A starch and MXene hydrogel combines stretchability, self-healing, conductivity, and biodegradability, enabling wearable sensors that track motion, support communication, and decompose safely in soil after disposal.
(Nanowerk Spotlight) A patch of soft material clings to the bend of a wrist. It stretches with every flick, heals itself if torn, and quietly sends signals that capture movement. Now imagine that when discarded, the patch does not linger as plastic waste but breaks down naturally in soil within weeks. This vision has driven years of work in flexible electronics, yet it has often collided with hard limits in chemistry and materials science.
Making devices that move like skin requires conductors that do not snap, gels that rejoin after damage, and adhesives that stick cleanly to a variety of surfaces. On top of this, the same devices must be safe for the environment once their use ends. The tension between high performance and sustainability has slowed progress.
Researchers tried mixing polymers with conductive particles such as carbon or metal flakes. These boosted conductivity but created weak points that led to brittle failure. Others built more elaborate networks of reversible chemical bonds, which improved recovery but made large-scale fabrication difficult.
A newer class of materials called MXenes has begun to change that equation. MXenes are flat sheets made of transition metal carbides or nitrides. Their surfaces form bonds with polymers, helping to spread stress and carry electrical charge. That combination suggests they could turn soft gels into strong, conductive, and self-repairing materials.
Schematic illustration of the preparation process of the hydrogel composed of amylopectin, PVA, and MXene nanosheets (SPM). (Image: Reprinted with permission by Wiley) (click on image to enlarge)
The researchers chose amylopectin, a highly branched starch polymer, as the foundation. Amylopectin offers many sites for bonding but forms weak gels on its own. Adding polyvinyl alcohol strengthens the network through hydrogen bonding. Borax dissolved in water introduces borate ions, which create reversible borate ester bonds. These dynamic links break and reform, allowing the gel to recover from damage.
MXene nanosheets reinforce the structure and open pathways for charge. They bond with the polymers and serve as stress transfer centers, distributing force across the network. The combination yields what the team calls the SPM hydrogel, made by physically kneading the components together with a roller machine. The process is water-based, runs at room temperature, and avoids complex chemistry, which makes it easier to scale.
Tests confirm the structure. Spectroscopy shows shifts consistent with new bonds, and microscopy reveals a porous three dimensional network with nanosheets spread evenly. In mechanical tests, the hydrogel reaches over 6100 percent strain before breaking, with tensile strength near 70 kilopascals. Adjusting MXene content tunes the balance between stretchability and strength.
Self-repair is both rapid and repeatable. After 200 cycles of cutting and healing, the gel still restores more than 95 percent of its strength. Rheological tests show that bonds break under strain but reform as soon as stress is released.
Adhesion is strong across surfaces including wood, glass, steel, plastic, pig skin, and human skin. Shear strength measures around 17 kilopascals on wood and 9 kilopascals on pig skin, with little decline over repeated use. Conductivity also improves with MXene content, reaching 1.45 millisiemens per centimeter at higher loadings.
Demonstrations highlight practical use. A cut gel interrupts current flow, and rejoining restores it immediately. Resistance changes predictably under strain, making the hydrogel suitable for sensing. A capacitive strain sensor built from the material shows stable performance under stretching, twisting, and bending, with consistent signals even after 100 cycles.
When worn, the sensor tracks movements of fingers, wrists, elbows, knees, and even cheeks. It operates during sweating and recovers after damage. The team also demonstrates communication by mapping finger bends to Morse code signals, transmitting words such as “SOS” and “I NEED HELP.” This suggests a role in assistive communication where sound is not available.
Biodegradation tests show that in soil, the gel loses more than 80 percent of its weight within 10 days and almost entirely disappears within 20 days. Titanium levels in the soil rise only slightly, indicating minimal release of MXene nanosheets.
The result is a hydrogel that unites high stretchability, conductivity, self-repair, adhesion, and biodegradability. Each component contributes: borate ester bonds enable healing, hydrogen bonds and polymer entanglement provide strength, and MXene nanosheets reinforce the structure while adding conductivity. The kneading process disperses the nanosheets evenly without harsh conditions, supporting scale-up.
By demonstrating a working sensor that records body motion, communicates through simple codes, and returns safely to the soil after disposal, the study points to a new class of wearable electronics. These devices could meet both the practical demands of human-machine interaction and the environmental standards increasingly required of modern materials.
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