Recyclable, conductive alginate-based hydrogels with high stretchability and low electrical hysteresis for wireless wearable sensors

Abstract

Soft electronics based on conductive hydrogels hold considerable promise for advanced wearable technologies. However, these systems face critical challenges, particularly in mitigating electronic waste and ensuring electrical stability. In this study, we present a highly stretchable and recyclable hydrogel composed of the natural polymer alginate (ALG) as the matrix and the lab-synthesized poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a conductive filler, ionically crosslinked using calcium chloride (CaCl₂). The CaCl₂-incorporating ALG/PEDOT:PSS hydrogel exhibited a stretchability of 138% and a low hysteresis of 2.95% (50% strain) while retaining stable electrochemical properties over 400 stretching cycles achieved without relying on a synthetic polymer matrix. Integrating ALG with conductive PEDOT:PSS established robust conductive pathways and reinforced intermolecular interactions, yielding a relative resistance change of 0.58 and a gauge factor of 0.58 at 100% strain. Skin-adaptable sensors fabricated from this hydrogel effectively detected both large-scale and subtle human movements in real-time. Furthermore, the integration of the hydrogel into wireless sensor systems afforded a consistent and reliable performance for real-time movement monitoring. These findings highlight the potential of the fabricated hydrogel for high-performance, stretchable electronic devices, particularly due to its excellent recyclability.