C. Chason, P.H. Wink Reis, L.C. Hsiao, O.D. Velev
North Carolina State University,
United States
Keywords: soft dendritic colloids, ionotronic, piezoelectric, piezoresistive, wearable multitouch tactile sensor
Summary:
Next-generation tactile sensors for wearable and human-machine interfaces require materials that are both soft and environmentally sustainable, contrasting with conventional rigid polymer and semiconductor based devices. We present a hydrogel-based sensor platform [1] utilizing calcium-crosslinked alginate [2] reinforced with soft dendritic colloids (SDCs) [3], delivering mechanical compliance and improved sensitivity for modern applications, including wearables, VR interfaces, and smart prosthetics. Our homocomposite hydrogels feature two concurrent sensing modes: piezoresistive and piezoionic. In the piezoresistive mode, indentation from 0 to 50% strain produces quantifiable changes in electrical resistance with a gauge factor of 0.25. The piezoionic mode allows for voltage signal generation that is sensitive to both strain and position, achieving up to 0.3 mV/kPa across pressures from 0 to 125 kPa. This dual-mode operation enables simultaneous measurement of force and spatial location, differentiating our system from single-mode alternatives. Electromechanical tests highlight a two-fold improvement in the piezoionic sensitivity of the new homocomposite gel cores compared to hydrogels made from molecular alginate alone due to the embedded SDC network. We correlate confocal microscopy data, used to probe SDC microstructure and crosslinking levels, with performance metrics to provide insight into the relationship between material composition and sensing efficiency. The homocomposite hydrogels are compatible with additive manufacturing, demonstrated by 3D-printed two-dimensional sensing arrays and recent integration with reusable circuit electrode interfacing for robust signal acquisition. The 3DP process also allows the facile fabrication of multitouch sensing arrays in the form of soft, thin gel films. The sustainable, biocompatible nature of the homocomposite material not only meets the increasing demand for eco-friendly electronics but also offers an adaptable platform for advanced multitouch tactile sensing. These results underscore the promise of SDC-reinforced hydrogels for next-generation soft sensors in health monitoring, soft robotics, and interactive systems, combining both user comfort and sustainability in device design.