Using a single penetrating interfascicular electrode to improve spatial selectivity of an extraneural polymeric cuff...

Damage to the peripheral nervous system severely disrupts motor control, sensory perception, and organ function, often resulting in long-term disability. To restore such impairments, peripheral nerve interfaces (PNIs) aim to achieve precise stimulation selectivity, yet current approaches face several limitations. Most PNIs rely on metal-based electrodes, which introduce a mechanical mismatch with soft neural tissue and are limited by low charge-injection capacity. The device design of these PNIs also suffers from a fundamental trade-off: highly invasive approaches enable high selectivity but provoke strong foreign-body responses, while less invasive designs minimize tissue damage but fail to provide sufficient selectivity. Although current-steering strategies have been explored to enhance selectivity, their performance remains inadequate for clinical application. Significant advances in PNIs are required to safely achieve higher selectivity.

In this work, a novel array consisting of a single penetrating interfascicular electrode (SPIF) added to an extraneural cuff (EC) array, termed SPIFEC, was developed using laser-based fabrication and polymeric materials. Electrochemical properties were characterized, and ex vivo experiments using whole rat sciatic nerve were conducted to assess fascicular selectivity. The implantation was assessed through computed tomography (CT) imaging.

The SPIFEC design includes seven extraneural electrodes and one double-sided interfascicular penetrating electrode. Electrochemical analysis revealed the polymeric electrodes had low impedance, high charge storage capacity and high charge-injection limit, when compared to previous reports on traditional metallic devices. Ex vivo studies demonstrated that the device achieved high fascicular selectivity, particularly in nerves with well-defined fascicles, outperforming a comparable non-penetrating cuff. CT imaging confirmed the interfascicular positioning of the penetrating electrode.

These results demonstrate the potential of this novel SPIFEC array in enhancing spatial selectivity for peripheral nerve applications. Further studies, including chronic in vivo testing, are required to fully evaluate long-term performance and clinical potential in neuroprosthetic systems.