Analysis of frictional forces in experimental models of stent retriever mechanical thrombectomy

Acute ischemic stroke (AIS) and mechanical thrombectomy (MT) are commonly studied in vitro using cerebral artery models made of nonbiological materials. However, these models often report higher recanalization rates than those observed clinically, suggesting a discrepancy between experimental models and clinical settings. We believe this may be partly due to the frictional interactions between blood clots, stent retrievers (SRs), and the vessel walls. Experiments were performed to measure the coefficients of static and kinetic friction between blood clots, common nonbiological model materials, and bovine carotid arteries (CAs). Additional friction testing was performed with nitinol SRs. Coefficients of static friction between blood clots and nonbiological materials were found to range from 0.1 to 0.2, increasing with decreasing clot hematocrit, but were significantly higher between blood clots and CAs (1.49, 0.57, and 0.46 for 0, 20, and 40% hematocrit clots, respectively). For 0% and 40% hematocrit clots, the coefficients of kinetic friction with nonbiological materials were less than 0.1, while significantly higher with CAs (0.26 and 0.23 for 0% and 40% hematocrit clots, respectively). However, no significant differences in the coefficients of kinetic friction were found between the different hematocrit clots. Testing with the nitinol SR showed no significant differences in the coefficients of kinetic friction for CAs (0.73) and silicone (0.78), suggesting that silicone could be a suitable model material for evaluating SR-vessel interactions in vitro. Overall, it is evident that discrepancies exist in the frictional forces between materials commonly used in experimental models of AIS and MT and those seen in vivo. The individual contributions of clot-artery, SR-artery, and clot-SR interactions during blood clot removal merit further investigation.