Stenting: biomaterials in mini-invasive cardiovascular applications

Cardiovascular diseases are one of the major causes of death in industrially developed countries. In particular, occlusive pathologies of coronary and peripheral arteries are the third cause of death in these countries. The introduction in the 1990s of endovascular techniques for percutaneous transluminal angioplasty (PTA) and eventually of the stenting procedure has dramatically modified revascularisation strategies [1]. In the last few years, the stenting technique has almost completely replaced PTA, due to the remarkably increased procedural success and fewer post-procedural complications. However, despite these relevant clinical results, the incidence of in-stent restenosis (ISR), the process of stenosis that may occur when a stent is deployed in a blood vessel, is still high, e.g. a large number of patients having received a coronary stent have an ISR ranging from 10% to 50% of all coronary stent implantations [2, 3]. In-animal preclinical studies and clinical trials demonstrated that this ISR is due to chemical, mechanical and physical properties of the stent materials together with surface characteristics. The deployment technique itself can also damage the monolayer of the endothelial cells lining the intima of the blood vessel wall. This rupture causes the consequent platelet activation, secretion of inflammation mediators and finally smooth muscle cell (SMC) activation and proliferation. These biological considerations suggest that endovascular devices have a double nature: on one side, they face the vessel wall and on the other one, they are in direct contact with the blood flow. This means that the ideal stent should not activate the tissue or the blood cells foreign body reaction (FBR). At present, the compatibility features could be improved by working on the stent design, surface treatments and active coatings. Analytical and bioanalytical chemistry has provided the basic instruments and the methods for the characterization of the new drug-eluting stents in terms of residual solvents, drug stability, drug uniformity and drug dissolution assays, contributing essential knowledge of in vitro drug stability and release and in the physiological conditions of the animal model.