Correlation Between Surface Hydrophilicity and Osteoblastic Differentiation on Microgrooved Titanium Substrata
Surface microgrooves and acid etching on titanium (Ti) have been proposed to enhance various cell behaviors. In this study, surface hydrophilicity, protein adsorption, and alkaline phosphatase activity of osteoblasts were analyzed and compared between microgrooved Ti, Ti with microgrooves and further acid etching, smooth Ti, and acid-etched smooth Ti. Correlations between the results of each experiment were analyzed using Pearson's correlation analysis, and the influential factor on alkaline phosphatase activity was determined using multiple stepwise regression analysis. Among groups, the Ti substrata with microgrooves and subsequent acid etching showed significantly greater surface hydrophilicity and alkaline phosphatase activity compared with smooth Ti, whereas the Ti substrata with only microgrooves showed the greatest protein adsorption. Multiple stepwise regression analysis determined the surface hydrophilicity of Ti as the influential factor on alkaline phosphatase activity. This study indicates that surface microgrooves and acid etching on Ti substrata enhance surface hydrophilicity, leading to increased alkaline phosphatase activity.
Figure 1. A schematic cross-sectional image and the structural nomenclature of microgrooved Ti substrata fabricated by photolithography. Note that ridge width and groove width were designed to be uniform in dimension. According to the isotropic principle, the bottom width inside the microgrooves with truncated V-shape can be calculated as (Groove width) – 2(Groove depth). Figure 2. Scanning electron microscopic images of (a) E0, (b) NE30/5, and (c) E30/5 (×200). See Table 1 for nomenclature and microstructural dimensions. Figure 3. The water-drop images on NE0, NE30/5, E0, and E30/5 captured by a video camera. Note that the images were captured in directions perpendicular to the surface microgrooves of NE30/5 and E30/5. See Table 1 for nomenclature.
Figure 4 . Multiple-comparison results of contact angle determination on titanium substrata with various surface topographies. The contact angles on NE30/5 and E30/5 were measured in a direction perpendicular to the surface microgrooves. Statistical significances were tested among NE0, NE30/5, E0, and E30/5 using 1-way analysis of variance (ANOVA). ** indicates a significant difference (P < .01). See Table 1 for nomenclature. Figure 5. Multiple-comparison results of bovine serum albumin adsorption on titanium substrata with various surface topographies. Statistical significances were tested among NE0, NE30/5, E0, and E30/5 using 1-way ANOVA. ** indicates a significant difference (P < .01). See Table 1 for nomenclature. Figure 6. Multiple-comparison results of the alkaline phosphatase activity test of MG63 human osteoblast-like cells on Ti substrata with various surface topographies after 1, 7, and 14 days of osteogenic culture. Statistical significances were tested among NE0, NE15/3.5, NE60/10, E0, E15/3.5, and E60/10 using 1-way ANOVA. * indicates a significant difference (P < .05). See Table 1 for nomenclature.
Figure 7. Scatter-plot results from Pearson's correlation analysis between contact angles and alkaline phosphatase activities. Left, Contact Angle and ALP 7 days. Right, Contact Angle and ALP 14 days. Significant correlation was noted between Contact Angle and ALP 14 days (P < .01). ** indicates that correlation is significant at the .01 level (2-tailed). See Table 2 for nomenclature of the variables, correlation coefficients, and overall results. Figure 8. Histogram (left) and normal probability-probability (P-P) plot (right) results from multiple stepwise regression analysis using ALP 14 days as the dependent variable. Contact Angle and BSA 6 h were used as the requested independent variables. Contact Angle was determined to be the influential factor on ALP 14 days. See Table 2 for nomenclature of the variables. ALP 14 days = 5.266 − 0.023 · [Contact Angle]. R = 0.749. R2 = 0.561.
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