Biodegradation of polyamide 4 in vivo

We determined that polyamide 4 (PA4), which is easily degraded in the environment, is also degraded in vivo. We previously reported that PA4 was degraded by activated sludge. However, the potential biodegradability of PA4 in vivo has not been evaluated. In the present study, we subcutaneously implanted various PA4 samples in the backs of rats, including non-woven fabric as well as film and mold. The weights of implanted and recovered non-woven cloth composed of the PA4 polymer started to decrease at 3 months. At 8.5 months, weights decreased by 90%. For the non-woven PA4 cloth with a fine structure, there was no significant decrease in weight until 8.5 months. These results showed that PA4 was degraded in vivo and that polymer structure was important in determining the degradation rates. Copolymers composed of PA4 and polycaprolactone were also degraded in vivo. Homopolymers of PA4 were not hydrolyzed in phosphate buffer at 37 °C after one year. These results suggested the possibility that biochemical reactions were implicated in the degradation of PA4 in vivo. Based on tissue sample observations, implanted PA4 did not modify surrounding tissues. Safety evaluation, mutagenicity testing using bacteria (Ames test), and in vitro cytotoxicity testing using Chinese hamster V79 cells suggested that PA4 had no mutagenicity or cytotoxicity. Our study demonstrates that PA4 has potential as a bioabsorbable polymer material for biomedical applications.