Objectives: To develop and test a new concept of the degradation kinetics of newly developed coronary stents consisting of magnesium alloys. Methods: Design of a coronary stent prototype consisting of the non-commercial magnesium based alloy AE21 (containing 2% aluminium and 1% rare earths) with an expected 50% loss of mass within six months. Eleven domestic pigs underwent coronary implantation of 20 stents (overstretch injury). Results: No stent caused major problems during implantation or showed signs of initial breakage in the histological evaluation. There were no thromboembolic events. Quantitative angiography at follow up showed a significant (p < 0.01) 40% loss of perfused lumen diameter between days 10 and 35, corresponding to neointima formation seen on histological analysis, and a 25% re-enlargement (p < 0.05) between days 35 and 56 caused by vascular remodelling (based on intravascular ultrasound) resulting from the loss of mechanical integrity of the stent. Inflammation (p < 0.001) and neointimal plaque area (p < 0.05) depended significantly on injury score. Planimetric degradation correlated with time (r = 0.67, p < 0.01). Conclusion: Vascular implants consisting of magnesium alloy degradable by biocorrosion seem to be a realistic alternative to permanent implants. P ermanent metallic implants are key treatment options in cardiovascular interventions. However, specific drawbacks limit their more widespread use. These limitations include thrombogenicity, permanent physical irritation, mismatches in mechanical behaviour between stented and non-stented vessel areas, long term endothelial dysfunction, inability to adapt to growth, non-permissive or disadvantageous characteristics for later surgical revascularisation, and chronic inflammatory local reactions. Degradable implants offer more physiological repair, reconstitution of local vascular compliance, and a temporary, limited, longitudinal, and radial straightening effect, including the possibility for growth. These implants are "fulfilling the mission and stepping away" 1 and may act as a new biomedical tool satisfying the requirements of compatibility and integration.2 However, most biodegradable synthetic polymer stents must have greater bulk to approximate the mechanical performance required in arteries. Many also induce exaggerated acute and chronic inflammatory responses during degradation. 3To address this issue, we developed and tested a new concept of degradation after endovascular implantation of tailored magnesium alloys. We anticipated a more useful combination of mechanical stability over a limited time and complete degradation of the implants. METHODS AlloysMagnesium alloys containing small amounts of aluminium, manganese, zinc, lithium, and rare earth elements were preselected for their mechanical aspects and tested in vitro for degradation kinetics (synthetic seawater, Ringer lactate, and porcine and human serum; calculated stent half lives for different magnesium alloys were between minutes and about half a year) and the potential in...

Current stent technology is based on the use of permanent implants that remain life long in the vessel wall, far beyond the time required for the prosthesis to accomplish its main goals of sealing dissection and preventing wall recoil. With the possibility to implant long vessel segments using antiproliferative drugs to prevent restenosis, the practice of transforming the coronary vessels into stiff tubes with a full metal jacket covering all side branches and being unable to adjust to the long-term wall changes, including wall remodeling with lumen ectasia becomes a serious concern. In this article, we describe the first biodegradable stent based on a magnesium alloy that allows controlled corrosion with release to the vessel wall and the blood stream of a natural body component such as magnesium with beneficial antithrombotic, antiarrhythmic, and antiproliferative properties. We also discuss the animal experiments and the initial clinical applications in 20 patients with implants below the knee, with final results soon to be released, and the plans for the first coronary study. The results of these last two studies will indicate whether the absence of a permanent implant and the antiproliferative properties shown in animals are sufficient to prevent the restenotic process in humans or whether the prosthesis must be modified by adding the biodegradable coating with conventional antiproliferative drugs.

Magnesium alloy stents are safe and are associated with less neointima formation; however, reduced neointima did not result in larger lumen.

No abstract

No abstract