An adhesive hydrogel whose stickiness can be turned off by shining infrared light on it could make for better bandages or allow robots to climb walls, according to the researchers who developed it (Chem Bio Eng. 2025, DOI: 10.1021/cbe.4c00177).
The hydrogel, made of N-isopropylacrylamide (NIPAAm), naturally adheres to a variety of surfaces, including glass, aluminum, steel, polyethylene terephthalate (PET) films, and skin. To make it removeable, researchers at Northwestern Polytechnical University and the Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, laced the NIPAAm with iron(II,III) oxide nanoparticles. The N-isopropyl group in NIPAAm forms intramolecular hydrogen bonds with water molecules, trapping water inside the hydrogel when it’s in its sticky state. Shining near-infrared light on the nanoparticles heats up the system, breaking the hydrogen bonds and spilling water onto the surface of the hydrogel; this changes the hydrogel’s surface energy, causing it to lose adhesion in seconds. Stickiness returns when the material cools.
Unlike other polymers the researchers have worked with, “the bulk hydrogels we have designed in this study do not produce residues and can be reused continuously without loss of performance,” says Yanfei Ma of the Lanzhou Institute, who conducted the research with Bin Li, Feng Zhou, and colleagues. That could make for bandages that are easier to attach and remove without skin damage than currently available hydrogel bandages, he says. It could also allow soft robots to climb up a wall or across a ceiling, gecko-style, switching the stickiness of their feet on and off.
Other researchers have explored embedding iron oxide nanoparticles in NIPAAm as a way to remotely target drugs to a tumor. This team will conduct in vitro studies to see how well their material performs in biological applications. They’ll also need to show it can be manufactured cost-effectively enough to compete with existing adhesives.