Hydration and preferential molecular adsorption on titanium in vitro.

Surface sensitive spectroscopies, Auger electron and X-ray photoelectron (XPS), were used to determine changes in titanium oxide composition, oxide stoichiometry, and adsorbed surface species as a function of exposure to human serum in a balanced electrolyte (serum/SIE) and 8.0 mM ethylenediaminetetraacetic acid in a balanced electrolyte (EDTA/SIE) at 37 degrees C. Before immersion, the oxide was near ideal TiO2, covered by two types of hydroxyl groups: acidic OH(s) with oxygens doubly coordinated to titanium, and basic Ti-OH groups singly coordinated. After extended exposure to both solutions, up to 5000 h (ca. 208 d), the surface concentration of OH groups increased and non-elemental P appeared. The P LVV Auger transition and P 2p spectra indicated the peak positions were similar to reference phosphate compounds. The adsorbed phosphate species were presumed to be either Ti-H2PO4 or Ti-HPO4-. The XPS data suggested that a lipoprotein and/or glycolipid film was adsorbed to the specimens exposed to serum/SIE. Analysis of the preferential lipoprotein/glycolipid adsorption using electrostatic bonding concepts contributed to the refinement of the hierarchical model for the Ti-tissue interface. The salient features are that Ti metal is not in direct contact with the biological milieu, rather there is a gradual transition from the bulk metal, near-stoichiometric oxide, Ca and P substituted hydrated oxide, adsorbed lipoproteins and glycolipids, proteoglycans, collagen filaments and bundles to cells.