BIO-MEDICAL TEXTILES

Recent decades have witnessed major development in medical textile production, the materials they are made of the and the technology used to produce them. 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 (sutures) or replacement surgery (vascular grafts or artificial ligaments).

Although the natural way to replace a defective body part would be transplantation, this is always not possible due to many reasons. Therefore, physicians use an artificial substitute (biomaterials) such as biotextiles. A foreign / synthetic material or part used to replace a body part is referred to as prosthesis, whereas most people are familiar with artificial knees or hips.

The main attribute of a biomedical textile is that it should fulfill the purpose for which it was designed. For example, sutures may require a biodegradable textile.

An artificial ligament is permanent and is able to react more with blood cells and the surrounding tissues, compared to an external bandage which is temporary and only contacts the outer skin tissue. An implantable device should be biocompatible. Biocompatibility testing evaluates the response of the host system to the medical textile. Results of this testing must be viewed along with the benefits of this device.

The biological requirements of a satisfactory artificial implant may be stated as follows:

 

• porosity
  Porosity determines the rate at which tissue, will grow and encapsulate the implant
   
• small circular fibers
  Small circular fibers are better encapsulated by human tissue than larger fibres with irregular cross-sections.
   
• non-toxicity
  Fibre polymer or fabrication techniques must be non-toxic and fibres should be free of contaminants.
   
• biodegradability / -stability
  Depending on the application, an implant must meet certain standards in terms of biodegredability and biostability. A suitable artificial surface for body cells to adhere to and grow on.

Biomedical textiles is a term that comprises a variety of subtypes such as:

Biomedical materials are used in applications such as soft tissue compatible artificial prostheses, artificial skin patches, artificial tendon and artificial corneas. Important properties that affect cell attachment and tissue growth are chemical structure, electric charge, hydrophilicity, hydrophobicity, roughness of the surface, micro heterogeneity and material flexibility.

Soft tissue compatible biological polymers are collagen, silk protein, cellulose and chitin / chitosan. Soft tissue artificial materials include silicone rubber, polyurethane, hydro gels and carbon fibre. Silicone rubber is a cross linked polymer of poly (dimethyl siloxane). It has been used in artificial breasts, ears and noses. 
 

Hard tissue compatible materials must have excellent mechanical properties compatible to hard tissue. Typical characteristics of polymers related to hard tissue replacements are good processability, chemical stability and bio compatibility. 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 around the implant to promote tissue growth.
 

Meshes find use in hernia repair and abdominal wall replacement, where mechanical strength and fixation are very important. Fibres 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 mesh is an example of fabrics used in hernia repair. Polypropylene is resistant to infection and is anti allergenic. Gore-Tex soft issue patch, which is used in hernia repair, is made of expanded PTFE. 
 

A developing area of research is the development of nerve guidance channels that are used to bridge the damaged nerve endings. Also, they facilitate the passage of molecules secreted by the nerve and bar fibrous tissue from infiltrating the area thus preventing repair.

An innovation is the use of electrically conducting polymers such as polypyrole to promote nerve regeneration by allowing a locally applied electrical stimulus. It is a blossoming field of textile research, since the nerve guidance channel may be a single continuous hollow tube, or it may be a hollow tube comprised of fibres. 
 

Natural and synthetic hydro gels physically resemble the eye tissue and hence have been used in ophthalmology as soft corneal lenses. Soft contact lenses are made of transparent hydro gel with high oxygen permeability. Hard contact lenses are made of poly (methyl methacrylate) and cellulose acetate butyrate. Flexible contact lenses are made from silicone rubber. 
 

Major requirements of dental polymers include translucence or transparency, stability, good resilience and abrasion resistance. Furthermore, insolubility in oral fluids, non-toxicity, relatively high softening point and easy fabrication and repair are also crucial for dental polymers.

The most widely used polymer for dental use is polymethyl methacrylate (PMMA) and its derivatives. Other materials for denture base polymers are polysulfone and polyether polysulfone, also called polyether sulfone PES. 
 

Textiles are developing into interdisciplinary high tech products with interesting chances on the market. Owing to the greater co-ordination among textile technologists and medical researchers, textile products for surgical procedures are being developed indigenously.

Textile structures in implantation are identified by structure, material composition, behavior of fibre surface and degradation. Developments of biologically friendly and predictable absorbable fibres will be of great interest, both as suture materials and as the basis of tissue engineering constructs.
Improved absorbable fibres will be of great interest, both as suture materials and as the basis of tissue engineering constructs.
Improved absorbable fibres will be necessary as new sterilization technologies are introduced to meet evolving environmental specifications.
Advances in textile technology will clearly bring a new and improved group of biomedical textiles.