Evaluation of ethylene oxide sterilization of tissue implants

The ability of ethylene oxide (ETO) gas to penetrate tissue matrices was evaluated using Bacillus subtilis var niger (NCTC 10073) spore strips sandwiched between sheets of various tissues exposed to ETO for varying periods. The decimal reduction times (min) obtained using commercially prepared spores were: 7.97 for naked spores, 7.34 between amnion, and 6.39 between amnio-chorion, indicating complete penetration of the matrix by the gas. Similar conclusions were reached using skin and dura mater. The possible protective effect of serum was evaluated by drying spores suspended in serum in different ways, followed by exposure to the gas. Decimal reduction times obtained were: 8.67 (dried at 37 degrees C); 8.09 (dried at 55 degrees C) and 8.97 (freeze-dried) confirming slight protection. However, in all cases sterilization was achieved following 100 min ETO exposure, giving a 2.5 times safety factor for the commercial ethylene oxide sterilizer.