Surface Functionalization of 3D-Printed Porous Ti-6Al-4V Scaffolds with PDA‑mHA-Col I Composite Coating Drives Macrophage Polarizationtoward the M2 Phenotype and Promotes Immunomodulation: An In Vitro Study

OBJECTIVE: To devise a bioactive surface functionalization approach for 3D-printed Ti- 6Al-4V scaffolds that influences macrophage polarization towards the pro-reparative M2 phenotype, therefore enhancing immunomodulation and facilitating good implant-soft tissue integration. METHODS: Porous Ti-6Al-4V scaffolds were produced by selective laser melting and then covered with a polydopamine-multi-element-doped hydroxyapatite-type I collagen (PDA-mHA-Col I) composite. The scaffolds' physicochemical characteristics were characterized. Murine RAW264.7 macrophages were cocultured with uncoated (T) or coated (TPMC) scaffolds. Cell viability, proliferation, apoptosis, adhesion, and polarization were assessed via CCK-8 tests, EdU staining, flow cytometry, phalloidin staining, ELISA, and qRT-PCR. The NF-κB, PI3K/Akt, and STAT6 signaling pathways were examined using Western blotting and targeted inhibitors. RESULTS: The PDA-mHA-Col I coating improved surface hydrophilicity while maintaining mechanical characteristics. XPS verified effective collagen immobilization, exhibiting a surface nitrogen concentration of 13.03%. The coating demonstrated stability after 7 days in PBS, retaining a nitrogen content of 11.74% and negligible titanium exposure. In comparison to the T group, the TPMC scaffold markedly enhanced macrophage adhesion, proliferation, and spreading, while diminishing apoptosis. It prompted M2 polarization, as shown by reduced expression of M1 markers (iNOS, CD86) and pro-inflammatory cytokines (TNF-α, IL-6), with elevated expression of M2 markers (Arg-1, CD206) and anti-inflammatory cytokines (IL-10, TGF-β1). The TPMC scaffold suppressed the phosphorylation of NF-κB p65 while simultaneously activating PI3K/Akt and STAT6 signaling pathways. The inhibition of PI3K or STAT6 somewhat mitigated the increase of M2 markers. DISCUSSION: The coating created a pro-healing milieu by inhibiting inflammatory signals and stimulating pro-reparative pathways, thus tackling a significant obstacle in oral and maxillofacial bone repair. CONCLUSIONS: The PDA-mHA-Col I composite coating facilitates macrophage M2 polarization by concurrently inhibiting NF-κB and activating PI3K/Akt/STAT6 signaling, presenting a viable immunomodulatory approach for oral and maxillofacial bone restoration.