Wearable sensors are one of the key components in applications such as motion monitoring, smart medical care, and human-computer interaction systems. In the present work, we focus on the simultaneous improvements of flexible sensors in both performance and functionality. Here, with a porous fiber network of multi-walled carbon nanotubes (MWCNTs)−polydimethylsiloxane (PDMS) as an active layer, a flexible pressure sensor with ultra-high sensitivity and superior capability of identifying transverse shear force and temperature signals is designed and constructed. The fibral MWCNTs−PDMS piezoresistive layer was formed with a scouring pad (SP) fiber network as skeleton, and the PDMS thin layer formed by self-assembly can effectively increase the initial resistance. Attributing to the unique compressibility of the fibral porous network and the adjustable nanoscale contacts, the MWCNT-PDMS/SP sensor exhibits a wide detection range (0−360 kPa), and in particular, an ultra-high sensitivity (84,818.2 kPa −1 when <100 pa). Beyond the highly sensitive characteristics, the sensor also has a high shear-force sensitivity (GF = 6.15 under 0.05 N). The sensor can still maintain a relatively stable performance even after operating for more than 10,000 pressure cycles, showing as a potential candidate for the applications of electronic skin, intelligent robots, etc.

To meet the growing demand for sustainable development and ecofriendliness, hydrogels based on biopolymers have attracted widespread attention for developing flexible pressure sensors. Natural globular proteins exhibit great potential for developing biobased pressure sensors owing to their advantages of high water solubility, easy gelation, biocompatibility, and low production cost. However, realizing globular protein hydrogel-based sensors with interfacial and bulk toughness for pressure sensing and use in wearable devices remains a challenge. This study focuses on developing a high-performance flexible pressure sensor based on a biobased protein hydrogel. Consequently, a flexible protein/polyacrylamide (PAM) hydrogel with a featured double-network (DN) structure linked covalently with hydrogen bonds was first synthesized via a one-pot method based on natural ovalbumin (OVA). The unique DN structure of the as-synthesized OVA/PAM hydrogel affords excellent mechanical performance, flexibility, and adhesion properties. The mechanical properties of the DN hydrogel were enhanced after further cross-linking with Fe 3+ and treatment with glycerol. Subsequently, the flexible pressure sensor was constructed by sandwiching a microstructured OVA/PAM dielectric layer between two flexible silver nanowire electrodes. The obtained sensor exhibits a high sensitivity of 2.9 kPa −1 and a short response time of 18 ms, ensuring the ability to monitor physiological signals. Based on its excellent performance, the fabricated sensor was used for monitoring the signals obtained using practical applications such as wrist bending, finger knocking, stretching, international Morse code, and pressure distribution. Particularly, we implemented a contactless delivery system using the fabricated OVA-based pressure sensors linked to unmanned vehicles and global positioning systems, providing a solution for low-risk commodity distribution during Coronavirus disease 2019 (COVID-19).

In recent years, hydrogels have become excellent optional materials for flexible sensors due to their high stretchability and biocompatibility. However, the instabilities of hydrogels including the tendency to dry out and the poor reusability seriously limit their applications. Herein, a double-network (DN) organohydrogel is derived by regulating the mechanical property, conductivity, and antidrying characteristic of the poly (acrylamide-co-acrylic acid) (P(AM-co-AA)) hydrogel. Specifically, the ionic coordination (CO2LFeIII) is imported as the secondary cross-link to strengthen the mechanical property, and LiCl in ethylene glycol (EG) solution enhances the conductivity and antidrying characteristics simultaneously. Benefiting from these improvements of material characteristics, the iontronic pressure sensor assembled from the DN organohydrogel demonstrates excellent performances such as a high sensitivity, fast response/recovery characteristic at different frequencies, and remarkable fatigue resistance. These properties also enable physiological signal detections in diverse scenarios. At the same time, with the help of abundant functional groups in the double network and solvent, the organohydrogel exhibits practical NH3 sensing performances including high response, strong gas selectivity, and excellent long-term stability, paving the way toward broader multiscene applications of hydrogels.

Linearity is an indispensable factor to be considered when evaluating the characteristics of a pressure sensor. Although different kinds of advanced materials and microstructures are explored to enhance the device performances, the nonlinear response of sensors caused by the attenuation of sensitivity as pressure increases still needs to be further addressed. In this spotlight, a sensitive flexible iontronic pressure sensor with highly linear response is reported here. The design of its hierarchical arete architecture (HAA) not only inherits the high sensitivity of hierarchical microstructures in a wide pressure range but also achieves ultrahigh linearity. Experimentally the HAA iontronic sensor is prepared by using a simple and low‐cost polycrystalline silicon template, and it demonstrates a high sensitivity of 20.98 kPa−1 in a broad range (0–37.5 kPa) with R2 up to 0.9921. Benefited from the combination of remarkable linearity, sensitivity, and other characteristics, practical applications around human health such as real‐time monitoring of tablets, recognition of respiratory airflows, and physiological signals detection are successfully demonstrated here. Based on these excellent performances, the HAA iontronic sensor can also be regarded as a promising choice in the fields of 5G communication, wearable devices, robotic intelligence, etc.