Humidity Sensing of Stretchable and Transparent Hydrogel Films for Wireless Respiration Monitoring

Respiratory monitoring plays a pivotal role in health assessment and provides an important application prospect for flexible humidity sensors.However,traditional humidity sensors suffer from a trade-off between deformability,sensitivity,and transparency,and thus the development of high-performance,stretchable,and low-cost humidity sensors is urgently needed as wearable electronics.Here,ultrasensitive,highly deformable,and transparent humidity sensors are fabricated based on cost-effective polyacrylamide-based double network hydrogels.Concomitantly,a general method for preparing hydrogel films with controllable thickness is proposed to boost the sensitivity of hydrogel-based sensors due to the extensively increased specific surface area,which can be applied to different polymer networks and facilitate the development of flexible integrated electronics.In addition,sustainable tapioca rich in hydrophilic polar groups is introduced for the first time as a second cross-linked network,exhibiting excellent water adsorption capacity.Through the synergistic optimization of structure and composition,the obtained hydrogel film exhibits an ultrahigh sensitivity of 13,462.1%/%RH,which is unprecedented.Moreover,the hydrogel film-based sensor exhibits excellent repeatability and the ability to work normally under stretching with even enhanced sensitivity.As a proof of concept,we integrate the stretchable sensor with a specially designed wireless circuit and mask to fabricate a wireless respiratory interruption detection system with Bluetooth transmission,enabling real-time monitoring of human health status.This work provides a general strategy to construct high-performance,stretchable,and miniaturized hydrogel-based sensors as next-generation wearable devices for real-time monitoring of various physiological signals.

Stretchable, self‐healable, and breathable biomimetic iontronics with superior humidity‐sensing performance for wireless respiration monitoring

Stretchable,self‐healing,and breathable skin‐biomimetic‐sensing iontronics play an important role in human physiological signal monitoring and human–computer interaction.However,previous studies have focused on the mimicking of skin tactile sensing(pressure,strain,and temperature),and the development of more functionalities is necessary.To this end,a superior humidity‐sensitive ionic skin is developed based on a self‐healing,stretchable,breathable,and biocompatible polyvinyl alcohol–cellulose nanofibers organohydrogel film,showing a pronounced thickness‐dependent humidity‐sensing performance.The as‐prepared 62.47‐μm‐thick organohydrogel film exhibits a high response(25,000%)to 98%RH,excellent repeatability,and long‐term stability(120 days).Moreover,this ionic skin has excellent resistance to large mechanical deformation and damage,and the worn‐out material can still retain its humidity‐sensing capabilities after self‐repair.Humidity‐sensing mechanism studies show that the induced response is mainly related to the increase of proton mobility and interfacial charge transport efficiency after water adsorption.The superior humidity responsiveness is attributed to the reduced thickness and the increased specific surface area of the organohydrogel film,allowing real‐time recording of physiological signals.Notably,by combining with a self‐designed printed circuit board,a continuous and wireless respiration monitoring system is developed,presenting its great potential in wearable and biomedical electronics.

Sensitive humidity sensor based on moisture-driven energy generation

The emergence of novel self-powered humidity sensors has attracted considerable attention in the fields of smart electronic devices and personal healthcare.Herein,self-powered humidity sensors have been fabricated using a moisture-driven energy generation(MEG)device based on asymmetric tubular graphitic carbon nitride(g-CN)films prepared on anodized aluminum(AAO)template.At a relative humidity(RH)of 96%,the MEG device can provide an open-circuit voltage of 0.47 V and a short-circuit current of 3.51μA,with a maximum output power of 0.08μW.With inherent self-powered ability and humidity response via current variation,an extraordinary response of 1.78×106%(41%-96%RH)can be gained from the MEG device.The possible power generation mechanism is that g-CN/AAO heterostructure can form ion gradient and diffusion under the action of moisture to convert chemical potential into electrical potential,evoking a connaturally sensitive response to humidity.Self-powered respiration monitoring device based on the sensor is designed to monitor human movement(sitting,warming up,and running)and sleep status(normal,snoring,and apnea),maintaining excellent stability during cumulative 12-h respiration monitoring.This self-powered humidity sensing technology has promising potential for extensive integration into smart electronic and round-the-clock health monitoring devices.