Protein incorporation within Ti scaffold for bone ingrowth using Sol-gel SiO2 as a slow release carrier

Porous titanium structures hold considerable promise as scaffolds for bone ingrowth in load bearing locations provided they are made osteoinductive by incorporation of bone growth factors. The purpose of the present research was to incorporate soybean trypsin inhibitor (STI) imitating growth factor into a porous Ti scaffold using sol-gel silica as a slow-release protein carrier. Alcohol-free TMOS-based sols (of pH 2 or 5) with dissolved STI were injected into Ti wire scaffolds yielding SiO(2) coating on the wire struts and SiO(2) beads entrapped in-between the wires. The formation of well-polymerized nanoporous SiO(2) was confirmed by FTIR, solid-state NMR, N(2) adsorption/desorption isotherms and BET analysis. In-vitro dissolution of silica and STI release in phosphate buffered saline (PBS) at 37 degrees C were measured by ICP-AES and Bradford assay, respectively. The biochemical activity of released STI protein was assessed by enzymatic assay. STI release was found to follow an attractive pattern of rapid release during the first 5 days followed by steady slow release for over one month. Despite certain conformational changes induced by the encapsulation procedure (detected by Circular Dichroism), the released STI retained most of its biological activity, especially when silica sol was prepared at the high protein-friendly pH = 5.