(226y) Reversible Patterning and Actuation of Hydrogels By Electrically Assisted Ionoprinting

The ability to pattern, structure, re-shape and actuate hydrogels is important for biomimetics, soft robotics, cell scaffolding and biomaterials. 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. Applying an oxidative bias to a patterned metal anode injects divalent ions into the charged polymer networks which form robust ionic crosslinks. The magnitude and duration of the applied current controls the degree of ionic binding to the polymer backbone. The bound charges change the local mechanical properties of the gel to induce relief patterns and in some cases evoke localized stress, causing rapid folding. These ionoprinted patterns are stable for months, yet the process is fully reversible by immersing the gel in a chelator solution. The ionically 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.