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The
materials requirement for the above biomedical applications vary markedly
according to the application being considered. The most important factor in
selection of bio-medical materials is for their bio-compatibility. A
bio-material may be bio-compatible in one application for a specific purpose,
but not in a similar application at a different site. Therefore,
specifications of bio-compatibility must include the conditions of use and
evaluation. One of the major problems encountered with artificial organs is
blood compatibility since many of these organs either handle blood directly
(heart, blood vessels) or come into contact with the blood in a membrane
exchange reaction (kidney, lungs, etc.)
For
a polymer to be used in biomedical device, it must have the appropriate
mechanical properties. The polymer must be available in reproducibly pure
form. It must have a good fabrication and must be stable enough that it should
not be adversely affected by the normal physiological environment. Above all
biomedical polymers (including additives and degradation products) should not
exhibit toxic or irritant qualities.
Many
biomedical applications require polymer systems with unique properties, such
as diffusion properties in membranes for dialysis, drug delivery applications,
oxygenators and biodegradable applications, including sutures and some drug
delivery systems.
Numerous
polymeric systems have been explored for use in cardiovascular systems. For
example the materials used in artificial heart studies include Polyvinyl
Chloride (PVC), silicone rubber (silatic), Polyurethane, Biomer and polyolefin
rubber. However among polyurethanes the most promising materials appear to be
some of the polyether urethane ureas.
Artificial
kidney is another example of an interesting development in the field of
biomaterials. Artificial kidney is often referred to as haemodialysis unit
which removes waste products from the blood with polymeric semipermeable
membrane. Which purifies the blood against artificial liquids in a process
known as hemodialysis or peritoneal dialysis. In peritoneal dialysis, silicone
elastomer or polyurethane elastomer is generally used as caterers to access
the peritoneal cavity A polyester cuff surrounds the segment of each catheter.
In haemodialysis, the dialyser is normally made of several thousand hollow
polymer fibers mounted in a polyurethane potting . The dialysis tubing is
generally made of PVC. The membranes used are generally based on cellulose or
cellulose derivatives.
Many
of the other biomedical applications of polymers involving implants are
related functions that do not have direct blood contact as occurs with
artificial organs and thus do not have problems in terms of blood
compatibility. Nevertheless these applications have certain specific
requirements and problems. Polymers for wound dressings and/or artificial skin
must have the flexibility and permeability of natural skin and also be able to
maintain these features for a long time period. A major use of plastics in
surgery is to replace soft tissue such as prosthetic breast, testicles etc.
The major polymer used here is poly (di-methylsiloxane).
Synthetic
Polymeric wound dressings such as silicons, polyurethanes, polyvinyl chloride
or polyethylene have made their appearance in the market recently. They are
generally thin layer films which have a synthetic adhesive as a coating on the
inner surface that adheres well to dry skin at the wound margins but does not
adhere to the wound site. Recently natural polymers such as collagen, fibrin,
fibronectin, alginate and hyaluronic acid have been studied as dressings for
dermal wounds.
Innovative
polymer applications will contribute significantly to the rapid development of
future medical technology. Key drivers will be microsystem technology,
minimally invasive surgical procedures and also dispersing and packaging
systems, which thanks to their easy handling, help the patient comply with the
physicians prescription. This scenario requires the development of
problem-solving products that can only be realised with high-performance
polymers. Present advances in materials science and biotechnology and rapidly
blurring the line between the worlds of synthetic and biological polymers and
their applications. Furthermore, synthetic polymers are being designed to
minic, either structurally or functionally as biological polymers.
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Polymers
are the most important and largest family of materials being used in medical
technology. Various polymers being used in conventional medical technology and
surgery include Polyvinyl Chloride, Polyethylene, Polypropylene, Polystyrene,
Polycarbonate, Acetal copolymers, Polybutylene terephthalate, Polyethylene
terephthalate, a variety of Liquid crystal polymers and some specialised
polymers synthesised through biotechnology route.