Scanning electrochemical microscopy as a local probe of oxygen permeability in cartilage

The use of scanning electrochemical microscopy, a high-resolution chemical imaging technique, to probe the distribution and mobility of solutes in art icular cartilage is described. In this application, a mobile ultramicroelec trode is positioned close (similar to 1 mu m) to the cartilage sample surfa ce, which has been equilibrated in a bathing solution containing the solute of interest. The solute is electrolyzed at a diffusion-limited rate, and t he current response measured as the ultramicroelectrode is scanned across t he sample surface. The topography of the samples was determined using Ru(CN )(6)(4-), a solute to which the cartilage matrix was impermeable. This reve aled a number of pit-like depressions corresponding to the distribution of chondrocytes, which were also observed by atomic force and light microscopy . Subsequent imaging of the same area of the cartilage sample for the diffu sion-limited reduction of oxygen indicated enhanced, but heterogeneous, per meability of oxygen across the cartilage surface. In particular, areas of h igh permeability were observed in the cellular and pericellular regions. Th is is the first time that inhomogeneities in the permeability of cartilage toward simple solutes, such as oxygen, have been observed on a micrometer s cale.