CHEMICAL MODIFICATION OF TITANIUM SURFACES FOR COVALENT ATTACHMENT OFBIOLOGICAL MOLECULES

The surface of implantable biomaterials is in direct contact with the host tissue and plays a critical role in determining biocompatibility. In order to improve the integration of implants, it is desirable to c ontrol interfacial reactions such that nonspecific adsorption of prote ins is minimized and tissue-healing phenomena can be controlled. In th is regard, our goal has been do develop a method to functionalize oxid ized titanium surfaces by the covalent immobilization of bioactive org anic molecules. Titanium first was chemically treated with a mixture o f sulfuric acid and hydrogen peroxide to eliminate surface contaminant s and to produce a consistent and reproducible titanium oxide surface layer. An intermediary aminoalkylsilane spacer molecule was then coval ently Linked to the oxide layer, followed by the covalent binding of e ither alkaline phosphatase or albumin to the free terminal NH2 groups using glutaraldehyde as a coupling agent. Surface analyses following c oating procedures consisted of X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM) . Enzymatic activity of coupled alkaline phosphatase was assayed color imetrically, and surface coverage by bound albumin was evaluated by SE M visualization of colloidal gold immunolabeling. Our results indicate that the linkage of the aminoalkylsilane to the oxidized surface is s table and that bound proteins such alkaline phosphatase and albumin re tain their enzymatic activity and antigenicity, respectively. The dens ity of immunolabeling for albumin suggests that the binding and surfac e coverage obtained is in excess of what would be expected for inducin g biological activity. In conclusion, this method offers the possibili ty of covalently Linking selected molecules with known biological acti vity to oxidized titanium surfaces in order to guide and promote the t issue healing that occurs during implant integration in bone and soft tissues. (C) 1998 John Wiley & Sons, Inc.