A soft magnetoelectric sensor feels touch, detects its own damage, and heals itself underwater without external power, mimicking biological skin’s layered sensing and repair.
(Nanowerk Spotlight) A cut on a fingertip triggers an immediate chain of events. Nerve endings fire a warning signal. The brain registers pain and pulls the hand away. And then the tissue begins to repair itself. This layered response, where sensing, warning, and healing work together, is so seamless that most people never think about it. But it is what engineers struggle to replicate in electronic devices.
The challenge sharpens when those devices must operate underwater. Divers rely on bulky equipment with limited dexterity. Submersible robots handle fragile objects in environments where even minor damage can cascade into total device failure. Power sources are scarce and sending a device back to the surface for repair interrupts critical tasks.
A sensor that could feel its surroundings, recognize when it has been hurt, and fix itself without human intervention would transform how machines interact with aquatic environments. Several research groups have pursued parts of this puzzle. Some have built soft robotic systems that detect damage and self-heal. Others have developed self-powered touch sensors or underwater proximity detectors. But no single device has combined all these functions in a package that works reliably in both air and water.
A study published in Advanced Materials (“A Self‐Healing Magnetoelectric Sensor with Pain Sensing for Underwater Soft Electronics”) presents that combination. Researchers developed a self-healing magnetoelectric sensory system (SMES) that integrates self-powered tactile and proximity sensing with a dedicated damage-detection layer and autonomous repair capability. The system operates in both air and underwater environments.
An amphibious, self-healing magnetoelectric system with integrated damage sensing. (a) Schematic illustration of the multilayered SMES, encapsulated in a self-healing elastomer (SHE), designed for underwater soft electronics. The SMES is applicable to both wearable smart gloves for wireless, noncontact interaction and robotic hands for mechanoreception with damage feedback. Optical photographs of (b) the damage sensor and (c) the self-powered proximity and tactile sensor, both exhibiting self-healing capability. (d) FESEM image and corresponding element analysis of EGaIn wires encapsulated in the SHE, with a cross-sectional view of a single EGaIn wire shown in (e). (f) Mechanical self-healing performance of the damage sensor at 50°C. (g) Comparison of the SMES with recent underwater soft sensors, highlighting its multifunctional advantages. (Image: Reproduced from DOI:10.1002/adma.202523052Digital Object Identifier (DOI), CC BY) (click on image to enlarge)
The device uses a multilayer architecture. The top layer functions as a damage sensor, analogous to a pain-sensing layer in biological skin. Beneath it sit three layers that collectively form a self-powered proximity and tactile sensor: an electrical coil layer, a spacer layer, and a bottom magnetic layer. All layers share the same core material, a self-healing elastomer made from a fluoropolymer blended with an ionic liquid and a small amount of crosslinker.
The fluorine-rich composition gives the elastomer a naturally water-repelling surface, which keeps it stable when submerged. The self-healing mechanism relies on reversible ion-dipole interactions between the ionic liquid’s cations and the fluorine atoms on the polymer backbone. Adding 0.5 wt% of the crosslinker restored elastic recovery to 92% without sacrificing the material’s ability to heal.
The elastomer also recovers its shape within approximately 3 seconds after being stretched to 500%. Under heated conditions, healing efficiency reached about 82% in air after seven days and nearly 100% underwater after 10 days. These numbers confirm that the aquatic environment the sensor is designed for does not compromise its self-repair performance.
A sensor also needs to conduct electricity, which is where liquid metal comes in. The team used eutectic gallium-indium, or EGaIn, patterned inside the elastomer using 3D-printed sacrificial metal templates. These patterned liquid metal conductors for stretchable electronics provide the flexibility and flowability needed for a sensor that must stretch and deform without losing electrical function.
The damage-sensing layer detected and recovered from pricking, puncturing, and cutting. When a syringe needle pricked the sensor, its electrical resistance spiked immediately and then returned to baseline without any external intervention. A heavy prick produced kiloohm-level resistance changes, while a gentle one caused only ohm-level changes. This distinction gives the system a way to differentiate between types of injury.
Puncture and cut damage required brief external pressure to bring severed surfaces into contact, after which the self-healing mechanism took over. After a seven-day healing period at room temperature, cut sensors withstood repeated large-scale stretching cycles. The sensor maintained these detection and repair capabilities even while fully submerged, healing from needle pricks, tweezer punctures, and knife cuts underwater.
The proximity and tactile sensing functions draw on electromagnetic induction, the same principle behind electric generators. When a magnet moves relative to the electrical coil inside the device, the changing magnetic flux generates a voltage. This makes the sensor entirely self-powered, requiring no external battery or wiring.
The critical factor governing output is speed. Faster relative motion between magnet and coil produces higher voltage. Distance also matters: output drops as the gap between sensor and magnet increases from 1 to 20 mm. The team optimized coil geometry and turn count to maximize the effective sensing area, finding that square-shaped helices outperformed circular and hexagonal alternatives.
For tactile sensing, external pressure compresses an internal air gap created by the spacer layer, bringing the coil closer to the built-in magnet and generating a measurable voltage. The damage-feedback layer on top did not reduce sensitivity in the low-pressure range. Instead, it improved tolerance to pressures up to 250 kPa, acting as a protective shield for the sensing layers beneath.
The sensor responded within approximately 41 milliseconds and maintained stable output after 10,000 loading cycles. It also retained consistent proximity sensing performance after 10 days of underwater immersion, including in simulated seawater. The elastomer showed no observable shrinkage or swelling, confirming long-term structural reliability in harsh aquatic conditions.
Two demonstrations showcased practical applications. The first was a smart diving glove for underwater wireless communication. Five SMES units, one on each finger, generated distinct voltage patterns when fingers approached each other without touching. An onboard circuit processed these patterns and transmitted them via Bluetooth to a smartphone, mapping them to commands such as “Normal,” “Going up,” or “Help.”
Red LEDs on the glove activated when the damage layer detected a severe injury to any finger sensor. Communication and damage alerting operated simultaneously without interference.
The second demonstration equipped a robotic hand with SMES units for underwater object handling. A three-color LED system provided visual damage feedback: green for normal operation, yellow for minor damage capable of autonomous repair, and red for severe structural damage requiring intervention. The team set a 150 kΩ resistance threshold as the empirical boundary between recoverable and critical injuries.
During normal grasping tasks, the mechanoreceptor produced two distinct electrical signal peaks during loading and unloading phases. Severe damage eliminated the unloading peak, leaving only a single loading signal. This signature change provided an immediate diagnostic indicator of critical structural compromise in the underlying sensor.
The physical separation between the damage-detection layer and the sensing layer avoids a problem common to earlier designs, where pain and touch sensing shared a single element and could not reliably distinguish one stimulus from the other. By dedicating a protective top layer to damage awareness, the SMES preserves the specificity of both functions.
This architecture points toward a broader shift in how engineers approach underwater electronics. Rather than designing devices that resist damage, the SMES accepts that damage will occur and builds in the capacity to detect, report, and recover from it autonomously. That strategy could extend well beyond diving gloves and robotic hands to underwater infrastructure monitoring, marine biology research tools, and autonomous submersible vehicles operating far from human oversight.
For authors and communications departmentsclick to open
Lay summary
Prefilled posts
Nanowerk Newsletter
Get our Nanotechnology Spotlight updates to your inbox!
Thank you!
You have successfully joined our subscriber list.
Become a Spotlight guest author! Join our large and growing group of guest contributors. Have you just published a scientific paper or have other exciting developments to share with the nanotechnology community? Here is how to publish on nanowerk.com.
