Gallium-based liquid metals such as eutectic gallium–indium (EGaIn) have long been viewed as the most promising intrinsically deformable conductors. They combine metallic-level conductivity, on the order of a million siemens per meter, with liquid-like flow at room temperature, allowing them to endure extreme strain without fracturing. Yet their practical adoption has been hampered by two stubborn problems. In air, gallium rapidly forms a self-limiting oxide shell roughly three nanometers thick that stabilizes droplet shape but acts as an electrical insulator, blocking electron transport between neighboring particles. At the same time, the metal’s very high surface tension, near 600 millinewtons per meter, makes it difficult to wet and pattern uniformly on soft elastomeric substrates. As a result, most liquid metal inks are electrically dead when deposited and require a separate thermal, mechanical, laser, or chemical activation step to rupture the oxide and establish conductive pathways.

The new work tackles both obstacles at once by wrapping each liquid metal particle in an ultrathin polymer shell and then exploiting the physics of the spray process itself. Bulk EGaIn is fractured into microscale droplets by tip sonication in a 5 weight percent aqueous PVA solution, run at 20 percent amplitude in pulsed mode to prevent overheating. PVA chains hydrogen-bond to the freshly formed gallium oxide surface, lowering particle surface energy and improving wettability. A centrifugation step removes free, unbound polymer, leaving particles with a controlled PVA layer estimated at 7 to 10 nanometers thick atop the 3 to 5 nanometer native oxide. Transmission electron microscopy and energy-dispersive X-ray spectroscopy confirmed this layered structure, with the carbon signal of the polymer conformally wrapping the oxygen-rich oxide shell. The team emphasizes that the PVA is retained after deposition, where it serves as a fusion mediator and adhesive bridge rather than an insulating barrier.

Getting the shell thickness right proved decisive. Particles carrying an excessively thick PVA coating, produced before the centrifuge refinement, showed improved wettability but could not make direct particle-to-particle contact, yielding films roughly eightfold less conductive than the optimized formulation. The refined PmLMP films reached an electrical conductivity of approximately 1.5 × 10^6 siemens per meter immediately after spraying. Zeta potential measurements help explain why: pristine particles carry a strongly negative surface charge of about −70 millivolts, creating an electrostatic barrier that keeps neighbors apart, while PVA modification reduces this to roughly −38 millivolts, allowing hydrodynamic forces during printing to push particles into intimate contact. Density functional theory calculations, using isopropanol as a model for the PVA repeat unit and hydroxylated gallium oxide as a surface model, supported the feasibility of a moderate hydrogen bond at the interface, with a counterpoise-corrected interaction energy of −23.2 kilojoules per mole.

The heart of the innovation is a synergistic mechano-fluidic mechanism that unfolds in a single deposition event. First, high-velocity impact of aerosolized particles delivers enough mechanical stress to rupture the oxide–polymer shell, exposing fresh metallic surfaces that coalesce on contact. Atomic force microscopy nanoindentation measured a yield force of 266.08 nanonewtons per particle, only slightly above the 200 to 250 nanonewtons reported for bare oxide-shelled particles, confirming that the ultrathin PVA layer does not meaningfully suppress rupturability. X-ray photoelectron spectroscopy provided chemical corroboration: screen-printed control films showed only oxidized gallium signals, whereas spray-printed films revealed distinct indium peaks and metallic Ga^0 features, consistent with shell rupture exposing the metallic core. The researchers estimate a critical impact velocity of only about 4 meters per second, well below the particle speeds achieved at the optimized 30 psi spray pressure.

Second and third, the drying process itself consolidates the network. Because the ink uses a binary solvent of deionized water and ethanol in a 3:1 volume ratio, a surface-tension gradient arises within each deposited droplet, driving Marangoni convection. High-speed imaging of fluorescent tracer particles and microparticle image velocimetry showed flow velocities up to 50 times faster, averaging a 22.4-fold increase, compared with a single-solvent system. These vortical flows redistribute particles, counteract gravitational sedimentation, and wedge smaller particles into the voids between larger ones, creating nanoscale point contacts where capillary stress concentrates. The team’s capillary-bridge model predicts a lateral force of roughly 79 nanonewtons at each interparticle meniscus, and under an illustrative contact radius of about 11 nanometers this corresponds to local stresses near 200 megapascals, plausibly sufficient to rupture residual shells. Transmission electron microscopy captured metallic neck formation at particle contacts, and the binary-solvent formulation delivered a threefold conductivity enhancement over the water-only control.

