Movement-Proof Wireless Power Brings Battery-Free Soft Implants Closer to the Clinic

One of the most stubborn obstacles in implantable medicine is not the implant itself but the battery that keeps it running. Batteries are rigid, bulky, and eventually exhausted, and replacing them means another surgery. Wireless power transfer promises to erase the battery altogether, letting a device outside the body energize a device inside it. Yet the approach has always carried a hidden fragility: the amount of power that crosses the tissue depends exquisitely on how far apart the two coils are, how well they are aligned, and whether the implant has been bent, stretched, or shifted by the very body movements it must survive. A pacemaker patch riding on a beating heart is never in the same place twice. A new study published in Nature Electronics by Nam and colleagues reports a wearable-to-implant power system engineered to tolerate exactly these variations, and the team demonstrates it by achieving untethered cardiac pacing in rabbit and pig models.

The core of the innovation is a circuit architecture known as a parity–time-symmetric, or PT-symmetric, system. The concept entered the wireless power arena in 2017, when researchers showed that a nonlinear PT-symmetric circuit could maintain robust power transfer across changing distances without any active tuning. In such a system, the transmitter and receiver are coupled resonators whose gain and loss are carefully balanced. When the coupling between them changes—because the distance or orientation changes—the coupled system automatically adjusts its oscillation frequency to remain in the symmetric regime, and the transfer efficiency stays remarkably flat. In other words, the physics of the circuit does the compensation that engineers would otherwise have to perform with sensors, feedback loops, and adjustable matching networks. The new work extends this principle from rigid laboratory coils to the far messier environment of living tissue and deformable electronics.

The system consists of two halves. On the outside is a self-oscillating wearable transmitter, a compact unit that generates an oscillating magnetic field without needing an external drive signal locked to a fixed frequency. Because the transmitter is self-oscillating, it naturally follows the resonant state of the coupled system as conditions change. On the inside is a stretchable receiver built from liquid metal, a material choice that lets the implanted coil deform freely with the surrounding tissue without cracking or losing its electrical properties. Conventional receivers made from solid copper traces on flexible substrates can survive some bending, but repeated strain at the millimeter scale of a moving organ eventually fatigues the conductors. Liquid-metal conductors, by contrast, remain electrically continuous even when stretched, twisted, and compressed, which is precisely what an implant attached to cardiac tissue experiences continuously.

The significance of combining these elements is best appreciated by considering what happens in a traditional inductive link. The efficiency of near-field coupling falls off steeply as the separation between coils grows or as they drift out of alignment, and deformation of the receiver changes its inductance and shifts its resonant frequency. For a soft implant, all three perturbations occur simultaneously and unpredictably. Earlier battery-free implants, including the fully implantable and bioresorbable cardiac pacemakers demonstrated in 2021, relied on near-field inductive coupling that worked well under controlled conditions but demanded careful positioning of the external power source. The PT-symmetric approach reported now absorbs those variations into the circuit dynamics, so the power delivered to the implant remains stable even as the geometry of the link changes throughout the day and with every heartbeat.

To validate the design, the researchers moved beyond benchtop tests with artificial phantoms and into large-animal models. In experiments with rabbits and pigs, the wearable transmitter powered a soft implantable device well enough to pace the heart without wires or batteries. Cardiac pacing is an unusually demanding test case: the implant must deliver precisely timed electrical stimuli to excite heart muscle, the power budget is unforgiving, and the mechanical environment is among the most dynamic in the body. The fact that the link tolerated the combined effects of respiration, motion, and tissue deformation while still delivering sufficient energy for reliable pacing suggests that the variation-tolerance is not a laboratory curiosity but a property that holds up under physiologically realistic conditions.

The study also sits within a broader materials-science context that has matured rapidly in recent years. Reviews of soft bioelectronics have catalogued the design and integration strategies needed to build devices that conform to biological tissue while maintaining long-term function, and complementary work on stretchable hermetic seals has addressed one of the field’s chronic weaknesses: keeping bodily fluids from permeating into stretchable electronics over time. A liquid-metal receiver must be encapsulated so that neither the metal nor the surrounding fluids leak across the interface, and advances in viscoplastic sealing strategies have made such packaging feasible without sacrificing mechanical compliance. The power system described in the new paper is thus the product of converging progress in circuit theory, soft materials, and encapsulation technology rather than a single isolated breakthrough.

From a clinical standpoint, the implications extend well beyond pacing. Battery-free bioelectronics have been proposed for nerve stimulation, wound monitoring, drug delivery, and closed-loop therapies in which a sensor and a stimulator work together. Every one of those applications inherits the same coupling problem: the implant moves, deforms, and drifts relative to whatever external source powers it. A power link that is insensitive to distance, alignment, and strain removes a fundamental constraint on where such devices can be placed and how they can be designed. An implant no longer needs to be anchored in a fixed orientation relative to a wearable patch, which simplifies surgical placement, improves patient comfort, and opens the door to implants on organs that are in near-constant motion.

There are, of course, questions that must be answered before such systems reach routine clinical use. The reported demonstrations were in animal models, and translating to humans will require attention to the long-term biocompatibility of the liquid-metal receiver and its packaging, the thermal footprint of continuous power delivery through tissue, and the regulatory pathway for a wearable component that patients must wear consistently. The efficiency of any wireless link also depends on the power levels involved; pacing requires relatively modest energy, and applications with higher demands may stress the PT-symmetric architecture differently. The nonlinear dynamics that make the circuit robust also impose constraints on how much power can be transferred before the system exits its stable operating regime, a trade-off that future engineering will need to map carefully.

Even with those caveats, the demonstration marks a meaningful shift in how the field thinks about wireless power for soft implants. Rather than treating movement and deformation as disturbances to be minimized, the design embraces them as conditions the circuit is built to withstand. That philosophical change—designing for variation rather than against it—may prove as important as any single performance metric. If the approach scales as its animal results suggest, the combination of a self-oscillating wearable transmitter and a stretchable liquid-metal receiver could become a standard platform for powering the next generation of untethered, battery-free medical implants, bringing the vision of soft electronics that live comfortably inside the moving, changing human body considerably closer to reality.

Subject of Research: Variation-tolerant wearable-to-implant wireless power transfer for soft, battery-free medical implants

Article Title: Wireless power transfer that tolerates movement and deformation for soft implants

Article References: Wireless power transfer that tolerates movement and deformation for soft implants. (2026). Nature Electronics. https://doi.org/10.1038/s41928-026-01715-z

Image Credits: AI Generated

DOI: 10.1038/s41928-026-01715-z

Keywords: wireless power transfer, parity-time symmetry, soft implants, liquid metal, cardiac pacing, wearable electronics, bioelectronics, stretchable electronics, battery-free implants, Nature Electronics, biomedical engineering, resonant coupling