The most common fiber used in surgical dressings is cotton. Regenerated cellulose, wood fibers and wool are also used. Cotton also forms the basis for most of the surgical dressings such as gauze, lint, bandages and plasters.

Absorbent Cotton Wool (Gossypium Absorbens; Syn. Absorbent Cotton, Absorbent Wool)

Learning Objectives

• Method of preparation of absorbent cotton wool
• Standards for surgical cotton
• Uses of surgical cotton

Cotton is obtained from the epidermal trichomes from the seeds of cultivated species of Gossypium. The hairs or trichomes are separated from the seed by a process called ginning. The trichomes in their natural state are covered with a waxy substance, which makes it nonabsorbable in nature. The fibers are defatted by boiling in alkali under pressure. This process saponifies the fat. The saponified fat is then washed and the fibers are bleached until they are white. It is then treated with dilute acid until it is free from all coloring matter. The fibers are now in a tangled state. They are mechanically combed, which arranges them in a more uniform manner. This process of defatting and bleaching gives a clean, white, fleecy product called “cotton wool.”

Standards: The following standards are specified for cotton wool in the British Pharmaceutical Codex (BPC):

1. The fibers should be well “carded,” that is, untangled by combing process.
2. It should be well bleached to obtain a white product.
3. It should be free from pieces of thread.
4. It should be reasonably free from leaves and shell from the plant or seed coat.
5. It should be reasonably free from dust, that is, particles of fiber and foreign matter.
6. The quality should be the same throughout.
7. It should offer appreciable resistance when pulled.
8. The average length of the fiber is five-eighths of an inch.
9. It should contain no more neps than the sample kept at the Manchester Testing House.
10. Absorbency test: 1 g of cotton compressed to a volume of about 20 ml is placed lightly by means of forceps on the surface of water at 20°C. It should sink or become saturated within 10 s.
11. The fibers should not turn brown or show appreciable signs of disintegration on heating to 110°C for 20 min.
12. Acidity test: A solution of bromocresol green should not become distinctly yellow when sprinkled over cotton.
13. Oxidizing substances: When 1 g of cotton is immersed in a solution of 0.5 g of cadmium iodide and 10 drops of glacial acetic acid in mucilage of starch, no blue color should develop.
14. Water-soluble extractive is limited to 1.5%.
15. The ash limit should not be more than 0.5%.

Uses:

1. It is used for absorbing wound exudates.
2. It is used for cleaning, swabbing and medicating wounds and for applying bactericidal solutions to the skin before surgery.
3. A thick layer of cotton wool is light in weight but provides good physical protection to the wound by providing warmth to the area and is a useful barrier to organisms.

Since cotton wool consists of loose fibers, it may stick to wounds and raw surfaces. Hence, the fibers have to be separated from the wound with the help of woven fabrics.

 

Learning Objective

• Other fibers used in the preparation of surgical dressings