Suture materials

• Natural synthetic
• Absorbable non absorbable
• Braided non braided

Sutures (also known as stitches) are divided into two kinds – those which are absorbable and will break down harmlessly in the body over time without intervention, and those which are non-absorbable and must be manually removed if they are not left indefinitely. The type of suture used varies on the operation, with the major criteria being the demands of the location and environment.

· Sutures to be placed internally would require re-opening if they were to be removed. Sutures which lie on the exterior of the body can be removed within minutes, and without re-opening the wound. As a result, absorbable sutures are often used internally; non-absorbable externally.

· Sutures to be placed in a stressful environment, for example the heart (constant pressure and movement) or the bladder (adverse chemical presence) may require specialized or stronger materials to perform their role; usually such sutures are either specially treated, or made of special materials, and are often non-absorbable to reduce the risk of premature degradation.

Absorbable sutures

Absorbable sutures are made of materials which are broken down in tissue after a given period of time, which depending on the material can be from ten days to eight weeks. They are used therefore in many of the internal tissues of the body. In most cases, three weeks is sufficient for the wound to close firmly. The suture is not needed any more, and the fact that it disappears is an advantage, as there is no foreign material left inside the body and no need for the patient to have the sutures removed.

Absorbable sutures were originally made of the intestines of sheep, the so called catgut.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 guitar, 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 majority of absorbable sutures are now made of synthetic polymer fibers, 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 proprietary formulations for its brands of synthetic absorbable sutures; various blends of polyglycolic acid (Biovek for example), polylactic acid or caprolactone are common.

Occasionally, absorbable sutures can cause inflammation and be rejected by the body rather than absorbed.

Non-absorbable sutures

Nonabsorbable sutures are made of materials which are not metabolized 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 are less antigenic (ie, do not provoke as much of an immune response) it would represent a way to reduce scarring.

There are several materials used for nonabsorbable sutures. The most common is a natural fiber, silk, which undergoes a special manufacturing process to make it adequate for its use in surgery. Other nonabsorbable sutures are made of artificial fibers, like polypropylene, polyester or nylon; these may or may not have coatings to enhance their performance characteristics. Finally, stainless steel wires are commonly used in orthopedic surgery and for sternal closure in cardiac surgery.