Light-Responsive Hydrogel Microcrawlers, Powered and Steered with Spatially Homogeneous Illumination.

Sub-millimeter untethered locomoting robots hold promise to radically change multiple areas of human activity such as microfabrication/assembly or health care. To overcome the associated hurdles of such a degree of robot miniaturization, radically new approaches are being adopted, often relying on soft actuating polymeric materials. Here, we present light-driven, crawling microrobots that locomote by a single degree of freedom actuation of their light-responsive tail section. The direction of locomotion is dictated by the robot body design and independent of the spatial modulation of the light stimuli, allowing simultaneous multidirectional motion of multiple robots. Moreover, we present a method for steering such robots by reversibly deforming their front section, using ultraviolet (UV) light as a trigger. The deformation dictates the robot locomotion, performing right- or left-hand turning when the UV is turned on or off respectively. The robots' motion and navigation are not coupled to the position of the light sources, which enables simultaneous locomotion of multiple robots, steering of robots and brings about flexibility with the methods to deliver the light to the place of robot operation.

A New Class of Single-Material, Non-Reciprocal Microactuators.

A crucial component in designing soft actuating structures with controllable shape changes is programming internal, mismatching stresses. In this work, a new paradigm for achieving anisotropic dynamics between isotropic end-states-yielding a non-reciprocal shrinking/swelling response over a full actuation cycle-in a microscale actuator made of a single material, purely through microscale design is demonstrated. Anisotropic dynamics is achieved by incorporating micro-sized pores into certain segments of the structures; by arranging porous and non-porous segments (specifically, struts) into a 2D hexagonally-shaped microscopic poly(N-isopropyl acrylamide) hydrogel particle, the rate of isotropic shrinking/swelling in the structure is locally modulated, generating global anisotropic, non-reciprocal, dynamics. A simple mathematical model is introduced that reveals the physics that underlies these dynamics. This design has the potential to be used as a foundational tool for inducing non-reciprocal actuation cycles with a single material structure, and enables new possibilities in producing customized soft actuators and modular anisotropic metamaterials for a range of real-world applications, such as artificial cilia.