Fabrication and characterization of nonplanar microelectrode array circuits for use in arthroscopic diagnosis of cartilage diseases

A process to fabricate nonplanar microelectrode array circuits was developed and the microelectrodes were characterized. These platinum microelectrode arrays are for recording streaming potential signals generated during indentation of articular cartilage. The nonplanar substrate was produced by permanent deformation of a 7-in-diameter circular stainless-steel wafer to form 32 semi-spherical caps (radius of curvature=4.65 mm and height=250 /spl mu/m) at the periphery. The wafer was covered with a 2.5-/spl mu/m-thick layer of insulating polyimide. Standard microelectronic processes were applied to produce 32 circuits (60 mm long /spl times/4 mm wide) with 37 exposed circular microelectrodes (diameter=100 /spl mu/m) centered over each semi-spherical cap. A 2.5-/spl mu/m-thick photodefinable polyimide layer encapsulated the conducting lines. Capacitances between one microelectrode and either another microelectrode or the metallic substrate were 14.6/spl plusmn/2.0 and 34.4/spl plusmn/3.3 pF, respectively, at 100 Hz. The impedance of the microelectrodes in a 0.15 M saline bath (PBS) was 0.25/spl plusmn/0.08 M/spl Omega/ while the crosstalk (V/sub induced//V/sub applied/) between two microelectrodes was 0.20/spl plusmn/0.11%, at 100 Hz. Indentation measurements were performed on articular cartilage in vitro showing streaming potentials that indicate electrode-tissue contact times and generation of streaming potentials.