A Stretchable Ionic Diode from Copolyelectrolyte Hydrogels with Methacrylated Polysaccharides

As the demand for soft and flexible devices steadily increases, the ionic applications demonstrated with gel materials have come under the spotlight. Here, stretchable and wearable ionic diodes (SIDs) made from polyelectrolyte hydrogels are introduced. Polyelectrolyte hydrogels are mechanically modified using methacrylated polysaccharides while preserving the ion-permselectivity of poly(sulfopropyl acrylate) potassium salt (PSPA) and poly([acrylamidopropyl]trimethylammonium chloride) (PDMAPAA-Q), forming ionic copolymers. Then, SIDs composed of polyelectrolyte copolymer hydrogels are fabricated in VHB substrates as a stretchable and transparent insulating layer which is engraved by a laser. The SIDs show rectifying behaviors beyond the stretch of 3 with the aid of perfect adhesion between hydrogels and elastomeric substrates, and preserve their rectifications over hundreds of cycles. The operation of the SID is visualized by a wearable ionic circuit which rectifies ionic currents and lightens the LED under the forward bias during finger movements.