An integrated portable bio-monitoring system based on tough hydrogels for comprehensive detection of physiological activities

Abstract

Advanced soft ion-conducting hydrogels have been developed rapidly in the integrated portable health monitoring equipment due to their higher sensitivity, sensory traits, tunable conductivity, and stretchability for physiological activities and personal healthcare detection. However, traditional hydrogel conductors are normally susceptible to large deformation and strong mechanical stress, which leads to inferior electro-mechanical stability for real application scenarios. Herein, a strong ionically conductive hydrogel (poly(vinyl alcohol)-boric acid-glycerol/sodium alginate-calcium chloride/electrolyte ions (PBG/SC/EI)) was designed by engineering the covalently and ionically crosslinked networks followed by the salting-out effect to further enhance the mechanical strength and ionic conductivity of the hydrogel. Owing to the collective effects of the energy-dissipation mechanism and salting-out effect, the designed PBG/SC/EI with excellent structural integrity and robustness exhibits exceptional mechanical properties (elongation at break for 559.1% and tensile strength of 869.4 kPa) and high ionic conductivity (1.618 S·m⁻¹). As such, the PBG/SC/EI strain sensor features high sensitivity (gauge factor = 2.29), which can effectively monitor various kinds of human motions (joint motions, facial micro-expression, faint respiration, and voice recognition). Meanwhile, the hydrogel-based Zn∥MnO₂ battery delivers a high capacity of 267.2 mAh·g⁻¹ and a maximal energy density of 356.8 Wh·kg⁻¹ associated with good cycle performance of 71.8% capacity retention after 8000 cycles. Additionally, an integrated bio-monitoring system with the sensor and Zn∥MnO₂ battery can accurately identify diverse physiological activities in a real-time and noninvasive way. This work presents a feasible strategy for designing high-performance conductive hydrogels for highly-reliable integrated bio-monitoring systems with excellent practicability.