Suture
A suture is a medical device that doctors, and especially surgeons, use to hold skin, internal organs, blood vessels and all other tissues of the human body together, after they have been severed by injury or surgery.  They must be strong (so they do not break), non-toxic and hypoallergenic (to avoid adverse reactions in the body), and flexible (so they can be tied and knotted easily). In addition, they must lack the so called "wick effect", which means that sutures must not allow fluids to penetrate the body through them from outside, which could easily cause infections.

# Absorbable and nonabsorbable sutures
Sutures 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 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Absorbable sutures were originally made of the intestines of sheep, the so called catgut.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 major part of the absorbable sutures used 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), lactic 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.

# Surgical needles for use with sutures
Traumatic needles are needles with holes or eyes which are supplied to the hospital separate from their suture thread. The suture must be threaded on site, as is done when sewing at home. Atraumatic needles with sutures comprise an eyeless needle attached to a specific length of suture thread.  The suture manufacturer swages the suture thread to the eyeless atraumatic needle at the factory.  There are several advantages to having the needle pre-mounted on the suture.  The doctor or the nurse or odp does not have to spend time threading the suture on the needle.  More important, the suture end of a swaged needle is smaller than the needle body.  In traumatic needles with eyes, the thread comes out of the needle's hole on both sides.  When passing through the tissues, this type of suture rips the tissue to a certain extent, thus the name traumatic.  Nearly all modern sutures feature swaged atraumatic needles.
There are several shapes of surgical needles, including:
- straight
- half curved or ski
- 1/4 circle
- 3/8 circle
- 1/2 circle
- 5/8 circle
- compound curve
Needles may also be classified by their point geometry; examples include:
- taper (needle body is round and tapers smoothly to a point)
- cutting (needle body is triangular and has a sharpened cutting edge on the inside)
- reverse cutting (cutting edge on the outside)
- trocar point or tapercut (needle body is round and tapered, but ends in a small triangular cutting point)
- blunt points for sewing friable tissues
- side cutting or spatula points (flat on top and bottom with a cutting edge along the front to one side) for eye surgery
Finally, atraumatic needles may be permanently swaged to the suture or may be designed to come off the suture with a sharp straight tug.  These "pop-offs" are commonly used for interrupted sutures, where each suture is only passed once and then tied.

# Sizes of sutures
Suture sizes are defined by the United States Pharmacopeia (U.S.P.).  Sutures were originally manufactured ranging in size from #1 to #6, with #1 being the smallest.  A #4 suture would be roughly the diameter of a tennis racquet string.  The manufacturing techniques, derived at the beginning from the production of musical strings, did not allow thinner diameters.  As the procedures improved, #0 was added to the suture diameters, and later, thinner and thinner threads were manufactured, which were identified as #00 (#2-0 or #2/0) to #000000 (#6-0 or #6/0).
Modern sutures range from #5 (heavy braided suture for orthopedics) to #11-0 (fine monofilament suture for ophthalmics).  Atraumatic needles are manufactured in all shapes for most sizes.  The actual diameter of thread for a given U.S.P. size differs depending on the suture material class.

# Suture techniques
Common suture stitching techniques include:
- Simple Interrupted Stitch
- Running Stitch
- Mattress
- Horizontal mattress
- Vertical mattress
- Figure 8
- Continuous locking
- Subcuticular

# Removal of sutures
Whilst some sutures are intended to be permanent, and others in specialized cases may be kept in place for an extended period of many weeks, as a rule sutures are a short term device to allow healing of a trauma or wound. According to about.com's article on nursing:

# Suture materials

# U.S.P. Needle Pull Specifications

# Other facts

## Tissue adhesives
In recent years, topical cyanoacrylate adhesives ("liquid stitches") have been used in combination with, or as an alternative to, sutures in wound closure.  The adhesive remains liquid until exposed to water or water-containing substances/tissue, after which it cures (polymerizes) and forms a flexible film that bonds to the underlying surface.  The tissue adhesive has been shown to act as a barrier to microbial penetration as long as the adhesive film remains intact. Limitations of tissue adhesives include contraindications to use near the eyes and a mild learning curve on correct usage.

## Antimicrobial sutures
Another recent development in wound closure involves the use of sutures coated with antimicrobial substances to reduce the chances of wound infection.  While long-term studies are not yet available, preliminary results indicate that these sutures are effective at keeping bacteria out of wounds.