Patent ID: 8840660

Claim:
An endoprosthesis comprising: a first portion having a first erodible metallic composition comprising magnesium or a magnesium alloy, the first portion having a first erosion rate, and a second portion having a second erodible metallic composition comprising an alloy of magnesium and an element selected from the group consisting of nitrogen, carbon, silicon, oxygen, sulfur, chromium, silver, gold, boron, and combinations thereof, the second portion having a second erosion rate slower than the first erosion rate, wherein the second portion is at least an outside surface of the endoprosthesis and the first portion is disposed inwardly of the second portion, the erosion rates being measured by suspending the endoprosthesis in a stream of Ringer's solution flowing at a rate of 0.2 m/second with all surfaces of the endoprosthesis being exposed to the stream of Ringer's solution, said Ringer's solution being a solution of distilled water containing 8.6 gram sodium chloride, 0.3 gram potassium chloride, and 0.33 gram calcium chloride per liter.