Ingenious humidity-powered micro-worm with asymmetric biped from single hydrogel

Abstract • Micro-worms have the potential to perform various works by interacting with the surroundings for drug delivery, biosensing, and microsurgery. Inspired by the reptile crawling movement, an ingenious humidity-powered hydrogel microscopic worm prepared by laser writing technology is reported. The micro-worms with asymmetric biped structure from single humidity responsive poly(ethylene glycol) diacrylate hydrogel can crawl forward like reptiles under the cyclic humidity. During dehydration shrinkage an adhesion force difference between biped and substrate is built through the difference in thickness of both feet, resulting in a displacement of micro-worm on the smooth glass substrate without any bias setting. The micro-worm could crawl 3.2 μm in one cycle of 10 s. A turning crawling except straight direction is demonstrated through adjusting to distribute the thicker part at a quarter corner and the micro-worm could turn with the speed at 2 degrees each second. The micro-worm can as well move forward under the substrate. Promising applications of this micro-worm are proved, which can carry the microspheres for a certain distance.