Stretchable liquid metal implant keeps wireless power flowing through body movement

Implantable bioelectronics have long promised a future of battery-free medical devices that sit quietly inside the body, delivering therapy or recording signals without wires, replacement surgeries, or bulky external hardware. Yet one stubborn engineering problem has kept that promise only partially fulfilled: getting power reliably from outside the body to inside it. A team of researchers in South Korea now reports a wireless power transfer system designed specifically to survive the messy, dynamic reality of a living body, in which coils shift, tissues deform, and electrical loads fluctuate from one heartbeat to the next. Writing in Nature Electronics, the group led by Dae-Hyeong Kim of Seoul National University and the Institute for Basic Science, together with colleagues at Kyung Hee University, Seoul National University Hospital and Pusan National University, demonstrates a wearable-to-implant power link that maintains stable delivery even under severe misalignment and stretching, and uses it to pace the hearts of large animals without a single tether.

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