Cartilage regeneration remains difficult due to a lack of blood vessels. Degradation of the extracellular matrix (ECM) causes cartilage defects, and the ECM provides the natural environment and nutrition for cartilage regeneration. Until now, collagen hydrogels are considered to be excellent material for cartilage regeneration due to the similar structure to ECM and good biocompatibility. However, collagen hydrogels also have several drawbacks, such as low mechanical strength, limited ability to induce stem cell differentiation, and rapid degradation. Thus, there is a demanding need to optimize collagen hydrogels for cartilage regeneration. In this review, we will first briefly introduce the structure of articular cartilage and cartilage defect classification and collagen, then provide an overview of the progress made in research on collagen hydrogels with chondrocytes or stem cells, comprehensively expound the research progress and clinical applications of collagen‐based hydrogels that integrate inorganic or organic materials, and finally present challenges for further clinical translation.

Osteosarcoma (OS) is the most common primary malignant bone tumor. In the clinic, usual strategies for OS treatment include surgery, chemotherapy, and radiation. However, all of these therapies have complications that cannot be ignored. Therefore, the search for better OS treatments is urgent. Black phosphorus (BP), a rising star of 2D inorganic nanoparticles, has shown excellent results in OS therapy due to its outstanding photothermal, photodynamic, biodegradable and biocompatible properties. This review aims to present current advances in the use of BP nanoparticles in OS therapy, including the synthesis of BP nanoparticles, properties of BP nanoparticles, types of BP nanoparticles, and modification strategies for BP nanoparticles. In addition, we have discussed comprehensively the application of BP in OS therapy, including single, dual, and multimodal synergistic OS therapies, as well as studies about bone regeneration and antibacterial properties. Finally, we have summarized the conclusions, limitations and perspectives of BP nanoparticles for OS therapy.

Critical-sized bone defects caused by trauma, tumor resection, and congenital disorders remain a major clinical challenge in orthopedic and craniofacial surgery, and injectable self-healing hydrogels offer attractive advantages for bone repair owing to their minimally invasive delivery, adaptability to irregular defect geometries, and dynamic structural properties. In this study, an injectable self-healing hydrogel was developed by combining phenylboronic acid–modified hyaluronic acid (HA-PBA) with amine-functionalized poly(ethylene glycol diglycidyl ether) (p-EGDE), forming a dynamic network through synergistic boronic ester bonding and boron–nitrogen coordination. The gelation behavior, rheological properties, self-healing ability, wet adhesion, degradation profile, and cytocompatibility were systematically evaluated in vitro , and the osteogenic performance and systemic biosafety were further assessed in a rat critical-sized calvarial defect model. The resulting hydrogels exhibited rapid gelation, pronounced shear-thinning behavior, autonomous self-healing, tunable wet adhesion, and controllable degradation. In vitro CCK-8 assays demonstrated that the hydrogels and their precursor components exhibited no significant cytotoxicity toward bone marrow mesenchymal stem cells, with cell viability exceeding 90% at all tested concentrations (2–32 mg/mL) and time points (24–72 h). In vivo evaluation showed that HA-PBA/p-EGDE hydrogels significantly promoted bone regeneration compared with the control group, while histological analysis of major organs confirmed good systemic biosafety. These results indicate that HA-PBA/p-EGDE hydrogels represent a promising injectable scaffold for bone defect repair.