Page 21 - Magnesium-based supports for stem cell therapy of vascular disease - Mónica Echeverry Rendón

BIODEGRADABLE MAGNESIUM-BASED SUPPORTS FOR THERAPY OF VASCULAR DISEASE A GENERAL VIEW
are the efficiency (maintenance of vascular patency) and safety (no release of adverse degradation products) of the device.[25]. Stents are class III medical devices, which according with ISO 10993-5(ISO, 2009), ISO 10993-4(ISO, 2006) and ASTM F 756–00 (ASTM, 2000) standard needs to be non-cytotoxic and have excellent hemocompatibility. The cytotoxicity needs to be of grade 0 or grade 1, which means cell viability is higher than 80% and the mean hemolysis less than 5%; despite this, some of the materials previously mentioned do not meet these requirements completely and in some cases failures of the sent devices can be associated with these material selections [30]. At the same time, the type of material, its surface and overall design of the stent play an important role in the biological response after implantation. In this way, the main goal after the degradation of the stent is the tissue regeneration of the vessel without adverse effects[25].
3.Clinical challenges to resorbable biomaterials for treatment of vascular stenosis
In a recent meta-analysis Katsanos and co-workers showed that for treatment of PAD, DES (drug-eluting stents) are superior to BMS (bare metal stents) or plain BA (balloon angioplasty), yet none of these solutions could fully prevent need of revascularization in all patients [31]. The advent of bioresorbable vascular scaffolds (BVS) i.e. degradable stents in 2011, set off a new era of treatment opportunities for CAD. Some of these have reached phase II clinical trials with moderate success [32,33]. The complexity of the development as well as phenotype of ‘mature’ atherosclerotic vascular pathologies [34], likely warrants the development of specifically acting stents. Drug-eluting stents have the advantage to inhibit excessive media i.e. smooth muscle cell proliferation, yet also inhibit reendothelialization for the same reason. This might correlate with the increased risk for long-term thrombotic events, albeit small [35]. At present, BMS have superior mechanical properties that allow for sufficiently small dimensions such as thickness of the struts. In contrast, polymer-based or magnesium-alloy-based BVS require thicker struts that require careful intraluminal placement to avoid short-term or long-term dispositioning i.e. dislocation effects, that might affect thrombogenesis. Thus, the need for an adequate bioresorbable stent with optimal mechanical strength and support of the healing of the vascular lesion without medial hyperplasia, is in high demand Fig.2.
Fig.2 There are multiple options for cardiovascular stents including permanent and degradable materials. For the last option an adequate bioresorbable stent with optimal mechanical strength and support of the healing of the vascular lesion without medial hyperplasia, is needed. In this therapy a progressive degradation and turnover of the stent material should be synchrony with the progress of the tissue healing.
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