Laser-Microfabricated Polymer Multielectrodes for Intraspinal Microstimulation.

OBJECTIVE: The overall goal of this study was to design, fabricate, and characterize a new polymer-based multielectrode for the spinal cord for the application of intraspinal microstimulation (ISMS). METHODS: Three-channel multielectrodes were fabricated from modified poly(dimethylsiloxane) (PDMS) and platinum-iridium (Pt-Ir) foil using nanosecond laser microfabrication techniques. These devices were compared against traditional 50 µm diameter Pt-Ir microwire electrodes mechanically and electrochemically in bench environments, and were assessed electrochemically and functionally in vivo in a domestic pig model. RESULTS: Polymer-based multielectrodes were significantly more flexible than microwire electrodes (p < 0.05) and had greater charge storage capacities in phosphate buffered saline (p < 0.05). In a domestic pig model, multielectrodes had significantly greater charge injection limits than microwire electrodes (p < 0.05). When stimulating within the quadriceps motor pool in the spinal cord, multielectrodes generated strong knee extensor joint torques of up to 4.4 ± 0.3 Nm and were able to extend the knee by up to 26 ± 1°. However, histological analyses showed that polymer-based multielectrodes, implanted with half-needle insertion aids, produced greater acute tissue damage compared to microwire electrodes (p < 0.05). Alternative insertion methods for these flexible electrodes should be explored to reduce acute tissue damage. CONCLUSION: The PDMS-based three-channel multielectrodes demonstrated improved flexibility and charge injection capabilities over traditional microwire electrodes, and were able to produce functional responses in vivo. SIGNIFICANCE: Polymer-based multielectrodes demonstrate improved functionality over microwire electrodes while remaining more flexible than silicon multielectrode designs. These features may in the future permit polymer-based multielectrodes to implement ISMS with greater efficacy and biocompatibility compared to traditional technologies.

Mechanically Stable Intraspinal Microstimulation Implants for Human Translation.

The goal of this study was to develop stable intraspinal microstimulation (ISMS) implants for use in humans to restore standing and walking after spinal cord injury. ISMS electrically activates locomotor networks within the lumbar region of the spinal cord. In animals, ISMS produced better functional outcomes than those obtained by other interventions, and recent efforts have focused on translating this approach to humans. This study used domestic pigs to: (1) quantify the movements and length changes of the implant region of the spinal cord during spine flexion and extension movements; and (2) measure the forces leading to the dislodgement of the ISMS electrodes. The displacement of the spinal cord implant region was 5.66 ± 0.57 mm relative to the implant fixation point on the spine. The overall length change of the spinal cord implant region was 5.64 ± 0.59 mm. The electrode dislodgment forces were 60.9 ± 35.5 mN. Based on these results, six different coil types were fabricated and their strain relief capacity assessed. When interposed between the electrodes and the stimulator, five coil types successfully prevented the dislodgement of the electrodes. The results of this study will guide the design of mechanically stable ISMS implants for ultimate human use.