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Nonwovens & Technical Textiles
  Technical textiles in medical applications: Sutures

It is highly unlikely that any textile fibres that exist today, have not, at sometime or the other, been considered for use in the present-day advanced medical field. Hospital rooms are upholstered with similar materials to those in our homes. The staff needs uniform and patient needs clothing. Thus, the largest use of textile fibres in the medical history is for items, which do not differ significantly in physical specifications or chemical type from those of our domestic surroundings, except for those for specialised applications. 

The general uses are, however, not commonly thought of as medical textiles - medical textiles are those, which are associated with speciality areas where the use of textile materials is of direct assistance in the medical and surgical treatment of the patient. While the major volume of these special medical textiles are for non-implantables, the most interesting uses of textiles for medical application are in the areas of extra corporeal and implantables. This has been shown in Table 1. The fibres for medical applications may be produced from common polyester or propylene or from some more exotic polymers such as polyglycolic acid esters or collagen.

Table 1: Medical textiles
Non-implantables Extracorporeal Implantables
a Drapes a Fabric reinforcements a Sature
b Pillows b Hellow fibers for dialysers and oxygeneratiors b Fabrics for heart values and percutaneous leads
c Wash cloths     c Patches for heart repair
d Surgical dressings     d Surgical reinforcement meshes
e Gauze     e Vascular grafts
f Elastic stockings     f Reinforced tubular meshes for veins and grafts
g Gowns     g Fibre reinforcement - bone plates and ligaments
h Caps     h Restraining loops for intraocular lences
i Surgical masks     i  
j Shoe covers     j  
k Sterile wraps     k  

 

To a large extent, these fibres are manufactured in the same way as the textile fibres are. However, commercial polymers contain additives and contaminants like plasticisers, stabilisers, residual monomers and catalysts and, sometimes, finishing agents. These are not only undesirable but may also be harmful in medical applications. Any material implanted within the body has to be inert as well as compatible with blood and other body fluids. In addition, it must cause no tissue irritation, be non-toxic, release no foreign material and cause no tumors with long-term use. In essense, such materials have to be treated as drugs.

Today, more and more people are aware that an operating room could not solely operate without the necessary materials. Consequently, one of the most important materials needed in the operating room are the sutures. Generally, sutures are surgical guts, or silk, cotton or metal thread, 18 or more inches long, threaded on a needle. It is used mainly for sewing or suturing together the edges and the surfaces of tissue, for checking the flow of blood, fastening drainage tubes in position, etc. Sutures are either interrupted, each stitch tied separately; Or continuous, the thread running in a series of stitches, only the first and last of which are tied. In the following paragraphs, one of the most important applications of textiles in medical field, sutures, along with its production techniques, is reviewed.

Types of Sutures

Raw Materials

Sutures are small lengths of yarn with needle attached to one end and are generally used to close lacerations, cuts and deliberate incision which have been made on an item or living being. The practice of suturing started at an early age in civilisation with the sewing of protective garments and, certainly by the time of the early Chinese culture, for closing wounds in humans. In fact, the Chinese started by using silk as their source for suturing filaments. Even today, silk remains as one of the most prominent material, used for this purpose by the physician.

Another age old suture still produced and used today is the gut suture, which is made from bovine stomachs and is basically a collagen monofilament. This protein derivative suture is derived from the sub-mucosa of sheep intestines or scrosa of bovine intestine by cutting the intestines in narrow ribbons after chemically and mechanically cleaning them. Several ribbons are then twisted together, dried, ground and polished.

The first new filament to come in this field is cellulose fibres followed by nylon and a number of other polymeric filaments, which included the olefins and polyester. All have been produced in numerous forms such as monofilaments and multifilaments, having different diameters and tensile strength. In the last 30 years, a more exotic entry into the suture field has been the addition of resolvable sutures made from synthetic polymeric materials. The typical example of this category include: Homopolymers and copolymers of glycolide, D L lactide and E-caprolactone. The resolvable sutures are bio-compatible and bio-degradable, as are silk and gut sutures, but can also be ejected from the interior of the body through natural body function. Table 2 shows the list of sutures most commonly used today, along with their general strength characteristics.

Among the natural polymers, silk is presently the most common material used. Polyglycolic acid (PGA), polylactic acid (PLA) and polyester are the other major synthetic polymers used to manufacture sutures. Polyester sutures fall into the category of non-absorbable and, as such, are used mostly for closing cutaneous or oral incisions where the suture can be easily removed when required. PGA and PLA sutures are bio-degradable and, as such, can be used internally for heart repair and for similar operations. By proper design of the polymer, the rate of absorption can be varied to match one's need.

