Sifeng Shi

Orthopedic regenerative medicine faces significant challenges in treating critical-sized bone defects, infections, and achieving spatiotemporal therapeutic control. Traditional hydrogels, while providing a biocompatible three-dimensional (3D) environment, often lack the dynamic responsiveness and mechanical strength required for effective bone repair. The integration of magnetic nanoparticles (MNPs), particularly iron oxides (Fe₃O₄, γ-Fe₂O₃), into hydrogel matrices has emerged as a transformative strategy to overcome these limitations. These magnetic nanocomposite hydrogels (MNHs) leverage the unique superparamagnetic properties of MNPs to enable remote and non-invasive control over their structure and function via external magnetic fields. This review comprehensively explores the design principles, synthesis methodologies, and multifaceted applications of MNHs in orthopedics. Key advancements discussed include their role in enhancing targeted drug delivery (eg, on-demand antibiotic or growth factor release), facilitating cell-based therapies through magnetic retention and mechanostimulation of mesenchymal stem cells (MSCs), and serving as dynamic scaffolds for bone tissue engineering with improved osteogenic commitment. Furthermore, MNHs exhibit great promise in anti-infective therapies by leveraging magnetic hyperthermia to eradicate biofilms and in diagnostic monitoring as contrast agents for MR. Despite their immense potential, clinical translation is contingent upon addressing critical challenges such as long-term biocompatibility of MNPs, scalability of fabrication, and achieving precise in vivo control of magnetic fields. Future perspectives highlight the convergence of MNHs with 4D bioprinting and artificial intelligence (AI) for designing patient-specific, intelligent systems. This review concludes that MNHs represent a paradigm shift towards personalized and adaptive regenerative solutions, poised to redefine treatment strategies in orthopedics and beyond.

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Orthopedic infection is one of the most intractable orthopedic problems. Bacteria resistant to antibiotics also develop gradually. Chitosan is widely used in the Biomedical field because of its high biocompatibility, biodegradability, and antibacterial activity. Chitosan-based drug delivery systems are frequently utilized to produce controlled medication release. When combined with antibiotics, synergistic antibacterial effects can be achieved. Chitosan-based nanoparticles are one of the most widely used applications in drug delivery systems. The focus of this review is to provide information on new methods being developed for chitosan-based nanoparticles in the field of bone infection treatment, including chitosan nanoparticles for antibacterial purposes, Ch-loaded with antibiotics, Ch-loaded with metal, and used as immune adjuvants. It may Provide ideas for the fundamental research and the prospects of future clinical applications of orthopedic infections.

Staphylococcus aureus can adhere to most foreign materials and form biofilm on the surface of medical devices. Biofilm infections are difficult to resolve. The goal of this in vitro study was to explore the use of chitosan-coated nanoparticles to prevent biofilm formation. For this purpose, S. aureus was seeded in 96-well plates to incubate with chitosan-coated iron oxide nanoparticles in order to study the efficiency of biofilm formation inhibition. The biofilm bacteria count was determined using the spread plate method; biomass formation was measured using the crystal violet staining method. Confocal laser scanning microscopy and scanning electron microscopy were used to study the biofilm formation. The results showed decreased viable bacteria numbers and biomass formation when incubated with chitosan-coated iron oxide nanoparticles at all test concentrations. Confocal laser scanning microscopy showed increased dead bacteria and thinner biofilm when incubated with nanoparticles at a concentration of 500 µg/mL. Scanning electron microscopy revealed that chitosan-coated iron oxide nanoparticles inhibited biofilm formation in polystyrene plates. Future studies should be performed to study these nanoparticles for anti-infective use.