Methods
We evaluated the residual formaldehyde levels
according to the European Standard EN14180. The
technique for extraction of formaldehyde was
based on the Japanese guideline ‘Sample/solvent
and Extraction Conditions’.2 This method is almost
identical to the ISO/DIS 10993-12 Biological Evaluation
of Medical Devices-Part 12: Sample Preparation
and Reference Materials (1994).3 An LTSF
sterilizer GEF 449 (Getinge AB, Getinge, Sweden)
was used in this study. This sterilizer has a 185-L
chamber, which is injected with 34–38% formalin
during operation. Formaldehyde solution was purchased
from Wako Pure Chemical Industries (Osaka,
Japan). The sterilization temperature was set at
55 8C.