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

Faced with complex and diverse tasks, researchers seek
to introduce
stimuli-responsive materials into the field of microrobots. Magnetic
helical microrobots based on shape-memory polymers demonstrate excellent
locomotion capability and programmable shape transformations. However,
the stimulation method of shape changes is still dependent on the
rising of ambient temperature and lacks the ability to address individuals
among multiple microrobots. In this paper, magnetic helical microrobots
were prepared based on polylactic acid and Fe3O4 nanoparticles, which demonstrated controlled locomotion under rotating
magnetic fields and programmable shape changes in their length, diameter,
and chirality. The transition temperature of shape recoveries was
adjusted to a range above 37 °C. At 46 °C, helical microrobots
had a fast shape change with a recovery ratio of 72% in a minute.
The photothermal effect of Fe3O4 nanoparticles
under near-infrared laser can actuate the shape recovery rapidly,
with a recovery ratio of 77% in 15 s and 90% in a minute. The stimulation
strategy also allows addressing among multiple microrobots, or even
within a single microrobot, selectively stimulating one or a part
to change its shape. Combined with the magnetic field, laser-addressed
shape changes were used for precise deployment and individual control
of microrobots. Multiple microrobots can be enriched at the targeted
point, heating the ambient temperature over 46 °C. The shape
changes of internal parts of microrobots help them to grasp and assemble
objects. Such microrobots have great potential in biomedicine and
micromanipulation.