Inscription of complex stent profiles on the polished surfaces of NiTiCo shape memory alloys by fiber lasers: Examining the impact of diffuse reflectance

Abstract

Drug eluting stents (DES) have become essential to alleviate stenosis with minimally invasive procedures. Nickel-titanium (NiTi) based shape memory alloys (SMAs) are the most suitable materials for self-expanding stents due to their good stability and superior thermo-mechanical properties. This work explains the inscription of complex DES profiles by fiber laser micro-cutting (FLMC) on Nickel-Titanium-Cobalt (NiTiCo) SMA surfaces polished with various grits (1000 P, 1500 P, 2000 P, 2500 P, 3000 P, and cloth polished) of abrasive sheets. The impact of the SMA surface diffuse reflectance on laser micromachining characteristics was investigated. The Fuzzy PROMETHEE II multi-criteria decision-making (FP II-MCDM) technique was employed to find the best-polished surface that provides the most desired responses (kerf quality, surface roughness, and depth of penetration) for clinical applications. The cloth-polished surface responds better in laser machining without compromising the kerf quality and surface roughness. A significant variation of 18 % in kerf quality was found between the 3000 P and the cloth-polished surfaces. This indicates that the surface diffuse reflectance has maximum impact when the surfaces are highly polished. For applications where surface roughness and kerf width are not a criterion, then polished surfaces between 1500 P and 2000 P give the maximum machining rate.