Anion-Dependent Layered Double Hydroxide-Reinforced Gelatin Methacryloyl Hydrogels for Osteoimmunomodulation and Bone...

Persistent inflammation and insufficient osteogenesis jointly limit the repair of critical-sized bone defects. This study aimed to develop an anion-programmable osteoimmunomodulatory hydrogel based on magnesium-aluminum layered double hydroxide (LDH) nanoparticles and gelatin methacryloyl (GelMA), determine whether LDH interlayer anions regulate immune-skeletal crosstalk, and evaluate whether this strategy enhances repair of critical-sized calvarial bone defects.

Chloride- and nitrate-intercalated MgAl-LDH nanoparticles (LDH-Cl^- and LDH-NO₃ ^-) were synthesized and characterized. Their cytocompatibility, cellular uptake, macrophage-polarizing effects, and osteogenic activity toward bone marrow mesenchymal stem cells (BMSCs) were evaluated in vitro. LDH nanoparticles were incorporated into photocrosslinked GelMA hydrogels and assessed in a murine critical-sized calvarial defect model. Transcriptomic sequencing was performed with three biological replicates per group, and cell-type-specific qRT-PCR was used to validate representative pathway-associated genes in vitro.

Thoroughly washed low- and high-magnification confocal images demonstrated FITC-LDH association/internalization in macrophages and BMSCs without apparent cytotoxicity. In lipopolysaccharide-activated macrophages, LDH nanoparticles reduced TNF-α and IL-1β expression while increasing TGF-β and IL-10 expression, with LDH-NO₃ ^- producing the strongest macrophage repolarization. LDH-NO₃ ^- also enhanced alkaline phosphatase activity, extracellular matrix mineralization, and osteogenic gene expression in BMSCs. After incorporation into GelMA hydrogels, LDH-NO₃ ^- promoted greater defect bridging, bone mineral density, collagen deposition, and osteocalcin expression in vivo. Transcriptomic analysis was consistent with increased PI3K/Akt-associated regenerative signaling and attenuation of NF-κB-associated inflammatory programs, and in vitro qRT-PCR showed concordant Akt1 and Rela transcriptional changes.

Interlayer anion engineering of LDH nanoparticles, particularly nitrate intercalation, provides a strategy for constructing immunoactive GelMA-based hydrogels that coordinate inflammation resolution and osteogenic repair in critical-sized bone defects.