Ionic shape-morphing microrobotic end-effectors for environmentally adaptive targeting, releasing, and sampling

Shape-morphing uses a single actuation source for complex-task-oriented multiple patterns generation, showing a more promising way than reconfiguration, especially for microrobots, where multiple actuators are typically hardly available. Environmental stimuli can induce additional causes of shape transformation to compensate the insufficient space for actuators and sensors, which enriches the shape-morphing and thereby enhances the function and intelligence as well. Here, making use of the ionic sensitivity of alginate hydrogel microstructures, we present a shape-morphing strategy for microrobotic end-effectors made from them to adapt to different physiochemical environments. Pre-programmed hydrogel crosslinks were embedded in different patterns within the alginate microstructures in an electric field using different electrode configurations. These microstructures were designed for accomplishing tasks such as targeting, releasing and sampling under the control of a magnetic field and environmental ionic stimuli. In addition to structural flexibility and environmental ion sensitivity, these end-effectors are also characterized by their complete biodegradability and versatile actuation modes. The latter includes global locomotion of the whole end-effector by self-trapping magnetic microspheres as a hitch-hiker and the local opening and closing of the jaws using encapsulated nanoparticles based on local ionic density or pH values. The versatility was demonstrated experimentally in both in vitro environments and ex vivo in a gastrointestinal tract. Global locomotion was programmable and the local opening and closing was achieved by changing the ionic density or pH values. This 'structural intelligence' will enable strategies for shape-morphing and functionalization, which have attracted growing interest for applications in minimally invasive medicine, soft robotics, and smart materials.