Abstract - Perfusion impairment of vessels by thrombus formation is the top global cause of death. Depending on the
location and disease pathology, thrombus composition varies, affecting treatment response and making identification of thrombus composition and its mechanical response sought after. The features of a fibrin network, which functions as the adhesive, have shown to influence thrombus strength, viscoelasticity, permeability and resilience to fibrinolysis. In previous studies, these features were analysed on fibrin gels made under static conditions, while in vivo thrombi are formed under flow. Therefore, the aim of this thesis is to form plasma thrombi in both the presence and absence of flow and evaluate the differences in the microstructure and mechanical properties.

Methods - Plasma thrombi in the presence and absence of flow were formed inside the Chandler loop. Recitrated PFP, pooled from three healthy volunteers, was to the Chandler loop tubings and spun at 0, 10 and 30 RPM to create shear rates of roughly 0 (static thrombus), 100 and 300 s^(-1) (flow thrombi). Six thrombi were formed for each shear rate, of which two were prepared for SEM imaging to determine the diameter of fibrin fibers. The other four thrombi were cut into three disks and were used for CLSM, unconfined compression testing and micro-indentation. With CLSM, the fiber density and pore size of the network were quantified and with unconfined compression testing and micro-indentation the global and local stiffness' of the thrombi, respectively. The global stiffness of the thrombi was measured at low (20-40\%) and high strains (75-80\%).

Results - Increased diameters were found for flow thrombi compared to static thrombi (p < 0.001 and p < 0.001). Furthermore, density increased p=0.017 and p=0.007) and pore size decreased (p < 0.001 and p < 0.001) for flow thrombi compared to static thrombi. Compression testing showed an increased stiffness for thrombi formed at 30 RPM compared to 0 and 10 RPM (20-40\%, p = 0.008 and p < 0.001 ; 75-80\%, p = 0.015 and p < 0.001). Lastly, only at high strains a significant stiffness increase was found between the 0 and 10 RPM (p=0.025).

Conclusions - The fiber diameter increased in the presence of flow compared to thrombi formed in the absence of flow. Furthermore, the density increased and the pore size decreased for flow thrombi compared to static thrombi. Lastly, the stiffness of the plasma thrombi was increased for the thrombi formed at 30 RPM compared to 0 and 10 RPM.