Precision neuroregulation combining liquid metal and magnetic stimulation

Electromagnetic field-based neuroregulation technology is a crucial technique for treating central nervous system and peripheral nervous system disorders. However, the use of invasive electrodes has unavoidable problems such as the risk of inflammation due to high hardness, electrical connections and the need for batteries. On the other hand, non-invasive magnetic stimulation has limitations such as centimeter-level focal areas and shallow stimulation depth. To enhance the precision and effectiveness of wireless magnetic stimulation, we employed a figure-8 magnetic stimulation coil (8-coil) to generate a magnetic field, combined with an injectable, highly conductive, and flexible liquid metal (LM) to produce a millimeter-scale focused electric field. A coaxial electric field measurement electrode was used to establish an agar phantom-based electric field measurement platform. The sciatic nerve of C57 mice was stimulated under acute anesthesia conditions, and electromyography (EMG) signals were collected to evaluate the enhancement of stimulation effects. Long-term safety was assessed through four weeks of implantation. Theoretical analysis and finite element simulations demonstrated that the combination of LM and the 8-coil generated a millimeter-scale enhanced vector electric field within the tissue. Measured electric field distributions closely aligned with theoretical and simulation results. In the sciatic nerve experiments on mice, 1 µL of LM under a 0.45 T magnetic field significantly increased EMG signals and leg movement amplitude by approximately 500%. Long-term implantation under magnetic stimulation revealed no adverse effects. This method utilizes focused electric fields to improve the precision and effectiveness of neuro-magnetic stimulation. It holds promise as a novel approach for precise stimulation. Preliminary evidence was provided for the safety of in vivo LM implantation under external magnetic fields.