title: A Biologically-Inspired Symmetric Bidirectional Switch.
abstract: Stimuli-sensitive hydrogels have been intensively studied because of their potential applications in drug delivery, cell culture, and actuator design. Although hydrogels with directed unidirectional response, i.e. capable of bending actuated by different chemical components reaction in response to several stimuli including water and electric fields, these hydrogels are capable of being actuated in one direction only by the stimulus. By contrast the challenge of building a device that is capable of responding to the same cue (in this case a temperature gradient) to bend in either direction remains unmet. Here, inspired by the structure of pine cone scales, we design a temperature-sensitive hydrogel with bending directed an imposed fishing line. The layers with same PNIPAAm always shrinks in response to the heat. Even the layers made with different chemical property, bends away from a warm surface, whether the warm surface is applied at its upper or lower boundary. To design the bending hydrogel we exploited the coupled responses of the hydrogel; a fishing line intercalating structure and change its construction. In addition to revealing a new capability of stimulus sensitive hydrogels, our study gives insight into the structural features of pine cone bending.
authors.affiliation: School of Interdisciplinary Bioscience and Bioengineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk, Korea.
authors.forename: Kahye
authors.initials: K
authors.lastname: Song
authors.affiliation: Department of Mathematics, University of California Los Angeles, Los Angeles, California, United States of America.
authors.forename: Shyr-Shea
authors.initials: SS
authors.lastname: Chang
authors.affiliation: Department of Mathematics, University of California Los Angeles, Los Angeles, California, United States of America.|Department of Biomathematics, University of California Los Angeles, Los Angeles, California, United States of America.
authors.forename: Marcus
authors.initials: M
authors.lastname: Roper
authors.affiliation: Department of Mechanical Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk, Korea.
authors.forename: Hyejeong
authors.initials: H
authors.lastname: Kim
authors.affiliation: School of Interdisciplinary Bioscience and Bioengineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk, Korea.|Department of Biomathematics, University of California Los Angeles, Los Angeles, California, United States of America.
authors.forename: Sang Joon
authors.initials: SJ
authors.lastname: Lee
mesh_terms: D000465:Algorithms; D001672:Biocompatible Materials / Q000737:chemistry; D055119:Elastic Modulus; D006361:Heating; D020100:Hydrogels / Q000737:chemistry*; D008422:Materials Testing; D008962:Models, Theoretical; D028223:Pinus / Q000737:chemistry; D013718:Tensile Strength
chemical_list: D001672:Biocompatible Materials; D020100:Hydrogels