Relationship Between Wear Debris Characteristics and Cytotoxicity for Nickel-Titanium Braided Stents

The interventional treatment approach involving the application of vascular stents has become a crucial method in treating cardiovascular diseases. The novel cross-braided vascular stent exhibits flexibility and excellent axial pliability, catering to the demands of complex scenarios such as bending, branching, and load-bearing in clinical applications. It has been successfully introduced into clinical practice. Biomedical nickel-titanium (NiTi) alloy, owing to its exceptional biocompatibility and shape memory properties, has become a prevalent material for woven stent fabrication. The wear debris generated by the frictional wear of the stent within the human body can induce adverse biological responses, posing a serious threat to the life and health of the patients. In this context, a thorough investigation into the wear characteristics of stent materials and their interaction with the biological system was crucial for further optimizing stent designs and improving treatment outcomes. To explore the mapping relationship between the wear debris characteristics of NiTi alloy and cytotoxicity, this study conducted in vitro friction and wear experiments using NiTi alloy materials, collecting wear debris samples under different wear parameters. The study delved into wear debris feature extraction and intelligent recognition algorithms. Using the YOLOv5s and U-net convolutional neural network models to obtain distribution statistics of wear debris size and shape types. In addition, wear debris and cytotoxicity experiments were conducted using the Cell Counting Kit-8 (CCK-8) staining method and live-dead cell staining approach to establish the correlation between wear debris characteristics (size and concentration) and cytotoxicity. The results indicated that wear debris under different conditions ranged from 0 to 50 μm, with the proportion of 0~10 μm wear debris exceeding 50%. The size distribution of wear debris exhibited a normal distribution under various experimental conditions. The predominant shape of the wear debris was irregular, with near-spherical wear debris constituting the smallest proportion. Both angle and friction times significantly influenced the size and shape distribution of wear debris, with size distributions being relatively similar at 24 400 and 43 200 friction times, but differed significantly from the wear debris generated after 14 400 friction cycles. The relationship between angle and wear debris distribution exhibited an inverted U-shaped trend, with the friction angle reaching an extremum at around 60°. Changes in lubrication conditions notably increased the proportion of small-sized and elongated wear debris, while decreasing the proportion of large-sized and nearly circular wear debris. Cytotoxicity experiment results demonstrated that when the concentration of wear debris was within the range of 0~500 mg/mL, the cytotoxicity of the cells was graded as 0 or 1. With an increase in the immersion time of wear debris samples, the cell proliferation rate of small-sized wear debris (0~15 μm) leaching solution experienced a slight decrease. However, the toxicity level remained at grade 0 and 1, aligning with the cytotoxicity standards for biomedical materials. Live-dead cell images confirmed cell survival and a favorable growth condition. The research findings provided a foundation for the study of wear properties and biocompatibility of nickel-titanium alloy braided stents, offering valuable insights for the design and performance improvement of stents.