Degradable and Recyclable Hydrogels for Sustainable Bioelectronics.

Hydrogel bioelectronics has been widely used in wearable sensors, electronic skin, human-machine interfaces, and implantable tissue-electrode interfaces, providing great convenience for human health, safety, and education. The generation of electronic waste from bioelectronic devices jeopardizes human health and the natural environment. The development of degradable and recyclable hydrogels is recognized as a paradigm for realizing the next generation of environmentally friendly and sustainable bioelectronics. This review first summarizes the wide range of applications for bioelectronics, including wearable and implantable devices. Then, the employment of natural and synthetic polymers in hydrogel bioelectronics is discussed in terms of degradability and recyclability. Finally, this work provides constructive thoughts and perspectives on the current challenges toward hydrogel bioelectronics, providing valuable insights and guidance for the future evolution of sustainable hydrogel bioelectronics.

Multifunctional Hydrogels for the Healing of Diabetic Wounds.

The healing of diabetic wounds is hindered by various factors, including bacterial infection, macrophage dysfunction, excess proinflammatory cytokines, high levels of reactive oxygen species, and sustained hypoxia. These factors collectively impede cellular behaviors and the healing process. Consequently, this review presents intelligent hydrogels equipped with multifunctional capacities, which enable them to dynamically respond to the microenvironment and accelerate wound healing in various ways, including stimuli -responsiveness, injectable self-healing, shape -memory, and conductive and real-time monitoring properties. The relationship between the multiple functions and wound healing is also discussed. Based on the microenvironment of diabetic wounds, antibacterial, anti-inflammatory, immunomodulatory, antioxidant, and pro-angiogenic strategies are combined with multifunctional hydrogels. The application of multifunctional hydrogels in the repair of diabetic wounds is systematically discussed, aiming to provide guidelines for fabricating hydrogels for diabetic wound healing and exploring the role of intelligent hydrogels in the therapeutic processes.

Biomimetic Microstructured Antifatigue Fracture Hydrogel Sensor for Human Motion Detection with Enhanced Sensing Sensitivity.

Antifatigue fracture performance and high sensing sensitivity are key characteristics for hydrogel sensors used in flexible electronic applications. Herein, inspired by human muscle tissues and epidermal skin tissues, an effective and straightforward strategy is proposed to fabricate hydrogel sensors for detecting human motion with antifatigue fracture performance and high sensing sensitivity. The crystalline regions and orientation along the stretching direction of cellulose nanofiber@carbon nanotube nanohybrids in the hydrogels provide antifatigue fracture performance (the crack does not expand after 2000 stretching cycles, and the fatigue threshold was calculated to be 187 J/m2), which protects hydrogels from severe damage during long-term use. In addition, the microstructured surfaces of the hydrogels with a random height distribution increase the contact area and improve the response to weak stimuli, resulting in a sensing sensitivity of 1.11 kPa-1, 18 times higher than that of a flat hydrogel. This sensing sensitivity is higher than those of most of the hydrogel-based pressure sensors that have been reported earlier. By integrating antifatigue fracture performance and enhanced sensing sensitivity, biomimetic microstructured hydrogel sensors show great potential for use in future flexible electronic applications.

Biomimetic Microstructured Hydrogels with Thermal-Triggered Switchable Underwater Adhesion and Stable Antiswelling Property.

The design of hydrogels with switchable adhesion and stable antiswelling property in a wet environment has remained a challenge. Here, we report a biomimetic hydrogel that can adhere and detach on-demand on various material surfaces, which is realized by thermal-triggered switchable shape transformation on hexagonal micropillar patterned hydrogels. The hydrogels are cross-linked by two cross-linkers of poly(ethylene glycol) dimethacrylate and 2-ureidoethyl methacrylate, which guarantee the strong mechanical property and stable antiswelling property in a wet environment. The hydrogels can maintain stable water content in solutions with variable pH, temperature, and salt concentration, and the change in volume does not exceed 2%. In addition, due to the dynamical hydrogen bonds and dipole-dipole interaction in the hydrogels, the hydrogels exhibit a thermal-triggered shape-memory effect. The hydrogel can recover shape more than 80% in 15 s. Furthermore, inspired by the surface structure of tree-frog footpads, the hexagonal micropillar patterned hydrogels exhibit improved underwater adhesion strength. The underwater adhesion strength of hexagonal micropillar patterned hydrogels is seven times more than that of flat hydrogels. Based on the shape-memory effect of hydrogels, the adhesion strength can be altered by a thermal stimulus. The adhesion strength of the microstructures recovered from the hydrogel surface decreased to 15.4% of the initial adhesion strength. The switchable underwater adhesion of hydrogels can be applied in the fields of transfer printing, medical adhesives, mobile robots, etc.