Unlike synthetic polymers derived from petroleum, natural polymers occur in nature and can be extracted. These polymers are either formed by addition polymerization or condensation polymerization processes. An excellent example of a naturally occurring polymer is the natural rubber found on trees, which is harvested as tree latex before being subjected to vulcanization processes. Other examples of naturally occurring polymers include proteins, cellulose, wool, DNA, and silk.

The FDA regulates four types of sterilization of medical devices made from natural polymers. These are autoclave, dry heat, ethylene oxide, and irradiation sterilization methods. The effectiveness and the suitability of the methods are dependent on the specific properties of each polymer material being sterilized. We will look at the different properties of polymers and the most compatible methods of sterilization.

Dry Heat Sterilization

Dry heat is one of the prevalent polymer sterilization methods, but it is more effective with synthetic polymers than natural polymers.

The dry heat sterilization involves exposing specimens containing bacteria to high temperatures through flaming, incineration, or a hot air oven. Generally, most naturally occurring polymers are not compatible with dry heat sterilization except viscose, showing fair results.

Irradiation

This method typically involves exposing packed polymer materials to radiation for sterilization purposes. The effectiveness of this method depends on the types of radiation used and their penetration levels. Gamma-ray and electronic beam methods have more penetrating power and are ideal for sterilization on large-scale polymer-made medical devices.

The standard E-beam radiation dosage amounts may range from between 2 to 4 megarads or 20 to 40 kilograys. However, the dosage amounts can vary based on the packaging density within the sterilization chamber and the sterilized natural polymer properties. It is important to note that the color and mechanical properties of some polymer types can be affected by radiation. Gamma rays are also popularly used to sterilize disposable medical equipment, including syringes, cannulas, and IV sets.

The natural polymers showing fair compatibility with gamma irradiation include cellulose, cellulose acetate, cotton, natural rubber, viscose, and rayon viscose. Cellulose and cellulose acetate are also fairly compatible with E-beam sterilization.

Ethylene Oxide

Ethylene oxide sterilization is ideal for polymer-made devices that cannot tolerate moisture or heat. The method is highly effective, although devices sterilized using the method require several hours of aeration to get rid of residual gas. Ethylene oxide is highly toxic, and devices need to be dried entirely before subjecting them to the gas. The natural polymers compatible with this method of sterilization include cellulose, cellulose acetate, and viscose.

Steam Autoclave

Steam autoclaving is another popular and highly recommended sterilization technique. Autoclaving involves using both hot moisture and heat to kill microbes and bacteria off the polymer substance. The cycle time and the suitable temperatures to be used depend on the polymer family. Typical cycles last between 15 to 30 minutes, with temperatures from 121 to 134 degrees Celsius. Most natural polymers used in the medical industry cannot withstand prolonged, repeated exposures to high temperatures and hot steam except cellulose, which shows fair compatibility with this sterilization method.