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

Abstract

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 ≈1 μm 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.

Multifunctional Coatings and Nanotopographies: Toward Cell Instructive and Antibacterial Implants

“…A noticeable change in cell morphology was that some cells became elongated due to “pinning” of osteoblast cells on bactericidal TiO 2 nanowire arrays . Similar results were reported from other groups using different materials or other cell lines …”

“…Inspired by nature, a number of studies have since been carried out to develop bactericidal nanotopographies on synthetic materials. They include silicon and diamond coated silicon, titanium and its alloy, polymers, stainless steel, and aluminium . Table 3 lists a summary of biomimetic bactericidal surfaces on various materials currently in development.…”

“…G) Black titanium (bTi). Reproduced under the terms of the Creative Commons Attribution 4.0 International license (CC BY 4.0) . Copyright 2017, Springer Nature.…”

“…Within 4 h of contact with the bTi surface, 95% ± 5% of E. coli , 98% ± 2% of P. aeruginosa , 92% ± 5% of Mycobacterium 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 bacterial cells were allowed to adhere up to 24 h …”

“…Nanotopographies with bactericidal potential and capacity to support bone cells populations would be ideal substrates for developing new medical implants, and the recent literature indicates this is possible (see previous section). However, it is difficult to design cell instructive surfaces with topography alone, i.e., there is typically a reduction in spreading and/or proliferation of bone‐related cell types on high aspect ratio bactericidal topographies compared to control Ti surfaces . A potential solution to achieve this would be the functionalization of such high aspect‐ratio nanotopographies with chemical ligands with integrin‐binding potential.…”