Recent Developments In Medical Textiles

An important field of application of textile in medicine has been developed such as wound care and preventing chronic wounds. Bandages and wound dressings are most commonly used because they are affordable and reusable. The medical textile should have bio-compatibility, flexibility and strength. In surgical dressings the "sorbagon" dressings are innovated to produce more comfort in the dressing of wounds. Some of the super absorbent polymers are innovated, which includes polyacrylate and sodium acrylate are made to improve the absorbency of the fibres. The recently developed calcium alginate.

Fibres have high super absorbing capacity. Recent advances and specific requirements necessitated innovation in surgical sutures which includes barbed, gelatin coated catgut sutures. A recent development of silk fibre includes "spider silk" which has been obtained from goat milk by injecting the genes of spider into mammary glands of goat. The textile materials have generated considerable interest in medical technology where materials in the form of monofilament, multifilament, woven and nonwovens structures are being used for bio and medical applications. The major requirement of the textile materials is the bioreceptivity and biocompatibility at the application site in human being.

1. INTRODUCTION

The term medical textile literally means textile used for medical purposes. Textile apart from being a vital part human life is long since been used in medical field, though the term has been coined very recently. Textile materials have wide range properties such as flexibility, elasticity, strength etc. Textiles used for medical purposes should be non-allergic, non-carcinogenic, non-toxic, and antistatic in nature, optimum fatigue endurance, bio-compatibility, flame proof, dyes must be non irritant. An important and growing part of the textile industry is the medical and related health care and hygiene sectors. The extent of the growth is due to the constant improvements and innovations in both textile technology and medical procedures. They are used in a number of separate and specialized applications which can be categorized as follows:

.Non-implantable materials: Wound dressing, bandages, plasters etc.

.Extracorporeal devices: Artificial kidney, liver and lungs.

.Implantable materials: Sutures, vascular grafts, artificial joints etc.

.Healthcare/hygiene products: Bedding, clothing, surgical gowns cloths, wipes

1.1. Recent Developments in Medical Textiles

1.1.1.Surgical Sutures

Fibres are also used as sutures in surgery. Sutures are sterile filaments which are used to hold tissues together until they heal adequately or to join tissues implanted prosthetic devices., Sutures are either braided or monofilament are mostly used to close wounds and approximate tissues. The textile materials have generated considerable interest in medical technology where materials in the form of monofilament, multifilament, woven and nonwoven structures are being used for bio and medical applications. The major requirement of the textile materials is the bioreceptivity and biocompatibility at the application site in human being. The medical textile group in the department of textile technology at IIT Delhi has been working on the development of antimicrobial biocompatible sutures and scaffolds for tissue engineering. Because of the lack of proper post-surgical care, the bacterial infection in stitched wounds is prevalent in many of the cases.

The development of an antimicrobial suture based on nylon and polypropylene monofilaments is being pursued in the medical textile group. The surface functionalization of the suture is carried out in such a way that the inherent characteristics, such as mechanical and knot strength of the suture are not affected. Both the high energy gamma radiation and the plasma irradiation are being used to activate the materials for the surface functionalization. An antimicrobial drug is immobilized on the suture surface which subsequently is released slowly into tissues surrounding the stitch and prevents the microbial invasion. The tissue compatibility of these sutures is excellent and no adverse reaction has been observed against these sutures.

1.1.2.Barbed sutures

Recently a bi-directional barbed suture has been developed which obviates the necessity to tie a knot. It has ability to put tension in the tissues with less suture slippage in the wound, as well as to more evenly distribute the holding forces there by reducing tissue distortion. The barbed suture with a steeper cutangle and a median cut depth have a higher tissue holding capacity than those with a moderate cutangle and a nominal cut depth.

1.1.3.Gelatin coated sutures

Gelatin coated sutures are having a superior handling characteristics. The gelatin coating given to the suture material improves the surface smoothness and reduces the fraying characteristics. It can be obtained by means of treating the suture with that of aqueous solution of gelatin to coat the suture and it is made to have a contact with that of fixative agent to crosslink gelatin. This process includes the step of contacting the coated suture with that of buffer solution and heats it to 50"aC for a particular period of time interval. Usually heating can be carried out for about 1-20hrs. Sometimes plasticizers can be incorporated into the gelatin solution. The plasticisers used are triethyl citrate, glycerin or other poly hydric alcohols. The plasticiser used is mainly to enhance the benefits of the gelatin coating. The fixative solution used in the process is a cross linking agent. The preferred cross linking agent is preferably a dialdehyde such as glyoxal, which may be used alone or in conjunction with formaldehyde or other aldehyde.

