Stretchability and self-healing ability are essential attributes of modern electronic sensors for wearable applications. Herein, intrinsically ultrastretchable, self-healing and transparent humidity sensors composed of ionic κ-carrageenan/polyacrylamide (PAM) double network (DN) organohydrogels are fabricated via a facile solvent-exchange strategy. Hygroscopic ethylene glycol (EG) and glycerol (Gly) are introduced in the organohydrogels to promote both anti-drying and humidity sensing capabilities. The organohydrogel sensors display unprecedented stretchability (1225% strain) and excellent sensing performance, including fast response (0.27 s) and recovery time (0.3 s), wide relative humidity (RH) detection range (4–90%), stability and linearity. The conductance of Gly-DN sensors increases more than 543 times with increasing RH from 4% to 90%. With sufficient sensitivity, the humidity sensors can monitor human respiration with stable and repeatable output. The enhanced sensitivity and moisture-holding ability are attributed to the ready formation of hydrogen bonds between water molecules and enormous hydrophilic groups, including –OH, SO₃ ⁻ and –NH₂, in the elaborate polymer networks and binary solvent. The hindering effect of polymer chains on the transport of conductive ions plays a key role in producing a transducing signal, which is proposed as the mechanism of the novel sensors.

Rapid advances in wearable electronics and mechno‐sensational human–machine interfaces impose great challenges in developing flexible and deformable tactile sensors with high efficiency, ultra‐sensitivity, environment‐tolerance, and self‐sustainability. Herein, a tactile hydrogel sensor (THS) based on micro‐pyramid‐patterned double‐network (DN) ionic organohydrogels to detect subtle pressure changes by measuring the variations of triboelectric output signal without an external power supply is reported. By the first time of pyramidal‐patterned hydrogel fabrication method and laminated polydimethylsiloxane (PDMS) encapsulation process, the self‐powered THS shows the advantages of remarkable flexibility, good transparency (≈85%), and excellent sensing performance, including extraordinary sensitivity (45.97 mV Pa⁻¹), fast response (≈20 ms), very low limit of detection (50 Pa) as well as good stability (36 000 cycles). Moreover, with the LiBr immersion treatment method, the THS possesses excellent long‐term hyper anti‐freezing and anti‐dehydrating properties, broad environmental tolerance (−20 to 60 °C), and instantaneous peak power density of 20 µW cm⁻², providing reliable contact outputs with different materials and detecting very slight human motions. By integrating the signal acquisition/process circuit, the THS with excellent self‐power sensing ability is utilized as a switching button to control electric appliances and robotic hands by simulating human finger gestures, offering its great potentials for wearable and multi‐functional electronic applications.

Growing health awareness triggers the public’s concern about health problems. People want a timely and comprehensive picture of their condition without frequent trips to the hospital for costly and cumbersome general check-ups. The wearable technique provides a continuous measurement method for health monitoring by tracking a person’s physiological data and analyzing it locally or remotely. During the health monitoring process, different kinds of sensors convert physiological signals into electrical or optical signals that can be recorded and transmitted, consequently playing a crucial role in wearable techniques. Wearable application scenarios usually require sensors to possess excellent flexibility and stretchability. Thus, designing flexible and stretchable sensors with reliable performance is the key to wearable technology. Smart composite hydrogels, which have tunable electrical properties, mechanical properties, biocompatibility, and multi-stimulus sensitivity, are one of the best sensitive materials for wearable health monitoring. This review summarizes the common synthetic and performance optimization strategies of smart composite hydrogels and focuses on the current application of smart composite hydrogels in the field of wearable health monitoring.