THE REDUCTION HALF CELL IN BIOMATERIALS CORROSION - OXYGEN DIFFUSION PROFILES NEAR AND CELL RESPONSE TO POLARIZED TITANIUM SURFACES

Mechanically assisted corrosion processes can greatly increase the oxi dation currents generated in passivating alloy systems like Co-Cr and titanium due to oxide film disruption. When oxide films are abraded, r epassivation and ionic dissolution both occur at rates that are orders of magnitude higher than undisrupted surfaces. The excess electrons g enerated by these anodic processes must be consumed in corresponding r eduction reactions that include the reduction of oxygen. If large enou gh, these reduction reactions may locally deplete the concentration of solution-dissolved oxygen and, in turn, affect cell behavior in the v icinity of the implant surface. To date, this hypothesis has not been tested. In the present study, a scanning electrochemical microscope wa s used to measure oxygen concentration profiles in vitro near a planar titanium electrode polarized to different voltages representative of those attainable by titanium undergoing mechanically assisted corrosio n. The potentials investigated ranged from 0 mV to -1000 mV (AgCl). Th e oxygen concentration as a function of distance from the titanium sur face was measured using a platinum-iridium microelectrode and an amper ometric technique. Also, preliminary experiments were performed to ass ess the response of rat calvarial osteoblast-rich cells cultured for 2 h on titanium samples polarized to two different potentials (0 mV and -1000 mV versus AgCl). The results of this study indicate that oxygen concentrations near titanium surfaces are affected by sample potentia ls out to probe-sample distances as great as 500 mu m. Within 2 mu m o f the surface, oxygen concentrations decreased by 15 to 25% for sample potentials between -100 and -500 mV. At potentials more negative than -600 mV, the oxygen concentration dropped rapidly to near zero by -90 0 mV. The cell experiments showed a statistically significant differen ce in the amount of cell spreading, as measured by projected cell area , between the two groups (p < 0.03), with the cells cultured at -1000 mV undergoing much less spreading. This implies that -1000 mV inhibits normal cell behavior at the titanium surface and that this is most li kely due, at least in part, to a diminished oxygen supply. (C) 1998 Jo hn Wiley & Sons, Inc.