Electrochemical polishing, characterisation and in vitro evaluation of additively manufactured CoCr stents with personalised designs.

Additive manufacturing (AM) technology has paved the way for manufacturing personalised stents. However, there is a notable gap in comprehensive microstructure analyses and in vitro evaluations of the AM CoCr stents using advanced methodologies. To address this gap, this study focuses on investigating the microstructure and in vitro performance of personalised CoCr stents manufactured through micro-laser powder bed fusion (µ-LPBF). The evaluation process begins with the measurements of dimensions and surface roughness, followed by in-depth microstructural analyses. To improve surface roughness and reduce excessive strut size, the µ-LPBF stents undergo electrochemical polishing. Importantly, in vitro stent deployments are carried out in artificial arteries manufactured based on actual patients' data. Compared to the commercial MULTI-LINK VISION CoCr stent, the µ-LPBF personalised stents have rough surface finish (average roughness: 1.55 µm for µ-LPBF vs. 1.09 µm for commercial) and compromised grain microstructures (elongated for µ-LPBF vs. equiaxed for commercial). However, the personalised stents demonstrate better performances in in vitro tests. Notably, compared to the commercial stent in the two studied cases, they deliver larger lumen gains (up to 11.24 %) and reduced recoils (up to 4 times). This study validates the merit of the lesion-specific designs and the feasibility of using AM technology for stent fabrication.

In silico evaluation of additively manufactured 316L stainless steel stent in a patient-specific coronary artery.

Additive manufacturing (AM) is an emerging method for the fabrication of stents, which is cost-saving and capable of producing personalised stent designs. However, poor surface finish and dimension discrepancy in the manufactured stents can significantly affect not only their own mechanical behavior but also mechanical response of arteries. This study investigates the effects of surface irregularities and dimension discrepancy of a 316L stainless steel stent, manufactured using laser powder bed fusion (LPBF), on its biomechanical performance, in comparison with the original design and a commercial stent. In silico simulations of stent deployment in a patient-specific coronary artery, based on intravital optical coherency tomography imaging, are conducted to assess the stent deformation as well as arterial stress and damage. Severe plastic strain concentrations (with a maximum value of 1.93) occur in the LPBF stent after deployment due to surface irregularities, suggesting a high risk of stent fracture. The LPBF stent is harder to expand due to its thicker struts and closed-cell design (diameter of 4.14 mm at the peak inflating pressure during deployment, compared to 4.58 mm and 4.65 mm for the designed and MULTI-LINK RX ULTRA stents, respectively). Also, the LPBF stent induces a higher level of stress concentration (with a maximum value of 23.04 MPa) to the arterial layers, suggesting a higher risk of tissue damage and in-stent restenosis. This study demonstrates a clear need for further development of the AM process for manufacturing medical implants, especially the surface finish and dimension accuracy.