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Micromachines 2016, 7(6), 98; doi:10.3390/mi7060098

Ionoprinted Multi-Responsive Hydrogel Actuators

Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27695, USA
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Academic Editor: Andreas Richter
Received: 27 April 2016 / Revised: 16 May 2016 / Accepted: 17 May 2016 / Published: 26 May 2016
(This article belongs to the Special Issue Polymeric Microsystems)
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Abstract

We report multi-responsive and double-folding bilayer hydrogel sheet actuators, whose directional bending response is tuned by modulating the solvent quality and temperature and where locally crosslinked regions, induced by ionoprinting, enable the actuators to invert their bending axis. The sheets are made multi-responsive by combining two stimuli responsive gels that incur opposing and complementary swelling and shrinking responses to the same stimulus. The lower critical solution temperature (LCST) can be tuned to specific temperatures depending on the EtOH concentration, enabling the actuators to change direction isothermally. Higher EtOH concentrations cause upper critical solution temperature (UCST) behavior in the poly(N-isopropylacrylamide) (pNIPAAm) gel networks, which can induce an amplifying effect during bilayer bending. External ionoprints reliably and repeatedly invert the gel bilayer bending axis between water and EtOH. Placing the ionoprint at the gel/gel interface can lead to opposite shape conformations, but with no clear trend in the bending behavior. We hypothesize that this is due to the ionoprint passing through the neutral axis of the bilayer during shrinking in hot water. Finally, we demonstrate the ability of the actuators to achieve shapes unique to the specific external conditions towards developing more responsive and adaptive soft actuator devices. View Full-Text
Keywords: hydrogel actuators; soft robotics; stimuli responsive systems; ionoprinting; pNIPAAm hydrogel actuators; soft robotics; stimuli responsive systems; ionoprinting; pNIPAAm
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Morales, D.; Podolsky, I.; Mailen, R.W.; Shay, T.; Dickey, M.D.; Velev, O.D. Ionoprinted Multi-Responsive Hydrogel Actuators. Micromachines 2016, 7, 98.

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