The human anatomy nervous system transmits signals to and from the brain for various voluntary and involuntary muscles. Nerve receptors also transmit data to the brain for heat, cold, pain and other sensations. The nerve fibers are protected by a covering or sheath. The ability to control, modify or block the signals from the receptors to the brain may be accomplished through selective electrical stimulation of a specific nerve path.
Design Objective
The objective of this study was to evaluate a proposed design concept for an electromechanical contact device which would provide the following characteristics:
- Suitable contact interface with the nerve sheath, allowing necessary electrical stimulation
- Device geometry and materials allows leads to be positioned on nerve sheath without damage to sheath
- Allow repositioning or removal, as required, without incurring nerve sheath damage.
"MSC Marc post-processing features make results plotting easy"
Design Material and Analysis Software Selection
Biocompatible materials must be used for leads, contact device body and the electrical contact surface. Materials selected for evaluation were:
- Injection molded Silicon for lead and contact device body
- Stainless steel lead wires
- Platinum Iridium foil electrical contact surfaces
The analysis to be performed necessitated the following software capabilities:
- Complex geometry meshing
- Highly non-linear materials
- Complex 3-D contact surfaces
- Large displacement
- Sliding friction between contact bodies
- Calculation of contact forces and stresses
Marc Finite Elements Analysis Model:
Materials & Geometry:
Molded Silicon was represented by the Mooney material library model available in the Marc materials library. The very thin Platinum Iridium foil was represented by a non-linear, stress-strain curve generated by material tensile test data.
An initial study was based on model geometry consisting of a rigid cylindrical contact surface simulating the nerve sheath; a molded Silicon central body containing the electrical leads; molded Silicon contact “fingers” wound helically around the rigid nerve sheath. The inner surfaces of the helical “fingers” were bonded to the very thin Platinum Iridium foil which, in turn, was connected to the electrical leads within the central body. The FEA model consisted of approximately 1,300 nodes and 8,200 hexahedral 8-node solid brick elements.
Modeling Procedure
The same model sub-assembly was also checked in tension using a distributed pressure loading incrementally applied to the inner foil surfaces. A final check used a single set of “fingers” and the simulated nerve sheath to verify functioning of the sliding friction contact mechanism between the 3-D contact sets and the simulated rigid nerve sheath. After successfully checking the model components, a final assembly of the model was generated, the model was loaded by an incrementally applied large displacement of the simulated nerve sheath. Model pull-off loading was performed using incrementally applied large displacements, moving the clamp assembly away from the simulated nerve sheath. The Marc software post processing features make results plotting easy.
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