Adhesive hydrogels are attractive biomaterials for various applications, such as electronic skin, wound dressing, and wearable devices. However, fabricating a hydrogel with both adequate adhesiveness and excellent mechanical properties remains a challenge. Inspired by the adhesion mechanism of mussels, we used a two-step process to develop an adhesive and tough polydopamine-clay-polyacrylamide (PDA-clay-PAM) hydrogel. Dopamine was intercalated into clay nanosheets and limitedly oxidized between the layers, resulting in PDA-intercalated clay nanosheets containing free catechol groups. Acrylamide monomers were then added and in situ polymerized to form the hydrogel. Unlike previous single-use adhesive hydrogels, our hydrogel showed repeatable and durable adhesiveness. It adhered directly on human skin without causing an inflammatory response and was easily removed without causing damage. The adhesiveness of this hydrogel was attributed to the presence of enough free catechol groups in the hydrogel, which were created by controlling the oxidation process of the PDA in the confined nanolayers of clay. This mimicked the adhesion mechanism of the mussels, which maintain a high concentration of catechol groups in the confined nanospace of their byssal plaque. The hydrogel also displayed superior toughness, which resulted from nanoreinforcement by clay and PDA-induced cooperative interactions with the hydrogel networks. Moreover, the hydrogel favored cell attachment and proliferation, owning to the high cell affinity of PDA. Rat full-thickness skin defect experiments demonstrated that the hydrogel was an excellent dressing. This free-standing, adhesive, tough, and biocompatible hydrogel may be more convenient for surgical applications than adhesives that involve in situ gelation and extra agents.

Adhesive hydrogels have gained popularity in biomedical applications, however, traditional adhesive hydrogels often exhibit short-term adhesiveness, poor mechanical properties and lack of antibacterial ability. Here, a plant-inspired adhesive hydrogel has been developed based on Ag-Lignin nanoparticles (NPs)triggered dynamic redox catechol chemistry. Ag-Lignin NPs construct the dynamic catechol redox system, which creates long-lasting reductive-oxidative environment inner hydrogel networks. This redox system, generating catechol groups continuously, endows the hydrogel with long-term and repeatable adhesiveness. Furthermore, Ag-Lignin NPs generate free radicals and trigger self-gelation of the hydrogel under ambient environment. This hydrogel presents high toughness for the existence of covalent and non-covalent interaction in the hydrogel networks. The hydrogel also possesses good cell affinity and high antibacterial activity due to the catechol groups and bactericidal ability of Ag-Lignin NPs. This study proposes a strategy to design tough and adhesive hydrogels based on dynamic plant catechol chemistry.

Conductive polymers are promising for bone regeneration because they can regulate cell behavior through electrical stimulation; moreover, they are antioxidative agents that can be used to protect cells and tissues from damage originating from reactive oxygen species (ROS). However, conductive polymers lack affinity to cells and osteoinductivity, which limits their application in tissue engineering. Herein, an electroactive, cell affinitive, persistent ROS‐scavenging, and osteoinductive porous Ti scaffold is prepared by the on‐surface in situ assembly of a polypyrrole‐polydopamine‐hydroxyapatite (PPy‐PDA‐HA) film through a layer‐by‐layer pulse electrodeposition (LBL‐PED) method. During LBL‐PED, the PPy‐PDA nanoparticles (NPs) and HA NPs are in situ synthesized and uniformly coated on a porous scaffold from inside to outside. PDA is entangled with and doped into PPy to enhance the ROS scavenging rate of the scaffold and realize repeatable, efficient ROS scavenging over a long period of time. HA and electrical stimulation synergistically promote osteogenic cell differentiation on PPy‐PDA‐HA films. Ultimately, the PPy‐PDA‐HA porous scaffold provides excellent bone regeneration through the synergistic effects of electroactivity, cell affinity, and antioxidative activity of the PPy‐PDA NPs and the osteoinductivity of HA NPs. This study provides a new strategy for functionalizing porous scaffolds that show great promise as implants for tissue regeneration.

Monovalent Li-substitution has been proven to be an effective strategy to resolve the pivotal problems confronted with P2-type layered Mn oxides, such as cooperative Jahn–Teller distortions of Mn3+ ions and drastic P2-(OP4)-O2 phase transformations occurring during desodiation. However, the cycling stability of most Li+-substituted P2-Na x Li y Mn1–y O2 remains far from satisfactory. We herein develop a facile Ti-substitution method to improve the cyclability by taking Na0.72Li0.24Mn0.76O2 (NLMO) as an example. As expected, the novel layered oxide cathode Na0.72Li0.24Ti0.10Mn0.66O2 (NLMTO-0.1) is able to deliver a very high reversible capacity of 165 mA h g–1 for over 80 cycles within the voltage range of 1.5–4.5 V (vs Na metal), which is among the best for the reported Na-storage cathode materials. Moreover, the structure–property relationship of Ti4+ substitution is scrutinized by an arsenal of 23Na/7Li solid-state nuclear magnetic resonance, dual-mode electron paramagnetic resonance, and synchrotron X-ray diffraction techniques. The results unequivocally substantiate that Ti substitution can effectively reduce the Li+/Mn4+ ordering in TMO2 slabs, assist the reversible migration of Li+ during Na+ extraction/intercalation, and ultimately enhance the reversibility of the oxygen redox process. This work provides a comprehensive insight into the structure chemistry in developing high-capacity and high-stability layered oxide cathodes.

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