Platelet adhesion on titanium oxide gels: effect of surface oxidation.

The correlations between titanium oxide layers on oxidized titanium (Ti) substrates and platelet adhesion were examined. Ti substrates were prepared by three different oxidation methods: the first one was treated with hydrogen peroxide (H2O2) solution, the second one was heated in air at moderate temperatures, and the third one was processed with both H2O2 and heating. The titanium oxide layers formed on the Ti substrates were characterized by wettability, chemical composition, thickness, and crystal phase. The platelet adhesion on these oxide layers was examined and correlated to the characterizations of the surface layers. The number of adhesive platelets seemingly correlated with the contact angle towards distilled water, because the number increased close to 70-80 degrees of the contact angle. The effect of surface oxidation on platelet adhesion was examined in detail and it was found that the composition and thickness of the oxide layer influenced platelet adhesion rather than wettability. Thick titanium oxide layers formed on Ti substrates by heating displayed less platelet adhesion than thin oxide layers on untreated Ti substrates. The largest number of adhesive platelets was found on H2O2-oxidized substrates; the substrates found on amorphous titanium oxide contained the Ti-peroxide radical species. The number of platelets, on the other hand, could hardly be observed on Ti substrates treated with H2O2 and subsequently heated above 300 degrees C. The titanium oxide layer on the substrate was thick and we found it to consist of only a few radical species. That is, the effect of heat treatment accelerates the growth of the oxide layer, and decomposes or decreases the number of radical species. Ti substrates with H2O2 and heat treatment above 300 degrees C held the least number of platelets, and were concluded to be the most inhibitory for platelet adhesion.