Shape-Programmable Chitosan Films as Soft Microrobots toward the Development of Chemo-Mechanical Sensors.

Recent advances in shape-morphing materials have shown promise for soft robotics, but such mechanodynamic behavior has yet to be applied in sensing platforms, especially with true reversibility. Here, we introduce a monocomponent chitosan film fabricated via a simple, cost-effective solvent-casting method that exhibits extraordinary properties. This film not only shows instantly reversible shape-morphing but also displays a bidirectional response to alkaline solutions. Characterization techniques revealed structural and functional differences between chitosan powder and film, highlighting its unique responsiveness. The film rapidly undergoes dramatic, high-angle bending in water due to a spontaneous diffusive gradient, and this shape transformation can be programmed by adjusting the aspect ratio. Controlled locomotion was achieved by stabilizing the deformed shape in a transient state through a water-ethanol-water solvent exchange. Utilizing this solvent-responsiveness, we developed a proof-of-concept ″strip-on-a-drop″ chemo-mechanical sensor for alcohol detection. Programmed deformation and MATLAB-based image analysis provided reliable bending angles to quantify the alcohol content. This versatile film holds potential for on-demand shape control and innovative sensing applications.