Temporal morphing of hydrogels with patterned cream as a sacrificial mask for controlled diffusion and swelling

Materials capable of undergoing controllable, transient deformations to perform temporary functions and subsequently recover their original shapes are of great interest for soft devices and adaptive systems. In hydrogels, such temporal morphing can be achieved by spatiotemporally regulating the transport of water or chemical stimuli. Here, we report a straightforward and adaptable strategy using a soluble pseudoplastic hand cream as a sacrificial mask to pattern the gel surface and enable asymmetric diffusion and thus controllable temporal morphing. The cream locally inhibits water diffusion, creating a transient swelling gradient that induces programmed, temporary deformations. As the cream dissolves and water diffusion gradually equilibrates, the hydrogel recovers its final equilibrium shape. The dynamics and intermediate configurations of the transient deformation are governed by the kinetics of water diffusion within the hydrogel, which is regulated by the spatial distribution and dissolution kinetics of the cream masking layer. The pseudoplastic nature of the cream allows easy patterning into diverse spatial distributions with tunable thickness, enabling complex shape transformations with tunable deformation and recovery dynamics. This sacrificial-mask-based temporal morphing strategy is applicable to various hydrogel materials. We further demonstrate the utility of this temporal morphing strategy in representative scenarios, including object transport through confined spaces and light signal control, highlighting its potential for time-dependent shape-morphing regulated functions.