Flow of capsules in compliant microvessels

A computational study using a three-dimensional fully-coupled fluid/structure interaction model is presented on the flow of deformable capsules in a compliant, inflating tube at small but finite inertia. Flow of single capsules and single-file flow of multiple capsules are considered, and the effects of deformability, size, and constitutive models on the capsule-vessel interaction are studied. Results in terms of transient capsule deformation, velocity, and tube flow rate are presented and compared against those in a rigid tube under similar transient flow conditions of the inflating tube. Vessel inflation is shown to significantly affect the deformation of capsules with large transient variations in their shape that are absent in the rigid tube. The rapidly increasing flow in the inflating tube causes an axial contraction of the capsules that increases with increasing tube deformability. The instantaneous capsule velocity also strongly varies as it traverses the inflating tube, with the peak velocity higher than that seen in the rigid tube. The mean capsule velocity is maximal at an intermediate tube deformability, unlike in the rigid tube where it increases with increasing flow rate. A notable interaction between the capsules and inflating vessel is observed in the form of oscillations in the flow rate, which are absent in the rigid tube. For the single-file flow of multiple capsules, the tube inflation causes an increased capsule density near the vessel inlet. The axial contraction is also much greater in this case than that of a single capsule.