Surgical papyrus has the first recorded use of
fibres as a medicine as long back as 4000 years. "Susanta Sambita"
tells us that about 2500 year ago textile fibres were used as medicine. There
are many materials used for medicinal purpose like horse hair, leather strips,
cotton, animal sinew and fibrous tree bark. With time, textiles have found their
way into a variety of medical applications.
In addition to protective medical apparel, textiles in fibre and fabric forms
are used as implants, filters and surgical dressings. Recent decades have
witnessed major developments in medical textile production, covering the fields
of materials as well as technologies. 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, artificial ligaments, etc).
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 or synthetic material or part used to replace a body part is referred to
as prosthesis. Most people are familiar with artificial knees or hips. Recent
reports show that 1 in 10 Americans has an implanted medical device.
The main attribute of a biomedical textile is that it should fulfil 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. Requirements of an implant(2)
The biological requirements of a satisfactory artificial implant may be stated
Porosity, which determines the rate at which
tissue will grow and encapsulate the implant.
Fibre diameter: Small circular fibres are better encapsulated by human tissue
than larger fibres with irregular cross-sections.
Non-toxicity, where fibre polymer or fabrication techniques must be non-toxic
and fibres should be free of contaminants.
Biodegradability and bio-stability depending on the application; A suitable
artificial surface for body cells to adhere to and grow on.
The properties of the polymer will influence the
success of the implantation in terms of its biodegradability. Table 1 shows some
of the areas of application, fibre used and type of fabrics for the implantable
materials. 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 1: Implantable materials
polyester, PTFE, Polypropylene, Steel
||PTFE, Polyester, polyamide, silk, polyethylene
contact lenses/ artificial cornea
Source: Handbook of technical textiles Edited by A R Horrocks and S C Anand,
University of Bolton, UK
Various types of implants
Sutures and ligatures
The term 'Ligature' denotes tying something such as blood vessel or a
pedicle, whereas 'suture' denotes sewing by means of a needle and a thread made
of suture material(2). Sutures are strategically located after a surgical
operation primarily to hold the basic structural elements in their required
sites and provide the necessary strength, retained over a period of two weeks
upwards, depending on the specific site. Sutures are either monofilament or
multifilament threads used in surgery for wound closure. The ideal suture is a
monofilament with a smooth surface that can pass through the skin without being
caught and can be tightened into a single knot. The polybutylene terephthalate (PBT)
suture is currently the most popular because of its acceptable strength and
Sutures are characterised as biodegradable or non-biodegradable. Biodegradable
sutures are used mainly for internal wound closures. Non-biodegradable sutures
are used to close exposed wounds and are removed when the wound is sufficiently
healed. These may again be of a natural or synthetic variety. The selection of
the suture will depend on physical and chemical characteristics and the
biological culture of the tissue in which it is placed.
The absorbable natural sutures are Catgut prepared from the intestine of
government inspected sheep. The great advantage of catgut is that it can be used
even in the presence of infection where a non-absorbable suture cannot be used.
The disadvantages of catgut are loss of tensile strength, doubted purity and
cost. Collagen was invented to overcome the disadvantages of catgut. The flexor
tendons of beefs are converted into dispersed fibrils, which are extruded and
reconstituted to form collagen sutures. The absorbable synthetic sutures are
Polyglycolic acid (dexon), which has the advantages of tensile strength, very
little tissue reactivity and knots well. The disadvantage however is that its
tensile strength falls in 15 days. Co-polymer is a suture, which overcomes the
disadvantage of polyglycolic acid in that its tensile strength does not fall
before 4-6 weeks.
The non-absorbable natural sutures are silk, waste silk, cotton, linen whereas
the synthetic ones are polyamide, polyester, polyethylene, and polypropylene.
Vicryl plus from Ethicon, is claimed to be the world's first and only suture
incorporating an antibacterial agent. It is designed to reduce bacterial
colonisation on the suture.
The number of implants used in the surgical treatment of vascular disease has
been steadily increasing over the last 20 years, so it is now considered a
common procedure(4). Such tubes replace or bypass part of a blood
vessel-principally arteries-and operate in a similar fashion to natural blood
However, while advances in vascular disease surgery have been made, synthetic
implants are still susceptible to thrombosis or clotting, occlusions and
infection caused by protein and cell adsorption and coagulation activation.
