Moving boundaries in micro-scale biofluid dynamics

Many critical issues in biofluid dynamics occur at the boundaries between fluids, solids, or both. These issues can be very complex since in many cases the boundaries are deformable and moving. Furthermore, different characteristic times, lengths, and material properties are often present which make any computational task taxing. The present review focuses on computational modeling techniques for moving boundaries and multi-component systems with emphasis on micro-scale biofluid physics, including i) the dynamics of leukocyte (white blood cell) deformation, recovery, and adhesion; and ii) the thin-film dynamics involving tear–structure interaction in soft contact lens applications. In these problems, multiple length scales exist, and at least one of them is on the order of 10 μm or smaller. After presenting appropriate computational techniques for moving boundaries, recent research on leukocyte deformation, recovery, and adhesion is reviewed in the context of multi-component, multi-time-scale, and micro-macro interactions. The soft contact lens problem is discussed from the viewpoint of large disparities in length scales due to high aspect ratios. Depending on the nature of the problem and the goal of the computation, alternative computational techniques can successfully address the physical and numerical challenges. A major interest of this article is to stress how moving boundary techniques can be applied to provide new insights into the physico-chemical behavior of complex biological systems. To treat different time and length scales with due care in a moving boundary framework is a grand challenge in developing first-principle-based computational capabilities. There are 175 references in this review article.