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Research Papers

Bio-Inspired Fast Actuation by Mechanical Instability of Thermoresponding Hydrogel Structures

[+] Author and Article Information
Xuxu Yang

Department of Engineering Mechanics,
Zhejiang University,
38 Zheda Road,
Hangzhou 310027, China
e-mail: xxyang@zju.edu.cn

Guorui Li

Department of Engineering Mechanics,
Zhejiang University,
38 Zheda Road,
Hangzhou 310027, China
e-mail: Guoruili@zju.edu.cn

Tingyu Cheng

Department of Engineering Mechanics,
Zhejiang University,
38 Zheda Road,
Hangzhou 310027, China
e-mail: T2cheng@ucsd.edu

Qian Zhao

Department of Chemical and
Biological Engineering,
Zhejiang University,
38 Zheda Road,
Hangzhou 310027, China
e-mail: qianzhao@zju.edu.cn

Chunxin Ma

Department of Chemical and
Biological Engineering,
Zhejiang University,
38 Zheda Road,
Hangzhou 310027, China
e-mail: chunxinma@zju.edu.cn

Tao Xie

Department of Chemical and
Biological Engineering,
Zhejiang University,
38 Zheda Road,
Hangzhou 310027, China
e-mail: taoxie@zju.edu.cn

Tiefeng Li

Department of Engineering Mechanics,
Soft Matter Research Center (SMRC),
Key Laboratory of Soft Machines and Smart
Devices of Zhejiang Province,
Zhejiang University,
38 Zheda Road,
Hangzhou 310027, China
e-mail: litiefeng@zju.edu.cn

Wei Yang

Department of Engineering Mechanics,
Zhejiang University,
38 Zheda Road,
Hangzhou 310027, China
e-mail: yangw@zju.edu.cn

Contributed by the Applied Mechanics Division of ASME for publication in the JOURNAL OF APPLIED MECHANICS. Manuscript received February 25, 2016; final manuscript received March 9, 2016; published online May 5, 2016. Editor: Yonggang Huang.

J. Appl. Mech 83(7), 071005 (May 05, 2016) (7 pages) Paper No: JAM-16-1108; doi: 10.1115/1.4032983 History: Received February 25, 2016; Revised March 09, 2016

Inspired by natural plants, thermoresponding hydrogel (TRH) structures have been designed to trigger mechanical instability with fast actuation. Tough Ca-alginate/poly(N-isopropylacrylamide) (PNIPAM) hydrogel has been synthesized by the hybrid of physically cross-linked alginate and covalently cross-linked PNIPAM. The tough Ca-alginate/PNIPAM hydrogel exhibits 30 kPa of elastic modulus, 280 J/m2 of fracture energies, and fivefold of uniaxial stretch. A multilayered structure made of (Ca-alginate/PNIPAM)/(Ca-alginate/poly (acrylamide)) hydrogels demonstrate fast actuation induced by mechanical instability. A finite-element simulation model is developed to investigate the deformation and to guide the structural design of the hydrogels. The instability-triggering mechanism can enhance the actuation performances of hydrogel structures in applications, such as drug delivery, microfluid control system, and soft biomimetic robotics.

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Figures

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Fig. 1

Uniaxial tensile tests of the TRH. (a) The hydrogel in its reference state. (b) The hydrogel is stretched five times of its initial length. (c) The hydrogel in its reference state with a cut of 3 cm. (d) The 3 cm cut remains stable when the hydrogel is stretched three times of its initial length. (e) The stretch–stress relation of the hydrogel sample with and without cut. (f) The deformation–temperature–time relationship of the hydrogel.

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Fig. 2

Snap-through hydrogel structure design and synthesis: (a) deformation of a thin plate under circumferential stress, (b) synthesis of a snap-through hydrogel structure, and (c) deformed snap-through hydrogel structure after the release of the prestretched NRH

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Fig. 3

(a)–(i) Actuation motion of snap-through hydrogel structure and (j) analysis of snap-through motion

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Fig. 4

FEM simulation analysis: (a) mesh and boundary condition in simulation, (b) distribution of stress in FEM simulation results, and (c) distribution of displacement in FEM simulation results

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Fig. 5

Experimental determination of fracture energy. (a) The sample without cut is used to measure the force–length curve. The area beneath the force–length curve gives the work done by the force to the sample, Uc). (b) The sample with a cut is used to measure the critical distance between the clamps, Lc, when the cut turns into a running crack.

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Fig. 6

(a) Schematics of a bilayer hydrogel beam and (b) schematics of an axisymmetric buckling shell

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