Hydrogels such as poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAM-AAc) can be photopatterned to create a wide range of actuatable and self-folding microstructures. Mechanical motion is derived from the large and reversible swelling response of this cross-linked hydrogel in varying thermal or pH environments. This action is facilitated by their network structure and capacity for large strain. However, due to the low modulus of such hydrogels, they have limited gripping ability of relevance to surgical excision or robotic tasks such as pick-and-place. Using experiments and modeling, we design, fabricate, and characterize photopatterned, self-folding functional microgrippers that combine a swellable, photo-cross-linked pNIPAM-AAc soft-hydrogel with a nonswellable and stiff segmented polymer (polypropylene fumarate, PPF). We also show that we can embed iron oxide (Fe₂O₃) nanoparticles into the porous hydrogel layer, allowing the microgrippers to be responsive and remotely guided using magnetic fields. Using finite element models, we investigate the influence of the thickness and the modulus of both the hydrogel and stiff polymer layers on the self-folding characteristics of the microgrippers. Finally, we illustrate operation and functionality of these polymeric microgrippers for soft robotic and surgical applications.

Solar-powered water desalination has been considered as one of the most promising solutions to alleviate clean water scarcity. In concentrated brine, the strong hydration ability of ions increases the required energy for water evaporation and thus lowers the desalination performances of most-existing solar vapor generators (SVGs). Here, a novel SVG is reported that exhibits superior desalination performance in brine than in pure water. This SVG is constructed by the complexation of oppositely charged polyelectrolytes into a hierarchically porous hydrogel (HPH), with interpenetrated polyaniline as efficient light absorbers. With controlled thermal management, the evaporation rate of this HPH-based SVG is 2.79 kg m⁻² h⁻¹ in simulated brine (3.5 wt% NaCl solutions) under one sun illumination, 67% higher than that in pure water (1.67 kg m⁻² h⁻¹) and more prominent than existing salt-resistant SVGs. Desalination tests with real seawater indicate that HPH is salt-resistant and sustainable for fast freshwater production. All-atom molecular dynamics simulations indicate that the unique interactions between the oppositely charged groups of the polyion complex and the mobile ions in brine can alter the water state, resulting in enhanced hydrability of the polymeric skeleton. This work provides a new approach for the development of next-generation SVGs with enhanced solar desalination performance.