Effects of titanium dioxide passive film crystal structure, thickness, and crystallinity on C3 adsorption.

The effects of titanium dioxide passive film crystal structure, thickness, and crystallinity on C3 adsorption from diluted human plasma were measured. Titanium dioxide surfaces created include (1) 70-nm anatase and rutile films comprising a mixture of amorphous and microcrystalline titanium dioxide, (2) 140-nm anatase and rutile films with greater crystallinity than the 70-nm films, (3) 70-nm aged anatase films with approximately the same crystallinity as that of the 140-nm anatase films, (4) sintered anatase and sintered rutile with no underlying metal, representing completely crystalline oxide films of infinite thickness, and (5) electropolished titanium. All combinations of experimental variables of surface type, exposure time, and plasma dilution were replicated four times. Anatase and rutile C3 surface concentrations increased with increased oxide thickness and crystallinity. The 70-nm aged anatase film isotherm more closely matched that of the 140-nm than of the 70-nm film, indicating that some property associated with oxide crystallinity is more influential in C3 adsorption than properties associated with oxide thickness alone. Concentrations of C3 were equal for equivalent anatase and rutile surfaces, except at high plasma concentrations and long exposure times, in which more C3 was adsorbed to anatase, suggesting that crystal structure may not be a significant controlling factor.