Abstract
This paper focuses on microstructural and mechanical characterization of metallic thin-walled tube produced with additive manufacturing (AM), as a promising alternative technique for the manufacturing of tubes as a feedstock for stents micromachining. Tubes, with a wall thickness of 500 μm, were made of 316L stainless steel using selective laser melting. Its surface roughness, constituting phases, underlying microstructures and chemical composition were analyzed. The dependence of hardness and elastic modulus on the crystallographic orientation were investigated using electron backscatter diffraction and nanoindentation. Spherical nanoindentation was performed to extract the indentation stress–strain curve from the load–displacement data. The obtained results were compared with those for a commercial 316L stainless steel stent. Both tube and commercial stent samples were fully austenitic, and the as-fabricated surface finish for the tube was much rougher than the stent. Microstructural characterization revealed that the tube had a columnar and coarse grain microstructure, compared to equiaxed grains in the commercial stent. Berkovich nanoindentation suggested an effect for the grain orientation on the hardness and Young’s modulus. The stress–strain curves and the indentation yield strength for the tube and stent were similar. The work is an important step toward AM of patient-specific stents.
Highlights
Stenosis is a gradual build-up of fatty and calcified deposits inside the arteries in a process called atherosclerosis, the principal cause of cardiovascular disease (CVD) and myocardial infarction
The development of stents, i.e., scaffolds made of metallic alloys or biopolymers, began in the mid-1980s, aiming to prevent restenosis and arterial recoil related to balloon angioplasty
The roughness parameters for the stent were 0.18, 0.26 and 1.23 lm, respectively. These results demonstrated a significant difference in terms of surface roughness parameters between the two samples
Summary
Stenosis is a gradual build-up of fatty (atheroma) and calcified (sclerotic) deposits inside the arteries in a process called atherosclerosis, the principal cause of cardiovascular disease (CVD) and myocardial infarction. The outcomes were compromised by an occurrence of vessel blockage triggered by acute arterial recoil and intima hyperplasia (restenosis) (Ref 2). The development of stents, i.e., scaffolds made of metallic alloys or biopolymers, began in the mid-1980s, aiming to prevent restenosis and arterial recoil related to balloon angioplasty. Stents proved effective in sustaining the blood vessels once expanded inside diseased arteries. Thin-strut DESs, made of metallic alloys such as Co-Cr alloy and coated with drugs, remain the favorable recommendations for treating patients with severe stenosis, thanks to their superiority in preventing in-stent restenosis (re-narrowing of the blood vessel due to intima hyperplasia) and late stent thrombosis (associated with less biocompatible materials and bulky struts such as in polymeric BRSs)
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