Influence of titanium dioxide nanorods with different surface chemistry on the differentiation of rat bone marrow mesenchymal stem cells

Abstract

In this study, four kinds of TiO₂ nanorods (TiO₂ NRs), with similar aspect ratios but different surface functional groups, i.e. amines (–NH₂), carboxyl groups (–COOH) and poly(ethylene glycol) (–PEG), were used to study their interaction with rat bone marrow stem cells (MSCs). The aspect ratios of the TiO₂ NRs were measured (50 to 65 nm in length and 8 nm in width) under transmission electron microscopy (TEM). The cellular uptake of the TiO₂ NRs was qualitatively studied by TEM and then quantified by inductively coupled plasma mass spectrometry (ICP-MS). The results showed that the MSCs ingested larger amounts of TiO₂–core NRs and TiO₂–NH₂ NRs than those of TiO₂–COOH NRs and TiO₂–PEG NRs, with similar intracellular distribution patterns. TiO₂–core NRs induced the highest cytotoxicity, as a result of the highest intracellular level of reactive oxygen species (ROS), which was lowered upon surface functionalization. The genotoxicity of the TiO₂ NRs was neglectable at tested concentrations, studied by the comet assay. The adipogenic and osteogenic differentiation potentials of the MSCs were firstly evaluated in terms of lipid droplet formation and calcium deposition respectively in the presence of the TiO₂ NRs. All of the TiO₂ NRs did not show an obvious influence on the adipogenic differentiation potential of the MSCs. But TiO₂–COOH NRs showed a significant impairment on the osteogenic differentiation behaviors. The influence of TiO₂ NRs on the osteogenic differentiation of the MSCs was further quantitatively studied by the expression of osteogenic markers (collagen type I and osteocalcein), at both gene and protein levels. The results confirmed the strongest hindrance of the osteogenic differentiation of the MSCs by TiO₂–COOH NRs, due to the up-regulation of transforming growth factor beta 1 (TGF-β1) and fibroblast growth factor (FGF-2). The results provide new information that the differentiation potential of the MSCs can be influenced by the presence of TiO₂ NRs with different surface functionalities, suggesting a careful analysis of the biological impact of nanomaterials.