Background: Intraspinal microstimulation (ISMS) has emerged as a promising neuromodulation technique for restoring standing and overground walking in individuals with spinal cord injury. Current and emerging ISMS implant designs connect the electrodes to the stimulator through lead wires that cross the dura mater. To reduce possible complications associated with transdural leads such as tethering and leakage of cerebrospinal fluid, we aim to develop a wireless, fully intradural ISMS implant based on our prior work in the cortex with the Wireless Floating Microelectrode Array (WFMA). Although we have extensive data about WFMA cortical stability, its mechanical and electrical stability in the spinal cord remains unknown. One of the quantifiable metrics to assess long-term implant stability is mechanical strain.
Objective: The aim of the current work is to develop a method to assess implant stability by measuring strain fields in a surrogate of the human spinal cord.
Methods: A physical model of the spinal cord was studied using an electromechanical testing apparatus, simulating typical spinal cord motion. Strain fields were digitally analyzed using an optical method known as digital image correlation (DIC).
Results: Displacement and strain were visualized using contour plots. The strain values in the vicinity of each WFMA device were significantly different from the strain values in the same locations in the control surrogate spinal cord.
Conclusion: The results demonstrate that DIC can be used for in-vitro screening of intraspinal implants. Accurate optical strain measurements will enable researchers to optimize implant design over a wide range of motion conditions.
Keywords: digital image correlation; spinal cord injury; wireless array.
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