Biomedical implants are used to aid or replace damaged tissues or organs. These materials are used in affecting repair to the body whether it is wound closure or replacement surgery. Recent reports show that 1 in 10 Americans has an implanted medical device.
Requirements of an implant
- Small circular fibers
- Biodegradability and bio-stability
- Sterilized (non-toxic)
- High tensile strength
- High knot security
- Flexible and smooth passage through tissues
- Good pliability
- Minimum tissue reaction
Bio degradable and Non-Biodegradable
Fibres are those which are absorbed by the body within 2–3 months after implantations and include cotton, viscose rayon, polyamide, polyurethane, collagen and alginate.
Fibres that are slowly absorbed within the body and take more than 6 months to degrade are considered non-biodegradable and include polyester (e.g. Dacron), polypropylene, PTFE and carbon.
Fabric Structures used in implants are,
Sutures and ligatures
The ideal suture is a monofilament. The polybutylene terephthalate (PBT) suture is currently the most popular.
The non-absorbable sutures are silk, waste silk, cotton, linen whereas the synthetic ones are polyamide, polyester, polyethylene, polypropylene. The absorbable synthetic sutures Polyglycolic acid (dexon).
Very little tissue reactivity
These are replaced in surgery to replace damaged thick arteries or veins from 6mm, 8mm or 1cm diameter. Straight or branched grafts are possible by using either the weft or warp knitting technology. Vascular graft is an artificial vein or artery used to replace segments of the natural cardiovascular system that are blocked or weakened.
Porous Teflon exhibits good bio-compatibility and anticoagulant activity. However, thin blood vessels, made from Teflon tubes lead to problem. The main requirements are blood compatibility, porous structure, re-absorbable, easy for tissue growth and avoid clotting.
Soft tissue implants
- Artificial prostheses,
- Artificial skin patches,
- Artificial tendon,
- Artificial corneas,
- It has been used in artificial breasts, ears and noses.
Soft tissue compatible biological polymers are collagen, silk protein, cellulose, chitin and chitosan. Soft tissue artificial materials include silicone rubber, polyurethane, hydro gels and carbon fiber. Silicone rubber is a cross linked polymer of poly (dimethyl siloxane).
Hernia repair Fibers can be woven or knitted into a mesh with each side designed with a specific porosity and texture to optimize its long term function. Polypropylene is resistant to infection and is antiallergenic. Gore-Tex soft tissue patch, which is used in hernia repair, is made of expanded PTFE.
Hard tissue implants
Applications include artificial bone, bone cement and artificial joints. Orthopedic implants are used to replace bones and joints, and fixation plates are used to stabilize fractured bones. Textile structural composites are replacing metal implants for this purpose. A non-woven fibrous mat made of graphite and Teflon is used.
Major requirements of dental polymers are,
- Translucence or transparency
- Good resilience and abrasion resistance
- Insolubility in oral fluids, non-toxicity, relatively high softening point and easy fabrication and repair.
The most widely used polymers are,
- poly (methyl methacrylate) (PMMA)
- Polysulfone and polyether polysulfone.