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.