The effect of nanotopography on calcium and phosphorus deposition on metallic materials in vitro.

To date, long-term functions of osteoblasts leading to calcium and phosphorus mineral deposition on nanometals have not been determined. Nanometals are metals with constituent metal particles and/or surface features less than 100 nm in at least one dimension. For this reason, the objective of this in vitro study was to determine the amount of calcium and phosphorus mineral formation on microphase compared to nanophase Ti, Ti6Al4V, and CoCrMo cultured with and without osteoblasts (bone-forming cells). The results of this study provided the first evidence of significantly greater calcium and phosphorus deposition by osteoblasts and precipitation from culture media without osteoblasts on nanophase compared to respective microphase Ti6Al4V and CoCrMo after 21 days; the greatest calcium and phosphorus mineral deposition occurred on nanophase CoCrMo while the greatest calcium and phosphorus mineral precipitation without osteoblasts occurred on nanophase Ti6Al4V. No differences were found for any type of Ti: wrought, microphase, or nanophase. Moreover, increased calcium and phosphorus mineral content correlated to greater amounts of underlying aluminum content on Ti6Al4V surfaces. Since, compared to microphase Ti6Al4V, nanophase Ti6Al4V contained a higher amount of aluminum at the surface (due to greater surface area), this may provide a reason for enhanced calcium and phosphorus mineral content on nanophase Ti6Al4V. Regardless of the mechanism, this study continues to support the further investigation of nanometals for improved orthopedic applications.