1.1.4.Catgut Polymer Composite Suture

The catgut material is bio-adsorbed and it will cause fewer tissue reactions. This can be reduced by producing catgut polymer composite suture. The catgut has the ability to degrade in the living tissue through the enzyme action. To avoid this degradation the material can be coated with a protective polymer sheet. The polymer used should have the ability to shield the collagen core from the enzymatic activity and it should be degradable by hydrolysis. The polyester reinforced by urethane and urea links are used as the suitable polymers. The coating can be carried out by passing the catgut filament through the polymer solution and then allow for hardening.

2. DRESSING MATERIALS:

2.1. Calcium Alginate Fibres

The raw material for the production of this fibre is alginic acid, a compound obtained from the marine brown algae. It posses a variety of properties, including the ability to stabilize viscous suspension, to form film layers, and to turn into gels. When the dressing made of this fibre is applied to wound, the reverse ion exchange take place, This fibre is placed on the wound in dry state and begin to absorb the exudates. The calcium ions are then gradually exchange against sodium ions that are present in the blood and wound exudates.

The fibre absorbs large amounts of secretion, starts to swell and in the presence turns into a moist gel that fills and securely covers the wound. Both the extent and the rate of gel formation depend on the available amount of secretions. The more exudates present the more rapid gel formation occur. Addition of excess sodium ion causes further dissolution of the gel, so that calcium alginate fibres remaining in the wound can be resorbed. if necessary, but mayh also without problems be rinsed out with physiological saline solution.

2.2. Sorbalgon

It is a supple, non-woven dressing made from high quality calcium alginate fibre with excellent gel forming forming properties. The dressing offers number of practical therapeutic advantages for wound healing over any other commonly uses textiles.

A Sorbalgon dressing absorbs approximately 10ml exudates per gram dry weight and thus proviede with an absorption capacity. They in addition differ from textile dressings with respect to applied mechanism of absorption. It takes wound secretion directly into the fibres i.e., using intra capillary forces. Germs and detritus are retained with in the gel structure as the fibre swell during subsequent gelatinization. The wound is thus effectively cleansed and a considerable reduction of micro organism can be attained.

Intra capillary absorption of exudates along with swelling and gelatinization however not affect the fundamental permeability of the dressing for moisture. The gel remains permeable to gas so that sorbalgon represents a dressing material that facilitates a permeable moist wound treatment, in contrast to an occlusive moist wound treatment with hydro colloids. This especially important in infected wounds where air penetration reduces the risk of dangerous infection with anaerobic bacteria.

It is not an woven, rather consist of supple, fibrous mat that has excellent shaping and packing capabilities. When the fibres swell during gelatinization and finally fill out the wound, a close contact to the wound is generated even in the almost in accessible areas, absorption of wounds exudates thus being ensured even at the deepest point of the wound. Despite it high absorption capacities it prevents the wound from drying out without difficulties. The gel like consistency of sorbalgon acts as a moist dressing during the whole therapy and helps to regulate physiological secretion. This creates a favourable micro climate for wound healing promoting granulation and epethelialisation.

2.3. Thin film dressing

An improved thin film dressing with an absorbant border has been developed. The dressing as a superior ability to rapidly take up and absorb body fluid and to prevent dressing leakage and wound maceration, while retaining the conformability of a thin layer and a support layer. The support layer is adhered to the occlusive layer and a layer by any suitable bonding means such as adhesive heat or ultrasonics.

3. SUPER ABSORBABLE POLYMER

Super absorbents are swellable cross linked polymer, which have the ability to absorb and store 400-600 times there owm weight of aqueous liquid by forming a gel. The liquid is then retained and not released, even under pressure. The absorption rate of the polymers differs according to their mechanism used for preparation. SAP cannot dissolve because of their 3-D polymeric network structure. Of the many different types of polymers, only a few can be made into useful fibers. This is because a polymer must meet certain requirements before it can be successfully and efficiently converted into a fibrous product. Some of the most important of these requirements are:

.Polymer chains should be linear, long, and flexible.

.Side groups should be simple, small, or polar.

.Polymers should be dissolvable or meltable for extrusion.

