Figure 5 FE-SEM images of (a) nt-TiO 2 and (b) nt-TiO 2 -P. Table 1 Chemical composition of nt-TiO 2 and surface-modified nt-TiO 2 Substrate Atomic percent   O C Ti N Si P nt-TiO2 56.4 22.2 20.5 0.9 – - nt-TiO2-A 49.9 27.5 16.3 3.2 3.1 – nt-TiO2-P 58.3 16.1 21.6 1.3 0.8 1.9 Interaction of bone cells with the surface-modified TiO2 nanotubes Adhesion, proliferation, and differentiation of osteoblasts To examine the cell behavior on the unmodified and modified TiO2 surface, the osteoblasts were cultured on sand-blasted Ti, nt-TiO2, and nt-TiO2-P

discs for 4 h and observed by FE-SEM (Figure 6). The osteoblast cells appeared as a dark phase in the FE-SEM image. After 4 h of culture, the osteoblast cells were mostly circular and barely spread on the Ti disc (Figure 6a). Stattic Osteoblast cell adhesion, spreading, and growth on the nt-TiO2 and nt-TiO2-P

surfaces (Figure 6b,c) were enhanced compared to those on the control Ti disc, selleck kinase inhibitor suggesting a good cell compatibility of nt-TiO2 and nt-TiO2-P. Figure 6 FE-SEM images of adhering osteoblasts on (a) Ti, (b) nt-TiO 2 , and (c) nt-TiO 2 -P for 4 h. Furthermore, the cytotoxic effect of PDA on osteoblast cells was analyzed by fluorescence microscopy using calcein-AM (green) and propidium iodide (red) as the markers which stain live and dead cells, respectively. Calcein-AM is highly lipophilic and cell Small molecule library in vivo membrane permeable. The calcein generated from the hydrolysis of calcein-AM by cytosolic esterase in a viable cell emits strong green fluorescence. Therefore, calcein-AM only stains viable cells. In contrast, propidium iodide, a nucleus-staining dye, can pass through only the disordered areas of the dead cell membrane and intercalates with the DNA double helix of the cell to emit a red fluorescence (excitation, Casein kinase 1 535 nm; emission, 617 nm). After 2 days of culture, green fluorescence areas were observed on all Ti, nt-TiO2, and nt-TiO2-P discs (Figure 7), suggesting the presence of live cells. A larger number of green fluorescence areas were identified on the nt-TiO2 and nt-TiO2-P discs (Figure 7b,c) than on the Ti discs (Figure 7a), indicating that the proliferation of osteoblasts was accelerated on

nt-TiO2 and nt-TiO2-P than on the Ti disc. The absence of red fluorescence in nt-TiO2-P (Figure 7c) suggests that the immobilized PDA does not have any cytotoxic effect on osteoblast cells. Figure 7 Fluorescence microscopy images of osteoblast cells marked with calcein-AM (green) and propidium iodide (red). The cells were cultured on (a) Ti, (b) nt-TiO2, and (c) nt-TiO2-P for 2 days. The viability of osteoblast cells on Ti, nt-TiO2, and nt-TiO2-P discs at 3 days was analyzed by MTT assay. Cell proliferation on the nt-TiO2 and nt-TiO2-P discs was significantly (P < 0.05) higher than that on the Ti disc (Figure 8) after 3 days of culture. This suggests that nt-TiO2 and nt-TiO2-P provide a favorable surface for osteoblast adhesion and proliferation.