EVALUATION OF POLY(DTH CARBONATE), A TYROSINE-DERIVED DEGRADABLE POLYMER, FOR ORTHOPEDIC APPLICATIONS

The polymerization of desaminotyrosinetyrosylhexyl ester (DTH) with ph osgene gives rise to poly(DTH carbonate), a new pseudopoly(amino acid) . To evaluate the performance of this bioabsorbable material in orthop edic applications, the tissue responses elicited by compression-molded pins of poly(DTH carbonate) and clinically used polydioxanone pins (P DS; Orthosorb(R)) were compared. The two types of pins were implanted in the paravertebral muscle and in the metaphyseal proximal tibia and distal femur of 10 White New Zealand Rabbits for 1, 2, 4, and 26 weeks . The tissue response was evaluated using histologic staining of soft- and hard-tissue sections, fluorescent bone marker incorporation, and backscattered electron imaging. In soft tissue, both poly(DTH carbonat e) and PDS elicited a mild inflammatory response resulting in encapsul ation. During the disintegration phase, the PDS implants triggered a f oreign body response involving the phagocytosis of polymeric debris by histiocytes and giant cells. No such response was observed for poly(D TH carbonate). In hard tissue, close bone apposition was observed thro ughout the 26-week test period for poly(DTH carbonate) implants. At th e 26-week time point, the poly(DTH carbonate) implants exhibited surfa ce erosion and were penetrated by new bone. In contrast, an intervenin g fibrous tissue layer was always present between the PDS pins and the bone. At 26 weeks, the PDS implants had partially resorbed and a fore ign body response characterized by infiltration of inflammatory cells, and bone resorption was observed in several of the implantation sites . This study indicates that poly(DTH carbonate) and PDS exhibit fundam entally different interactions with hard tissue, and that poly(DTH car bonate) is a promising orthopedic implant material. (C) 1995 John Wile y & Sons, Inc.