Solvent-Cast-Assisted Printing of Biomimetic Morphing Hydrogel Structures with Solvent Evaporation-Induced Swelling Mismatch

A facile approach is reported for manufacturing morphing hydrogel structures based on solvent-cast-assisted printing. Poly(stearyl acrylate-co-acrylic acid) (P(SA-co-AAc)) ethanol solution is printed into fibers in air, where evaporation of the solvent led to sol-gel transition of the "ink". The printability of ink can be effectively regulated by polymer concentration (C-p) and nozzle diameter. After swelling the printed structures into water, the alkyl chains of SA units are segregated into hydrophobic domains, crosslinking the tough hydrogels. The swelling ratio and mechanical properties of printed gel varied with evaporation time before being swollen in water. Smooth hydrogel fibers with a diameter of approximate to 200 mu m and good mechanical properties can be obtained by evaporating 70-80 wt% of the solvent in 1 h. The upper layer of printed fibers, undergoing less evaporation period, exhibits higher swelling ratio yet reduced modulus than the bottom one. Using this swelling mismatch, diverse morphing hydrogel constructs are achieved by controlling the printed patterns. After swelling, these hydrogel constructs show controllable deformations with bioinspired morphologies. This facile strategy could be applicable for the printing of other tough physical hydrogels that are soluble in low boiling-point solvents, with controllable architectures and morphing capacity under external stimuli.