The effects of carbon nanotubes on the proliferation and differentiation of primary osteoblasts

The effects of single-walled carbon nanotubes (SWNTs), double-walled carbon nanotubes (DWNTs) and multi-walled carbon nanotubes (MWNTs) on the proliferation, differentiation, adipocytic transdifferentiation and mineralization of primary osteoblasts were investigated. SWNTs, DWNTs and MWNTs with the same mean length of 5-15 mu m and various diameters were shown to reduce the viability of osteoblasts and inhibit the adipocytic trans-differentiation in a time-and dose-dependent manner. The order of inhibition effect is SWNTs > DWNTs > MWNTs. Carbon nanotubes (CNTs) inhibited the formation of mineralized nodules greatly and dose-dependently during the final stage of osteoblast differentiation, revealing 50% decrease in the formation of mineralized nodules at the concentration of 50 mu g ml(-1). The expression of important proteins such as Runx-2 and Col-I in osteoblasts was also greatly inhibited upon interacting with CNTs. Transmission electron microscope (TEM) results revealed that the effects on cellular behavior may be exerted by the CNTs from inside and outside the cells.