Ultrafast Fabrication of Gradient Nanoporous All-Polysaccharide Films as Strong, Superfast, and Multiresponsive Actuators

The design of smart hydrogel actuators fully constructed from natural polymers for assessing the biomedical applications is important but challenging. Herein, an extremely simple, green, and ultrafast strategy is presented for preparing robust gradient all-polysaccharide polyelectrolyte complex hydrogel actuators. Driven by diffusing of low molecular weight chitosan into high molecular weight sodium alginate solution, a nanoporous, ultrastrong, and gradient chitosan/sodium alginate complex hydrogel film with adjustable thickness can be directly generated on the interface of two solutions within minutes. The as-prepared film can provide superfast temperature, ionic strength, and pH-triggered programmable deformations, and perform a distinct sequential double folding behavior due to the competitive effect between complexed and noncomplexed segments of polyelectrolyte. Besides, patterning Ca2+ to locally crosslink sodium alginate in the film enables various more complex shape transformations. This green and simple diffusion-driven strategy provides significant guidance for fabricating bio-friendly actuators with applications in drug delivery, tissue engineering, soft robotics, and active implants.