Biochemical surface modification of Ti-6Al-4V for the delivery of protein to the cell-biomaterial interface

Biochemical surface modification involves delivery of biomolecules to the tissue-implant interface to induce desired cell and tissue responses. We have previously had success in immobilizing and retaining bioactive molecules on Co-Cr-Mo but not on Ti-6Al-4V. The purpose of this study was to modify the gamma-aminopropyltriethoxysilane (APS) scheme to enable successful attachment of protein to the surface of Ti-6Al-4V. Ti-6Al-4V samples were silanized with organic (acetone) solutions of APS and dried at increasing temperatures. Concentrations resulting in 2-4 NH2 per nm2 of nominal surface area were incubated in physiological saline for up to 96 hr to assess retention of amino groups. A model protein, trypsin, was coupled to silanized Ti-6Al-4V via glutaraldehyde. The samples were then incubated in saline, and the activity of residual immobilized enzyme was quantified. After drying at 45, 80, or 115 degrees C, the NH2 groups were lost from the surface by 24 hr of incubation in saline. On samples dried at 150 degrees C, with 4% APS, the number of NH2 groups increased after 8 hr and remained relatively constant through 96 hr. Likewise, at 150 degrees C with 2% APS the surface density of NH2 groups reached a maximum at 24 hr and remained relatively constant up to 96 hr. When incubated for 96 hr, Ti-6Al-4V with 4% APS and dried at 150 degrees C retained approximately 31% of the activity initially immobilized, whereas protein on 45 degrees C or adsorbed samples was lost by 24-48 hr.