Serious post-surgical problems occur in some 10% of surgical patients, which
includes approximately a 2% rate of vascular graft infections. As a result, some
grafts have to be replaced only a few months after being implanted.
New test device: Vascular graft is an artificial vein or artery used to
replace segments of the natural cardiovascular system that are blocked or
weakened(3). Grafts are implanted to bypass the blockages and restore
the circulation. These are replaced in surgery to replace damaged thick arteries
or veins from 6 mm, 8 mm or 1 cm diameter. Straight or branched grafts are
possible by using either the weft or warp knitting technology. Knitted vascular
grafts have a porous structure, which allow the graft to be encapsulated with
new tissue. The disadvantage is that this can cause hemorrhage (blood leakage)
through the interstices directly after the implantation. In an attempt to reduce
this risk, knitted grafts with internal and external velour surfaces are used.
Another method is to seal or percolate the graft with the patient's blood after
implantation. Porous Teflon exhibits good bio-compatibility and anticoagulant
activity. However, thin blood vessels, made from Teflon tubes lead to problems.
The tube consists of an inner layer of collagen, the tube itself providing
strength. Research is targeted to produce artificial blood vessels of less than
3 mm diameter. The main requirements are blood compatibility, porous structure,
re-absorbable, easy for tissue growth and avoid clotting.
Soft tissue implants
Attempts have been made to replace or augment
most of the soft tissues in the body(5).
*Connective tissues: skin, ligament, tendon, cartilage
*Vascular tissue: blood vessels, heart valves
*Organs: heart, pancreas, kidney
*Other: eye, ear, breast
Most soft tissue implants are constructed from
*Possible to choose and control the physical and mechanical properties
*Flexibility in manufacturing
"Soft tissue implants" can also be
designed for soft tissue repair.
A major problem with implanted materials is their
compatibility with host tissues(6). Researchers at Clemson University have
recently patented methods for texturising soft tissue implants with micron-scale
surface texture to optimise their compatibility with human body tissue. This
method optimises anchorage and histocompatibility of implants to tissue without
causing inflammatory tissue to form at the implantation site. The surface layer
defines a three-dimensional pattern with an exterior surface defining a
plurality of spaces and a plurality of solid surface portions.
Unlike previous implants with relatively large pore entry diameters, an implant
device using this technology promotes cellular anchorage of the device at the
implantation site through the growth of mature collagen, causing a minimal yet
desirable encapsulation of the embedded portion of the device. The Clemson
surface texture technique provides a significant improvement in the
histocompatibility of implants since it results in the development of a highly
desirable, thin, mature, and stable connective tissue capsule around the implant
material. This type of surface eliminates the undesirable chronic inflammatory
response observed in virtually all implant materials that typically results in
the deformation of the implantation site and often damages to the implant.
Biomedical materials are used in applications such as soft tissue compatible
artificial prostheses, artificial skin patches, artificial tendon and artificial
corneas(3). 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,
chitin and 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, dental works and noses.
Meshes find use in hernia repair and abdominal wall replacement, where
mechanical strength and fixation are very important(3). Fibres can be
woven or knitted into a mesh with each side designed with a specific porosity
and texture to optimise 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 tissue 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(3). Typical characteristics of polymers
related to hard tissue replacements are good processability, chemical stability
and biocompatibility. Applications include artificial bone, bone cement and
artificial joints. Orthopaedic implants are used to replace bones and joints,
and fixation plates are used to stabilise fractured bones. Textile structural
composites are replacing metal implants for this purpose. A nonwoven fibrous mat
made of graphite and Teflon is also used around the implant to promote tissue
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(3). An innovation is the use of
electrically conducting polymers such as polypropylene 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 hydrogel with high oxygen permeability(3). 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, insolubility in oral fluids,
non-toxicity, relatively high softening point and easy fabrication and
repair(3). 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.
Dr J Hayavadana, H L Vijaya Kumar: Potential of
Intelligent Textiles in Biomedical Field, Osmania Univ, India, Asian
Textile Journal, Feb 2004.
Handbook of technical textiles, Edited by A R
Horrocks, and S C Anand, University of Bolten, UK, WoodHead publishing
limited, UK, published year 2000.
The authors are with the Department of Textile
Technology, Indian Institute of Technology, New Delhi 110 016.