Prof. Tao XIE's Group

      Shape memory polymer (SMP) can recover from temporary shape to permanent shape under multi-stimulation. Typically, temporary shapes can only be programmed in a non-omnidirectional fashion through uniaxial stretching, biaxial stretching, bending, twisting, and compression, without significant volume change.

      Recently, our group introduced lyophilization into the programming of SMP. The lyophilization causes crystallization of polyethylene glycol (PEG) segments during water removal. This leads to a porous SMP in its temporarily expanded state in which it can shrink omnidirectionally when heated above the melting transition of the PEG segments. Therefore, we achieves omnidirectional shape memory effect (Fig. 1). After swelling, the PEG hydrogels can be programmed again. It is expected to be used in preparing multifunctional composites with novel controllable phase separation structure. This work has recently been published on Macromolecular Rapid Communications (DOI: 10.1002/marc.201600746).

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Fig. 1. Omnidirectional shape memory effect. a) Lyophilization-based omnidirectional shape memory cycle and its comparison with a conventional shape memory cycle. b) The expanded porous dried gel and the corresponding shrunken dried gel. The scale bars represent 1 cm.

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Fig. 2. Mechanistic comparison between the a) lyophilization-based shape memory behavior and b) cryogelation to form permanent porous gels.