In biomedical microdevices and medical applications there is a need to analyze fluid transport of solid structures with sizes comparable to channel dimensions. Examples include manipulation of biological cells in microfluidic devices or transport of thrombin particles in blood vessels. Computational modeling of such macroparticles is very difficult when the particle size is bigger than the size of the computational control volume (mesh element). In performing such simulations, conventional Lagrangian model of micro particles is not suitable since this approach doesn’t account particle’s volume blockage of the supporting Eulerian computational mesh. Other approaches such as deforming mesh or volume of fluid are either impractical of computationally very intensive or limited to structured meshes. We have developed a ‘macroparticle’ methodology where the large particle is represented as a large cluster of smaller particles (marker particles) that is “embedded” on a background computational grid. The macroparticle is then represented by blocking the cells in the background mesh that are overlapped by individual micro-particles. The discrete surface of the macroparticle is represented by partially or fully blocked cells of the background computational mesh. The translation /rotation/deformation motion of the macroparticle is calculated using a 6-DOF model with fluid pressure and shear forces acting on the particle surface used as forces and moments in calculating macroparticle position, velocity, acceleration and rotation. The size of the background grid determines the accuracy of the particle shape definition and the flow solution. The relevant physics and chemical conservation laws for each macroparticle are solved in a coupled, iterative method with the equation systems governing the background fluid domain.

This methodology has been successfully used for simulations of macroparticle-laden fluids in micro channels in biochips. As an application of this novel method, we have applied this technology to simulate a moving clot in blood flow and process of clot mechanical dissolution (thrombolysis).

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