Bidirectional and biaxial curving of thermoresponsive bilayer plates with soft and stiff segments

Jingkai Guo, Tanvi Shroff, Chang Kyu Yoon, Jiayu Liu, Joyce C. Breger, David H. Gracias, Thao D. Nguyen

Research output: Contribution to journalArticlepeer-review

Abstract

Curved bilayer plates with soft and stiff segments are widely observed in nature, such as plant cell walls, insect exoskeletons and reptile skins. We report an unusual biaxial and bidirectional bending of microfabricated bilayer plates composed of a swellable, photopolymerized poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAM-AAc) layer and a regular array of SU-8, a stiff, non-swellable epoxy. Hydrogels such as pNIPAM-AAc exhibit large and reversible swelling in water in response to a temperature change through the lower critical solution temperature (LCST). The stimuli responsive behavior was harnessed in the composite structure containing materials with mismatched swelling and elastic properties to produce actuation and mechanical motion. The structure undergoes reversible bending along two different axes in response to a temperature cycle through the LCST. Cooling the patterned bilayer structure leads to bending upwards about one axis, while heating leads to bending downwards about a different axis, 90o from the first. To understand the mechanism of this biaxial bending behavior, we developed a finite element model of the patterned bilayer structure. A constitutive model that combined the hyperelastic and swelling behavior was used to describe the thermoresponsive hydrogel. The model was applied to investigate the effects of geometric factors of the patterned bilayer on the bending behavior of the composite structure.

Original languageEnglish (US)
Pages (from-to)6-12
Number of pages7
JournalExtreme Mechanics Letters
Volume16
DOIs
StatePublished - Oct 2017
Externally publishedYes

Keywords

  • Finite element simulation
  • Self-folding
  • Shape change
  • Soft-robotics

ASJC Scopus subject areas

  • Bioengineering
  • Chemical Engineering (miscellaneous)
  • Engineering (miscellaneous)
  • Mechanics of Materials
  • Mechanical Engineering

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