A superstable, flexible, and scalable nanofluidic ion regulation composite membrane.

Two-dimensional layered membranes with high and stable ion transport properties have various applications in nanofluidic devices; however, their construction remains a considerable challenge. Herein, we develop a superstable aramid nanofiber/graphite composite membrane with numerous one-dimensional and two-dimensional nano-confined interspaces for ultrafast ion transport. The fabricated flexible and scalable membrane exhibits high tensile strength (∼115.3 MPa) even after immersion in water for 90 days. Further, the aramid nanofiber/graphite conductor features the surface-charge-governed ion transport behavior. The ionic conductivity of the membrane at a low potassium chloride concentration of 10-4 mol/L can be enhanced by 16 times that of the bulk counterpart. More importantly, its structure and ionic conductivity remain unchanged even after immersion in different harsh solutions (e.g., acid, base, and ethanol) for over 30 days. Molecular dynamics simulations reveal that the superstability of the membrane is attributable to the robust interchain interactions within the aramid nanofibers and the strong interfacial interactions between the aramid nanofibers and graphite nanosheets. This study highlights the superior structural stability of the proposed flexible and scalable aramid nanofiber/graphite composite membrane, which could be employed in advanced nanofluidic devices for application under extreme working environments.

Mussel-Inspired Tough Hydrogel with In Situ Nanohydroxyapatite Mineralization for Osteochondral Defect Repair.

Repairing osteochondral defects is a considerable challenge because it involves the breakdown of articular cartilage and underlying bone. Traditional hydrogels with a homogenized single-layer structure cannot fully restore the function of osteochondral cartilage tissue. In this study, a mussel-inspired hydrogel with a bilayer structure is developed to repair osteochondral defects. The hydrogel is synthesized by simultaneously polymerizing two layers using a one-pot method. The resulting upper and lower gelatin methacryloyl-polydopamine hydrogel layers are used as cartilage and subchondral bone repair layers, respectively. Polydopamine-induced hydroxyapatite in situ mineralization takes place in the lower layer to mimic the structure of subchondral bone. The bilayer hydrogel exhibits good mechanical properties for the synergistic effect of covalent and noncovalent bonds, as well as nanoreinforcement of mineralized hydroxyapatite. To improve the tissue-inducibility of hydrogels, transforming growth factor ß3 is immobilized in the upper layer to induce cartilage regeneration, while bone morphogenetic protein 2 is immobilized in the lower layer to induce bone regeneration. Bone and cartilage repair performance of the hydrogel is examined by implantation into a full-thickness cartilage defect of a rabbit knee joint. The bilayer-structure hydrogel promotes regeneration of osteochondral tissue, thus providing a new option for repair of osteochondral defects.

Plant-inspired adhesive and tough hydrogel based on Ag-Lignin nanoparticles-triggered dynamic redox catechol chemistry.

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.

Mussel-inspired dopamine oligomer intercalated tough and resilient gelatin methacryloyl (GelMA) hydrogels for cartilage regeneration.

Gelatin methacryloyl (GelMA) hydrogels are widely used for tissue regeneration. Nonetheless, a pure GelMA hydrogel cannot efficiently serve for cartilage regeneration because of weak mechanical properties and brittleness. In this study, we established a mussel-inspired strategy for tuning the mechanical properties of GelMA hydrogels by intercalating oligomers of dopamine methacrylate (ODMA) into the chain of GelMA. After the ODMA intercalated, the hydrogel became tough and resilient. This is because ODMA intercalation reduces the high density of entangled GelMA chains and introduces additional sacrificial physical cross-linking into the hydrogel. Rheological analysis showed that the ODMA-GelMA hydrogel was mechanically stable at body temperature. The hydrogel also manifested a sustained protein release because of the ODMA catechol groups. Furthermore, the ODMA-GelMA hydrogel was found to have good biocompatibility and affinity for cells and tissues because of the catechol groups on ODMA. In vitro, the hydrogel promoted mesenchymal stem cell adhesion and growth, and in vivo, it promoted cartilage regeneration after loading with chondroitin sulfate or TGF-ß3. The hydrogel can serve as a growth-factor-free scaffold for cartilage regeneration. This hydrogel not only provided a favorable microenvironment for cartilage repair but also could serve as a promising candidate material for repair of other tissues. This mussel-inspired strategy of introduction of reactive oligomers instead of polymers into a brittle hydrogel network may be extended to the development of other tough hydrogels for biomedical applications.

Conductive and Tough Hydrogels Based on Biopolymer Molecular Templates for Controlling in Situ Formation of Polypyrrole Nanorods.

Conductive hydrogels (CHs) have gained significant attention for their wide applications in biomedical engineering owing to their structural similarity to soft tissues. However, designing CHs that combine biocompatibility with good mechanical and electrical properties is still challenging. Herein, we report a new strategy for the fabrication of tough CHs with excellent conductivity, superior mechanical properties, and good biocompatibility by using chitosan framework as molecular templates for controlling conducting polypyrrole (PPy) nanorods in situ formation inside the hydrogel networks. First, polyacrylamide/chitosan (CS) interpenetrating polymer network hydrogel was synthesized by UV photopolymerization; second, hydrophobic and conductive pyrrole monomers were absorbed and fixed on CS molecular templates and then polymerized with FeCl3 in situ inner hydrophilic hydrogel network. This strategy ensured that the hydrophobic PPy nanorods were uniformly distributed and integrated with the hydrophilic polymer phase to form highly interconnected conductive path in the hydrogel, endowing the hydrogel with high conductivity (0.3 S/m). The CHs exhibited remarkable mechanical properties after the chelation of CS by Fe3+ and the formation of composites with the PPy nanorods (fracture energy 12 000 J m-2 and compression modulus 136.3 MPa). The use of a biopolymer molecular template to induce the formation of PPy nanostructures is an efficient strategy to achieve conductive multifunctional hydrogels.