TiO2 nanoparticles synergize with substrate mechanics to improve dental pulp stem cells proliferation and differentiation.

ABSTRACT

Multiple studies exist on the influence of TiO2 nanoparticle uptake on cell behavior. Yet little is known about the lingering influence of nanoparticles accumulation within the external environment which is particularly important to stem cell differentiation. Herein, dental pulp stem cells were cultured on hard and soft polybutadiene substrates, where 0.1 mg/mL rutile TiO2 nanoparticles were introduced once, 24 h after plating. In the absence of TiO2, the doubling time on soft substrate is significantly longer, while addition of TiO2 decreases it to the same level as on the hard substrate. FACS analysis indicates particle uptake initially at 25% is reduced to 2.5% after 14 days. In the absence of TiO2, no biomineralization on the soft and snowflake-like hydroxyapatite deposits on the hard substrate are shown at week 4. With the addition of TiO2, SEM/EDAX reveals copious mineral deposition templated on large banded collagen fibers on both substrates. The mineral-to-matrix ratios analyzed by Raman spectroscopy are unremarkable in the absence of TiO2. However, with addition of TiO2, the ratios are consistent with native bone on the hard and dentin on the soft substrates. This is further confirmed by RT-PCR, which showed upregulation of markers consistent with osteogenesis and odontogenesis, respectively.