Dynamic behaviors of capsules on rough surfaces induced by shear flow under gravity

Abstract

We use a finite element method to investigate dynamic behaviors of capsules on rough surfaces induced by shear flow under gravity, which has a more practical significance for related applications such as medical implants. Our model is set as a neutral rough surface, which does not have the adhesive bonds normally assumed by micro-molecular simulations. Our results demonstrate that the capsule exhibits three motion modes: adhesion, slip, and detachment mainly depending on the shear rate, which are similar to the phenomena in which adhesive bonds (linear spring) are assumed between capsules and a smooth surface. At low shear rates, the capsule was slightly deformed, and its bottom in contact with the rough surface, hence, promotes adhesion. However, it is surprising to find that, at relatively high shear rates, the effect of capsule deformability on its adhesion dynamics is far more complex than just promoting adhesion. High deformability of the capsule gives it a concave shape at its bottom, thereby no adhesion formation in the middle. The appearance of this specific capsule shape inhibits the adhesion of the capsule but makes the capsule slip. In addition, it is interesting to note that when the shear rate exceeds a critical value, the slip state no longer appears but changes to detachment.