Wireless Power Transfer-Enabled Optogenetic Stimulation of Hypoglossal Motoneurons in Mice for Functional Studies in Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is a widespread sleep-related breathing disorder linked to cardiovascular and cognitive complications. Although continuous positive airway pressure (CPAP) remains the standard therapy, poor patient adherence limits its effectiveness. Hypoglossal nerve stimulation is a promising alternative, and optogenetic activation offers superior spatiotemporal precision. However, before clinical use, this approach requires thorough validation in animal models using platforms that preserve natural behavior. This work proposes a fully wireless alternative to conventional optogenetic platforms which rely on tethered optical fibers, restricting the animal's mobility, inducing tissue inflammation, and limiting experimental flexibility. Fully implantable, miniaturized systems with wireless power transfer (WPT) and control capabilities address the need for reduced invasiveness, enabling natural behavior and long-term studies. We present the design and the in vivo validation of a battery-free, wireless optogenetic platform for in vivo studies on small laboratory mice, designed to minimize device size, weight, and invasiveness. A conformal WPT system of inductive resonant transmitting coils at 13.56 MHz is proposed to be integrated into the laboratory cage hosting the mice. A miniaturized, lightweight, and flexible receiving system (weighing less than 0.6 g) is designed to be implanted on the back of the mouse in a saddle-like configuration. The implanted device hosts the rectification circuitry, used to drive a microscale light-emitting diode (LED) positioned over the hypoglossal nuclei. In this way, optogenetic stimulation without fiber-optic tethers is obtained. Full-wave electromagnetic simulations and experimental validation are first carried out to assess the WPT link performance, demonstrating high tolerance to relative translational and angular displacement between the transmitting and receiving coils, and stable harvested power across the cage volume. For a transmitted power of 1.5 W, a minimum DC power of 20 mW has been obtained in the worst-case position of the mouse inside the cage, sufficient for the LED operation. Finally, in vivo experiments are presented, confirming not only the LED activation but also the hypoglossal nerve stimulation, fully compliant with the radiant flux requirements for optogenetic neurostimulation under realistic conditions. These results demonstrate the feasibility and robustness of the proposed WPT system for untethered, battery-free optogenetic stimulation in lightweight murine models with OSA, providing a platform for preclinical neuroscience research, paving the way toward next-generation low-invasiveness neuromodulation strategies.