STABILITY OF TRYPSIN IMMOBILIZED ON INORGANIC ORTHOPEDIC BIOMATERIALS

Biochemical surface modification of biomaterials utilizes immobilized biomolecules to induce preferred tissue responses. Although several te chniques are available for immobilizing biomolecules on organic substr ates, comparatively few are available for use with inorganic materials , such as those used in many orthopedic applications. The present stud y investigated the stability/elutability of a model enzyme immobilized on Co-Cr-Mo and Ti-6Al-4V alloys using p-nitrophenyl chloroformate (p -NPC). Trypsin-conjugated biomaterials were incubated in cell culture medium at 37 degrees C for up to 96 hr, and the residual immobilized a ctivity was measured. Although all samples initially bound enzymatical ly active trypsin, significant decreases were observed within the firs t 2 hr of incubation. Immobilization of trypsin on Co-Cr-Mo treated wi th 0.65 mg p-NPC/cm(2) of nominal surface area gave significantly high er residual activity than on untreated samples at 24-96 hr of incubati on and prevented the nearly complete loss of enzymatic activity that w as observed with free (not immobilized) enzyme. Derivatization of Ti-6 Al-4V with p-NPC was not beneficial to the level of immobilized enzyma tic activity after incubation in medium for longer than 6 hr.