(31) i360: An Ultra-Thin, Flexible, Circumferential Spinal Cord Interface for Bidirectional, High-Resolution Interfacing

Introduction: Spinal cord injury (SCI) can cause severe, debilitating manifestations that affect millions worldwide. Although spinal cord stimulation has shown promise in restoring partial motor function, existing approaches target predominantly dorsal structures, leaving the remaining circumferential regions of the spinal cord underutilized. We present a novel, ultra-thin, flexible device (“i360”) designed to wrap around the spinal cord, delivering high-resolution, bidirectional interfacing. We hypothesize that this circumferential approach can more comprehensively engage spinal networks critical for locomotion and rehabilitation.

Methods: We fabricated thin-film electrode arrays using advanced lithography techniques on a 4 μm-thick parylene-C substrate. Gold was deposited to form interconnects, while PEDOT:PSS was applied to the electrode sites to lower impedance and increase charge transfer efficiency. Before implantation, each device underwent extensive in vitro testing.
In vivo experiments were conducted in rodent, porcine, and human cadaver models. We utilized freely moving rodent models for simultaneous neural recordings and locomotor analyses via markerless kinematic tracking. Neural signals were processed using high-fidelity filtering and feature extraction, with spatiotemporal maps constructed to visualize activity across the electrode array. Porcine and cadaver studies evaluated the anatomical scalability and clinical feasibility of the i360 device.

Results: In vitro characterization of the i360 devices confirmed stable electrode performance, with impedance measurements in the 1–6 kΩ range at 1 kHz. In vivo validation was carried out in anesthetized and freely moving rodent models, where the i360 was implanted around the thoracic spinal cord. In freely moving animals, high-fidelity neural signals were recorded in parallel with locomotor tasks, and spatiotemporal mapping revealed distinct electrode regions that strongly correlated with phases of gait. Markerless motion capture synchronized these neural data with precise kinematic outputs, confirming signal acquisition under physiologically relevant conditions. Furthermore, targeted stimulation through the i360 in anesthetized rodents elicited controllable muscle activation. Additional porcine and human cadaver studies confirmed anatomical and physiological relevance scalability and surgical placement, underscoring the i360’s potential for clinical translation.

Conclusion: The i360 platform represents a significant advance in spinal cord interfacing by using an ultra-thin, flexible, nonpenetrating array for circumferential spinal cord engagement. By enabling high-resolution recordings and targeted stimulation across the entire perimeter of the spinal cord, this device facilitates refined functional mapping, supports the development of closed-loop neuromodulation protocols, and holds substantial promise for improving outcomes in SCI rehabilitation.