[Metallic biomaterials for coronary stents]

The introduction of coronary stents is a milestone in interventional cardiology. Two landmark studies have shown that stainless steel stents significantly decrease the restenosis rate as compared to balloon angioplasty. This fact led to a marked increase of stent implantation since the first stent implantation by Jacques Puel in 1986. Although the concept of coronary stenting significantly improved the interventional therapy of coronary artery disease, restenosis remains a major unsolved drawback of this technique. In addition to procedure and disease related factors like implantation pressure and plaque burden, data suggest that the stent as a medical implant plays a crucial role in the process of neointima formation. Since its introduction in cardiology, more than 50 different stents of different configuration and material have been developed. Although recent publications report of promising results using biodegradable materials, almost all coronary stents commercially available at the moment are made of metallic alloys. Whereas first generation stents were made exclusively from stainless steel and only minor interest was focussed on the stent material in the manufacture of coronary stents, recent studies strongly suggest that the metallic alloy used has a direct impact on the extent of neointima formation. Thus, metallic alloys differ not only with respect to mechanical features, but also by their biocompatible properties. These two factors are of major importance in the induction of vessel wall injury, inflammatory processes and cell proliferation. In the first part, the present paper reviews the metallurgic characteristics of metallic materials, which are currently used or under investigation in the production of coronary stents. In the second part, clinical and experimental results are summarized with respect to their biocompatibility and impact on the process of restenosis formation.