In vivo implant mechanics of single-shaft microelectrodes in peripheral nervous tissue

The VSAMUEL consortium developed silicon-based, electrode arrays (referred to as ACREO electrodes), that may one day provide a highly selective neural interface for neuroscience or neural prosthesis applications. We previously reported on the successful insertion into brain tissue. In the present work, we investigated the feasibility of implanting the ACREO electrodes into peripheral nerve. We compared the implant mechanics of single shaft silicon ACREO electrodes (25 times 38 times 15000 mum) and conventional tungsten needle electrodes (50mum diameter). Experimentally measured implant forces were measured in vivo (1 acute rabbit, 2 mm depth, 2 mm/s velocity). The force required for the tungsten electrode to first penetrate the perineurium was in average 7.4 plusmn 3.9 mN, whereas the maximum force the electrode had to withstand during the entire insertion/retraction was 11.3 plusmn 2.8 mN. It was not possible to facilitate perpendicular insertion of the ACREO electrode without breaking it. The critical buckling force of the ACREO electrode was theoretically estimated to 1-4 mN, which proved consistent with the experimentally measured break force (5.1 plusmn 2.1 mN). Bending moment analysis showed that tungsten could withstand ultimate stresses 4-10 times higher than our silicon-based electrodes. Before the ACREO electrodes can be safely used for peripheral and spinal cord implants we recommend to shorten and thicken the probes to increase their mechanically strength.