Conductive hydrogels are promising interface materials utilized in bioelectronics for human-machine interactions. However, the low-temperature induced freezing problem and water evaporation-induced structural failures have significantly hindered their practical applications. To address these problems, herein, an elaborately designed nanocomposite organohydrogel is fabricated by introducing highly conductive MXene nanosheets into a tannic acid-decorated cellulose nanofibrils/polyacrylamide hybrid gel network infiltrated with glycerol (Gly)/water binary solvent. Owing to the introduction of Gly, the as-prepared organohydrogel demonstrates an outstanding flexibility and electrical conductivity under a wide temperature spectrum (from −36 to 60 °C), and exhibits long-term stability in an open environment (>7 days). Additionally, the dynamic catechol-borate ester bonds, along with the readily formed hydrogen bonds between the water and Gly molecules, further endow the organohydrogel with excellent stretchability (≈1500% strain), high tissue adhesiveness, and self-healing properties. The favorable environmental stability and broad working strain range (≈500% strain); together with high sensitivity (gauge factor of 8.21) make this organohydrogel a promising candidate for both large and subtle motion monitoring.

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It is still a challenge to achieve both excellent mechanical strength and biocompatibility in hydrogels. In this study, we exploited two interactions to form a novel biocompatible, slicing-resistant, and self-healing hydrogel. The first was molecular host-guest recognition between a host (isocyanatoethyl acrylate modified β-cyclodextrin) and a guest (2-(2-(2-(2-(adamantyl-1-oxy)ethoxy)ethoxy)ethoxy)ethanol acrylate) to form "three-arm" host-guest supramolecules (HGSMs), and the second was covalent bonding between HGSMs (achieved by UV-initiated polymerization) to form strong cross-links in the hydrogel. The host-guest interaction enabled the hydrogel to rapidly self-heal. When it was cut, fresh surfaces were formed with dangling host and guest molecules (due to the breaking of host-guest recognition), which rapidly recognized each other again to heal the hydrogel by recombination of the cut surfaces. The smart hydrogels hold promise for use as biomaterials for soft-tissue repair.

Self-assembled monolayers (SAMs) of alkanethiols on gold have been employed as model substrates to investigate the effects of surface chemistry on cell behavior. However, few studies were dedicated to the substrates with a controlled wettability in studying stem cell fate. Here, mixed hydroxyl (-OH) and methyl (-CH3) terminated SAMs were prepared to form substrates with varying wettability, which were used to study the effects of wettability on the adhesion, spreading, proliferation and osteogenic differentiation of mesenchymal stem cells (MSCs) from human and mouse origins. The numbers of adhered human fetal MSCs (hMSCs) and mouse bone marrow MSCs (mMSCs) were maximized on -OH/-CH3 mixed SAMs with a water contact angle of 40~70° and 70~90°, respectively. Hydrophilic mixed SAMs with a water contact angle of 20~70° also promoted the spreading of both hMSCs and mMSCs. Both hMSCs and mMSCs proliferation was most favored on hydrophilic SAMs with a water contact angle around 70°. In addition, a moderate hydrophilic surface (with a contact angle of 40~90° for hMSCs and 70° for mMSCs) promoted osteogenic differentiation in the presence of biological stimuli. Hydrophilic mixed SAMs with a moderate wettability tended to promote the expression of αvβ1 integrin of MSCs, indicating that the tunable wettability of the mixed SAMs may guide osteogenesis through mediating the αvβ1 integrin signaling pathway. Our work can direct the design of biomaterials with controllable wettability to promote the adhesion, proliferation and differentiation of MSCs from different sources.

Natural matrices are engineered with black phosphorus nanosheets to generate therapeutic nanocomposite hydrogels with promising multi-functions, providing a facile and efficient therapeutic strategy for bone tissue engineering.

Humidity sensors have been widely used for humidity monitoring in industrial fields, while the unsatisfactory flexibility, time consumption, and expensive integration process of conventional inorganic sensors significantly limit their application in wearable electronics. Using paper-based humidity sensors is considered a feasible method to overcome these drawbacks because of their good flexibility and roll-to-roll manufacturability, while they still face problems such as poor durability and low sensitivity. In this study, we report a high-performance paper-based humidity sensor based on a rationally designed bilayered structure consisting of a nanoporous cellulose nanofiber/carbon nanotube (CNF/CNT) sensitive layer and a microporous paper substrate. The vast number of hydrophilic hydroxyl groups on the surface of CNF and paper fibers enables fast water molecule exchange between the humidity-sensitive material and the external environment via hydrogen bonding, endowing the paper-based sensor with an excellent humidity responsive property. The obtained sensor displays a maximum response value of 65.0% (ΔI/I 0) at 95% relative humidity. Furthermore, the mechanical interlocking structure formed between the CNF/CNT layer and the paper layer provides the sensor with strong interlayer adhesion. Benefiting from the unique structure, the sensor also exhibits outstanding bending (with a maximum curvature of 22.2 cm–1) and folding durability (up to 50 times). Finally, as a proof of concept, a simple humidity-measuring device is assembled, which demonstrates an excellent responsive property toward human breath and the change of air humidity, indicating a great potential of our paper-based humidity sensor toward practical applications.

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