Étude toxicologique d'un acier TWIP pour le développement de nouveaux stents biorésorbables

Details

Supervisors

Jacques, Pascal ; Lison, Dominique

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil biomédical

Abstract

enAtherosclerosis is one of the most important cardiac pathology in the world. Currently, a possible solution is the implantation of a medical device to restore the blood flow in the diseased vessels, and the interest of using biomaterials for coronary implants is now rapidly increasing. Over the years, coronary angioplasty was associated with different revolutionary technologies and the most recent evolution is the use of bioresorbable stents. After the angioplasty, these biodegradable scaffolds should provide a sufficient mechanical support to the artery until the vessel is fully recovered. It would then start to gradually dissolve, avoiding late adverse local response (such as late thrombosis and restenosis) and leaving only a healed vessel wall behind. Twinning-Induced Plasticity (TWIP) steel (Fe-Mn-C) has been proposed as a candidate material for the development of new metallic bioresorbable implants due to its excellent mechanical properties. In this study we assessed, using an in vitro model, the cytotoxicity of a TWIP steel powder on endothelial cells, in direct contact with the stent surface immediately after implantation. Firstly, we characterized the TWIP powder (Fe-22Mn-0.47C) and then cells were exposed directly to TWIP powder, or to corrosion extracts. Cellular responses were assessed in vitro on human umbilical vein endothelial cells (HUVECs) using two different cytotoxicity assays: the water-soluble tetrazolium salt (WST-1) assay and a bioluminescence assay. In some tests, the antioxidant catalase was added to the solution to assess the possible implication of ROS in the cytotoxicity. Finally, the different cytotoxicity assays used were validated by analyzing any potential interference between the TWIP powder and reaction reagents. In some tests, two substitutes to cells were used: vitamin C for the WST-1 assay and ATP disodium salt for the luminescence test. We showed that the TWIP powder influences the absorbance signal produced by the conversion of the WST-1 into formazan. This interference seems to be related to the presence of Mn in the alloy. Tetrazolium-based assays are therefore not a useful tool for testing the cytotoxicity of Mn alloys. However, the Mn does not influence the bioluminescent assay and therefore it seems to be a suitable test procedure for this class of materials. Our luminescence results showed that only direct contact with TWIP powder affected cell viability, not in the presence of the antioxidant catalase, or after indirect contact, indicating that released ions were not responsible of the cytotoxic activity. These results supported our hypothesis of the implication of ROS generated during the TWIP corrosion in the endothelial cells toxicity. The demonstration of the implication of ROS in the cytotoxicity of TWIP materials raises concern about the biocompatibility of biodegradable alloys for vascular implants and should be taken into account during the development of new metallic bioresorbable stents. Furthermore, our results strongly highlight the need to perform at least two independent cytotoxicity tests for each material to be studied.