The length of sutures varies considerably. Each suture depends on the character of the work and the nature of the operation. For instance, deep work in the pelvis requires a much longer suture than would be necessary in suturing an area closer to the surface of a wound. Experience and judgement, along with the desire of the surgeon, must be the determining factors in details and selection of sutures.

Table 2: Satures examples
  Diameter
(mm)
Breaking strength
(kg)
Knot strength
(kg)
Catgut 0.317 3.042 1.718
PGA 0.254 2.774 1.772
Silk 0.264 2.407 1.543
Polyester 0.246 3.858 1.681

Absorbable Sutures

Surgical Gut

Surgical guts are also known as catgut and is made from the sub-mucous layer of a sheep's intestine. Once cleaned, dried and twisted into threads of various sizes, they are prepared for use by special processes that include innumerable inspections of gauze and tensile strength and scrupulous sterilisation. The length of time for complete absorption of surgical gut in a wound varies according to the action of certain hardening agents.

Fascia Lata

This muscle connective tissue of beef has been used in reconstructive orthopedic surgery and for the repair of hernias. It is not a true absorbable suture, but becomes a part of the tissue after the wound has healed.

Non-absorbable Sutures

Silk

This is prepared from the thread spun by the silkworm larva in making its cocoon. It may be twisted or braided, and it comes in sizes comparable with surgical gut. Its characteristics are:

  • High tensile strength.

  • Relatively inexpensive.

  • Less tissue reaction.

Cotton

This is made from cotton fibres. The strands are twisted and used for both internal and external suture. It should always be used wet for maximal strength.

 Nylon

This is a synthetic polyamide material, which can be used in the form of:

  •  Monofilament

  •  Multifilament

  •  Braided

  • The main disadvantage is that a triple knot must be tied.

Wire

This material has maximal flexibility and tensile strength, yet causes little or no local reaction in the tissue in which it is placed.

Dacron

This is a synthetic polyester fibre that has greater tensile strength, minimal tissue reaction, maximal visibility, non-absorbent and non-fraying qualities.

Linen

This is made of twisted linen thread; It has sufficient tensile strength, but is rarely used as suture material.

Silver Wire Clips

Many styles of clips are available for the purpose of holding the edges of the tissue in approximation. They tend to produce some scarring when used in the skin, but may be used when the wound is infected.

Silkworm Gut

This is made from the fluid secreted by the silkworm when they are ready to form their cocoons. The disadvantage is that they must be soaked in normal saline for about 10 minutes before use to make them pliable.

Mesh

This type of suture is made of stainless steel, usually used for hernia repairs and large defects. It is rarely used.

Tantalum

This is a bluish bray metal that is non-irritating to the body tissues. It is used because of its high tensile strength and its inert reaction to tissues.

Properties

Some of the characteristic properties considered in selecting a suture material are: Absorption, pliability, knot tying, holding strength and tissue reaction.

A suture must hold its strength for a period of 10 to 12 days to allow healing to complete. If bio-absorbability is required, then, the rate of absorption becomes a criterion. Furthermore, the suture must be pliable for the surgeon to handle and tie it properly, and at the same time, must hold a knot without slipping. Lastly, the suture must not cause a tissue or skin reaction or irritation.

Production

Absorbable sutures were originally made of the intestines of sheep, the so-called catgut. The manufacturing process was similar to that of natural musical strings for violins and guitars, and also of natural strings for tennis racquets. The inventor, a 10th century surgeon named al-Zahrawi reportedly discovered the dissolving nature of catgut when his lute's strings were eaten by a monkey. Today, gut sutures are made of specially prepared beef and sheep intestine, and may be untreated (plain gut), tanned with chromium salts to increase their persistence in the body (chromic gut), or heat-treated to give more rapid absorption (fast gut).

However, the major part of the absorbable sutures used are now made of synthetic polymer, ie, fibres, which may be braided or monofilament; These offer numerous advantages over gut sutures, notably ease of handling, low cost, low tissue reaction, consistent performance and guaranteed non-toxicity. In Europe and Japan, gut sutures have been banned due to concerns over bovine spongiform encephalopathy (mad cow disease), although the herds from which gut is harvested are certified BSE-free. Each major suture manufacturer has its own preparatory formulations for its brands of synthetic absorbable sutures; Various blends of polyglycolic acid (Vicryl for example), lactic acid or caprolactone are common.

Non-absorbable sutures are made of materials which are not metabolised by the body, and are used therefore either on skin wound closure, where the sutures can be removed after a few weeks, or in some inner tissues in which absorbable sutures are not adequate. This is the case, for example, in the heart and in blood vessels, whose rhythmic movement requires a suture, which stays longer than three weeks, to give the wound enough time to close. Other organs, like the bladder, contain fluids, which make absorbable sutures disappear in only a few days, too early for the wound to heal. Inflammation caused by the foreign protein in some absorbable sutures can amplify scarring, so if other types of suture were less antigenic (ie, do not provide as much of an immune response), it would represent a way to reduce scarring.

