EVALUATION OF A SERIES OF TYROSINE-DERIVED POLYCARBONATES AS DEGRADABLE BIOMATERIALS

A series of four polycarbonates derived from the ethyl, butyl, hexyl, and octyl esters of desaminotyrosyl-tyrosine was prepared by condensat ion polymerization. The resulting polymers had weight average molecula r weights ranging from 120,000-450,000, and their chemical structure w as confirmed by elemental analysis, nuclear magnetic resonance, and Fo urier transform infrared spectroscopy. The polycarbonates were evaluat ed as degradable biomaterials. Their surface properties were determine d by electron spectroscopy for chemical analysis, attenuated total ref lectance-Fourier transformed infrared spectroscopy, and contact angle measurement. The degree of surface hydrophobicity was related to the l ength of the alkyl ester pendent chain. The tensile properties were de pendent on the chemical structure of the polymers: For thin, solvent c ast film specimens, the tensile modulus varied from 1.2-1.6 GPa, and t he strength at break from 60-220 MPa. The degradation of polymeric fil ms was followed in vitro by measuring changes in mechanical strength f or up to 40 weeks, and the decrease in molecular weight and changes in surface chemistry for up to 80 weeks. The length of the pendent chain affected the degradation behavior and strength retention; the polymer s with short pendent chains were more readily hydrolyzable. For steril ization, ethylene oxide treatment was less destructive, as judged by m olecular weight retention, than gamma-irradiation. Spin-cast films of all tested polycarbonates were not cytotoxic toward cultured rat lung fibroblasts. The cell response was influenced by the chemical structur e of the polymer. The least hydrophobic polycarbonate (having a short ethyl ester pendent chain) was a more stimulating substrate for cell g rowth than the more hydrophobic polymers (carrying longer alkyl ester pendent chains). (C) 1994 John Wiley and Sons, Inc.