title: Omnidirectional Shape Memory Effect via Lyophilization of PEG Hydrogels.
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 (Rf) and recovery ratio (Rr) 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.
authors.affiliation: State Key Laboratory of Chemical Engineering, College of Chemical and Biological Engineering, Zhejiang University, Hangzhou, 310027, China.
authors.forename: Di
authors.initials: D
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Chemical Engineering, College of Chemical and Biological Engineering, Zhejiang University, Hangzhou, 310027, China.
authors.forename: Xuhui
authors.initials: X
authors.lastname: Xia
authors.affiliation: Advanced Membrane Technology Research Centre, Universiti Teknologi Malaysia, Johor, 81310, Malaysia.
authors.forename: Tuck W
authors.initials: TW
authors.lastname: Wong
authors.affiliation: State Key Laboratory of Chemical Engineering, College of Chemical and Biological Engineering, Zhejiang University, Hangzhou, 310027, China.
authors.forename: Hao
authors.initials: H
authors.lastname: Bai
authors.affiliation: Institute of Biomaterial Science, Helmholtz-Zentrum Geesthacht, Kantstr. 55, Teltow, 14513, Germany.
authors.forename: Marc
authors.initials: M
authors.lastname: Behl
authors.affiliation: State Key Laboratory of Chemical Engineering, College of Chemical and Biological Engineering, Zhejiang University, Hangzhou, 310027, China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Zhao
authors.affiliation: Institute of Biomaterial Science, Helmholtz-Zentrum Geesthacht, Kantstr. 55, Teltow, 14513, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Lendlein
authors.affiliation: State Key Laboratory of Chemical Engineering, College of Chemical and Biological Engineering, Zhejiang University, Hangzhou, 310027, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Xie
mesh_terms: D005612:Freeze Drying; D020100:Hydrogels / Q000737:chemistry*; D010316:Particle Size; D011092:Polyethylene Glycols / Q000737:chemistry*; D016062:Porosity; D013499:Surface Properties
chemical_list: D020100:Hydrogels; D011092:Polyethylene Glycols
keywords: freeze drying; hydrogels; polymer processing; shape memory polymers