BIODEGRADATION AND TUMORIGENICITY OF IMPLANTED PLATES MADE FROM A COPOLYMER OF EPSILON-CAPROLACTONE AND L-LACTIDE IN RAT

Flat plates made from a copolymer of epsilon-caprolactone and L-lactid e (P-CL-LA) [50:50 (w/w), molecular weight 1.62 x 10(5); 20 x 10 x 1 m m size] were subcutaneously implanted into 50 young, male Wistar rats (P-CL-LA group). After 24 months the plates had become a mass of small pieces, which were concentrated in an area of 3 x 2 x 1 mm. For compa rison, 50 rats were implanted with medical-grade polyethylene plates ( PE group) while another set of 50 rats was subjected to the same opera tion but without an implant (Sham Op group). Tumors arose in 25 rats f rom the P-CL-LA group: 24 were malignant mesenchymal tumors at the imp lant sites. In the PE group, tumors appeared in 16 rats (14 at the imp lant sites and two ectopically). The average tumor latency was 578 +/- 84 days in the P-CL-LA group and 452 +/- 102 days in the PE group. Th ere was no difference in tumor incidence between the P-CL-LA and PE gr oups (p < 0.05). In the Sham Op group, two malignant tumors appeared o ver 2 years. Pathologically, these induced tumors arose from the infla mmatory cells surrounding Be degrading fragments of P-CL-LA within the tissue capsule. This indicates that relatively slowly degrading mater ial can induce malignant tumors at a similarly high rate to nonabsorba ble medical grade PE, at least in this animal model. (C) 1998 John Wil ey & Sons, Inc.