Iodine-treated starch as easy-to-use, biodegradable material with controllable swelling and stiffening properties

We introduce starch as a new material for MEMS applications, especially in biomedical areas. Starch can be used for micromachined sensors and actuators that need non-electrically triggered and driven actuation or release mechanisms (e.g., stents, valves, one-time release devices) or temporary stiffening of flexible needles for implantation (e.g., flexible neural probes). Our experiments show that starch-gel, formed by heating starch in water undergoes heavy shrinking during dehydration and re-swells quickly when immersed in water. When the starch-gel was immersed into a solution containing iodine, swelling became slow, gradual and heavily dependent on the temperature and on the thickness of the starch. Microfabricated silicon springs dipcoated with approximately 7.5 μm thick starch retracted 100 μm during dehydration and deployed within a few minutes in water at 37°C. When the starch was treated with iodine, the springs deployed within 40 min at 37°C but barely at 23°C. Starch electrically insulates electrodes and can be patterned using spin-coating and dry etching.