Application of Technical Textiles in Everyday Life

Implantable Medical Textile Materials

These materials are used in effecting repair to the body whether it be wound closure (sutures) or replacement surgery (vascular grafts, artificial ligaments, etc.). Table 4.4 illustrates the range of specific products employed within this category with the type of materials and methods of manufacture. Biocompatibility is of prime importance if the textile material is to be accepted by the body and four key factors will determine how the body reacts to the implant. These are as follows:

The most important factor is porosity which determines the rate at which human tissue will grow and encapsulate the implant.

• Small circular fibres are better encapsulated with human tissue than larger fibres with irregular cross-sections.
• Toxic substances must not be released by the fibre polymer, and the fibres should be free from surface contaminants such as lubricants and sizing
• The properties of the polymer will influence the success of the implantation in terms of its Polyamide is the most reactive material losing its overall strength after only two years as a result of biodegradation. PTFE is the least reactive with polypropylene and polyester in between.

Table 4.4 Implantable Materials

Sutures

Sutures for wound closure are either monofilament or multifilament threads that are categorised as either biodegradable or nonbiodegradable. Biodegradable sutures are used mainly for internal wound closures and nonbiodegradable sutures are used to close exposed wounds and are removed when the wound is sufficiently healed.

Soft-tissue implants

The strength and flexibility characteristics of textile materials make them particularly suitable for soft-tissue implants.A number of surgical applications utilise these characteristics for the replacement of tendons, ligaments, and cartilage in both reconstructive and corrective surgery. Artificial tendons are woven or braided porous meshes or tapes surrounded by a silicone sheath. During implantation the natural tendon can be looped through the artificial tendon and then sutured to itself in order to connect the muscle to the bone. Textile materials used to replace damaged knee ligaments (anterior cruciate ligaments) should not only possess biocompatibility properties but must also have the physical characteristics needed for such a demanding application. There are two types of cartilage found within the body, each performing different tasks. Hyaline cartilage is hard and dense and found where rigidity is needed, in contrast, elastic cartilage is more flexible and provides protective cushioning.

Orthopaedic implants

Orthopaedic implants are those materials that are used for hard tissue applications to replace bones and joints. Also included in this category are fixation plates that are implanted to stabilise fractured bones. Fibre-reinforced composite materials may be designed with the required high structural strength and biocompatibility properties needed for these applications and are now replacing metal implants for artificial joints and bones. To promote tissue ingrowth around the implant a nonwoven mat made from graphite and PTFE (e.g. Teflon) is used, which acts as an interface between the implant and the adjacent hard and soft tissue.

Cardiovascular implants

Vascular grafts are used in surgery to replace damaged thick arteries or veins 6mm, 8mm, or 1 cm in diameter. Commercially available vascular grafts are produced from polyester (e.g. Dacron) or PTFE (e.g. Teflon) with either woven or knitted structures . Straight or branched grafts are possible by using either weft or warp knitting technology. Polyester vascular grafts can be heat set into a crimped configuration that improves the handling characteristics.

During implantation the surgeon can bend and adjust the length of the graft, which, owing to the crimp, allows the graft to retain its circular cross-section. Knitted vascular grafts have a porous structure which allows the graft to become encapsulated with new tissue but the porosity can be disadvantageous since blood leakage (haemorrhage) can occur through the interstices directly after implantation. This effect can be reduced by using woven grafts but the lower porosity of these grafts hinders tissue in growth; in addition, woven grafts are also generally stiffer than the knitted equivalents.

The first artificial vascular graft was produced from polyamide fibre in 1956. Polytetraflouroethylene (PTFE) fibre soon replaced polyamide and then polyester fibre was introduced. The implants are made from variety of synthetic materials. The main fibres include polyester, PTFE. Polypropylene, polyacrylonitrile. However polyester and PTFE are most common vascular prosthesis currently available.

