Residual stresses in coronary artery stents

In western industrial countries, coronary heart disease is the most common cause of death, The reason is a coronary sclerosis, which by the generation of plaques narrows the inner lumen of an artery and, thus, deteriorates th e blood supply, This leads to symptoms like burning pain or increased press ure in the chest, and finally to an undersupply and damage of the heart mus cle. In order to keep those portions of arteries that are covered by a plaq ue open, the stent technique was developed in the 1980s and is increasingly used since about 13 years, These stents are usually made of Mires or of a slotted tube and are of two kinds: self-expanding and balloon expanding, Bo th types are implanted after being mounted on a catheter and expanded in th e desired position. Self-expanding stents make use of the elastic deformati on, while the other group of stents are expanded by a balloon, which brings about a plastic deformation of certain regions of the stent structure. Thu s, after implantation, parts of these stents undergo two steps of distinct plastic deformation. First during compression, which is necessary for the m ounting procedure on the catheter (crimping), and secund during expansion f or implantation, In this article, the residual stresses generated during cr imping and expansion are presented and discussed. These stresses are stored in the structure of a portion of a stent after implantation and are superi mposed on those stresses generated by the more than 700 million cyclic hear t beats during the patient's life. This work is a part of several interdisc iplinary research projects by the authors in order to gain reliable fail-sa fe criteria for the static and cyclic mechanical properties of coronary ste nts, (C) 2000 John Wiley & Sons. Inc. J Biomed Mater Res (Appl Biomater) 58 : 69-71. 2001.