Self-Powered Respiratory Monitoring Strategy Based on Adaptive Dual-Network Thermogalvanic Hydrogels

Abstract

As a low-grade sustainable heat source, the breath waste heat exhaled by human bodies is always ignored, although producing a greater temperature than ambient. Converting this heat into electric energy for use as power sources or detecting signals is extremely important in cutting-edge wearable medicine. This heatto-electricity conversion is possible with thermogalvanic hydrogels. However, challenges remain in their antifreezing and antidrying properties, significantly restricting the durability of thermogalvanic gels in practical applications. Herein, a dual-network poly(vinyl alcohol)/gelatin (PVA/GEL) gel thermogalvanic device with Fe(CN) 63−/4− as a redox pair is developed, with an outstanding low-temperature durability and antidrying capacity. These features result from the use of a binary H 2 O/ GL (glycerin) solvent to limit hydrogen bonding between water molecules. The prepared thermogalvanic gel patch is capable of easily converting physiological data into understandable electrical impulses using the temperature difference between the ambient environment and the heat produced by human breathing, realizing a simple self-powered respiratory monitoring strategy for the first time. Even below zero temperature, the gel patch-based mask can operate normally, implying it fits into low-temperature environments. This study sheds fresh light on the development of active wearable medical electronics that are powered by demic low-level heat.

Anhydrous Thermogalvanic Gel for Simultaneous Waste Heat Recovery and Thermal Management of Electronics

“…In recent years, quasi-solid hydrogel-based thermogalvanic electrolytes have been extensively studied for low-grade thermal energy harvesting, and great advances have been made in low-cost waste heat utilization by improving electrodes, electrolytes, and devices. − However, thermogalvanic gel-based thermoelectricity is inescapably confronted with the challenge of extreme environments; at subzero temperatures, hydrogel inevitably freezes and loses conductivity and flexibility, which severely limits the thermoelectric performance and potential applications in low temperature environments. − Significant efforts have been invested toward research into the environmental adaptability of hydrogel-based thermogalvanic, including binary solvent, systems, such as dimethyl sulfoxide (DMSO)/H 2 O, glycerol/H 2 O, , and betaine or proline/H 2 O . On the other hand, even at room temperature, hydrogels lack long-lasting moisture due to the constant water evaporation, hampering their long-term usability. − Therefore, double network hydrogels and nanocomposite hydrogels have attempted to solve the above problems. Since ethylene glycol (EG) is widely used as an antifreeze agent in industry with good antifreeze properties and DMSO is a good solvent with a high boiling point and stable chemical properties, the combination of the advantages of DMSO/EG binary solvent is expected to prepare a new antifreeze organogel for applications in extreme environments.…”

“…13−19 However, thermogalvanic gel-based thermoelectricity is inescapably confronted with the challenge of extreme environments; at subzero temperatures, hydrogel inevitably freezes and loses conductivity and flexibility, which severely limits the thermoelectric performance and potential applications in low temperature environments. 20−24 Significant efforts have been invested toward research into the environmental adaptability of hydrogel-based thermogalvanic, including binary solvent, systems, such as dimethyl sulfoxide (DMSO)/H 2 O, 25 glycerol/H 2 O, 26,27 and betaine or proline/H 2 O. 28 On the other hand, even at room temperature, hydrogels lack long-lasting moisture due to the constant water evaporation, hampering their long-term usability.…”

“…28 On the other hand, even at room temperature, hydrogels lack long-lasting moisture due to the constant water evaporation, hampering their long-term usability. 29−31 Therefore, double network hydrogels 27 and nanocomposite hydrogels 32 have attempted to solve the above problems. Since ethylene glycol (EG) is widely used as an antifreeze agent in industry with good antifreeze properties and DMSO is a good solvent with a high boiling point and stable chemical properties, the combination of the advantages of DMSO/EG binary solvent is expected to prepare a new antifreeze organogel for applications in extreme environments.…”

A strong and tough gelatin/polyvinyl alcohol double network hydrogel actuator with superior actuation strength and fast actuation speed

“…Recently, gelatin/polyvinyl alcohol (GA/PVA) double network hydrogels have been developed as wearable medical electronics due to their excellent sensitivity and biocompatibility. 33,34 However, the application range of GA/PVA double network hydrogels is severely limited in terms of their poor mechanical properties, and the fracture energy of hydrogels is rarely mentioned. In this work, the GA/PVA double network hydrogel has been toughened through a salt solution soaking strategy, obtaining splendid stiffness and toughness with a fracture stress of 1.8 MPa, an elastic modulus of 1.3 MPa, and a fracture energy of 16 kJ m À2 .…”

Polystyrene-Based Triboelectric Nanogenerators for Self-Powered Multifunctional Human Activity Monitoring

“…This has paved the way for the development of various ecofriendly energy-harvesting technologies such as triboelectric nanogenerators (TENGs), which can effectively harness mechanical energy into useful electricity. Owing to their properties like simplicity, low cost, light weight, and high performance, − TENGs not only have demonstrated great potential as a sustainable power source in various smart, flexible, and wearable electronic systems but also are instrumental in several applications like self-powered motion sensors, , voice sensors, blue energy, − wind energy harvesting, − health monitoring, − human–machine interaction, , and smart cities . Roots of their versatility lie in their uncomplicated structure , and vast range of tribomaterials with varying degrees of electropositivity/negativity .…”