In vitro bone biocompatibility of poly(anhydride-co-imides) containing pyromellitylimidoalanine

Poly(anhydride-co-imides) are currently under study for applications involving bone. The cytotoxicity of a series of poly(anhydride-co-imides) with osteoblast-like cells (MC3T3-E1) was evaluated. The imide component of the copolymers was based on pyromellitylimidoalanine and the anhydride component was based on either sebacic acid or 1,6-bis(carboxyphenoxy)hexane. Cell adhesion and proliferation on the sur faces of the polymer discs were observed by environmental scanning electron microscopy. During the first 24 hours of attachment, the cells showed normal morphology when cultured on copolymers containing 1,6-bis(carboxyphenoxy)hexane. The cells did not adhere to the polymers containing sebacic acid, probably due to the rapid degradation of the polymer surfaces. Concurrently, the effects of polymer breakdown products on osteoblast-like cells were evaluated by studying their proliferation (cell numbers), viability (dye exclusion), morphology (light microscopy), and phenotypic expression. The morphology of osteoblast-like cells cultured in the presence of the polymer breakdown products pyromellitylimidoalanine and pyromellitic acid was found to be similar to that of the same cells grown on tissue culture polystyrene and consisted of a characteristic polygonal shape. With use of a monoclonal antibody to osteocalcin, these cells were shown to demonstrate preserved osteoblast phenotype with growth over a 21-day period. In addition, the cells reached confluency after 3-4 days, similar to cells grown on tissue culture polystyrene. This in vitro evaluation showed that the poly(anhydride-co-imides) evaluated are non-cytotoxic and may be viable biomaterials for orthopaedic applications.