Nanoscale Topography on Black Titanium Imparts Multi-biofunctional Properties for Orthopedic Applications

We have developed a chlorine based reactive ion etching process to yield randomly oriented anisotropic nanostructures that render the titanium metal surface 'black' similar to that of black silicon. The surface appears black due to the nanostructures in contrast to the conventional shiny surface of titanium. The nanostructures were found to kill bacteria on contact by mechanically rupturing the cells as has been observed previously on wings of certain insects. The etching was optimized to yield nanostructures of approximate to 1 mu m height for maximal bactericidal efficiency without compromising cytocompatibility. Within 4 hours of contact with the black titanium surface, 95% +/- 5% of E. coli, 98% +/- 2% of P. aeruginosa, 92% +/- 5% of M. smegmatis and 22% +/- 8% of S. aureus cells that had attached were killed. The killing efficiency for the S. aureus increased to 76% +/- 4% when the cells were allowed to adhere up to 24 hours. The black titanium supported the attachment and proliferation of human mesenchymal stem cells and augmented osteogenic lineage commitment in vitro. Thus, the bioinspired nanostructures on black titanium impart multi-biofunctional properties toward engineering the next-generation biomaterials for orthopedic implants.