.Chains should be capable of being oriented and crystallized.

Common fiber-forming polymers include cellulosic (linen, cotton, rayon, acetate), proteins (wool, silk), polyamides, polyester (PET), olefins, vinyls, acrylics, polytetrafluoroethylene (PTFE), polyphenylene sulfide (PPS), aramids (Kevlar, Nomex), and polyurethanes (Lycra, Pellethane, Biomer). Each of these materials is unique in chemical structure and potential properties. For example, among the polyurethanes is an elastomeric material with high elongation and elastic recovery, whose properties nearly match those of elastin tissue fibers. This material when extruded into fiber, fibrillar, or fabric form derives its high elongation and elasticity from alternating patterns of crystalline hard units and noncrystalline soft units. Although several of the materials mentioned above are used in traditional textile as well as medical applications, various polymeric materials both absorbable and nonabsorbable have been developed specifically for use in medical products. Chemical structures of some of these materials are illustrated in Figure 3.1.

Fig.3.1. Fibrous materials developed for use in medicine.

The reactivity of tissues in contact with fibrous structures varies among materials and is governed by both chemical and physical characteristics. Absorbable materials typically excite greater tissue reaction, a result of the nature of the absorption process itself. Among the available materials, some are absorbed faster (e.g., polyglycolic acid, polyglactin acid) and others more slowly (e.g., polyglyconate). Semiabsorbable materials such as cotton and silk generally cause less reaction, although the tissue response may continue for an extended time. Nonabsorbable materials (e.g., nylon, polyester, and polypropylene) tend to be inert and to provoke the least reaction. To minimize tissue reaction, the use of catalysts and additives is carefully controlled in medical-grade products.

Water absorbent Polymer

Water absorbent polymers are known as hydro-gel, water crystal, super absorbent polymers etc., are simply a type of plastic that possesses some unique water absorbing qualities. This is due to the presence of sodium or potassium molecules that form bridges between the long hydro carbon chains. These bridges are known as cross linking, which enables the polymer to form into a huge single super molecule, including its ability to degrade in the environment and breakdown into simpler molecules, and hold significant amount of water. When water comes in contact with super absorbent an electrical repulsion takes with in the particles. When this happens, water is drawn into the particles resulting in swelling of each particle. At maximum absorption capacity each particle will expand to over 30 times its original volume. When water evaporates it shrinks, returning to unswollen state.

3.2. Sodium acrylate polymer

Most SAP currently used are sodium acrylate based polymers having 3-D network like molecular structure formed by joining millions of identical units of acrylic acid. Which has been substantially neutralized with sodium hydroxide and enables SAP to absorb water or water based solution into the spaces in the molecular network, forming a gel and locking up liquid.

3.3. .Polyacrylate:

PAC can function as both an antiscalant and a dispersant. Polymeric antiscalant are generally low molecular weight polymers, whereas polymeric dispersant consist of higher molecular weight. Dispersant do not stop the formation of scale, but instead keeps the scale particles suspended in the buld fluid by imparting a negative charge to the particles. These negatively charged ones repel one another and aggregation into large particles of scale. PAC comprises about 5% of many laundry detergent formulations because 0f its dispersant properties. A cross linked form of sodium salt of polyacrylic acid is used as super absorbent material in diapers and other hygienic products. Cross linked PAC has a great affinity for swollen in a compatible solvent. Because of the presence of charged groups on the polymer chain the polymer will be highly expanded in aqueous solution.

4. SPIDER SILK

Modified goat milk will contain web protein .A goat that produces spider's web protein is about to revolutionist the materials industry. It is Stronger and more flexible than steel, spider silk offers a lightweight alternative to carbon fibre. Up to now it has been impossible to produce "spider fibre" on a commercial scale. Unlike silk worms, spiders are too anti-social to farm successfully. Now a Canadian company claims to be on the verge of producing unlimited quantities of spider silk - in goat's milk. Using techniques similar to those used to produce Dolly the sheep, scientists at Nexia Biotechnologies in Quebec have bred goats with spider genes. New kids on the block Called Webster and Pete, the worlds first "web kids" cannot dangle from the ceiling, nor do they have a taste for flies. In fact they look like any other goat. But when they mate, it is hoped they will sire nanny goats that produce milk that contains the spider silk protein. This "silk milk" will be used to produce a web-like material called Biosteel. Naturally occurring spider silk is widely recognized as the strongest, toughest fibre known to man.

