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Flexible conductive materials and flexible electronic devices are driving the development of the next generation of cutting‐edge wearable electronics. However, the existing hydrogel‐based flexible conductive materials have limited tensile capacity, low toughness, and poor anti‐fatigue performance, resulting in narrow sensing area and insufficient durability. In this paper, a conductive nanocomposite hydrogel with high ductility, toughness, and fatigue resistance is prepared by combining silver coated copper (Ag@Cu) nanoparticles with gelatin followed by one‐step immersion in sodium sulfate (Na2SO4) solution. The salting‐out of gelatin in Na2SO4 solution greatly improve the mechanical properties of this gelatin‐based hydrogel. The uniform distribution of Ag@Cu nanoparticles inside the whole hydrogel endow the composite hydrogel with excellent electrical conductivity (1.35 S m−1). In addition, it displayed high and stable tensile strain sensitivity over a wide strain range (gauge factor = 2.08). Therefore, the Ag@Cu‐Gel hydrogel is sensitive and stable enough to be successfully utilized as flexible wearable sensor for detecting human motion signals in real time, such as bending of human joints, swallowing, and throat vocalization. Furthermore, this hydrogel is also suitable for application as electronic skin for bionic robots. The above results demonstrate the promising application of Ag@Cu‐Gel hydrogel for wearable electronics.

Flexible and wearable strain sensors have received extensive attention in the preparation of human−machine interface equipment, intelligent robots, and personalized health-monitoring biosensors. However, it has been a formidable challenge to develop materials with satisfying stretchability, sharp and quick sensitivity, and good linearity. Herein, we report a multifunctional nanocomposite hydrogel with outstanding stretchability, fatigue resistance, and electrical conductivity by adding Ag nanoparticle-coated graphene oxide (Ag/TA@GO)-based nanocomplexes into a polyacrylamide (PAM) hydrogel matrix. This Ag/TA@GO-PAM nanocomposite hydrogel shows an ultrahigh stretchability of 1250% and excellent conductivity (0.15 S•m −1 ). The sensitivity is improved to GF = 3.1; meanwhile, the preeminent linear sensing property is achieved in the ultrawide strain range of 0 to 1000%, with a high R 2 value of 0.994. Moreover, when the Ag/TA@GO-PAM hydrogel is assembled into a wearable strain sensor with a sandwiched structure, it can detect large and delicate motions (for example, facial expression and pronunciation), with excellent sensitivity and durability. In addition, the nanocomposite hydrogel is further explored from practical aspects for circuit assembly and repair, E-skin of bionic robots, and information encryption. Therefore, this study provides a basis for multifunctional wearable nanocomposite hydrogel sensors.

Conductive hydrogel is a vital candidate for the fabrication of flexible and wearable electric sensors due to its good designability and biocompatibility. These well-designed conductive hydrogel–based flexible strain sensors show great potential in human motion monitoring, artificial skin, brain computer interface (BCI), and so on. However, easy drying and freezing of conductive hydrogels with high water content greatly limited their further application. Herein, we proposed a natural polymer-based conductive hydrogel with excellent mechanical property, low water loss, and freeze-tolerance. The main hydrogel network was formed by the Schiff base reaction between the hydrazide-grafted hyaluronic acid and the oxidized chitosan, and the added KCl worked as the conductive filler. The reversible crosslinking in the prepared hydrogel resulted in its resilience and self-healing feature. At the same time, the synthetic effect of KCl and glycerol endowed our hydrogel with outstanding anti-freezing property, while glycerol also endowed this hydrogel with anti-drying property. When this hydrogel was assembled as a flexible strain sensor, it showed good sensitivity (GF = 2.64), durability, and stability even under cold condition (−37°C).

Hydrogel-based flexible electronic devices are essential in future healthcare and biomedical applications, such as human motion monitoring, advanced diagnostics, physiotherapy, etc. As a satisfactory flexible electronic material, the hydrogel should be conductive, ductile, self-healing, and adhesive. Herein, we demonstrated a unique design of mechanically resilient and conductive hydrogel with double network structure. The Ca2+ crosslinked alginate as the first dense network and the ionic pair crosslinked polyzwitterion as the second loose network. With the synthetic effect of these two networks, this hydrogel showed excellent mechanical properties, such as superior stretchability (1,375%) and high toughness (0.57 MJ/m3). At the same time, the abundant ionic groups of the polyzwitterion network endowed our hydrogel with excellent conductivity (0.25 S/m). Moreover, due to the dynamic property of these two networks, our hydrogel also performed good self-healing performance. Besides, our experimental results indicated that this hydrogel also had high optical transmittance (92.2%) and adhesive characteristics. Based on these outstanding properties, we further explored the utilization of this hydrogel as a flexible wearable strain sensor. The data strongly proved its enduring accuracy and sensitivity to detect human motions, including large joint flexion (such as finger, elbow, and knee), foot planter pressure measurement, and local muscle movement (such as eyebrow and mouth). Therefore, we believed that this hydrogel had great potential applications in wearable health monitoring, intelligent robot, human-machine interface, and other related fields.

Wireless mesh network (WMN), as a new generation of wireless network technology, has raised increasing concerns in recent years. Due to the strong mobility nature of the clients in WMNs, the handover events frequently occur. Therefore, taking into consideration the openness of the wireless communication channel, the handover authentication protocols for WMNs have to be both efficient and secure, which remains a challenge. In this paper, an anonymous batch handover authentication protocol is proposed using group signature technique to pre-distribute handover keys. Unlike existing protocols based on group signature, the proposed protocol does not involve group signature correlation operations in the handover authentication phase, hence achieving a better performance.

To ensure the reliability and integrity of data in the cloud storage server, some scholars provided various data integrity auditing schemes. However, the most existing data integrity auditing schemes only support the static data and may be unsuitable for the dynamic operations of data. To overcome this difficulty, we propose a fuzzy identity-based dynamic auditing of big data, which combines the structure of the Merkle hash tree (MHT) with the Index logic table (ILT). Our scheme not only performs the dynamic operations of data block in the ILT, namely modification, insertion and deletion, but also efficiently executes dynamic operations of the ILT on the structure of the MHT. We also elaborate the security, characteristics and performance analysis of the proposed scheme separately. The analysis results show that the proposed scheme costs less time than the structure of the original MHT to generate the root node hash value during the metadata generation phase and update the root node hash value during the dynamic operations. Furthermore, when users store the new ILT in local storage, they require lower communication cost to update root node hash value than users without storing the ILT, and fewer interactions between the cloud storage server and users in the dynamic operations process. INDEX TERMS Big data, cloud storage, data integrity, dynamic operation, fuzzy identity-based.