Retention of enzymatic activity immobilized on silanized Co-Cr-Mo and Ti-6Al-4V

Biochemical surface modification of biomaterials utilizes immobilized biomolecules to induce preferred tissue responses. Operational stability, or retention of biological activity, of biochemically modified biomaterials is a fundamental determinant of their usefulness. The present study investigated retention of enzymatic activity immobilized on silanized Co-Cr-Mo and Ti-6Al-4V. A model enzyme, trypsin, was immobilized on monolayers and multilayers of silane deposited from aqueous or organic solutions of gamma-aminopropyltriethoxysilane (APS). Trypsin-conjugated biomaterials were incubated in cell culture medium at 37 degrees C for up to 96 h, and the residual immobilized activity was measured. Retention of bioactivity in physiological saline was dependent on the type of material and on the method of silanization. Activity of enzyme adsorbed on the metals was lost within 24-48 h. Both mono- and multilayers of APS deposited on Co-Cr-Mo by aqueous silanization effectively retained enzymatic activity throughout the 96 h incubation period. The monolayer retained approximately 23% of the activity initially present, and the multilayers retained approximately 50% of the initial activity. Organic silanization of Co-Cr-Mo was marginally effective as it initially slowed the loss of activity. However, all activity was lost by 48-72 h of incubation. Neither organic nor aqueous silanization enhanced retention of enzymatic activity on Ti-6Al-4V.