Nanostructured magnesium has fewer detrimental effects on osteoblast function

Abstract

Efforts have been made recently to implement nanoscale surface features on magnesium, a biodegradable metal, to increase bone formation. Compared with normal magnesium, nanostructured magnesium has unique characteristics, including increased grain boundary properties, surface to volume ratio, surface roughness, and surface energy, which may influence the initial adsorption of proteins known to promote the function of osteoblasts (bone-forming cells). Previous studies have shown that one way to increase nanosurface roughness on magnesium is to soak the metal in NaOH. However, it has not been determined if degradation of magnesium is altered by creating nanoscale features on its surface to influence osteoblast density. The aim of the present in vitro study was to determine the influence of degradation of nanostructured magnesium, created by soaking in NaOH, on osteoblast density. Our results showed a less detrimental effect of magnesium degradation on osteoblast density when magnesium was treated with NaOH to create nanoscale surface features. The detrimental degradation products of magnesium are of significant concern when considering use of magnesium as an orthopedic implant material, and this study identified a surface treatment, ie, soaking in NaOH to create nanoscale features for magnesium that can improve its use in numerous orthopedic applications.

Keywords: degradation; detrimental effects; nanostructured magnesium; osteoblasts.

Figure 1

Surface morphology of magnesium treated with NaOH viewed under scanning electron microscopy at 2000× for (A) control (untreated), (B) 1N20, (C) 5N20, and (D) 10 N20, and at 80,000× for (E) control (untreated), and (F) 10N20. Notes: Scale bars represent 10 μm (A–D) and 200 nm (E and F).

Figure 2

Surface topography of the magnesium samples scanned by atomic force microscopy for (A) control (untreated), (B) 1 N20, (C) 5 N20, and (D) 10 N20.

Figure 3

Changes in pH values of the culture media at 4, 24, 48, 72, 96, and 120 hours of osteoblast proliferation on polystyrene, magnesium controls without cells (Mg-control-no cells), untreated magnesium controls as well as magnesium treated with 1N20, 5N20, and 10N20. Note: A decrease in pH was observed for the polystyrene (^◆P < 0.05). A significant increase in pH was observed at 24 hours for all samples except the polystyrene (*P < 0.001; ^◆P < 0.01). As expected, by 72 hours, only the Mg-control-no cells showed a significant increase in pH (P < 0.01). Values represent the difference between the original pH of the medium and the pH obtained after 4 hours for n = 3.

Figure 4

Greater osteoblast adhesion density on polystyrene when cultured in the presence of NaOH-treated nanostructured magnesium than untreated control magnesium. Notes: Compared with the polystyrene substrate alone, all the other samples except 10N20 decreased osteoblast adhesion (*P < 0.05; ^◆P < 0.01; ^◇P < 0.001; ^▲P < 0.02). Values represent the mean ± standard deviation for n = 3.

Figure 5

Greater osteoblast density on polystyrene when cultured in the presence of NaOH-treated nanostructured magnesium than untreated control magnesium. Notes: Cell density on the polystyrene substrates was significantly greater than on the other substrates for all proliferation times (*P < 0.05). Values represent the mean ± standard error of the mean for n = 3; ^▲P < 0.05; ^◆P < 0.001.