Photothermal-Responsive Shape-Memory Magnetic Helical Microrobots with Programmable Addressable Shape Changes

Faced with complex and diverse tasks, researchers seekto introducestimuli-responsive materials into the field of microrobots. Magnetichelical microrobots based on shape-memory polymers demonstrate excellentlocomotion capability and programmable shape transformations. However,the stimulation method of shape changes is still dependent on therising of ambient temperature and lacks the ability to address individualsamong multiple microrobots. In this paper, magnetic helical microrobotswere prepared based on polylactic acid and Fe3O4 nanoparticles, which demonstrated controlled locomotion under rotatingmagnetic fields and programmable shape changes in their length, diameter,and chirality. The transition temperature of shape recoveries wasadjusted to a range above 37 degrees C. At 46 degrees C, helical microrobotshad a fast shape change with a recovery ratio of 72% in a minute.The photothermal effect of Fe3O4 nanoparticlesunder near-infrared laser can actuate the shape recovery rapidly,with a recovery ratio of 77% in 15 s and 90% in a minute. The stimulationstrategy also allows addressing among multiple microrobots, or evenwithin a single microrobot, selectively stimulating one or a partto change its shape. Combined with the magnetic field, laser-addressedshape changes were used for precise deployment and individual controlof microrobots. Multiple microrobots can be enriched at the targetedpoint, heating the ambient temperature over 46 degrees C. The shapechanges of internal parts of microrobots help them to grasp and assembleobjects. Such microrobots have great potential in biomedicine andmicromanipulation.