Embolus Analogues (EAs) can provide understanding of the mechanical characteristics of blood clots of cardiac origin. Bovine EAs (n = 29) were fabricated with varying concentrations of thrombin (0-20 NIHU/ml blood). Histological staining confirmed that EA composition compared sufficiently with human samples reported in literature. EAs were mechanically described under seven testing conditions: tensile, compression, shear wave ultrasound elastography (SWE), parallel plate rheometry, indentation, creep and relaxation. The Young modulus of bovine EAs in tension varied from 7 kPa (5% strain) to 84 kPa (50% strain). The compressive Young modulus increased with increasing thrombin concentration, which was in agreement with the SWE results. There was no significant difference in Young modulus throughout the clot (p < 0.05). The EAs displayed a non-linear response under parallel plate rheometry, creep and stress relaxation. The 3rd order Mooney-Rivlin constitutive equation and Standard Linear Solid model were used to fit the non-linear stress-strain response and time-dependent properties, respectively. This is the first study in which bovine EAs, with and without addition of thrombin, are histologically and mechanically described with corresponding proposed constitutive equations. The equations and experimental data determined can be applied for future numerical and experimental testing of mammalian EAs and cardiac source clots.

Background and Purpose— Cardiogenic emboli account for 15% to 20% of acute ischemic stroke cases worldwide. However, the chance of such emboli, of varying sizes, causing a stroke under various flow types has not been evaluated. Methods— A patient-specific aortic arch model was fabricated from a medical image dataset of a 77-year-old male case, with atrial fibrillation and distal occlusion of the right M1 vessel. One hundred and eighty mammalian embolus analogs (EAs) were released one by one into the model under normal and atrial fibrillation flow conditions. A further 270 clots were fabricated using varying levels of thrombin (5–20 National Institutes of Health units thrombin). The effect of releasing several clots simultaneously was also examined by grouping EAs into 18 multiples of 5, 4, 3, and 2 clots, resulting in 504 EAs released. Results— EAs with a length of ≤10 mm were the most common geometry to travel through the common carotid arteries (44%); however, longer clots also traveled through these narrow vessels. Twenty two percent of EAs ranged from 10–20mm in length, 27% from 20–30mm and 7% were >30 mm in length. Higher density clots increased the propensity for clots to travel along the cerebral vessels ( P <0.05). Releasing more clots during each test, increased the probability of at least one clot traveling through an aortic arch branching vessel. Conclusions— Embolus trajectory through the branching vessels of the aortic arch is not exclusively dependent on embolus size. EAs tend to travel proportionally with outlet flow rates, with a greater chance of a stroke caused by multiple breakaway emboli.

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In vitro simulations of the trajectory and lodgement locations of emboli within the circle of Willis (CoW) are crucial in understanding the associated hemodynamic effects in stroke patients. A clot was fabricated from the hemolymph of a crustacean species. Clots were injected into the internal carotid artery via a cerebral flow facility housing a manufactured CoW human model. The trajectory of the clot was tracked and its hemodynamic effects monitored. The clots traveled with an average velocity of 88 mm/s along the ipsilateral side with momentary pauses along high curvature regions before finally lodging within the distal branches of the ipsilateral middle cerebral artery (MCA). These clots either elongated along the branching vessels or compressed against a bifurcation point. A blocked M1-segment of the MCA reduced the efferent blood pressure and flow rates by (15-77%) and (20-100%) respectively with a re-distribution of the flow towards the other efferent vessels. Mimicking blood clots with crustacean hemolymph provides a much lower biohazard risk than using human or mammalian blood clots and a superior alternative to synthetic materials. The geometry of the distal MCA vasculature will determine the end morphology of the lodged clot. Clotting severely reduces the distal flow rates and pressures.