Computations on locomotion of spheroidal particle driven by force and torque in shear-thinning fluid

Shear-thinning is a typical non-Newtonian rheological characteristic of biological fluids such as blood and mucus. Extensive studies have been conducted on self-propelled particles. The dynamics of externally actuated particles in non-Newtonian fluids have garnered widespread attention in recent years. Understanding the dynamic behavior of externally driven micro-particles in complex media is crucial for their biomedical applications. In this work, we employ the finite element method to numerically simulate the motion characteristics of spheroidal particles in shear-thinning fluids under two actuation modes: force-induced translation and torque-driven rotation, by coupling the continuity equation, momentum conservation equation, and the Carreau constitutive equation. The results show that particle eccentricity e affects the non-uniform distribution of local apparent viscosity, which is an important factor influencing the particle's locomotion speed. Furthermore, by quantifying the effects of the viscosity ratio β and Carreau number Cu on particle motion characteristics under the two modes, it is revealed that the non-uniform distribution of local shear rate induced by particle geometric anisotropy is the core mechanism governing the motion performance. These results provide useful guidance for the design of externally driven microrobots operating in biological media.