Measurement of intrafascicular insertion force of a tungsten needle into peripheral nerve

Microfabricated silicon array structures, such as those being developed by the VSAMUEL consortium may one day provide inexpensive yet highly selective chronically implanted interfaces to the peripheral nervous system. In the present study we examined the feasibility of implanting such microelectrodes into peripheral nerve tissue by characterizing the mechanical forces required for implantation. We conducted in-vitro implantation experiments into excised rabbit peripheral nerve with electrosharpened tungsten needles similar in dimension to the VSAMUEL probes. A needle was manually advanced through the epineurium and perineurium using a micro-manipulator. The force applied to the needle during the insertion process was measured using a custom built force detection device. We found that a force greater than 2 mN was necessary to insert the needle. Clear dimpling of the nerve surface was also observed prior to penetration.