Size-Optimized LDH Nanoplatelet-Reinforced GelMA Hydrogels Orchestrate Osteoimmunomodulation for Critical-Sized Bone...

Large bone defects remain difficult to heal because effective regeneration requires not only osteogenesis but also a favorable immune microenvironment. Layered double hydroxides (LDHs) are promising bioactive nanomaterials, yet the influence of nanoparticle size on osteoimmunomodulation and bone repair remains insufficiently understood.

MgAl-LDH nanoparticles with lateral sizes of 50 and 100 nm were synthesized and characterized, then evaluated for cellular uptake, cytocompatibility, macrophage polarization, and osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs). LDH nanoparticles were further incorporated into GelMA hydrogels and tested in a murine critical-sized calvarial defect model. Transcriptomic profiling was performed to explore the underlying regenerative mechanisms. Data distribution was assessed using the Shapiro-Wilk test, and normally distributed datasets were analyzed by one-way ANOVA followed by Tukey's post hoc test.

Both LDH formulations showed well-defined hexagonal morphology, good colloidal stability, and negligible cytotoxicity. Compared with 100 nm LDH, 50 nm LDH exhibited greater cellular internalization and more effectively shifted macrophages from a pro-inflammatory to a pro-regenerative phenotype (p < 0.05). In BMSCs, LDH treatment enhanced alkaline phosphatase activity, matrix mineralization, and osteogenic gene expression, with the 50 nm group showing the strongest effects (p < 0.05). In vivo, GelMA-LDH hydrogels significantly promoted bone regeneration relative to GelMA alone, with superior performance observed for the 50 nm LDH group (p < 0.05). RNA sequencing and qPCR analyses identified a regeneration-associated molecular signature that was consistent with activation of Wnt/β-catenin-associated signaling together with attenuation of NF-κB-related inflammatory pathways.

Size-optimized MgAl-LDH nanoplatelets, particularly the 50 nm formulation, act as an effective nano-bio interface to couple immunomodulation with osteogenesis. GelMA-LDH nanocomposite hydrogels therefore represent a promising nanomedicine strategy for critical-sized bone defect repair, although further mechanistic validation is still required.