Beetle-inspired oil-loaded shape memory micro-arrays with switchable adhesion to both solid and liquid

Surfaces with switchable adhesion have been vigorously investigated over the past decades by mimicking the unique adhesive mechanisms of living systems. However, designing a universal intelligent adhesive surface for both solid and liquid remains a challenge. Herein, drawing inspiration from the controllable capillary forces generated by muscle movements and oil-secretion on the foot pads of the beetle (Hemisphaerota cyanea), we report a novel oil-loaded shape memory polymer (SMP) micropillars with such smart controllability. Based on the shape memory effect (SME) of the SMP, the pillars can be reversibly switched between the tilted state and the upright state, which simultaneously changes the distribution of the trapped oil, and thus generates different capillary forces. This variation results in reversible adhesion behaviors of the surface to diverse solids including flat glass, CD disk, polytetrafluoroethylene (PTFE), rough glass, sandpaper, nylon net, and liquid droplets like acid, basic, salt-containing water droplets, and some organic liquids such as glycol, glycerol, and formamide. Given its smart adhesion, the surface was further applied in in-situ gripping/release of solid objects and directed liquid shedding. This work provides a new design strategy for smart adhesive materials, which may contribute to the development of smart grippers, microfluidics, etc.