Water vapor assisted aramid nanofiber reinforcement for strong, tough and ionically conductive organohydrogels as high-performance strain sensors.

Conductive organohydrogels have gained increasing attention in wearable sensors, flexible batteries, and soft robots due to their exceptional environment adaptability and controllable conductivity. However, it is still difficult for conductive organohydrogels to achieve simultaneous improvement in mechanical and electrical properties. Here, we propose a novel "water vapor assisted aramid nanofiber (ANF) reinforcement" strategy to prepare robust and ionically conductive organohydrogels. Water vapor diffusion can induce the pre-gelation of the polymer solution and ensure the uniform dispersion of ANFs in organohydrogels. ANF reinforced organohydrogels have remarkable mechanical properties with a tensile strength, stretchability and toughness of up to 1.88 ± 0.04 MPa, 633 ± 30%, and 6.75 ± 0.38 MJ m-3, respectively. Furthermore, the organohydrogels exhibit great crack propagation resistance with the fracture energy and fatigue threshold as high as 3793 ± 167 J m-2 and ∼328 J m-2, respectively. As strain sensors, the conductive organohydrogel demonstrates a short response time of 112 ms, a large working strain and superior cycling stability (1200 cycles at 40% strain), enabling effective monitoring of a wide range of complex human motions. This study provides a new yet effective design strategy for high performance and multi-functional nanofiller reinforced organohydrogels.

Nanofiber Composite Reinforced Organohydrogels for Multifunctional and Wearable Electronics.

Composite organohydrogels have been widely used in wearable electronics. However, it remains a great challenge to develop mechanically robust and multifunctional composite organohydrogels with good dispersion of nanofillers and strong interfacial interactions. Here, multifunctional nanofiber composite reinforced organohydrogels (NCROs) are prepared. The NCRO with a sandwich-like structure possesses excellent multi-level interfacial bonding. Simultaneously, the synergistic strengthening and toughening mechanism at three different length scales endow the NCRO with outstanding mechanical properties with a tensile strength (up to 7.38 ± 0.24 MPa), fracture strain (up to 941 ± 17%), toughness (up to 31.59 ± 1.53 MJ m-3) and fracture energy (up to 5.41 ± 0.63 kJ m-2). Moreover, the NCRO can be used for high performance electromagnetic interference shielding and strain sensing due to its high conductivity and excellent environmental tolerance such as anti-freezing performance. Remarkably, owing to the organohydrogel stabilized conductive network, the NCRO exhibits superior long-term sensing stability and durability compared to the nanofiber composite itself. This work provides new ideas for the design of high-strength, tough, stretchable, anti-freezing and conductive organohydrogels with potential applications in multifunctional and wearable electronics.

Solvent-Exchange-Assisted Wet Annealing: A New Strategy for Superstrong, Tough, Stretchable, and Anti-Fatigue Hydrogels.

Hydrogels are widely used in tissue engineering, soft robots, wearable electronics, etc. However, it remains a great challenge to develop hydrogels possessing simultaneously high strength, large stretchability, great fracture energy, and good fatigue threshold to suit different applications. Herein, a novel solvent-exchange-assisted wet-annealing strategy is proposed to prepare high performance poly(vinyl alcohol) hydrogels by extensively tuning the macromolecular chain movement and optimizing the polymer network. The reinforcing and toughening mechanisms are found to be "macromolecule crystallization and entanglement". These hydrogels have large tensile strengths up to 11.19 ± 0.27 MPa and extremely high fracture strains of 1879 ± 10%. In addition, the fracture energy and fatigue threshold can reach as high as 25.39 ± 6.64 kJ m-2 and ≈1233 J m-2 , respectively. These superb mechanical properties compare favorably to those of other tough hydrogels, organogels, and even natural tendons and synthetic rubbers. This work provides a new and effective method to fabricate superstrong, tough, stretchable, and anti-fatigue hydrogels with potential applications in artificial tendons and ligaments.

Nrf2 in keratinocytes protects against skin fibrosis via regulating epidermal lesion and inflammatory response.

Nuclear factor-E2-related factor 2 (Nrf2) is a master transcription factor in antioxidant response, protecting against oxidative damage and various diseases. Previous studies suggest that Nrf2 is suppressed in fibrotic skin and Nrf2 agonists represent a therapeutic strategy, which is mainly attributed to Nrf2 function in fibroblasts. However, constitutive activation of Nrf2 may endow cells with proliferation and survival advantage, facilitating skin tumorigenesis. Non-invasive and mild modulation of Nrf2 via topical application may be helpful. Keratinocytes, which are essential for epidermal formation and function maintenance, have been shown to modulate differentiation of fibroblasts in different stages of fibrosis. In this respect, the role of Nrf2 in keratinocytes in skin fibrosis remains elusive. In the present study, bleomycin (BLM)-induced skin fibrosis model was applied to keratinocyte-specific Nrf2 knockout (Nrf2(K)-KO) mice generated with Keratin 14-Cre/loxp system. BLM treatment significantly suppressed Nrf2 expression in the epidermis. Nrf2 deficiency in keratinocytes exacerbated BLM-induced skin fibrosis according to dermal thickness, and immunostaining of collagen and α-SMA. One-dose BLM treatment led to the emergence of apoptotic cells in the epidermis and an elevated number of macrophages and neutrophils in the dermis, which was aggravated by Nrf2 deficiency, as indicated by TUNEL staining, and expression of F4/80 and Ly6G. In line with in vivo evidence, NRF2 silencing in HaCaT cells significantly decreased cell survival rate in response to BLM due to suppressed expression of antioxidative genes and increased intracellular levels of reactive oxygen species (ROS). The mRNA levels of chemokines and cytokines that are capable of recruiting macrophages and neutrophils, including Mcp-1, Il-6 and Il-8, were increased by Nrf2 deficiency in primary mouse keratinocytes. Moreover, bardoxolone methyl (CDDO-Me), a potent Nrf2 activator, ameliorated BLM-induced skin fibrosis after topical administration. These findings indicate that Nrf2 in keratinocytes protects against skin fibrosis via regulating cell resistance to apoptosis and expression of cytokines and chemokines. The restoration of Nrf2 through topical application might be a potential pharmacologic approach to combat skin fibrosis.