Radioisotope ion implantation and ion beam mixing of cardiovascular stents for treatment of coronary artery diseases

In order to re-open narrowed coronary arteries, a balloon is inflated to widen the artery. In some cases, stents, small cylindrical nets that are expanded by the balloon and stay in the artery while the balloon is withdrawn, are used to keep the arteries open. However, cells may overgrow the stents, leading to a re-narrowing of the artery (restenosis). In order to avoid cell growth, β-radiation can be used. For this purpose, the β-emitter has to be deposited onto the stent or has to be alloyed into the stent surface. The isotopes must stay at the stent and must not be dissolved into the blood stream. Ion beam techniques are well known for their excellent adhesion. The β-emitter Phosphorus-32 was ion implanted into stents, while Yttrium-90 was galvanically deposited and ion beam mixed. As the stent is a complicated three-dimensional body, the influence of the ion beam process parameters on the stent performance has to be investigated. Pin-pull tests on flat model samples and ultrasound treatment in saline solution—as a severe test—of model samples and stents showed that adhesion and resistance against sonification of the Y-coatings could be improved by ion beam mixing, lowering the washout rate in saline. Ion implantation of P showed very low losses by washout, showing the stents to be appropriate for clinical use.