Hygroscopic Tunable Multi-shape Memory Polymers

Tunable multi-shape memory polymers offer intriguing opportunities for memorizing multiple temporary shapes with tunable transition temperatures from one material composition. However, such multi-shape memory effects have been exclusively correlated with the thermoresponsive behaviors of materials, significantly limiting applications in heat-sensitive scenarios. Here we report on a nonthermal tunable multi-shape memory effect in hygroscopic cellulosic polymers, which exhibit a broad, reversible hygromechanical response at ambient temperatures. The polymers present a unique moisture memory effect, enabling diverse multi-shape memory behaviors (dual-, triple- and quadruple-shape memory effects) with excellent performance under highly tunable and independent control of humidity alone. Owing to the tissue-like mechanics and bio-benign triggering conditions, bio-adaptive medical devices such as self-deployable stents and self-tightening sutures were successfully demonstrated under physiological circumstances, exhibiting autonomous shape recovery in a fast and programmable fashion while supplying a biocompatible recovery stress that can be further tailored to tissue-specific requirements over a broad range (0.1 to 4 MPa). Such hygroscopic tunable shape memory effects with great design flexibility readily extend the implications of shape memory polymers beyond the conventional thermomechanical regimes.