High-Performance Magnetically Actuated MXene-Based Microelectrodes for Epineural Interfacing

Spinal cord interfaces hold promise in restoring motor function following spinal cord injury (SCI), yet current designs face trade-offs between the degree of invasiveness and interfacial impedance. Here, we present a magnetically actuated robotic spinal cord probe (RSCP) composed of a composite material combining MXene (Ti₃C₂T_x) with Poly(2,3-dihydrothieno-1,4-dioxin)-poly(styrenesulfonate) (PEDOT:PSS), referred to as MxP. This interface is integrated with a magnetic elastomer (ME) substrate to enable soft, remote, and minimally invasive actuation and positioning. We demonstrate that magnetic actuation achieves >5 mm deflection with modest fields (∼100 mT), sufficient to conform to spinal cord anatomy. Impedance measurements using a tissue-mimicking phantom reveal that magnetic positioning significantly reduces interfacial impedance by up to 27% within the biologically relevant frequency range (5-5000 Hz) for stimulation and recording. Furthermore, the MxP electrodes demonstrate superior electrochemical stability over 21 days in phosphate-buffered saline than its MXene counterpart. Stereotaxic implantation of the RSCP's in mice followed by immunohistochemistry analysis revealed minimal gliosis and microglial activation over 3 weeks, confirming in vivo biocompatibility. This work presents magnetically actuated RSCP's as a potential solution to the invasiveness-impedance trade-off in spinal cord interfaces, establishing a foundation for improved therapeutic outcomes in SCI treatment.