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.

A graphene oxide conductive hydrogel is reported that simultaneously possesses high toughness, self-healability, and self-adhesiveness. Inspired by the adhesion behaviors of mussels, our conductive hydrogel shows self-adhesiveness on various surfaces and soft tissues. The hydrogel can be used as self-adhesive bioelectronics, such as electrical stimulators to regulate cell activity and implantable electrodes for recording in vivo signals.

Antibacterial hydrogel has received extensive attention in soft tissue repair, especially preventing infections those associated with impaired wound healing. However, it is challenging in developing an inherent antibacterial hydrogel integrating with excellent cell affinity and superior mechanical properties. Inspired by the mussel adhesion chemistry, a contact-active antibacterial hydrogel is proposed by copolymerization of methacrylamide dopamine (MADA) and 2-(dimethylamino)ethyl methacrylate and forming an interpenetrated network with quaternized chitosan. The reactive catechol groups of MADA endow the hydrogel with contact intensified bactericidal activity, because it increases the exposure of bacterial cells to the positively charged groups of the hydrogel and strengthens the bactericidal effect. MADA also maintains the good adhesion of fibroblasts to the hydrogel. Moreover, the hybrid chemical and physical cross-links inner the hydrogel network makes the hydrogel strong and tough with good recoverability. In vitro and in vivo tests demonstrate that this tough and contact-active antibacterial hydrogel is a promising material to fulfill the dual functions of promoting tissue regeneration and preventing bacterial infection for wound-healing applications.

Glycosaminoglycan-based hydrogels are widely used for cartilage repair because glycosaminoglycans are the main component of the cartilage extracellular matrix and can maintain chondrocyte functions. However, most of the glycosaminoglycan-based hydrogels are negatively charged and cell-repellant, and they cannot host cells or favor tissue regeneration. Inspired by mussel chemistry, we designed a polydopamine-chondroitin sulfate-polyacrylamide (PDA-CS-PAM) hydrogel with tissue adhesiveness and super mechanical properties for growth-factor-free cartilage regeneration. Thanks to the abundant reactive catechol groups on the PDA, a cartilage-specific PDA-CS complex was formed by the self-assembly of PDA and CS, and then the PDA-CS complex was homogenously incorporated into an elastic hydrogel network. This catechol-group-enriched PDA-CS complex endowed the hydrogel with good cell affinity and tissue adhesiveness to facilitate cell adhesion and tissue integration. Compared with bare CS, the PDA-CS complex in the hydrogel was more effective in exerting its functions on adhered cells to upregulate chondrogenic differentiation. Because of the synergistic effects of noncovalent interactions caused by the PDA-CS complex and covalently cross-linked PAM network, the hydrogel exhibited super resilience and toughness, meeting the mechanical requirement of cartilage repair. Collectively, this tissue-adhesive and tough PDA-CS-PAM hydrogel with good cell affinity creates a growth-factor-free and biomimetic microenvironment for chondrocyte growth and cartilage regeneration and sheds light on the development of growth-factor-free biomaterials for cartilage repair.

2D conductive nanosheets are central to electronic applications because of their large surface areas and excellent electronic properties. However, tuning the multifunctions and hydrophilicity of conductive nanosheets are still challenging. Herein, a green strategy is developed for fabricating conductive, redox-active, water-soluble nanosheets via the self-assembly of poly(3,4-ethylenedioxythiophene) (PEDOT) on the polydopamine-reduced and sulfonated graphene oxide (PSGO) template. The conductivity and hydrophilicity of nanosheets are highly improved by PSGO. The nanosheets are redox active due to the abundant catechol groups and can be used as versatile nanofillers in developing conductive and adhesive hydrogels. The nanosheets create a mussel-inspired redox environment inside the hydrogel networks and endow the hydrogel with long-term and repeatable adhesiveness. This hydrogel is biocompatible and can be implanted for biosignals detection in vivo. This mussel-inspired strategy for assembling 2D nanosheets can be adapted for producing diverse multifunctional nanomaterials, with various potential applications in bioelectronics.because of their fascinating properties such as large surface areas, numerous active sites, and high conductivity and mechanical strength. [4] In particular, the emerging class of redox-active 2D conductive nanosheets such as covalent organic framework [5] and redox-active heteroatomloaded carbon nanosheets [6] has been used in various areas, e.g., catalysis, solar cells, photochemical water splitting, organic rechargeable battery cathodes, and bioelectronics. The common approach of fabricating conductive nanosheets via mechanical exfoliation lacks effective function tunability. Incorporation of inorganic redox couples such as transition-metal ions has frequently been used to make conductive nanosheets redox active. [7] However, these redox couples often involve toxic and precious-metal ions, and this hinders their biomedical applications. There is therefore an urgent need to develop green and costeffective approaches to fabricating biocompatible, redox-active, and conductive nanosheets for future bioelectronic and biomedical applications.Composites of conductive nanosheets and hydrogels are considered to be promising candidates for use in next-generation soft and flexible bioelectronics. [8] Poly(3,4-ethylenedioxythiophene) (PEDOT) is an ideal conductive material for flexible electronics because of its high electrical conductivity and excellent chemical stability. [9] However, because of the hydrophobicity and intrinsic chemical structure of PEDOT, the production of PEDOT nanosheets and their uniform dispersion in a hydrogel matrix is challenging. In addition, interfacial adhesion between the hydrogel and tissues is of critical importance, especially for electronic skin and implantable bioelectrode. [10] It is desire to develop flexible and tissue-adhesive bioelectronics so that they can tightly integrate with surrounding tissues. Recently, adhesive hydrogels based on mussel-inspired c...