PSI - Issue 15

Enzoh Langi et al. / Procedia Structural Integrity 15 (2019) 41–45 Langi et al. / Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction Atherosclerosis is a process, in which a fatty material builds-up inside the arterial walls (Widmer et al., 2016). This leads to a partial or total blockage of arteries, the so-called stenosis. In 1977, the first balloon angioplasty procedure was performed in Zurich, Switzerland, by Andreas Gruentzig to treat stenotic coronary artery (Byrne et al., 2017). Since then, stenting has developed as a standard procedure for treatment of coronary artery stenosis. Stents demonstrated their capability and decrease the adverse events in acute heart attack caused by severe stenosis (Peters et al., 2009). However, the use of stents in diseased arteries is still undermined by clinical complications related to the mechanical performance (Klein et al., 2009; Cheng et al., 2010). The most widely deployed stents are metallic ones, made of stainless steel, cobalt chromium (CoCr) alloys or nitinol. However, stents available in the market offer a limited range of sizes and geometries, which might not be suitable for a patient’s unique vessel and lesion. Consequently, patient-specific stents are currently on the research agenda, with an aim to treat stenosis more effectively. Fabrication of stents was pursued employing a variety of processes such as photo etching, electroforming, laser cutting, micro-electro-discharge machining, casting and moulding (Schuessler et al., 2007). However, these methods are not suitable to produce personalised stents with varied geometry and stiffness across the length to best fit the variety of diseased arteries, especially for long and tortuous ones. The additive manufacturing (AM) techniques permit production of patient specific implants by taking advantage of complex geometric and design freedom (Mullen et al., 2009). To ensure the use of AM in vascular stents, their microstructures, properties and performance must be studied. This paper focuses on microstructural charaterisation of metallic stents manufactured with additive manufacturing, in comparison with stents produced by traditional methods. 2. Method 2.1. Material and sample preparation A 316L stainless steel SLMed tube (3 mm outside diameter and 150 µm wall thickness) and a commercial 316L stainless stent (Multi-Link RX Ultra of Abbott; 100 µm strut thickness) were investigated. The tube and the stent are depicted in Figure 1. They were cut into pieces, approximately 4 mm in length, and then cold mounted using epoxy resin and conductive filler (Buehler) in a 1:1 ratio.

316L stainless steel stent

Fig. 1. SLMed 316L stainless steel tube (a), mounted and polished along the longitudinal (b) and radial (c) directions, and commercial 316L stainless steel stent (d) mounted and polished along the longitudinal (e) and radial (f) directions.