IN-VIVO EVALUATION OF POLYURETHANES BASED ON NOVEL MACRODIOLS AND MDI

A series of novel polyurethane elastomers based on methylenediphenyl d iisocyanate, 1,4-butanediol and the macrodiols, poly(hexamethylene oxi de), poly(octamethylene oxide), and poly(decamethylene oxide) were imp lanted subcutaneously in sheep for periods of 3 and 6 months. The spec imens that were subjected to 3 months of implantation were strained to 250% of their resting length, while those implanted for 6 months had no applied external strain. SEM examination of the explanted specimens revealed that the novel materials displayed resistance to environment al stress cracking. Proprietary materials, Pellethane 2363-80A, Biomer and Tecoflex EG-80A, which had been implanted under identical conditi ons, showed evidence of significant stress cracking. The extent of str ess cracking in the 3-month strained experiment was similar to that fr om the 6-month unstrained experiment. Stress cracking was also observe d in Pellethane 2363-55D, when implanted for 6 months (unstrained). Ne ither changes in molecular weight nor in tensile properties provided a clear indication of early susceptibility to degradation by environmen tal stress cracking.