Favorable modulation of osteoblast cellular activity on Zr-modified Co-Cr-Mo alloy: The significant impact of zirconium on cell-substrate interactions.

Cobalt-chromium-molybdenum alloys exhibit good mechanical properties (yield strength: ~530 MPa, ultimate tensile strength: ~1114 MPa, elongation-to-failure: ~47.3%, and modulus: ~227 GPa) and corrosion resistance. In recent years, from the perspective of osseointegration, they are considered to be lower in rank in comparison to the widely used titanium alloys. We elucidate here the significant and favorable modulation of cellular activity of Zr-modified Co-Cr-Mo alloys. The average grain size of Co-Cr-Mo alloy samples with and without Zr was 104 ± 27 and ~53 ± 11 μm, respectively. The determining role of small addition of Zr (0.04 wt. %) to the Co-Cr-Mo alloys in favorable modulation of cellular activity was accomplished by combining cellular biology and materials science and engineering. Experiments on the influence of Zr addition to Co-Cr-Mo alloys clearly demonstrated that the cell adhesion, spread and cell-substrate interactions were enhanced in the presence of Zr. The spread/growth rate of cells was ~120% on the Co-Cr-Mo alloy and 190% per day on the Co-Cr-Mo-Zr alloy. While the % area covered by the cells increased from ~5.1 to ~33.6% on Co-Cr-Mo alloy and ~19.2 to ~47.8% on Co-Cr-Mo-Zr alloy after 2 and 24 hr of incubation. Similarly, the cell density increased from ~1354 to ~3424 cells/cm on Co-Cr-Mo alloy and ~3583 to ~7804 cells/cm on Co-Cr-Mo-Zr alloy after 2 and 24 hr of incubation. Additionally, stronger vinculin focal adhesion contact and signals associated with actin stress fibers together with extracellular matrix protein, fibronectin, were noted.