Flexible electronics have been rapidly advancing and have garnered significant interest in monitoring physiological activities and health conditions. However, flexible electronics are prone to detachment in humid environments, so developing human-friendly flexible electronic devices that can effectively monitor human movement under various aquatic conditions and function as flexible electrodes remains a significant challenge. Here, we report a strongly adherent, self-healing, and swelling-resistant conductive hydrogel formed by combining the dual synergistic effects of hydrogen bonding and dipole-dipole interactions. The hydrogel has a commendable linear operating range (∼200% strain, GF = 1.44), stability of electrical signals for 200 cycles, excellent conductivity (2.18 S m-1), self-healing properties (∼30 min), and durable underwater adhesion stability. The conductive hydrogel can be developed into a flexible electronic sensor for detecting motion signals, such as joint flexion and swallowing, as well as for real-time underwater communication using Morse code. Additionally, the integration of this polymer with a low contact impedance facilitates real-time, high-fidelity detection of electroencephalogram (EEG) signals, serving as a flexible electrode. It is believed that our hydrogel will have good prospects in future wearable electronics.

Conductive hydrogels are characterized by their extraordinary stretchability, flexibility, and biocompatibility, making them ideal materials for flexible wearable sensors. However, they often encounter challenges such as freezing and water loss, which can adversely affect their conductivity and stretching performance. In this study, we introduce a conductive hydrogel incorporating polyethylene glycol (PEG), acrylic acid (AA), acrylamide (AM), and lithium chloride (LiCl), which exhibits low-temperature tolerance, resistance to drying, self-adhesion, and mechanical robustness. The hydrogel's excellent mechanical properties, including an elongation at break of 1120% and a toughness of 2.9 MJ m(-3), are attributed to the formation of a tight polymer network between P(AA-AM) and PEG through hydrogen bonding. The multiple hydrogen bonding system between PEG and the polymer networks, combined with the hydration of LiCl and electrostatic interactions between the carboxyl group and Li+, significantly enhances the hydrogel's freezing resistance (down to -60 degrees C), water retention (with only 20% water loss after 15 days), and self-adhesion (with an adhesion strength to pig skin of up to 55.08 kPa). When employed as a flexible sensor, the P(AA-AM)/PEG/LiCl hydrogel exhibited excellent sensing properties for monitoring various human motions, with an impressive gauge factor of 1.91 and electrical conductivity of 4.50 S m(-1) Moreover, it maintained a high electrical conductivity (3.82 S m(-1)) even at -20 degrees C. The conductive hydrogel consistently produced stable and reliable electrical signals in response to external mechanical stimuli, making it a preferred material for human motion monitoring.

形状记忆水凝胶（SMHs）作为一种智能软材料备受关注.目前复杂的制备工艺和缓慢单一的形状变形阻碍了其在智能柔性驱动器中的应用.本研究以丙烯酰胺（AAm）、α-甲基丙烯酸（MAA）、丙烯腈（AN）为原料,N,N,N′,N′-四甲基乙二胺（TEMED）为促进剂,利用氢键和偶极-偶极相互作用的协同效应,简单自由基聚合方法构建了热响应形状记忆超分子水凝胶（P（AMA））.研究结果表明,水凝胶具有高韧性（1.11±0.06 MJ/m~3）,高拉伸强度（0.22±0.02 MPa）和超过1000%的应变.可逆物理交联点的解离和重建赋予了水凝胶优异的热响应形状记忆行为:在10℃条件下5 min即可固定为临时形状,并在37℃条件下10 s内恢复原始形状.本研究构建的P（AMA）形状记忆超分子水凝胶具有易制备、低成本、坚韧和可编程形状变形等优点,在柔性驱动器、软机器人和电子皮肤等领域具有良好的应用前景.

Flexible and piezoelectric hydrogels show great potential in the fields of wearable sensors, soft robotics, and the human-machine interface. However, these existing piezoelectric hydrogel sensors lack adhesive properties to the skin, limiting their further application. Here, by introducing the methacryloxyethyltrimethylammonium chloride (DMC) and the sodium p-styrenesulfonate (NaSS) into the polyacrylonitrile (PAN) piezoelectric hydrogel, a polyelectrolyte hydrogel (PN(x)D(y)A(z)) was prepared through the electrostatic interaction between the polyelectrolytes. The obtained hydrogels exhibited good mechanical properties (fracture stress and fracture strain were 140.65 +/- 4.52 kPa and 499 +/- 9.54%, respectively) and excellent adhesion (adhesion to pig skin surface was 22.78 kPa), excellent mechanical-electric response performance, and could produce stable electrical signal output (similar to 65 mV) during 3000 stress-discharge cycles. When used as a flexible strain sensor, the PN(x)D(y)A(z) hydrogel accurately monitors a variety of body signals and exhibits excellent biocompatibility. Therefore, the flexible and piezoelectric PN(x)D(y)A(z) hydrogel will have broad application prospects in the field of soft electronics.

Photothermal hydrogel adhesives have yielded promising results for wound closure and infected wound treatment in recent years. However, photothermal hydrogel bioadhesives with on-demand removability without additional nanomaterials-based photothermal agents have rarely been reported in the literature. In this work, an injectable intrinsic photothermal hydrogel bioadhesive with an on-demand removal trait is developed through dynamic cross-linking of gelatin (Gel), tannic acid (TA) quinone, and borax for closing skin incisions and accelerating methicillin-resistant Staphylococcus aureus (MRSA) infected wound healing. The TA quinone containing polyphenol and quinone groups with multifunctional adhesiveness and intrinsic photothermal performance confer the hydrogel adhesive with near-infrared (NIR) responsive antibacterial activity. The cross-linking of pH-sensitive boronic ester (polyphenol-B) and Schiff base bonds endow the hydrogel with great self-healing capacity and on-demand removability. Moreover, the hydrogel possesses good biocompatibility, injectability, and hemostasis. The in vivo experiment in a rat cutaneous incision model and full-thickness MRSA-infected wound model indicate that the smart hydrogel can close wounds efficiently and treat infected ones, demonstrating its superiority in noninvasive treatment of cutaneous incisions and enhancing infected full-thickness wound healing.

Recent breakthroughs in cell transplantation therapy have revealed the promising potential of bone marrow mesenchymal stem cells (BMSCs) for promoting the regeneration of growth plate cartilage injury. However, the high apoptosis rate and the uncertainty of the differentiation direction of cells often lead to poor therapeutic effects. Cells are often grown under three-dimensional (3D) conditions in vivo, and the stiffness and components of the extracellular matrix (ECM) are important regulators of stem cell differentiation. To this end, a 3D cartilage-like ECM hydrogel with tunable mechanical properties was designed and synthesized mainly from gelatin methacrylate (GM) and oxidized chondroitin sulfate (OCS) via dynamic Schiff base bonding under UV. The effects of scaffold stiffness and composition on the survival and differentiation of BMSCs in vitro were investigated. A rat model of growth plate injury was developed to validate the effect of the GMOCS hydrogels encapsulated with BMSCs on the repair of growth plate injury. The results showed that 3D GMOCS hydrogels with an appropriate modulus significantly promoted chondrogenic differentiation of BMSCs, and GMOCS/BMSC transplantation could effectively inhibit bone bridge formation and promote the repair of damaged growth plates. Accordingly, GMOCS/BMSC therapy can be engineered as a promising therapeutic candidate for growth plate injury.