Process optimization revealed how sensitively the mechanism depends on spray parameters. Ultrasonic amplitudes above 50 percent, despite producing smaller particles, introduced enough energy to generate gallium oxide and hydroxide byproducts that interfered with coalescence, so 20 percent amplitude proved optimal. Conductivity saturated at carrier-gas pressures above 30 psi, where kinetic energy reliably exceeds the rupture threshold. Working distance mattered too: at 6 centimeters, air resistance dissipated too much particle energy, while at 3 centimeters the balance of partial solvent evaporation and retained impact energy enabled efficient fusion. The resulting process patterned conductive traces with nominal linewidths down to 50 micrometers and coated areas larger than 20 by 20 square centimeters, and a batch-printed 4 by 4 array showed an average conductivity of 1.55 × 10^6 siemens per meter with limited pixel-to-pixel variation.

Electromechanical testing underscored the practical payoff. Under monotonic tension, PmLMP traces retained electrical continuity beyond 200 percent strain and up to 800 percent, with relative resistance rising only gradually to about 2.8, whereas unmodified particle films lost continuity through droplet beading and over-coated films fractured near 100 percent strain. Cyclic testing at 100 percent strain over 50,000 seconds, roughly 1,400 stretch-release cycles, showed reproducible resistance modulation with limited drift. Integrated light-emitting diodes stayed illuminated through twisting, 100 percent stretching, and bending, and star-shaped LED arrays printed on table-tennis balls, tennis balls, and basketballs remained operational, demonstrating conformability across curvatures. On nonpolar substrates such as PDMS and Ecoflex, an oxygen-plasma pretreatment improved trace uniformity by increasing surface polarity for hydrogen bonding.

The team then pushed the platform toward real devices. Because the printed interconnects are conductive on arrival, standard components, including a microcontroller, resistor, and LEDs, could be pick-and-placed directly onto as-printed flexible circuits that remained functional after folding. A flexible wound-healing patch carrying 640-nanometer red LEDs, driven at 10 hertz and encapsulated in Ecoflex, accelerated macroscopic wound closure relative to untreated controls over seven days in a murine full-thickness excisional wound model. Large-area conductive patterns were printed directly onto textile banners, and the same platform, paired with a LiCl-hydrogel skin interface, served as a wearable electromyography and electrocardiography system. Wireless EMG signals transmitted over Bluetooth Low Energy controlled a remote-controlled vehicle in real time, while custom software visualized ECG waveforms and computed heart rate. Together, these demonstrations sketch a manufacturing route in which liquid metal circuits emerge from an ordinary airbrush already alive with current, opening possibilities for wearable healthcare, bio-integrated electronics, and human-interactive devices that no longer wait for a sintering oven to switch them on.

Subject of Research: Post-treatment-free spray deposition of PVA-modified liquid metal particles for soft and wearable electronics

Article Title: Synergistic Mechano‐Fluidic Self‐Fusion of Poly(Vinyl Alcohol)‐Modified Liquid‐Metal Particles for Post‐Treatment‐Free Soft Electronics

Article References: Yook, K.-Y., Kim, S., Kim, C., Kang, M., Lee, Y., Kim, M., Park, K., Han, S. Y., Cho, S.-W., Lee, G.-H., Son, K., Jang, H., Kim, T. Y., & Seo, J. (2026). Synergistic Mechano‐Fluidic Self‐Fusion of Poly(Vinyl Alcohol)‐Modified Liquid‐Metal Particles for Post‐Treatment‐Free Soft Electronics. Advanced Science, Article e78062. https://doi.org/10.1002/advs.78062

Image Credits: AI Generated

DOI: 10.1002/advs.78062

Keywords: liquid metal, soft electronics, spray printing, EGaIn, poly(vinyl alcohol), self-fusion, wearable sensors, Marangoni convection, capillary forces, stretchable conductors, electromyography, wound healing

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