A Porous Media Model for Blood Flow within Reticulated Foam

Assessment and visualization of hemodynamic loading in aneurysm sac and neck: Effect of foam insertion

Shape memory polymer (SMP) foam is often proposed as the future alternative of coils in aneurysm treatment devices. Present work numerically investigates the unsteady, three-dimensional simulation of blood flow in a cerebral aneurysm filled with SMP foam. Simulations are conducted on patient-specific geometries with realistic blood velocity waveform imposed at the inlet while SMP foam is treated as a porous medium. The present study introduces a "loading risk map" that helps to visualize the hemodynamic effect of foam insertion on the aneurysm sac and neck. The loading risk maps suggest that while the SMP foam subdues the flow and wall shear pulsations in the aneurysm sac, the pressure distribution is minimally affected. The maps suggest that while the downstream lip is the most risk-prone site for both geometries, downstream vascular anatomy significantly influences foam efficiency in reducing pressure and wall shear stress loading.

Blood-clotting model and simulation analysis of polyvinyl alcohol-chitosan composite hemostatic materials

The blood-clotting performance and characteristics of hemostatic materials are critical for their development and actual application. Based on the theory of porous media and characteristics of a non-Newtonian fluid, this study proposed an adsorption factor to characterize the porosity generation and blood coagulation process of hemostatic materials. On this basis, we constructed a physical model of blood coagulation in a porous medium integrated with the power-law fluid model to study the proposed poly(vinyl alcohol)-chitosan (PVA-CS) composite hemostatic material. Moreover, we simulated the dynamic blood flow process and blood coagulation process in the PVA-CS hemostatic material by introducing the physical model. The simulation results show that the blood begins to coagulate, which affects the porosity and permeability of the blood-containing area, resulting in changing the porosity after blood flowed into the hemostatic material. The porosity, permeability, and blood flow rate will approach zero until the generated blood coagulation entirely blocked the porous medium. Besides, simulation can provide the pressure and velocity distribution varying in the coagulation process of hemostatic materials. The temperature will also influence the hemostatic performance of the PVA-CS material. In all, the proposed simulation method enabled the coagulation mechanism of PVA-CS to be revealed from the perspective of blood flow in porous media combined with the adsorption factor.

Experimental Study on Hydraulic Conductivity and Resistance in Silty Sediments

Hydraulic conductivity k as a function of void ratio e and particle diameter for silty sediment was experimentally investigated, and an empirical formula for the estimation of hydraulic conductivity was proposed. Seepage resistance for flow in silty sediment was deliberated. Based on the findings of the study, it was concluded that hydraulic conductivity k could be expressed as an exponential function of void ratio e and median particle diameter d50 {3.1 μm < d50 < 87 μm and 0.26 < e < 4}. It was further found that the formula of seepage resistance factor (?), a form of friction factor, varies linearly with Reynolds number (Re) for silty sediments. A family of such λ-Re curves for various particle diameter d50 is presented.