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 μm) at the periphery. The wafer was covered with a 2.5-μm-thick layer of insulating polyimide. Standard microelectronic processes were applied to produce 32 circuits (60 mm long ×4 mm wide) with 37 exposed circular microelectrodes (diameter=100 μm) centered over each semi-spherical cap. A 2.5-μm-thick photodefinable polyimide layer encapsulated the conducting lines. Capacitances between one microelectrode and either another microelectrode or the metallic substrate were 14.6±2.0 and 34.4±3.3 pF, respectively, at 100 Hz. The impedance of the microelectrodes in a 0.15 M saline bath (PBS) was 0.25±0.08 MΩ while the crosstalk (V_induced/V_applied) between two microelectrodes was 0.20±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.