Next-gen biomimetic actuators: bilayer hydrogel evolution in the 21st century and its advancements from a post-2020 perspective

Bilayer hydrogel actuators, composed of two hydrogel sheets exhibiting distinct swelling rates or ratios, have emerged as a promising class of smart materials. Their asymmetrical responsive properties enable controllable deformations, including bending and buckling. Recently, these smart materials have garnered significant attention for their versatile applications, playing crucial roles as manipulators or grippers, walkers and swimmers, and biomimetic devices. This perspective serves as a celebratory piece, illuminating the evolutionary journey of these smart materials and delving into their recent advancements post-2020. It provides readers with a focused spotlight on the current state-of-the-art materials, offering insights into their capabilities and projecting potential expansion avenues in the near future.