Omnidirectional Shape Memory Effect via Lyophilization of PEG Hydrogels. Issue 7 (14th February 2017)

• Record Type: Journal Article
• Authors: Chen, Di; Xia, Xuhui; Wong, Tuck W.; Bai, Hao; Behl, Marc; Zhao, Qian; Lendlein, Andreas; Xie, Tao
• Is Part Of: Macromolecular rapid communications. Volume 38:Issue 7(2017)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2017-02-14
• Subjects: freeze drying -- hydrogels -- polymer processing -- shape memory polymers; Macromolecules -- Periodicals; Polymers -- Periodicals; Chemistry -- Periodicals; 547.705
• DOI: 10.1002/marc.201600746
• Languages: English
• ISSNs: 1022-1336

Abstract

Abstract : A novel shape memory programming method is presented utilizing lyophilization of a crosslinked hydrogel with a thermal transition in its dry state. The method allows significant omnidirectional shrinkage upon heating triggered recovery from a porous dried gel to a compact structure, which can hardly be achieved by other programming methods. Abstract : Device applications of shape memory polymers demand diverse shape changing geometries, which are currently limited to non‐omnidirectional movement. This restriction originates from traditional thermomechanical programming methods such as uniaxial, biaxial stretching, bending, or compression. A solvent‐modulated programming method is reported to achieve an omnidirectional shape memory behavior. The method utilizes freeze drying of hydrogels of polyethylene glycol networks with a melting transition temperature around 50 °C in their dry state. Such a process creates temporarily fixed macroporosity, which collapses upon heating, leading to significant omnidirectional shrinkage. These shrunken materials can swell in water to form hydrogels again and the omnidirectional programming and recovery can be repeated. The fixity ratio ( R f ) and recovery ratio ( R r ) can be maintained at 90% and 98% respectively upon shape memory multicycling. The maximum linear recoverable strain, as limited by the maximum swelling, is ≈90%. Amongst various application potentials, one can envision the fabrication of multiphase composites by taking advantages of the omnidirectional shrinkage from a porous polymer to a denser structure.