Imparting Stress-Free Reversible Shape Memory Copolyesters within Physiological Range Actuation via Cocrystallization Phase Transitions

Stress-free two-way shape memory polymers have great practical potential in smart biomedical devices without repeated programming. Despite several progresses that have been achieved, an ultimate goal yet to be fulfilled is body-temperature-triggered programmable shape actuation featuring customizable shapes. In this work, we demonstrate the use of the cocrystallizable copolyester phase in the pseudoeutectic point as the actuation phase and the high crystalline temperature of homopolymer chain segments as the shifting-geometry-determining phase to fabricate the copolymer networks via thiol–ene click chemistry. Structural anisotropy arises from the partial melting of double-crystalline phases after thermomechanical programming, which affords the resultant network architecture an actuation strain of up to 16.2% through melting-induced contraction and crystallization-induced elongation under stress-free conditions. Noteworthily, within the same polymer network, the thin film could further be reconfigured into the three-dimensional (3D) structure via dynamic transesterification that allows achieving a synergetic benefit, notably realizing a unique reversible transformation for bestowing the material with peculiar adjustability while not losing its 3D-shaped support upon the destruction of the anisotropic structure. Our study offers useful guidelines in designing shape-shifting materials and could better target their specific applications in biomedical devices.