@article{morales_palleau_dickey_velev_2014, title={Electro-actuated hydrogel walkers with dual responsive legs}, volume={10}, ISSN={["1744-6848"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84893866937&partnerID=MN8TOARS}, DOI={10.1039/c3sm51921j}, abstractNote={Stimuli responsive polyelectrolyte hydrogels may be useful for soft robotics because of their ability to transform chemical energy into mechanical motion without the use of external mechanical input. Composed of soft and biocompatible materials, gel robots can easily bend and fold, interface and manipulate biological components and transport cargo in aqueous solutions. Electrical fields in aqueous solutions offer repeatable and controllable stimuli, which induce actuation by the re-distribution of ions in the system. Electrical fields applied to polyelectrolyte-doped gels submerged in ionic solution distribute the mobile ions asymmetrically to create osmotic pressure differences that swell and deform the gels. The sign of the fixed charges on the polyelectrolyte network determines the direction of bending, which we harness to control the motion of the gel legs in opposing directions as a response to electrical fields. We present and analyze a walking gel actuator comprised of cationic and anionic gel legs made of copolymer networks of acrylamide (AAm)/sodium acrylate (NaAc) and acrylamide/quaternized dimethylaminoethyl methacrylate (DMAEMA Q), respectively. The anionic and cationic legs were attached by electric field-promoted polyion complexation. We characterize the electro-actuated response of the sodium acrylate hydrogel as a function of charge density and external salt concentration. We demonstrate that "osmotically passive" fixed charges play an important role in controlling the bending magnitude of the gel networks. The gel walkers achieve unidirectional motion on flat elastomer substrates and exemplify a simple way to move and manipulate soft matter devices and robots in aqueous solutions.}, number={9}, journal={SOFT MATTER}, publisher={Royal Society of Chemistry (RSC)}, author={Morales, Daniel and Palleau, Etienne and Dickey, Michael D. and Velev, Orlin D.}, year={2014}, pages={1337–1348} }
 @article{palleau_morales_dickey_velev_2013, title={Reversible patterning and actuation of hydrogels by electrically assisted ionoprinting}, volume={4}, ISSN={["2041-1723"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84881440081&partnerID=MN8TOARS}, DOI={10.1038/ncomms3257}, abstractNote={The ability to pattern, structure, re-shape and actuate hydrogels is important for biomimetics, soft robotics, cell scaffolding and biomaterials. Here we introduce an 'ionoprinting' technique with the capability to topographically structure and actuate hydrated gels in two and three dimensions by locally patterning ions via their directed injection and complexation, assisted by electric fields. The ionic binding changes the local mechanical properties of the gel to induce relief patterns and, in some cases, evokes localized stress large enough to cause rapid folding. These ionoprinted patterns are stable for months, yet the ionoprinting process is fully reversible by immersing the gel in a chelator. The mechanically patterned hydrogels exhibit programmable temporal and spatial shape transitions, and serve as a basis for a new class of soft actuators that can gently manipulate objects both in air and in liquid solutions.}, number={1}, journal={NATURE COMMUNICATIONS}, publisher={Springer Nature}, author={Palleau, Etienne and Morales, Daniel and Dickey, Michael D. and Velev, Orlin D.}, year={2013}, month={Aug} }
 @article{palleau_reece_desai_smith_dickey_2013, title={Self-Healing Stretchable Wires for Reconfigurable Circuit Wiring and 3D Microfluidics}, volume={25}, ISSN={["1521-4095"]}, DOI={10.1002/adma.201203921}, abstractNote={This article describes the fabrication of self-healing stretchable wires formed by embedding liquid metal wires in microchannels composed of self-healing polymer. These stretchable wires can be completely severed with scissors and rapidly self-heal both mechanically and electrically at ambient conditions. By cutting the channels strategically, the pieces can be re-assembled in a different order to form complex microfluidic networks in 2D or 3D space.}, number={11}, journal={ADVANCED MATERIALS}, publisher={Wiley}, author={Palleau, Etienne and Reece, Stephen and Desai, Sharvil C. and Smith, Michael E. and Dickey, Michael D.}, year={2013}, month={Mar}, pages={1589–1592} }