SCANNING ELECTROCHEMICAL MICROSCOPY OF METALLIC BIOMATERIALS - REACTION-RATE AND ION RELEASE IMAGING MODES

The Scanning Electrochemical Microscope (SECM) is a nonoptical scannin g microscopic instrument capable of imaging highly localized electrica l currents associated with charge transfer reactions on metallic bioma terials surfaces. The SECM operates as an aqueous electrochemical cell under bipotentiostatic control with a microelectrode and sample indep endently biased as working electrodes. Microelectrode current and posi tion is recorded as it is scanned very near a metallurgically polished planar sample surface. To date, the SECM has imaged metallic biomater ials surfaces in oxygen reaction rate imaging (ORRI) and ion release a nd deposition imaging (IRDI) modes. In ORRI, sample and microelectrode are biased at sufficiently negative potentials to reduce absorbed oxy gen. As the microelectrode scans areas of active oxygen reduction, loc alized diffusion fields with decreased oxygen solution concentrations are encountered and resultant decrements in microelectrode current are observed. In IRDI mode the sample is positively biased and the microe lectrode is negatively biased. The microelectrode detects anodic disso lution products with highest currents being observed over the most act ive areas. Performance of the SECM has been evaluated on Ni minigrids, gamma-1 Hg-Ag dental amalgam crystals, and sintered beads of Co-Cr-Mo alloy which represent significantly different geometries and corrosio n processes to help demonstrate the potential of this instrument. The SECM is a valuable tool for imaging microelectrochemical processes on the surfaces of metallurgically polished metallic biomaterials samples and a wide variety of other surfaces of biological interest where cha rge transfer reactions occur. The SECM allows selective biasing of met allic biomaterials surfaces and Faradaic reactions can be selectively imaged while the surface is in the active, passive, or transpassive st ate. (C) 1993 John Wiley & Sons, Inc.