment
- Site of implantation
- Mechanical properties of the material
- Chemical and degradation properties of the material
How long does it normally take to see proliferation of fibroblasts and the formation of granulation tissue?
Fibroblasts and the formulation of granulation tissue is typically 3-5 days following implantation.
What are the two ways in which biomaterials may be absorbed into the body?
Phagocytosis - by foreign body giant cells
Hydrolysis - following reaction with water, results in the cleavage of susceptible molecular functional groups
Briefly explain the problem with bacterial biofilms:
Bacteria are bonded to the implant and are relatively ‘safe’ from destruction due to the physical and chemical properties of the biofilm.
What are the four stages that are involved in the formation of a biofilm?
- Reversible attachment - initial attachment depends on biomaterial surface characteristics, bacterial cell surface characteristics and extracellular fluid
- Irreversible attachement - bacteria becomes less susceptible to detachment following glycocalyx “slime” layer
- Differentiation - glycocalyx provides protection of sessile bacteria and concentrates nutrients allowing for bacterial survival and
- 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
