Flow alters fibrin molecular and network structure and decreases binding of fibrinolytic enzymes.

Thrombolysis with tissue Plasminogen Activator (tPA), approved for treating acute ischemic stroke (AIS) within 3-4.5 h of symptom onset, converts Plasminogen (Plg) to Plasmin to degrade fibrin, while fibrin also enhances Plg activation by binding to both tPA and Plg. Therefore, in this study, we investigated whether arterial-like flow, characteristic of AIS, alters fibrin structure and susceptibility to fibrinolysis. Using a newly developed platform for quantitative imaging and spectroscopy, we found that flow generates denser fibrin networks with reduced molecular transport despite reduced protofibril packing within fibrin fibers. Raman spectroscopy revealed an α-helix-to-β-sheet transition, accompanied by reduced Plg and tPA binding, although the reduction in tPA binding emerged only after prolonged flow exposure. Consistently, multi-scale molecular dynamics simulations showed that the Plg binding site destabilized at lower forces than the primary tPA binding site. Together, these multi-scale findings help explain the limited efficacy and narrow therapeutic window of thrombolysis.