In-vivo testing of a novel wireless intraspinal microstimulation interface for restoration of motor function following spinal cord injury.

BACKGROUND: Spinal cord injury causes a drastic loss in motor and sensory function. Intraspinal microstimulation (ISMS) is an electrical stimulation method developed for restoring motor function by activating the spinal networks below the level of injury. Current ISMS technology uses fine penetrating microwires to stimulate the ventral horn of the lumbar enlargement. The penetrating wires traverse the dura mater through a transdural conduit that connects to an implantable pulse generator. OBJECTIVE: A wireless, fully intradural ISMS implant was developed to mitigate the potential complications associated with the transdural conduit, including tethering and leakage of cerebrospinal fluid. METHODS: Two wireless floating microelectrode array (WFMA) devices were implanted in the lumbar enlargement of an adult domestic pig. Voltage transients were used to assess the electrochemical stability of the interface. Manual flexion and extension movements of the spine were performed to evaluate the mechanical stability of the interface. Post-mortem 9T MRI imaging was used to confirm the location of the electrodes. RESULTS: The WFMA-based ISMS interface successfully evoked extension and flexion movements of the hip joint. Stimulation thresholds remained stable following manual extension and flexion of the spine. CONCLUSION: The preliminary results demonstrate the surgical feasibility as well as the functionality of the proposed wireless ISMS system.

The use of digital image correlation for measurement of strain fields in a novel wireless intraspinal microstimulation interface.

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.

Preparation of a neural electrode implantation device for in-vivo surgical use.

An instrument designed for the implantation of neural electrode array devices has been refined in preparation for use in cortical implantation procedures in non-human primates. This instrument has undergone extensive testing to ensure its successful first use in a live surgical setting. This work describes the modifications made to the instrument and the testing performed on it during that preparatory period as well as planned future modifications and augmentations.