1
Q
Define biomaterial.
A
– it’s a non-viable material that is used in a device to interact with the biological system.
2
Q
Describe general features of biomaterials.
A
- They can be generated from a wide range of compounds – polymers, metals and ceramics.
- It doesn’t necessarily have to be implanted or in direct contact – e.g. haemodialysis and culture vessels for growing cell/tissues for later implantation.
- There are also some instances of remote contact – e.g. bypass, in heart surgery.
- Differences in bioactivity – some are benign and not bioactive such as a heart valve, while hydroxyapatite hip implants are bioactive (makes up 50% of bone weight and is used in preventing ingrowth of bone implants and promotes osseointegration).
3
Q
What are some uses for biomaterials?
A
- Can be used as a replacement or to compensate for diseased organs – e.g. dialysis.
- Assist healing – e.g. sutures, bone screws.
- Improve function of an organ – e.g. contact lenses
- Correct function/abnormality – e.g. rod for spinal cord to decrease curvature.
- Cosmetic surgery
- Replace rotten and dead tissue – e.g. dental amalgam (fillings)
4
Q
Define biocompatibility.
A
– the ability of a material to perform the appropriate host response in a specific application.
5
Q
Define the host response.
A
– response of the host organism (either local or systemic) to the biomaterial.
6
Q
What are the required features of a biomaterial?
A
- Biocompatibility
- - Biomaterials should always be biocompatible and that’s why they are subjected to the similar trials as drugs.
- - A biomaterial should generally be non-toxic, non-immunogenic (in a few rare cases you may want to trigger the immune system)
- - There are various degrees of biocompatibility – which depends on the intended use:
- —> Biologically inert – little or no integration in surrounding tissues and little effect on biological environment surrounding it.
- —> Fully integrated – may be attached or colonised into surrounding tissue – no distinct boundary between biomaterial and surrounding tissue. ‘blurred’
- – Examples of the appropriate host response are resistance to clotting, resistance to bacteria - Appropriate mechanical properties
- - Can range from very rigid and providing mechanical support (bone plates, spinal rods) to very flexible/compliant (artificial ligaments, patches and meshes).
- - e.g. Hernias – it’s when there’s protrusion of an organ through a wall of cavity that contains it. In one type, a piece of bowel is poking into the groin area/upper part of thigh, due to loosening. What happens is that they insert a mesh that is stapled, triggering growth of connective tissue of the cavity to prevent further protrusion.
- - The material may be very dense or very porous – porosity can allow cells to pass through, important in integration or cell response.
- - The material can be altered to promote or avoid interactions with surrounding tissue. Sometimes gels are used to avoid adhesion of biomaterial. - Appropriate stability – altered depending on intended time of exposure for the biomaterial:
- - Can range from seconds or minutes – hypodermic needles, surgical instruments to months - sutures, or life - pacemaker, joint replacements.
- - It may be preferred for the biomaterial to be degradable, such as with resorbable sutures and materials that release drugs. - Ability to be sterilised
- It has to be machinable – so you can make it size and shape you want
7
Q
Briefly describe history of biomaterials.
A
- There’s evidence of use of sutures – fibre linens, heads of biting ants in both ancient Greece (where they used metallic sutures) and ancient Egyptian civilisations. – used to bite the wound together.
- Biomaterials began to become significantly developed in 19th century – with dialysis machines being developed.
- It’s agreed that there were 3 generations of biomaterials – first generation, second generation and third generation.
8
Q
Describe features of first generation biomaterials.
A
- Includes historical devices.
- Materials were generally widely available industrialised materials that were not specified for medical use.
- Mostly specified by their requirement – to replace tissue without being degraded by the host. Success was mainly accidental.
- Most biomaterials were biologically inert – the success was if the body didn’t reject it and the patient survived.
- Later on metals were used a lot, but then (1940s) plastics were discovered.
- E.g. gold teeth, wooden limbs, Vatalium – used in orthopaedics, silicon rubber, polythene, pacemakers.
9
Q
Describe features of second generation biomaterials.
A
o More sophisticated biomaterials.
- Biomaterials were more bioactive – they were intended to elicit a controlled reaction in the host tissue to induce the desired effect. E.g. controlled drug release - the contraceptive implant developed in 2001.
- Also included development of resorbable materials - with rates of degradation tailored to their function. E.g. biodegradable PGA used in sutures.
- E.g. bioactive glasses and ceramics, implantable drug-delivery devices, biodegradable devices.
10
Q
Describe features of third generation biomaterials. Define tissue engineering and describe its general method.
A
- The goal was to stimulate and support regeneration of functional tissue by using tissue engineering technology.
- – Tissue engineering – the process by which functional tissues are regenerated via careful selection of living cells, materials and metabolic conditions – the regenerated tissue is then implanted back into the body.
- –>Typically the cells are seeded onto a scaffold (of synthetic polymer or natural material) and are grown in vitro until they form a tissue which is implanted back as prosthesis.
- –> The scaffold is usually a bioresorbable polymer, that is engineered so that it’s adhesive to cells.
- –> The cells and scaffold are placed into a metabolically and mechanically supportive environment with a growth media to help cells grow.
- –> Also includes microelectrode devices for monitoring and/or stimulating tissues
11
Q
Describe the features of regenerative medicine.
A
- Tissue engineering allows us to replace damaged organs or tissue.
- It is already in clinical use for skin replacement.
- In development are methods for blood vessel, heart valves, bone and complex organs such as the lung and heart (myocardium) replacement.
- Can involve biomaterials that will stimulate the body – in development, e.g. some artificial limbs can teach people to walk again. Or specialised dressing that contains a device that can measure certain parameters about the wound – how wet, how salty etc.
- E.g. Tracheobronchial transplantation with a stem-cell-seeded bioartificial nanocomposite study: The damaged trachea biomaterial’s shape was determined by MRI, and was then propagated in culture and the airway was replaced with a tailored bioartificial nanocomposite (in 2011)
12
Q
Define cell/tissue culture.
A
–> Defined as when there are cells are harvested and provided with a liquid medium that substitutes for tissue fluids, causing them to proliferate and be maintained in an artificial environment.
13
Q
What are the two main classes of cells in cell cultures?
A
–> There are two main classes of cells in cell culture
- Primary cells
- - if the cells are derived directly from tissues via enzymatic dissociation or from outgrowth of small fragments (this is explant culture) – Hayflick limited.
- - Enzymatic digestion will break down the surrounding ECM and release trapped cells. - Cell lines
- - cells that have been growing for years and are present as stock in the lab, originated from primary cells but have since become immortalised – have no Hayflick limit.
- - Many are derived from malignancies.
- - Cell lines are generally preferred as they are uniform – clones from parent cell.
- - E.g. HeLa cell line.
14
Q
Describe the process of serial passaging in cell culture. What are its uses?
A
- -> cells are stuck to culture, proteolytic agents and chelating agents are used to disrupt integrins (by acting on calcium) and this will make cells less sticky.
- Cells are then seeded in new medium and cycle repeats itself.
- Allows cell line to be maintained for long periods of times. Also allows cell expansion.
