Biomimetic Intelligent Polymer with Synchronous Color and Shape Responses and Its Application in Soft Robots and Actuators

Mimic octopuses can freely alter their shape and color to imitate the natural enemies of predators and thus avoid predation. Herein, a shape-color dual-responsive polyurethane (PU) was designed by imitating the mimic octopuses. To acquire reversible deformation, crystalline polycaprolactone (PCL) was selected as the soft segment and switching phase of the PU, while uniformly distributed hydrogen bonds inside the PU served as the internal stress provider. After programming, the synergistic effect of the internal stress provider and switching phase enabled the prepared PU to exhibit a reversible shape memory effect (SME) with an average reversible strain of 10.98%. To realize synchronous thermochromism, a merocyanine diol (MC(OH)₂) was synthesized and used as a chain extender, which endows PU with reversible and stepless color change across a wide activation temperature range. The dynamic reversibility of hydrogen bonds under thermal stimulation was identified as the primary mechanism underlying the PU's reversible, stepless thermochromism. Because the activation temperature of the reversible SME falls within the thermochromic response temperature range, the prepared PU undergoes reversible contraction and expansion under cyclic heating and cooling, accompanied by a reversible color transition between light pink and dark purple. A bilayer PU/paper composite was further fabricated by bonding the programmed PU to paper. It can achieve reversible bending, which is used as soft robots and actuators. This facile and novel strategy offers a blueprint for developing mimic-octopus-inspired polymer with potential applications in soft actuators, fashion industry, smart textiles, anticounterfeiting, stealth robotics, four-dimensional printing, etc.