Hysteresis-free and high sensitivity strain sensing of ionically conductive hydrogels

Hydrogels are promising materials for soft and implantable strain sensors owing to their large compliance (E<100 kPa) and significant extensibility (εmax >500%) compared to other polymer networks. Further, hydrogels can be functionalized to seamlessly integrate with many types of tissues. However, most current methods attempt to imbue additional electronic functionality to structural hydrogel materials by incorporating fillers with orthogonal properties such as electronic or mixed ionic conduction. Although composite strategies may improve performance or facilitate heterogeneous integration with downstream hardware, composites complicate the path for regulatory approval and may compromise the otherwise compelling properties of the underlying structural material. Here we report hydrogel strain sensors composed of genipin-crosslinked gelatin and dopamine-functionalized poly(ethylene glycol) for in vivo monitoring of cardiac function. By measuring their impedance only in their resistive regime (>10 kHz), hysteresis is reduced and the resulting gauge factor is increased by ~50x to 1.02±0.05 and 1.46±0.05 from approximately 0.03-0.05 for PEG-Dopa and genipin-crosslinked gelatin respectively. Adhesion and in vivo biocompatibility are studied to support implementation of strain sensors for monitoring cardiac output in porcine models. Impedance-based strain sensing in the kilohertz regime simplifies the piezoresistive behavior of these materials and expands the range of hydrogel-based strain sensors.

Bio-Based Polymer Electrolytes for Electrochemical Devices: Insight into the Ionic Conductivity Performance

With the continuing efforts to explore alternatives to petrochemical-based polymers and the escalating demand to minimize environmental impact, bio-based polymers have gained a massive amount of attention over the last few decades. The potential uses of these bio-based polymers are varied, from household goods to high end and advanced applications. To some extent, they can solve the depletion and sustainability issues of conventional polymers. As such, this article reviews the trends and developments of bio-based polymers for the preparation of polymer electrolytes that are intended for use in electrochemical device applications. A range of bio-based polymers are presented by focusing on the source, the general method of preparation, and the properties of the polymer electrolyte system, specifically with reference to the ionic conductivity. Some major applications of bio-based polymer electrolytes are discussed. This review examines the past studies and future prospects of these materials in the polymer electrolyte field.