Hypoxia-mimicking cobalt-doped multi-walled carbon nanotube nanocomposites enhance the angiogenic capacity of stem cells from apical papilla.

Adequate and timely vascularization is crucial for the success of dental pulp tissue engineering. Hypoxia, an important driving force of angiogenesis, plays an important role in this process. However, few studies have investigated the fabrication of hypoxia-simulating biomaterials for dental applications. In this study, a novel hypoxia-mimicking, multi-walled carbon nanotubes/cobalt (MWCNTs/Co) nanocomposite was prepared using the metal-organic framework (MOF) route for the in situ insertion of MWCNTs into CoO polyhedra. The obtained nanocomposites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Cobalt ion release of MWCNTs/Co was analyzed in vitro. Cell viability and proliferation were assessed by culturing stem cells from apical papilla (SCAP) with MWCNTs/Co nanocomposites. The angiogenic capacity of SCAP after exposure to nanocomposites was evaluated by enzyme-linked immunosorbent assay (ELISA), western blotting and the Matrigel angiogenesis assay. Our results proved that the synthesized MWCNTs/Co nanocomposites possessed a well-designed connecting structure and could release cobalt ions in a sustained way. The MWCNTs/Co nanocomposites at 50 μg/mL significantly upregulated hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) protein expression in SCAP, with no apparent cellular cytotoxicity. The conditioned medium collected from SCAP treated with MWCNTs/Co markedly promoted endothelial cells vessel formation. In conclusion, hypoxia-mimicking MWCNTs/Co nanocomposites exhibit promising angiogenic potential for dental tissue engineering and might provide an alternative solution for translational applications.