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

The core difficulty is familiar to anyone who has wrestled with wireless phone chargers. Conventional inductive coupling depends on two coils being tuned to the same resonant frequency, like two tuning forks sharing a pitch. When the coils are perfectly aligned and the load is steady, energy flows efficiently across the gap. But inside a body, nothing stays still. A patient moves, breathes, and shifts posture; the implant stretches with surrounding tissue; the electrical impedance at the implant’s output changes as it stimulates muscle. Each of these disturbances shifts the resonance of the system, and once transmitter and receiver drift out of tune, power transfer efficiency collapses. The result is an implant that works beautifully on the bench but fails unpredictably in the clinic, a problem engineers have documented since early analyses of radio-frequency coils in implantable devices in the 1980s.

The Korean team’s solution attacks the problem on two fronts simultaneously: the circuit architecture and the materials. On the circuit side, they built the power link around a nonlinear parity-time symmetric circuit, an approach first demonstrated for robust wireless power transfer by researchers at Stanford University in 2017. In a parity-time symmetric system, the transmitter and receiver form a symmetric resonator pair, and the transmitter continuously adjusts its own operating frequency to match whatever frequency the receiver settles at. Instead of demanding that the two coils stay perfectly tuned, the system lets the receiver’s resonance wander and follows it in real time. A feedback circuit in the wearable transmitter detects changes and provides automatic frequency adaptation, so that misalignment, mechanical deformation, or load impedance fluctuations no longer break the resonance that carries the power.

On the materials side, the implantable receiver is built from liquid metal. Rather than patterning the receiver’s coil and interconnects from rigid copper, the researchers used liquid metal conductors encapsulated in soft elastomers, fabricated through a multistep process involving photolithographically defined copper traces that guide liquid metal deposition, vertical interconnect vias etched through insulating elastomer layers, and off-the-shelf electronic components integrated onto liquid metal pads. Because the conductors are intrinsically stretchy, the receiver’s electrical resistance barely changes when the device deforms. That matters because resistance-induced losses are what erode efficiency in stretchable electronics: a conventional serpentine metal trace stretches by uncoiling and thinning, raising resistance and shifting the coil’s electrical properties. A liquid metal channel simply changes shape while keeping its cross-section and conductivity largely intact, minimizing resistance-induced power losses during deformation.

The performance numbers reported in the paper are striking. The system maintains power transfer efficiency above 50 percent even when the receiver is stretched by 30 percent or displaced laterally by 30 millimeters from the transmitter. For context, conventional inductively coupled systems can lose the bulk of their efficiency at a fraction of that misalignment. The team also tested the system under bending, tilting, and rotational misalignment, tracking both operating frequency and transfer efficiency through each disturbance, and compared the parity-time symmetric architecture against a conventional negative-impedance-converted system in simulations and in live animals. In those comparisons, the conventional system’s efficiency maps showed sharp drop-offs as separation and strain increased, while the parity-time symmetric system held a broad, stable operating range. A radar chart comparison against previously reported stretchable wireless bioelectronic devices, scored on efficiency, alignment tolerance, strain insensitivity, stretchability, and conductivity, placed the new system at the most balanced and superior overall performance among state-of-the-art devices.

The demonstration that turns this from an elegant circuit exercise into a potential medical technology is cardiac pacing. The researchers packaged the liquid metal receiver as a wireless pacemaker with electrodes made from a silver-gold nanowire composite embedded in an elastomer, designed to be sutured onto the surface of the heart. The wearable transmitter, powered by an 11-volt lithium-ion battery and managed by a microcontroller-controlled power unit, was mounted on the outside of the body. The received power is rectified on the implant and used to deliver controlled electrical stimulation to the cardiac tissue. Because the entire power link tolerates the constant motion of a large animal, the pacing could continue under highly dynamic in vivo conditions that would destabilize a conventional link.

In experiments, the team first validated the system in rabbit models, implanting the liquid metal receiver subcutaneously and using an LED indicator on the receiver to visualize successful power transfer as the axial and lateral separation between transmitter and receiver coils increased. The parity-time symmetric system maintained consistent activation across the tested positions, whereas the conventional system failed to power the implant at increased distances and lateral misalignments. The team then moved to a porcine model, whose heart size and physiology are much closer to humans. Fully untethered pigs with wearable transmitters attached to their backs received wireless epicardial pacing, with electrodes sutured onto the heart surface. The system not only paced the heart reliably but also terminated tachyarrhythmias, dangerously fast heart rhythms, under those same dynamic conditions, demonstrating that the power link could support not just routine pacing but active intervention during cardiac events.

The control side of the system reflects a deliberate design for real-world use. The wearable power management unit regulates power from the battery and provides regulated outputs to the transmitter circuits through a microcontroller-controlled switch, and the microcontroller was programmed using the Arduino IDE, with source code available from the corresponding authors. Smartphone control was implemented using a commercially available Bluetooth Low Energy terminal application, meaning a clinician or patient could in principle adjust the system with ordinary consumer hardware rather than bespoke equipment. That kind of practical engineering detail, mundane as it sounds, often separates laboratory demonstrations from technologies that can actually be deployed and maintained outside a research environment.

The implications extend well beyond pacemakers. Fully implantable bioelectronic systems, from neuromodulation devices and brain-computer interfaces to bioresorbable stimulators and injectable sensors, all face the same power bottleneck, and many of the most exciting recent devices in the field, including millimetre-scale bioresorbable optoelectronic systems and programmable ultrasonic implants, depend on some form of wireless energy delivery. A power link that tolerates strain, misalignment, and load variation could serve as a general-purpose energy backbone for soft, body-conformal devices that move with organs rather than fighting them. The authors’ comparison framework, scoring devices on efficiency, alignment tolerance, strain insensitivity, stretchability, and conductivity, also gives the field a clearer yardstick for evaluating future designs.

Cautious optimism is warranted. The work was demonstrated in animal models, and the path to human devices will require the usual gauntlet of biocompatibility validation, long-term reliability testing, and regulatory review; the liquid metal, elastomers, and nanocomposite electrodes involved have strong precedents in the soft bioelectronics literature but must prove themselves in chronic implants. Still, the combination of a self-tuning nonlinear circuit and an intrinsically stretchable liquid metal receiver addresses the two failure modes, resonance drift and deformation losses, that have most reliably broken wireless implants. If the variation tolerance demonstrated in freely moving pigs carries through to clinical devices, the era of truly untethered, maintenance-free implantable medicine moves considerably closer, powered by a transmitter you wear and a receiver that bends with every beat of your heart.

Subject of Research: Variation-tolerant wearable-to-implant wireless power transfer for implantable bioelectronics such as wireless cardiac pacemakers

Article Title: A wearable-to-implant wireless power transfer technology with variation tolerance

Article References: Nam, S., Seo, T., Yoo, S., Park, C., Kim, T., Yu, M., Kim, Y., Kang, H., Yeom, D., Cho, Y., Cho, H., Lee, D., Kim, J. H., Sunwoo, S.-H., Lee, S., Moon, J., Lee, S.-P., Kim, S., & Kim, D.-H. (2026). A wearable-to-implant wireless power transfer technology with variation tolerance. Nature Electronics. https://doi.org/10.1038/s41928-026-01714-0

Image Credits: AI Generated

DOI: 10.1038/s41928-026-01714-0

Keywords: wireless power transfer, parity-time symmetry, liquid metal electronics, implantable bioelectronics, cardiac pacing, stretchable electronics, wearable devices, resonant inductive coupling, soft materials, biomedical engineering, Nature Electronics, tachyarrhythmia