3D-Printed Stacked Ionic Assemblies for Iontronic Touch Sensors

Sensing is the process of detecting and monitoring any physico-chemical environmental parameters. Herein, new self-powered iontronic sensors, which utilize touch-induced ionic charge separation in ionically conductive hydrogels, are introduced for potential use in object mapping, recognition, and localization. This is accomplished using high-resolution stereolithography (SLA) 3D printing of stacked ionic assemblies consisting of discrete compartments having different ion transport properties. The latter assemblies readily allow programming the output voltage magnitude and polarity by means of variations in ion type, charge density, and cross-linking density within the iontronic device. Voltages of up to 70 mV are generated on application of compressive strains of as much as 50% (approximate to 22.5 kPa), with the magnitude directly proportional to stress, and the polarity dependent on the sign of the mobile ion. As a proof-of-concept demonstration, the resulting touch sensors are integrated on the fingertip to enable the tactile feedback, mimicking the tactile perception of objects for recognition applications. In addition, it is proposed that streaming potential is the underlying mechanism behind the iontronic touch sensors. The electromechanical response is therein consistent with a streaming potential model.