Now that some of the basics of suture requirements and material properties have been identified, the following is a presentation of steps taken to manufacture a typical multi-filament suture.

Multi filaments are purchased or manufactured by the suture manufacturer. However, these products are produced from specially approved raw materials and manufactured through specially approved procedure. The multi filament yarn is then twisted on a common ring twister. The number of twist per inch or cm is determined by the producer and can be very high. This twist is a factor in the final properties of the suture and affects the 'Feel' and knot tying faciliities.

The next operation is to braid a number of twisted yarn ends into a single strand. First, the yarn is wound onto braider bobbin and placed on a braiding machine. The number of carriers used in braiding vary with the suture specifications. Normally, a suture plant is equipped with braiders having 6 to 24 carriers. The braided suture material can be described as looking like a miniature 'Sash' or sash cord or ski rope.

After the braiding operation, stretching operation follows. The stretching unit is equipped with two sets of dual rollers, and like any other stretching system, the delivery set moves faster than the feed set. Normally, a coat of finish is applied to the braided yarn as it is stretched. After testing of quality parameters, the spools are stored for next operation.

Next operation is the needle attaching operation. The braided yarn is cut to desired lengths, generally from 150 mm to 900 mm. One end of the suture - about 25 mm - is t dipped in a polymer solution and placed in an oven for curing. This operation makes the end stiff and easier to handle while attaching the needles. There are, generally, two ways for attaching the needles. In the first method, the needles have holes drilled in the end opposite to the sharp pointed end, the yarn is pushed into the hole and then held in place by crimping the needle barrel into the yarn. The other method utilises a needle that has two lobes, flat configuration on the end, instead of a hole. The yarn is placed on top of this configuration and then a special clamping device folds the two lobes on top of the yarn, thus holding the two firmly together. Whatever may be the method that is used, testing of security of attachment is very important.

Sterilisation and packaging are the two final operations performed during suture manufacture. Generally, the completed suture is rolled into a circle of 25 mm in diameter and then placed in a small package. Sterilisation is done by two methods. One is a toxic gas sterilisation in which ethylene oxide is used and the other is by radiation. In gas sterilisation, several thousand packages of sutures are placed in trays, which are then placed in a steriliser. The steriliser is located in an air-tight room wherein the air pressure is higher than that used in the steriliser while the gas is present. Radiation sterilisation is carried out in a similar manner except that the radiation box and personal safeguards are different. The needle attachment and sterilisation steps are the classic operations related to suture manufacturing technique.

After sterilisation, the packages are sealed and are ready for marketing.

Conclusion

Application of textiles in the medical field has come a long way since its first recorded use in the Edwin Smith Surgical Papyrus nearly 4,000 years ago; The description is of the use of stitches to repair wounds. It is, of course, quite likely to assume that hand woven cloth or spider webs were used, even earlier, to stop bleeding.

In the Susanta Sambita of Indian literature, written approximately 2,500 years ago, a variety of suture materials are mentioned, namely, horse hair, leather strips, cotton, animal sinews and fibrous tree bark.

The manufacture of modern day sutures made from polymers is not difficult. Standard or slightly modified fibre spinning units are usually adequate. However, the most important factor in suture spinning is the outstanding characteristics of the particular polymer being processed, and the biological characteristics of the tissue in which it is to be placed.

Further, the anticipated time of healing, the potential contamination and infection, the patient's physical condition and the past post-operative course of the patient are other considerations, which generally, govern the choice of a particular type of suture.

References

1. James O Threlkeld: IFJ, October 1994, Page 34.

2. Raul De Persia, Alberto Guzman, Lisandra Rivera & Jessica Vazgwz: Mechanics of Biomaterials: Sutures After the Surgery, Applications of Engineering Machines in Medicine, May 2005, F1.

3. Jim Fowler and John Hagewood: IFJ, October 1994, Page 28.

4. John Hagewood: IFJ, October 1994, Page 10.

 5. Rakesh Gupta: Fibre World, January 1989, FW 2.

6. Rakesh Gupta: Fibre World, March 1989, FW 4.

Acknowledgement

The author acknowledges with thanks the management of MANTRA for giving permission to publish this paper.

Note: For detailed version of this article please refer the print version of The Indian Textile Journal December 2008 issue.

Dr S K Basu

Director, Man Made Textiles Research Association (MANTRA),

Surat, Gujarat.

published December , 2008
 
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