Bidirectional Propulsion of Bioinspired Microswimmer in Microchannel at Low Reynolds Number

Abstract

Swimming of micro-scale bodies is different from macro-scale counterparts due to low Reynolds number (Re) fluid-swimmer interaction. The Re is defined as the ratio of inertial force to viscous force and it can be expressed as, Re =ρ𝑣𝑙/µ, where ρ and µ are the density and viscosity of the fluid medium, v and l are the velocity and length of the swimmer. For microswimmers, due to the small length scale Re < 1, the inertial forces are negligible compared to viscous forces. Unlike the macroscale swimmers which exploit the inertial force for locomotion, microswimmers must use a different strategy to propel in low Re condition. These strategies are already available and used by microorganisms, which are perfect low Re swimmers, for example, Spermatozoon exploits their tail flexibility and anisotropic drag to swim, and E. coli bacteria use their helical tail to generate a non-reciprocal motion. By mimicking these microswimmers, researchers have developed many bioinspired microswimmers/microrobots having the potential to perform biomedical tasks like drug delivery, cell manipulation, in-situ sensing, and detoxification. Theoretical modeling and simulation of microswimmers are generally done by assuming that the microswimmer is in an infinite fluid medium, but the type of biomedical applications aimed are in confined environments with boundaries. Also, the environments are very complex, and it requires precise control and efficacy. In this paper, we present the modeling of flagellated magnetic microswimmer (inspired by Spermatozoon) in a microchannel using the finite element method. The dynamics were simulated by incorporating the complete hydrodynamic interactions (HI), that is intra-HI between the parts of the swimmer and inter-HI between the swimmer and the boundary walls of the channel. The parametric dependence analysis reveals that swimmer kinematics are dependent on the length and width of the tail, the head radius, width of the channel, and the actuation frequency of the driving magnetic field. These dependencies are explored to find a navigation control mechanism for the propulsion of microswimmer in a channel.