Nanoparticle- and MSC-reinforced thermosensitive chitosan hydrogel for controlled antibiotic release and bone regeneration.

Critical-sized bone defects pose major challenges in orthopedic tissue engineering due to their limited self-repair capacity and high risk of infection. To address these issues, we developed an injectable, thermoresponsive, and biodegradable chitosan (CS)-based hydrogel reinforced with mesoporous zinc-silicate (mZS) nanoparticles and platelet-derived microparticles (PMPs). The mZS nanoparticles, characterized by a rod-like zinc core encapsulated in a mesoporous silica sheath, exhibited a hydrodynamic diameter of 1423.45 ± 222.43 d.nm and a zeta potential of -24.03 ± 0.90 mV. Incorporation of β-glycerophosphate and increasing concentrations of mZS reduced gelation time (5-10 min) and improved hydrogel porosity, mechanical integrity, and surface roughness-supporting cell adhesion and proliferation. The mZS/CS hydrogels demonstrated sustained antibiotic release, potent antibacterial activity, and high cytocompatibility with the murine embryonic fibroblast cell line (C3H10T1/2). PMPs enriched the matrix with osteoinductive growth factors, thereby promoting the osteogenic differentiation of C3H10T1/2 cells without the need for external inducers. In vivo, the mZS/CS + PMP + C3H10T1/2 construct significantly accelerated bone regeneration in a rat tibial defect model, achieving bone formation within 21 days, as confirmed by radiography, Alizarin Red staining, histology and Micro-CT. The hydrogel's dual antibiotic-loading capacity (mZS pores and CS matrix) provided localized infection control, reducing inflammation and enhancing wound healing, as observed in an infected rat model. This multifunctional platform integrates bone mineralization, probable osteoinduction, antimicrobial defense, and tissue support, making it a strong candidate for bone repair, cartilage regeneration, and 3D bioprinting applications. Additionally, it shows promise in treating osteoporosis and reducing the need for systemic antibiotics post-surgery.