Design of Coils for Generating an Induced Electric Field Suitable for Peripheral Nerve Stimulation

Peripheral nerve electrical stimulation, widely used for neuropathic pain treatment and neural regeneration, often has drawbacks such as adverse biological reactions and unintended neural activation in surrounding tissues. As an alternative, peripheral nerve magnetic stimulation offers a promising, less invasive method, enabling targeted nerve stimulation without direct tissue contact. however, its application is limited by issues like the bulkiness of coils and excessive heat generation due to high current levels. To overcome these limitations, we developed a miniaturized, implantable coil interface, specifically designed for nerve modulation. Our approach, supported by simulations and animal experiments, involved optimizing coil design to achieve a strong electric field gradient. A 4-leaf rhombus coil configuration yielded the highest gradient at the center of the coil interface. In rat sciatic nerve experiments, the coil interface with a 200 µs rise time and 25 V amplitude rectangular pulse successfully induced a compound muscle action potential in the tibial anterior and gastrocnemius muscles, demonstrating that rise time influences selectivity and stimulation of nerve activation. This study highlights the potential of small-scale, low-energy magnetic coils as a practical and effective alternative to traditional electrical stimulation, opening avenues for advanced, less invasive neural modulation and future therapeutic applications.