Tissue compatibility of tyrosine-derived polycarbonates and polyiminocarbonates: an initial evaluation

Compression-molded disks of two tyrosine-derived polymers [poly(desaminotyrosyl-tyrosine-hexyl ester carbonate) and poly(desaminotyrosyl-tyrosine hexyl ester iminocarbonate)], two polymers derived from Bisphenol A [poly(Bisphenol A iminocarbonate) and poly(Bisphenol A N-phenyliminocarbonate)], and two clinically used standard materials [poly(D,L-lactic acid) and high-density polyethylene] were implanted subcutaneously in the back of Sprague-Dawley rats. The tissue response elicited by these materials was evaluated histologically at 7, 30, and 120 days postimplantation, based on the total cell density (including fibroblasts, monocytes, giant cells, and macrophages) at the implantation site. The tissue response observed for the two tyrosine-derived polymers was mild, comparable to the two standard materials, medical-grade poly(L-lactic acid) and high density polyethylene. The two Bisphenol A-containing polymers elicited significantly more severe tissue responses. These results indicate that the use of derivatives of the natural amino acid L-tyrosine in the synthesis of degradable implant materials improved the tissue compatibility of these materials relative to chemically related polymers that contain Bisphenol A, an industrial diphenol. The tyrosine-derived polyiminocarbonate and polycarbonate are therefore promising candidates for a detailed evaluation of their biocompatibility, including long-term implantation studies in higher mammals.