The major requirements of a good vascular graft include

• Non-fraying
• Flexibility
• Durability
• Biocompatibility
• Stability to sterilization
• Resistance to bacteria/viruses

Knitted polyester vascular prosthesis has become the standard vascular graft for replacement of arterial vessels of 6mm and greater. However while this has many features required by a surgeon, such as ease of handling, saturability, and conformability, it has one major disadvantage; it is not blood-tight. The knitted structure, by its nature, is porous, which is what is required for rapid incorporation by tissue in growth from the host. At the time of surgery the surgeon has to percolate the graftusingsome of  the patients own blood,  which is taken before heparinisation- a time consuming process which can be difficult to carry out satisfactorily. This prevents its use when patients are heparinised such as cardiopulmonary bypass and in emergency aneurismal surgery when percolating is not possible.

Hernia repair

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.

Hard tissue implants

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.

Nerve guidance channel

A developing area of research is the development of nerve guidance channels that are used to bridge the damaged nerve endings and 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.

Biomaterials in ophthalmology

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 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.

Hard tissue implants

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.

Nerve guidance channel

A developing area of research is the development of nerve guidance channels that are used to bridge the damaged nerve endings and 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.

Biomaterials in ophthalmology

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.

Dental biomaterials

Major requirements of dental polymers include translucence or transparency, stability, good resilience and abrasion resistance, insolubility in oral fluids, non-toxicity, relatively high softening point and easy fabrication and repair. The most widely used polymer for dental use is poly (methyl methacrylate) (PMMA) and its derivatives. Other materials for denture base polymers are polysulfone and polyether polysulfone.

Tissue engineering

Tissue engineering is one of the fastest growing research fields in modern medicine. Tissue engineering unites cell and molecular biologists, clinicians and surgeons, bioreactors and biomaterial specialists. The spectrum ranges from the multiplication of simple skin cells for burnt victims to the regeneration of entire tissues and organs from the patient’s own cells. Tissue engineering is the replacement of damaged tissues or organs with biologically based systems. Tissue engineering seeks to create functional substitutes for damaged tissues by combining engineering principles with those of life sciences.

A small number of healthy cells are taken from a patient and allowed to multiply in the laboratory culture. These are then combined with an absorbable polymer that may be shaped to mirror the target organ or tissue. This may be fabricated in a number of ways including a three dimensional arrangement of fibres into a scaffold. The scaffold material provides structural integrity and mechanical stability in the short term. The cells are added to the scaffold and allowed to adhere and grow on the plastic material. The cell/scaffold is implanted into the patient and as the cells develop and form tissue, the plastic breaks down and is removed from the body. Thus the fundamental application of a scaffold is to grow new tissues/organs by culturing isolated cells on templates. Textile structures form an important class of porous scaffolds.

Embroidery technology is being widely used for medical textiles and tissue engineering. Embroideries complement the field of technology and medical textiles in a unique way since they combine very high architectural variability with the freedom of adjusting the mechanical properties in a wide range and matching it with the mechanical properties of the host tissue.

Healthcare & hygienic products

An important area of textile is the healthcare and hygiene sector among other medical applications. The range of products available for healthcare and hygiene is vast, but they are typically used either in the operating theatre or in the hospital wards for hygienic, care and safety of the staff and patients. They could be washable or disposable.

Operating theatre

This includes surgeon’s gown, caps and mask, patient drapes and cover cloth of various sizes.

1. Surgical gown: It is essential that the environment of the operating theatre is clean and strict control of infection is maintained. A possible source of infection to the patient is the pollutant particle shed by the nursing staff, which carries bacteria. Surgical gowns should act as barriers to prevent the release of pollutant particles into the air. Traditional surgical gowns are woven cotton goods that not only allow the release of particles from the surgeons but also a source of contamination generating high levels of dust (lint). Disposable non-woven surgical gowns have been adopted to prevent these sources of contamination to patients and are often composite materials of nonwoven and polyethylene films.
2. Surgical masks:-They should have higher filter capacity, high level of air permeability, lightweight and nonallergic.
3. Surgical caps: – These are made from nonwoven materials based on cellulose.
4. Surgical drapes and cover cloths: – These are used to cover patients or to cover working areas around patients. It should be completely impermeable to bacterial and also absorbent to body perspiration and secretion from the wound.

Table 4.5 Healthcare and hygiene products: Product application