Immunomodulation by Macrophage Functions on Nano-Engineered Titanium Implants

Objectives: Macrophages play a central role in immunomodulation during early wound healing which in turn can determine the speed and extent of osseointegration around titanium dental implants. Nano-engineered titanium modifications including titania nanotubes (TNTs) have been suggested as favourable bone/dental implant surfaces.
Methods: In this study, we investigated macrophage functions on various Ti surfaces in an attempt to achieve suitable immunomodulation for bone healing. Briefly, TNTs (50 nm and 70 nm diameter, TNT-50 and TNT-70) on Ti surfaces were fabricated by an anodization process and characterized by SEM (scanning electron microscope) imaging. The biological activity of murine bone marrow-derived macrophages (BMM) on TNTs/Ti (with controls of smooth and micro-rough Ti) was investigated using cell proliferation, live/dead and cell attachment assays. The cellular spread morphology was also examined using SEM. We also investigated macrophage phenotype (M1/M2 macrophage) using immunofluorescence staining, cytokine levels and gene expression. In addition, osteoclastic cellular activity was measured through F-actin staining and TRAP activity.
Results: Our results indicated that TNTs/Ti increased M2 macrophage phenotype expression and suppressed osteoclast differentiation. In particular, TNT-70 significantly decreased macrophage cell growth and spreading/adhesion. Also, TNT-70 upregulated M2 macrophage marker expression and significantly inhibited osteoclast differentiation. To summarize, TNTs modified Ti enhanced the M2 macrophage phenotype and decreased osteoclast activity, which has implications for bone healing in the dental implant micro-environment.
Conclusions: These results provide new insight into the immunomodulation abilities of the TNTs/Ti implants towards achieving early osseointegration of titanium dental implants.