Soft sensors convert movement, temperature and moisture into electrical signals. Repeated bending and friction can cause their metal conductors to peel from the underlying polymer, while physical damage, such as cuts, can disable the device. Commonly used petroleum-derived substrates are also environmentally unfriendly as they are difficult to recycle.
Researchers at the College of Design and Engineering at the National University of Singapore (NUS CDE) have developed a soft, stretchable substrate that repairs itself, grips metal conductors firmly and can be remoulded or broken down after use. It could make wearable patches and electronic skin used in applications such as health monitoring and virtual reality more durable while enabling the recovery of valuable components, thus reducing electronic waste.
The new material, called an intrinsically dynamic biosubstrate (IDBS), was developed by researchers led by Assistant Professor Zhai Wei from the Department of Mechanical Engineering at NUS CDE. Their findings were published in Nature Sustainability on 19 June 2026.
"We regarded durability and recyclability as two parts of the same design equation," said Asst Prof Zhai. "The substrate must hold a device together during use, and also allow controlled disassembly at the end of its life."
A challenging balancing act
The researchers synthesised IDBS by heating and combining two naturally occurring compounds: lipoic acid, found in living cells, and phytic acid, abundant in plant seeds and grains. The process required no catalysts or organic solvents and produced a molecular network held together by three complementary types of bonds. Dynamic disulfide bonds can rearrange to form new connections across damaged surfaces, thereby enabling repair. Ester bonds that are more stable reinforce the network and maintain its structure, while hydrogen bonds absorb energy as the material stretches and help it to adhere to metal. Working together, these bonds balance the molecular motion required for self-repair with the stability needed for repeated use.
One of the team's formulations stretched to more than eight times its original length before breaking. At room temperature, a severely damaged sample recovered more than 80 per cent of its strength within six hours and more than 90 per cent within 24 hours. In contrast, most reported self-healing elastomers did not reach 80 per cent within six hours. In addition, repair efficiency remained above 90 per cent through five cycles.
This could prevent minor damage from rendering an entire sensor unusable, although the tests allowed 24 hours for full repair.
Overcoming attachment issues
A wearable sensor is only as reliable as the bond holding its metal conductors to the substrate. A self-repairing material offers little benefit if those conductors still peel away. The team therefore tested IDBS with zinc circuits for electronic skin and silver films for electrodes that pick up heart and muscle signals.
Heat helped IDBS grip both metals. For the zinc circuits, warming the assembly at 85 degrees Celsius made its polymer chains more mobile and exposed groups that could bond with the metal. Subsequent cooling reformed the network, increasing adhesion about tenfold over room-temperature attachment. During heat-assisted silver deposition, the more mobile chains allowed particles to penetrate beneath the surface, where they bonded to IDBS and anchored the coating.
The team used peel tests to measure the force required to pull a coating from its base. Silver adhered three times more strongly to IDBS than to polydimethylsiloxane (PDMS), a silicone commonly used in soft electronics, and one and a half times more strongly than to styrene-ethylene-butylene-styrene (SEBS), a rubber-like thermoplastic used in stretchable devices.
The researchers' electronic-skin prototypes tracked temperature, moisture from breathing and strain. Silver electrodes on IDBS recorded heart and muscle signals comparable to commercial electrodes. After 800 friction cycles against artificial skin, the IDBS electrodes still produced clear signals; on PDMS, however, the silver detached and the signals deteriorated.
"Soft-sensor design often focuses on the conductor, with the substrate treated as passive support," added Dr Dang Chao, Research Fellow from the Department of Mechanical Engineering at NUS CDE and first author of the paper. "Our work demonstrates that engineering the substrate can be just as important to preserving the signal, and it is key to creating a reliable, durable sensor device."
A new lease on life
Importantly, the substrate's heat-responsive network also enables disassembly. At the end of the device's life, reheating softens IDBS so zinc circuits and various electronic components can be removed intact before the substrate is remoulded. Alternatively, ethanol breaks down IDBS, allowing the researchers to clean the circuits, recover silver particles for conductive inks and reprocess the residue as an adhesive.
After three remelting cycles, IDBS retained more than 90 per cent of its original stretchability. A life-cycle assessment estimated lower impacts than PDMS, SEBS and polyurethane across most categories, including global warming and ecotoxicity. A circular-use model produced the lowest burdens, although it assumed a 95 per cent recycling rate.
"Next, we plan to expand the use of such substrate systems from the sensing elements to the electronic components that process their signals," said Asst Prof Zhai. "This will require the substrate to bond reliably not only with metal circuits, but also with chips and other components. We also need to improve its heat resistance so it can withstand the manufacturing conditions used for flexible circuit boards."