Its tensile strength is greater than steel and it is 25 percent lighter than synthetic, petroleum-based polymers. These qualities will allow Biosteel to be used in applications where strength and lightness are essential, such as aircraft, racing vehicles and bullet-proof clothing. Kind to humans another advantage of spider silk is that it is compatible with the human body. That means Biosteel could be used for strong, tough artificial tendons, ligaments and limbs. The new material could also be used to help tissue repair, wound healing and to create super-thin, biodegradable sutures for eye-or neurosurgery.

5. ANTIMICROBIAL TEXTILE

Antibacterial fibre is produced by entrapping the metal ion with a cation exchange fibre having a sulphonic or carboxyl group through an ion exchange reaction reaction. The antibacterial metal ion is silver or silver in combination with either copper or zinc. The great advantage of this material is that those are not to react with tissue. Flexible products such as sponges and textile wites, which have protracted antimicrobial effect. The wipes are impregnated with biocides by spra8ying, dipping or soaking for use in medical field.

ACTICOAT dressing

It provides broader and faster protection against fungal infection than conventional antimicrobial products. The dressings are layered with mono crystalline silver known to have antimicrobial and antifungal properties, creating a protective barrier as silver ions are consumed. Acticoat has the faster kill rate and was effective against more fungal species. The product can be applied to variety of wounds including graft and donor sites and surgical wounds.

5.2. Antimicrobial Wound Dressing

Kerlix AMD is pure cotton treated with anecia's polyhexamethylene biguandine agent. These antimicrobial agents resist bacterial growth with in the dressing as well as reducing bacterial penetration through the product. Wound covering, is made of a hydrophobic bacteria-adsorbing material which comprises the antimicrobial active component which is not released into wounds, it is preferably made of mixture of hydrophobic fibres and fibre comprising antimicrobial property.

6. COMPRESSION BANDAGES

The basic function of bandages is compression, retention and support. This is obtained by properties intrinsic to the component and further enhanced and re-enforced supportively by the process of weaving and finishing relevant to the required end use. The regulation of the blood flow and prevention of swelling is closely interlinked with this property and there by enhancing improved healing healing process. It provides necessary support to restrict movement and speed up the healing process.

7. TEXTILE PERFORMANCE PRINCIPLES

Textile materials for medical applications typically have specific performance requirements relating to strength, stiffness, abrasion resistance, and mechanical Patency.

Strength: Among the many factors affecting a fabric's strength (fiber type, molecular orientation, crystallinity) is the variability in properties especially elongation of its constituent elements. Usually, the greater the variability in elongation at break, the lesser the strength. Products requiring high strength (e.g., artificial ligaments) must incorporate elements whose properties range within a narrow limit.

Stiffness: Bending stiffness which governs the handling, comfort, and conformability of a fabric is a critical parameter in a number of medical applications. A low value is usually desirable. For example, a suture with low bending stiffness requires fewer throws to tie a secure knot and has higher knot strength. The most important factors affecting bending stiffness are the shape of the fiber and the modulus, linear density, and specific gravity of the material. Generally, the higher the denier or the modulus or the lower the specific gravity, the higher the bending stiffness. For example, polyester has a higher modulus than that of nylon, and will result in a stiffer material.

Polypropylene, with a lower density than nylon, should have a higher stiffness, assuming all other factors are equal. In addition, a trilobal or tubular structure produces a stiffer product than does a solid circular structure of the same area or linear density. Monofilament materials are much stiffer than multifilament. With all other factors constant, the bending stiffness of a monofilament product such as a suture of denier T will be roughly n times greater than a multifilament structure with n filaments of denier T/n each. The use of multifilament yarns and/or fine-denier fibers in the yarn produces a more flexible and supple end product. Knot efficiency-the ratio of the tensile strength of knotted to unknotted thread is affected by elongation at break and bending stiffness. Most often, the greater the elongation, or the lower the stiffness, the greater the knot efficiency.

Abrasion Resistance: Whenever fibers, yarns, or fabrics rub against themselves or other structures, abrasion resistance assumes an important role. A high value is usually desirable, especially in applications such as artificial ligaments or tendons. The abrasion resistance of a yarn is influenced by several factors:

.The denier of the fiber (the lower the denier, the lower the resistance).

.The amount of twist in the yarn that binds the fibers together (the lower the twist, the lower the resistance).

