Shape memory polymers (SMPs), which can recover from fixed temporary shapes to their original shape under external stimuli, have wide potential applications in flexible electronics, biological medicine, and aerospace, among other areas. Most previously investigated shape memory polymers are thermo-responsive polymers, in which temporary shapes are fixed by vitrification or crystallization of switching domains, and the shape recovery is induced by heat. Considering the limitations of using heat as a trigger to recover the original shape in practical biomedical applications, new stimuli have to be explored to realize shape memory effect.

Because of the reversible and dynamic nature of supramolecular interactions, there is a great advantage of introducing them into SMPs. The Smart Polymer Group led by Professor Chen Tao from the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences (CAS), has successfully constructed self-healing shape memory hydrogels on the basis of supramolecular interactions (Chem. Commun. 2014, 50, 12277-12280). Moreover, the group has achieved pH- and sugar-induced shape memory effect by the selection of a particular supramolecular interaction system (Macromol. Rapid Commun. 2015, 36, 533-537). However, SMPs on the basis of reversible supramolecular interactions still suffer from limitations such as poor mechanical strength and finite shape memory performance. Recently, the group has prepared a novel mechanical stretchable supramolecular hydrogel with triple shape memory effect at macro/micro scale, an achievement published in Chemical Science (Chem. Sci. 2016, DOI: 10.1039/C6SC02354A).

Acrylamide (AAm) was polymerized firstly in the presence of phenylboronic acid grafted alginate (Alg-PBA) and poly (vinyl alcohol) (PVA). After immersion in alkaline solution to generate reversible PBA-diol ester bonds, hydrogels with good mechanical performance due to the presence of double network structure are obtained. Through adjustment of the ratio of two networks, a series of hydrogels with tunable mechanical strength can be obtained.

As the dynamic PBA-diol ester bonds are pH-responsive, they can be used as temporary crosslinks for shape fixing and realize the shape memory property. In addition, the chelation of alginate with Ca2+ can also endow the hydrogel shape memory effect. By combining these two non-interfering interactions, triple shape memory can be realized both at macroscale and microscale.

Besides memorizing temporary shapes, dynamic PBA-diol ester bonds endow the hydrogel with a self-healing property. Taking advantage of shape memory as well as self-healing capability, the as-prepared hydrogel retains shape memory ability after the self-healing process. And this idea clarifies the competence of living creatures and contributes to the creation of novel biomimic materials.

For more information, please contact:

Professor Zhang Jiawei: zhangjiawei@nimte.ac.cn 

Professor Chen Tao: tao.chen@nimte.ac.cn