Learning Objective

• Sterilization methods for surgical catgut

Sheep intestine may be normally infected with pathogenic spore-forming bacteria responsible for tetanus and gas gangrene. Hence, sterilization process is very essential and it should be thorough. The final sterilized gut should be checked by sterility testing.

The processed catgut can be sterilized by either of the following methods:

1. Dry heat sterilization
2. Chemical method
3. Irradiation sterilization

Heat process: Chemically, the gut consists of collagen, which if heated in the presence of moisture gets converted into gelatin. Hence, before the catgut is exposed to heat sterilization, it should be made free from moisture.

The guts of suitable lengths are coiled on heat-resisting fiber card and placed in glass tubes with labels made of heat-resistant material. The tubes are then placed in a drying oven, the temperature of which is slowly raised. Once the gut is dried thoroughly, it can be heat-sterilized by any one of the following two methods:

1. The tubes can be autoclaved at a temperature of 160°C for several hours. As water must be absent, the autoclave should contain an anhydrous fluid such as toluene or xylol.
2. Heating can also be done in a nonpressure vessel containing anhydrous fluid with a high boiling point. Here again, the temperature of 160°C should be maintained.

The tubes can then be filled with a sterile tubing fluid and sealed by fusion of the glass under strict aseptic conditions.

Chemical method: The chemical process makes use of iodine. However, immersion in iodine causes a variation in the absorption time of the suture in the body. Ethylene oxide provides a more effective means of chemically sterilizing the sutures.

Irradiation process: The gut is packed in aluminum foil envelopes containing 90% isopropyl alcohol as a preservative. The envelopes are then passed through an irradiation area on a conveyer system. Thus, the catgut is sterilized when sealed in its final container. As the process is a rapid one, there is no lengthy hold up of material as in other processes. Each suture receives a minimum dose of 2.5 megarads. The exterior of the packet can be sterilized before opening by immersion in a solution of 1% formaldehyde in 90% isopropyl alcohol.