Titanium Oxide Layers prepared by Metal Plasma Immersion Ion Implantation and Deposition (MePIID) as Hemocompatible Surfaces

BACKGROUND: Titanium oxide is known for a good bio- and hemocompatibility, but this has not yet been correlated with crystal structure or electronic properties of this semiconductor. These physical features may be interesting because surface charges interact with charges of the protein and induce conformational changes of the protein with a change of function. Also chemical oxidation of proteins on the surface is under discussion for blood clotting activation.
METHOD: For this study Titanium oxide layers were deposited on oxidised Si as model substrate from a plasma produced by cathodic arc evaporation under addition of oxygen to the ambient near the substrate. The redox state of amorphous titanium oxide was additionally changed by ion implantation of Chromium, the electronic prop-erties of rutile TiO2 were changed by low dose implantation of the n-doping element Phosphorous. Both types of ion implantation should prevent an electron transfer from the protein to the surface. Blood platelet adherence and activation as well as clotting time were determined as parameters of hemocompatibility.
RESULTS: In dependence of the deposition parameters amorphous and nanocrystal-line structures, crystalline layers composed of anatase and brookite as well as layers dominated by the rutile phase have been obtained. The activation of the plasmatic clotting cascade was only minimally influenced by the crystal size and the crystallite structure of the titanium oxide films. As a trend, amorphous, nanocrystalline and fine-grained layers showed higher clotting times than well crystallized rutile films. Ion im-plantation of Cr or P strongly prolongated the clotting time, indicating a lower clotting activation. Only for P+-doped rutile both, enhanced clotting time and improved platelet adhesion, are observed. Contrasting tendencies in the dependence of clotting time and platelet adhesion on the Cr implanted Ti oxide have been stated.
CONCLUSION: Low dose P+ implantation into TiO2 can improve its blood compatibility, but it has to be worked out whether this effect really is due to modifications in the electronic properties of the TiO2 or due to biochemical effects. There was almost no effect of the crystal structure on the blood compatibility.