Metal stent with surface layer of noble metal oxide and method of fabrication

In a process for producing a biocompatible stent, a tubular substrate of the stent adapted for diametric expansion has a layer of a noble metal oxide formed over at least the outer surface of greater diameter of the substrate, the substrate being composed of a metal or an alloy thereof that is non-noble or less-noble than the layer's noble metal. An interface region adapted to prevent corrosion and to provide a firm bond between the surface of the substrate and the noble metal oxide layer is established, at least in part, by forming the noble metal oxide layer with a progressively varying concentration of noble metal-to-oxide with depth of the layer such that a surface of pure noble metal and negligible oxide of the layer is in closest proximity to the surface of the substrate. In one embodiment of the process, the interface region is established by forming the surface of pure noble metal and negligible oxide thereof in direct contact with the metal or alloy of the substrate surface. In another, the interface region is established by first creating an oxide of the substrate metal or alloy thereof at the substrate surface, and then forming the noble metal oxide layer as above, but in contact with the substrate metal or alloy oxide. Alternatively, the noble metal oxide layer has no progressively varying concentration but simply overlies an oxide of the substrate metal or alloy.