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A flexible neural implant was designed and fabricated using an novel integration approach that offers the advantages of both silicon and polymer based implants: high density electrodes and precise insertion on one side and mechanical flexibility suitable for reduced tissue strain due to micro-motion during chronic implantation on the other side. This was achieved by separating the device into silicon or polymer areas, depending on their desired functionality. The tip, where the recording and stimulation electrodes would be placed, was kept of silicon: a choice that doesn't call for any compromise to be made regarding the high density electrode and possible local circuit integration later on. The bevel shaped sharp silicon tip also proved to facilitate the probe insertion, offering a behavior very much similar to the classical rigid silicon probes. On the other side, most of the 1 cm long shank of the probe was made out of polyimide. This led to more than one order of magnitude reduction of the forces necessary to bend the shank. The flexible shank proved also to be more robust than silicon probes, sustaining significant deformation in any direction without fracture. The 9mm deep in-vivo implantation were successfully achieved without buckling for 10 µm/s and 100 µm/s insertion speeds.

Closed loop systems, in which stimulation parameters are adjusted according to recorded signals would reduce the occurrence of side effects of stimulation and broaden current therapeutic options. As a step towards a closed-loop clinical system, we developed a single electrode stimulation / recording system for an in vitro microelectrode array. The system was used in vitro to simultaneously stimulate and record cardiac cells. Results indicated that stimulation artifacts depend on the distance between recording electrode and stimulating electrode and on the voltage amplitude. No artifact reduction algorithm was required for detecting cardiac action potentials 2ms after stimulation if the stimulation pulses were less than or equal to ± 1.5 V, and the distance from stimulation site was more than 200 µm. Cardiac signal propagation was also investigated with this system.