The role of friction forces in arterial mechanical thrombectomy: a review

Multiple clinical trials have demonstrated the superiority of mechanical thrombectomy (MT) over intravenous thrombolysis (tPA) in treating acute ischemic stroke (AIS). Stent retriever (SR) and aspiration techniques are the standard methods for removing occluded emboli, with evolving technologies improving MT efficiency. However, procedural success remains uncertain. Frictional forces, specifically clot-vessel, clot-SR, and SR-vessel interactions, play a critical role in MT outcomes. This review examines frictional forces during MT and their impact on success, analyzing publications from 2015 to 2025. We focus on studies that calculated friction or retrieval forces using in vitro models. We have also included current trends, limitations, and future perspectives on studying and understanding frictional forces and their implementation into in silico models. Findings indicate that fibrin-rich clots are more difficult to retrieve than red blood cell (RBC)-rich clots due to their higher friction coefficient, three to four times greater, an observation supported by multiple studies. SR-vessel and SR-clot friction also influence MT effectiveness. SR-vessel interaction plays a crucial role in acutely curved vessels, as SR compression reduces its efficiency. In SR-clot interaction, RBC-rich clot fragmentation is linked to relative interaction forces. In summary, obtaining in vivo frictional values remains challenging, and inconsistencies persist in past in vitro studies. Further, a deeper understanding of frictional forces is essential for optimizing MT, improving current SRs, and developing next generation thrombectomy technologies.