UC San Diego

MP35N (Co-Ni-Cr-Mo alloy) is an important stent implant material for which many aspects, that include nano- structured surfaces, are yet to be understood. We have created radially emanating metallic nanopillar structures on the surface of stent alloy wires using RF plasma. The exposure of a stent alloy wire, 250 ,[mu]m diameter Co-Ni- Cr-Mo alloy (MP35N), to parameter-controlled RF environment resulted in dense surface microstructural textures consisting of high-aspect-ratio dendritic nanopillars/nanowires. Local compositional analyses by EDS and XPS show increased values of Mo contents on the outer edges of protruding nanopillars, indicating a possibility of the higher Mo content phase contributing to the differential plasma sputter etching on the MP35N surface and resultant nanowire formation. A comparative investigation on single phase alloy versus multi-phase alloy seems to point to the importance of phase- segregation for successful nanowire formation by RF plasma treatment. Some specific single phased materials such as Fe-Ni and Fe-Cr alloys or Pt metal wire did not form the structures similar to those with a more complex MP35N under similar RF processing conditions. This study demonstrates the creation and characterization of unique nano-structured surfaces on stent alloy wires using this RF plasma process; where such nano-structured surfaces can be useful for favorably influencing cell behaviors