Nanoparticles (NPs) are tiny materials used in a wide range of industrial and medical applications. Titanium dioxide (TiO2) is a type of nanoparticle that is widely used in paints, pigments, and cosmetics; however, little is known about the impact of TiO2 on human health and the environment. Therefore, considerable research has focused on characterizing the potential toxicity of nanoparticles such as TiO2 and on understanding the mechanism of TiO2 NP-induced nanotoxicity through the evaluation of biomarkers. Uncoated TiO2 NPs tend to aggregate in aqueous media, and these aggregates decrease cell viability and induce expression of stress-related genes, such as those encoding interleukin-6 (IL-6) and heat shock protein 70B’ (HSP70B’), indicating that TiO2 NPs induce inflammatory and heat shock responses. In order to reduce their toxicity, we conjugated TiO2 NPs with polyethylene glycol (PEG) to eliminate aggregation. Our findings indicate that modifying TiO2 NPs with PEG reduces their cytotoxicity and reduces the induction of stress-related genes. Our results also suggest that TiO2 NP-induced effects on cytotoxicity and gene expression vary depending upon the cell type and surface modification.

The innate immune response is the earliest cellular response to infectious agents and mediates the interactions between microbes and cells. Toll-like receptors (TLRs) play an important role in these interactions. We have already shown that TLRs are involved with the uptake of titanium dioxide nanoparticles (TiO2 NPs) and promote inflammatory responses. In this paper, we compared role of cellular uptake and inflammatory response via TLR 4 to lipopolysaccharide (LPS) and TiO2 NPs. In the case of LPS, LPS binds to LPS binding protein (LBP) and CD 14, and then this complex binds to TLR 4. In the case of TiO2 NPs, the necessity of LBP and CD 14 to induce the inflammatory response and for uptake by cells was investigated using over-expression, antibody blocking, and siRNA knockdown experiments. Our results suggested that for cellular uptake of TiO2 NPs, TLR 4 did not form a complex with LBP and CD 14. In the TiO2 NP-mediated inflammatory response, TLR 4 acted as the signaling receptor without protein complex of LPS, LBP and CD 14. The results suggested that character of TiO2 NPs might be similar to the complex of LPS, LBP and CD 14. These results are important for development of safer nanomaterials.

Although mechanostructural signals from the surrounding matrix have been known to regulate cell functions, the effects of substrate fluidity are poorly understood. Here, we demonstrate that the adhesion and morphology of cells are regulated by the fluidity on widely used biodegradable polymer substrates, rather than the substrate elasticity. We have designed cell culture films with different elasticity and fluidity using poly­(ε-caprolactone-co-D,l-lactide) (CL-DLLA). The elasticity was successfully controlled by adjusting the amorphous–crystal phase transition temperature (T m ) of CL-DLLA without changing the surface wettability; i.e., the CL-DLLA displays more viscous (liquidlike) behavior at 37 °C with increasing DLLA contents. The fluidity was varied by chemically cross-linking the polymer networks. This CL-DLLA system was used to test the effect of variations in a substrate’s fluidity on cell behavior. Differences were observed in adhesion, spreading and morphology of NIH 3T3 fibroblasts. Increasing the fluidity decreased cell spread area but enhanced the formation of spheroids. Although direct comparison of the elastic modulus between cross-linked and non-cross-linked samples are difficult, it was found that the substrate stiffness produced little changes in cell spread area, indicating that cells sense more dynamic nature of their surrounding environment. These findings will serve as the basis for new development of tissue engineering scaffolds and engineered stem cell niche as well as investigation of dynamic effects of mechanostructural stimuli on cell fate.