Multilayered structure on titanium implants promotes diabetic osseointegration through synergetic regulation of oxidative balance and immune homeostasis in microenvironment

Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia and chronic inflammation, which is considered a relative contraindication for implantation in clinical practice. In the pathological microenvironment of DM, the endless vicious cycle of oxidative stress-immune disorder-chronic inflammation severely inhibits new bone formation, causing the stagnant healing and poor osseointegration. Herein, we design a multilayered structure composing of 18β-glycyrrhetinic acid modified chitosan (CS-GA) and gelatin (Gel) embedded with trimanganese tetroxide nanozymes (Mn₃O₄) on the surface of titanium implant through layer-by-layer self-assembly technique (LBL), namely LBL-GA@Mn. In vitro biological tests show that under the action of Mn₃O₄, LBL-GA@Mn effectively alleviates the intracellular adverse state of oxidative stress and hypoxia while restoring mitochondrial function in macrophages stimulated by simulated DM microenvironment. At the same time, given the immunomodulatory effects of CS-GA, the multilayered structure reprograms macrophages into anti-inflammatory M2 type by activating oxidative phosphorylation and PI3K-AKT signaling pathways, effectively ameliorating inflammatory responses and exerting osteogenic cascade effects. Consequently, the conditioned medium collected from macrophages on LBL-GA@Mn significantly accelerates the osteoblast differentiation. More importantly, in a bone defect model of T2DM rat, the LBL-GA@Mn implant can achieve a satisfactory result of anti-inflammation and implant-osseointegration through the synergetic regulation of oxidative balance and immune homeostasis. This study provides an effective surface modification strategy of implant for the synergistic treatment of diabetic bone injury.