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Sterile cotton is fabric devoid of active organic contaminants, such as harmful bacteria. There may be applications for the material in industrial "clean room" processes that require a critically controlled environment, but it was primarily developed for medical purposes. The unique properties of cotton, particularly its hypoallergenic quality, make it ideal for this. Various technologies have been developed to render it sterile.
The individual fibers that are attached to a cotton plant's seed pod are uniformly thin and quite long, averaging 1 inch (2.5 cm). When spun, the fibers tightly twine together into a dense and strong thread relative to its size. The thread can be both knitted and woven. There are many cotton products used in a hospital or medical setting, and most of them need to be sterilized to prevent exposing patients to potentially contagious bacteria, viruses, and other harmful pathogens.
Bed sheets and nurse's scrub uniforms are some of the cotton products that a hospital cannot afford to dispose after single use. It may be insufficient, however, to simply sanitize them for reuse. If they were used, for example, by a patient admitted for an infectious disease, they are a bio-hazard and must be rid of any organic trace of the previous user. Most hospitals have an in-house autoclave for this purpose. The autoclave is essentially an oven that sterilizes its content with steam and pressure to at least 250° Fahrenheit (121° C) for 15 minutes.
Woven cotton has properties particularly well suited to medical applications. It is unaffected by most organic liquids. There have been no documented human allergic reactions to the textile. Loosely woven, it is highly absorbent; tightly woven, it is nearly waterproof.
One environment in which sterile equipment is absolutely required is the operating room. There are two woven sterile cotton products used here exclusively: a twill weave towel and a gauze weave sponge. The former is a general purpose towel, used for example to line a surgical instrument tray. The sponge is so-named for its use to absorb and clear away excess blood during surgery. A similar sterile cotton gauze cloth is used as wound pads and also as adhesive sterile bandages.
Industrial scale sterilization of disposable operating room towels, surgical gauze sponges, and adhesive bandages, such as the brand name Band-Aid®, is usually performed by irradiation. Within a heavily shielded chamber, these products, as well as other medical instruments such as hypodermic needles and surgical scalpels, are exposed to radioactive cobalt emitting deadly gamma rays. While this process is technically hazardous, it is very effective and leaves the resulting sterile cotton products radioactively harmless.