.The orientation of molecules in the fibers (the higher the orientation, usually the lower the resistance).

The surface coefficient of friction (the higher the coefficient, the lower the resistance).
Therefore, one can conclude that micro denier fibers, low-twist yarns, rough surfaces, and highly oriented materials generally exhibit low abrasion resistance. However, coating a bundle of fibers with a low-friction polymer can enhance its resistance to abrasion.

Mechanical Patency: Implanted products that must bear loads over the long term and maintain their dimensional integrity require a high degree of mechanical Patency that is, the ability to resist permanent change in physical size, shape, structure, and properties. The factors that contribute to mechanical Patency include:

.The chemical, biological, and stress environment into which the implant is placed.

.The nonreactivity of the polymer with the environment.

.The size of the fibers.

.The structure of the fabric (consolidated structures made of highly interlocked woven material or warp knits provide an advantage).

.Perhaps most importantly, the viscoelastic properties of the material.

Thus, material selection is extremely critical for products such as ligament prostheses that must continue to bear loads. The material specified must be able to resist the elongation or growth that may occur as a result of stress relaxation during each cycle of operation in the body. If no such material is available, then biological tissues will need to be integrated into the assemblage to provide partial support of the load and contribute to the product's long-term Patency.

8. CONCLUSION

Thus the application of textile in high performance and specialized fields are increasing day by day. There will be an increasing role for medical textile in future. Thus the textile will be used in all extra corporal devices, external or implanted materials, healthcare and hygienic products. Textile materials continue to serve an important function in the development of a range of medical and surgical products. The introduction of new materials, the improvement in production techniques and fiber properties, and the use of more accurate and comprehensive testing have all had significant influence on advancing fibers and fabrics for medical applications. As more is understood about medical textiles, there is every reason to believe that a host of valuable and innovative products will emerge.

9. REFERENCES

1. Development of Antimicrobial Suture by Radiation-induced Graft polymerization of acrylonitrile into Polypropylene Monofilament I. Influence of Synthesis Conditions.B. Gupta, R. Jain, N. Anjum and H. Singh j In Pres (2004)

2. Development of Antimicrobial Suture by Radiation-induced graft polymerization of acrylonitrile into Polypropylene Monofilament II. Characterization and Structural Investigations. B. Gupta, R. Jain, N. Anjum and H. Singh J. Appl. Polym. Sci., In Press (2004)

3. Plasma Induced Graft Polymerization of Acrylic acid onto PET Films: Characterization and Human Smooth Muscle Cell Seeding. B. Gupta, C. Plummer, J. Hilborn, I. Bisson and P. Frey. Biomaterials, 23, 863 (2002)

4. Plasma Induced Graft Polymerization of Acrylic acid onto poly(ethylene terephthalate) Films. B. Gupta, J. Hilborn, I. Bisson, P. Frey and C. Plummer. J. Appl. Polym. Sci., 81, 2993 (2001)

5. Gupta BS, Milam BL, and Patty RR, "Use of Carbon Dioxide Lasers in Improving Knot Security in Polyester Sutures," J App Biomat, 1:121-125, 1990.

6. Gupta BS, and Kasyanov VA, "Biomechanics of the Human Common Carotid Artery and Design of Novel Hybrid Textile Compliant Vascular Grafts," J Biomed Mat Res, 34:341-349, 1997.
7. Williams SK, Carter T, Park PK, et al., "Formation of a Multilayer Cellular Lining on a Polyurethane Vascular Graft Following Endothelial Cell Seeding," J Biomed Mat, 26(1):103-117, 1992.

8. Soldani G, Panol G, Sasken HF, et al., "Small-Diameter Polyurethane-Polydimethylsiloxane Vascular Prostheses Made by a Spraying, Phase-Inversion Process," J Mat Sci, Mat in Med, 3:106-113, 1992.

Antimicrobial Polypropylene Suture- Indian Patent, Applied (2004).
Antimicrobial Polypropylene Suture- Indian Patent, Applied (2004).
High Strength PLA Filament- Indian Patent, Applied 581/DEL/2003
Antimicrobial Nylon Suture- Indian Patent, 190584 (2003).
Antimicrobial Nylon Suture- Indian Patent, 3032/DEL/98.

About the author :

Mr. Gopalkrishnan is working in Sardar Vallabhbhai Patel Institute Of Textile Management.

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