Shape-switching microrobots for medical applications: the influence of shape in drug delivery and locomotion.

The effect of dynamic shape switching of hydrogel bilayers on the performance of self-folding microrobots is investigated for navigation in body orifices and drug release on demand. Tubular microrobots are fabricated by coupling a thermoresponsive hydrogel nanocomposite with a poly(ethylene glycol)diacrylate (PEGDA) layer, to achieve spontaneous and reversible folding from a planar rectangular structure. Graphene oxide (GO) or silica-coated superparamagnetic iron oxide nanoparticles are dispersed in the thermoresponsive hydrogel matrix to provide near-infrared (NIR) light sensitivity or magnetic actuation, respectively. The NIR light-responsive microstructures are fabricated for triggered drug delivery while magnetic nanocomposite-based microrobots are used to analyze the role of shape in locomotion. Experimental analysis and computational simulations of tubular structures show that drug release and motility can be optimized through controlled shape change. These concepts are finally applied to helical microrobots to show a possible way to achieve autonomous behavior.