Sutures

1. Sutures

2. I. Introduction Sutures are probably the largest group of devices implanted in humans. Although they seem to be of small concern to the medical community, few devices have been made of so many different materials. By definition, a suture is a thread that either approximates and maintains tissues until the natural healing process has provided a sufficient level of wound strength or compresses blood vessels in order to stop bleeding.

3. II. History Since the beginning of surgical history (5000-3000 BC), sutures have been used as the means of repairing damaged tissues, cut vessels, and surgical incisions. As time has passed, a variety of suture materials have been used: flax, hair, linen strips, pig bristles, grasses, mandibles of pincher ants, cotton, silk, the gut of an animal, nylons, polyesters, and metals. The earliest use of gut can be traced back to the ancient Greek physician Galen. The eighteenth century brought the use of buckskin and silver wire, and the nineteenth brought the ability to chemically alter the properties of gut. By the twentieth century, cotton and treated natural materials have come to be the most widely used materials for suturing. After the invention of nylon and polyester propagated the popularity of cotton and treated natural materials, polyethylene, polypropylene, polyglycolic acid, polyglactin 910, and a large number of textile materials entered into the menu of choices for sutures.

4. III. Regulation The United States Pharmacopoeia (USP) is the official compendium for the suture industry. It sets standards and guidelines for suture manufacture. Suture sizes are given by a number representing diameter ranging in descending order from 10 to 1 and then 1-0 to 12-0, 10 being the largest and 12-0 being the smallest at a diameter smaller than a human hair.

5. IV. Classification Sutures can be classified into one of two groups, absorbable and nonabsorbable. Absorbable sutures are, as the name implies, temporary due to their ability to be “absorbed” or decomposed by the natural reaction of the body to foreign substances. It is important to note that not all absorbable sutures have the same resistance level to absorption, but each can be formulated or treated in order to obtain a desired decomposition rate. Nonabsorbable sutures are, in like manner, sutures that are not dissolved or decomposed by the body’s natural action. Such sutures are generally not naturally occurring materials (with the exception of silk). Silk & nylon, while being classified as nonabsorbable, actually dissolve after a long period of time compared to that of the absorbable materials

6. V. Manufacturing Sutures are manufactured with a wide variety of parameters. They can be monofilament or many filaments twisted together, spun together, or braided. They can also be dyed, un-dyed, coated, or not coated. With the goal of understanding the effects of so many variations of suture type, the properties and material of which they are composed are and have been studied in depth. The use of sutures is one of the most common practices in the medical field and thus has direct effect on a great majority of the world’s population.

7. VI. Design Currently, sutures are designed to result in the most desirable effect for any given situation as determined by those administering the sutures. Taken into consideration in the manufacture and use of sutures are properties such as stress-strain relationship, tensile strength, rate of retention, flexibility, intrinsic viscosity, wettability, surface morphology, degradation, thermal properties, contact angle of knots, and elasticity. Properties such as stress-strain relationship and tensile strength have a direct effect on how much force at a given rate the closure will be able to withstand. For example, a cough would impose a fast rate of elongation whereas edema or hemorrhage would impose a slow rate of elongation. Knotting causes a severe decrease of strength in the suture material. Thus when there is a break in the suture, it occurs most frequently at the site of the knot. As you can see, there are several factors biomedical engineers must consider when designing sutures.

8. VII. Application Patient safety, as in every other area of the medical field, is one of the major determining factors of suture manufacture and use. As mentioned before, the composition and properties of a suture are the crucial elements in the decision of what type to use. For example,an incision into the lung would need to be closed using a suture with a high elasticity level, slow degradation rate, and high tension strength level. If a suture is applied in a situation in which it is not suitable, the patient’s safety is endangered. In short, a surgery is never successful if the wound, insertion point, or incision is not sutured or closed in a proper manner as to promote healing in a timely and safe fashion.  Another factor to be taken into consideration is the effect of inserting the suture into the tissue. If the suture is of a rough morphology (e.g. braided), the tissue will swell more and is more susceptible to infection than if a smooth suture (e.g. monofilament) is used. A failure of a suture is simply its breaking or not meeting the requirements for which it was intended.

9. VIII. Testing As technology advances, testing techniques improve and become more specific for the application of sutures. The greatest percentage of testing is done on those suture materials already existing in practice. This is due to the virtual newness of the application of testing techniques to the suture product although, a fairly small, yet increasingly important number of tests are done on possible new suture materials.  The USP determines the procedures and parameters for standard suture tests. Sutures are tested immediately after removal from their sterile packages without drying or conditioning. Sutures are tested in a variety of areas including accurate measurements, knot pull breaking strength, needle attachment, viscoelastic properties, tissue reaction and cell response, allergenicity and more. In all strength tests, it is important to keep in mind that the breaking strength retention of absorbable and nonabsorbable sutures should be considered separately because the strength retention of the absorbable sutures will be quite different than that of the nonabsorbable suture.

10. IX. Technological Advances The use and need for a suture is clearly not a problem that needs a solution, but a solution that needs improvement. Currently there are many efforts to improve almost every aspect of the suture and its use. Also, new techniques for testing make it possible to gain a clearer understanding of the properties of sutures. This is necessary so that the most efficient and best suited suture will be applied in every case where a suture is needed. If it were not for the technological advances that have occurred in society, modern suture production and use would not exist and sutures would not be dependable.