Heterogeneous three-layer scaffolds were fabricated by mimicking the biochemical composition and structure of the hyaline cartilage, calcified cartilage, and subchondral bone of the osteochondral tissue for the repair of osteochondral defects. The hyaline cartilage layer was composed of collagen I (50.0 wt %) and sodium hyaluronate (50.0 wt %). The calcified cartilage layer and subchondral bone layer were composed of collagen I, sodium hyaluronate, and nanohydroxyapatite with different proportions. N-Hydroxysuccinimide/N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride was used to mediate the crosslinking reaction of the amine groups of collagen with carboxyl groups of sodium hyaluronate. The hyaline cartilage layer and calcified cartilage layer were designed as dense structures, while the subchondral bone layer was designed as a relatively loose structure by adjusting the crosslinking degree. The scaffolds displayed a uniform and interconnected porous structure and possessed a high porosity over 85%, which were conducive to cellular adhesion and proliferation. The scaffolds could remain at 50−75% after 30 days of degradation owing to crosslinking, providing enough time for the regeneration of the osteochondral tissue. Especially, the hyaline cartilage layer and calcified cartilage layer preferred to induce the proliferation of chondrocytes, while the subchondral bone layer was more conducive to the proliferation of osteoblasts. In conclusion, the heterogeneous multilayer scaffolds could serve as implant materials for osteochondral reconstruction.

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Hydrogels are considered a promising wound dressing owing to their ability to absorb wound exudates and their moist network structure for skin regeneration. It is of great significance to give added multiple functions to hydrogels for wound healing. In this paper, we present a gelatin-based hydrogel with self-healing ability, conductivity, and antibacterial and antioxidant activities. Dopamine was added into an alkaline solution to polymerize into polydopamine (PDA), which was used to reduce AgNO 3 into Ag nanoparticles (AgNPs) to gain a PDA@ AgNP composite. Polypyrrole-grafted gelatin (PPyGel) was dissolved in a PDA@AgNP solution and ferric ions were used as a cross-linking agent to form PDA@AgNPs-PPyGel-Fe hydrogels. The as-prepared hydrogels are soft and ductile and exhibit porous structures with pore sizes from 20 to 50 μm. The hydrogels have high water absorption ability, indicating the potential to absorb wound exudates. PPy and Fe 3+ endow the hydrogels with slightly higher conductivity than that of skin tissue, indicating the ability to effectively transmit bioelectric signals for skin regeneration. The ionic interactions and hydrogen bonding in hydrogels make them possess self-healing ability, and the self-healing process can be completed in 30 min. PDA confers hydrogels with effective antioxidant activities, while AgNPs endow hydrogels with good antibacterial activities. Moreover, the hydrogels possess good blood compatibility and cytocompatibility. In sum, the developed hydrogel has potential applications as wound dressings.