Thermochemically treated miniature tubes as semifinished products for vascular stents

Abstract

A method for increasing the fatigue strength of a tubular semifinished product for a medical implant, such as a stent or a cardiac valve, which includes providing a tubular semifinished product formed from a bioresorbable magnesium alloy, iron, or an iron-based alloy; and applying pressure at a temperature equal to, or less than, 420° C., internally against an inner surface of the tubular semifinished product such that the outer circumference of the tubular semifinished product is subject to plastic deformation by at least 0.2%.

What is claimed is: 
     
         1 . A method for increasing the fatigue strength of a tubular semifinished product for a stent or a cardiac valve, the method comprising the steps of:
 a) providing a tubular semifinished product for a stent or a cardiac valve, the semifinished product formed from a bioresorbable magnesium alloy, iron, or an iron-based alloy; and   b) applying pressure at a temperature equal to, or less than, 420° C., internally against an inner surface of the tubular semifinished product such that an outer circumference of the tubular semifinished product is subject to plastic deformation by at least 0.2%.   
     
     
         2 . The method of  claim 1 , wherein the pressure applies a molten metal or molten metal alloy to the inner surface and influences a degradation property and/or biocompatability of the semifinished product. 
     
     
         3 . The method of  claim 2 , wherein the semifinished product is formed from iron and the degradation property is accelerated. 
     
     
         4 . The method of  claim 2 , wherein the inner surface is alloyed by diffusion of the molten metal or alloy into the inner surface. 
     
     
         5 . The method of  claim 4 , wherein diffusion depth is varied by the temperature and time that the pressure is applied. 
     
     
         6 . The method of  claim 2 , wherein the inner surface has a lower modulus of elasticity after applying the metal or metal alloy. 
     
     
         7 . The method of  claim 2 , wherein the metal alloy is a eutectic alloy. 
     
     
         8 . The method of  claim 2 , wherein luminal and abluminal surfaces of the semifinished product comprise different chemical compositions. 
     
     
         9 . The method of  claim 1 , wherein the pressure applies a chloride-containing salt, magnesium nitrate, magnesium nitrate hexahydrate or citric acid against the inner surface.