Effects of geometric parameters on swimming of micro organisms with single helical flagellum in circular channels

We present a computational fluid dynamics (CFD) model for the swimming of micro organisms with a single helical flagellum in circular channels. The CFD model is developed to obtain numerical solutions of Stokes equations in three dimensions, validated with experiments reported in literature, and used to analyze the effects of geometric parameters, such as the helical radius, wavelength, radii of the channel and the tail and the tail length on forward and lateral swimming velocities, rotation rates, and the efficiency of the swimmer. Optimal shapes for the speed and the power efficiency are reported. Effects of Brownian motion and electrostatic interactions are excluded to emphasize the role of hydrodynamic forces on lateral velocities and rotations on the trajectory of swimmers. For thin flagella, as the channel radius decreases, forward velocity and the power efficiency of the swimmer decreases as well; however, for thick flagella, there is an optimal radius of the channel that maximizes the velocity and the efficiency depending on other geometric parameters. Lateral motion of the swimmer is suppressed as the channel is constricted below a critical radius, for which the magnitude of the lateral velocity reaches a maximum. Results contribute significantly to the understanding of the swimming of bacteria in micro channels and capillary tubes

Effects of geometric parameters and flow on microswimmer motion in circular channels

Micro swimming robots offer many advantages in biomedical applications, such as delivering potent drugs to specific locations in targeted tissues and organs with limited side effects, conducting surgical operations with minimal damage to healthy tissues, treatment of clogged arteries, and collecting biological samples for diagnostic purposes. Reliable navigation techniques for microswimmers need to be developed for navigation, positioning and localization of robots inside the human body in future biomedical applications. In order to develop simple models to estimate trajectories of magnetically actuated microswimmers blood vessels and other conduits, effects of the channel wall must be understood well. In this thesis, experimental and numerical model results are presented on swimming of microswimmers with a magnetic head and a helical tail in laminar flows inside circular channels filled with glycerol. Designed to mimic the swimming behavior of biological organisms at low Reynolds number flows, the microswimmers are manufactured utilizing a 3D printer and a small magnet and consist of a helical tail and a body that encapsulates the magnet. The swimming motion results from the synchronized rotation of the artificial swimmer with the rotating magnetic field induced by three electromagnetic-coil pairs. In order to obtain linear and angular velocities and to analyze the motion of the microswimmer, a computational model is developed to obtain solutions of quasi-steady Stokes equations, which govern the swimming of the microswimmers and the flow inside the channel. Experiments and numerical simulations are carried out for a number of cases with different geometric parameters and flow rates in the channel. Numerical simulation results agree well with experimentally measured velocities of the swimmer validating the experimental results. It is also presented a discussion on the influence of geometric parameters of the tail, such as wavelength, amplitude and length, and the direction of rotation of the swimmer on its trajectory based on the observed behavior in experiments and numerical solutions. Moreover, a computational fluid dynamics (CFD) model for swimming of microorganisms with a single helical flagellum in circular channels is presented. The CFD model is developed to obtain numerical solutions of Stokes equations in three dimensions, validated with experiments reported in literature and used to analyze the effects of geometric parameters, such as the helical radius, wavelength, radii of the channel and the tail and the tail length on forward and lateral swimming velocities, rotation rates and the efficiency of the swimmer. Optimal shapes for the speed and the power efficiency are reported. Effects of Brownian motion and electrostatic interactions are excluded to emphasize the role of hydrodynamic forces on lateral velocities and rotations on the trajectory of swimmers. For thin flagella, as the channel radius decreases, forward velocity and the power efficiency of the swimmer decreases as well; however, for thick flagella, there is an optimal radius of the channel that maximizes the velocity and the efficiency depending on other geometric parameters. Lateral motion of the swimmer is suppressed as the channel is constricted below a critical radius, for which the magnitude of the lateral velocity reaches a maximum. Results contribute significantly to the understanding of the swimming of bacteria in micro channels and capillary tubes

Magnetic helical microswimmers in poiseuille flow

We analyze the motion of artificial magnetic microswimmers which mimic the swimming of natural organisms at low Reynolds numbers. Artificial magnetic microswimmers consist of a rigidly connected helical tail and a magnetic head. Magnetic swimmers are actuated with three orthogonal electromagnetic coil pairs. The swimmer motion is examined in the laminar flow which is introduced to channel with syringe pump. We recorded videos for forward (pusher-like swimming / in the head direction) and backward (puller-like swimming / in the tail direction) motion of swimmers. Swimmers have non-stable helical trajectories for forward motion and stable straight trajectories for backward motion. The flow effects on trajectories are observed for swimmers with different geometric parameters in the circular channels. Experiment results show that helical wavelengths of the trajectories are affected with the flow. Additionally, the flow has more pronounced effect on the trajectories of the swimmers in wide channels. Moreover, circular confinement in narrow channels leads to more stable trajectories; in wide channels swimmers follow complex trajectories. A CFD model is used to compare experiments with simulations and to analyze the effects of hydrodynamic interactions

Effects of poiseuille flows on swimming of magnetic helical robots in circular channels

This study reports experimental and numerical model results on swimming of microswimmers inside circular channels. Designed to mimic the swimming behavior of biological organisms at low Reynolds number flows, a number of microswimmers are manufactured utilizing a 3D printer and consist of a helical tail and a body that encapsulates a small magnet. The swimming motion results from the synchronized rotation of the artificial swimmer with the rotating magnetic field induced by three electromagnetic-coil pairs. In order to obtain linear and angular velocities and to analyze the motion of the microswimmer, a computational model is developed to obtain swimmer velocities from the solutions of three-dimensional steady Stokes equations which govern the flow around the swimmers inside the channel. Experiments and numerical simulations are carried out for a number of configurations with different geometric parameters and flow rates in the channel filled with glycerol. Numerical results agree well with experimentally measured average velocities of swimmers. Results describe the influence of the flow rate, length of the tail, diameter of the channel, and the direction of the rotation of the swimmer on the velocity and trajectories of microswimmers

Experimental characterization of helical swimming trajectories in circular channels

Trajectories of microorganisms and artificial helical swimmers in confinements are important in biology and for controlled swimming in medical applications. Numerical studies on the locomotion of model microorganisms and spherical particles are reported in the literature. Here, we report experimental results on the trajectories and velocities of artificial helical swimmers in circular channels. Trajectories are recorded by a digital camera and images are processed to obtain the radial position and the orientation of the swimmer. Tail length, channel diameter, rotation frequency and the rate of the Poiseuille flow are varied in the experiments. Experimental results demonstrate that confinement and flow affect the orientation of swimmer and the swimming performance. Swimmers follow stable helical trajectories in the forward direction when the tail pushes the swimmer. However, when the tail pulls the swimmer in the backward direction trajectories converge to a straight line in the narrow channel, whereas helical trajectories are observed for pullers as well in the wide channel

Characterization and modeling of micro swimmers with helical tails and cylindrical heads inside circular channels

Micro swimming robots offer many advantages in biomedical applications, such as delivering potent drugs to specific locations in targeted tissues and organs with limited side effects, conducting surgical operations with minimal damage to healthy tissues, treatment of clogged arteries, and collecting biological samples for diagnostic purposes. Reliable navigation techniques for micro swimmers need to be developed to improve the localization of robots inside the human body in future biomedical applications. In order to estimate the dynamic trajectory of magnetically propelled micro swimmers in channels, that mimic blood vessels and other conduits, fluid-micro robot interaction and the effect of the channel wall must be understood well. In this study, swimming of one-link robots with helical tails is modeled with Stokes equations and solved numerically with the finite element method. Forces acting on the robot are set to zero to enforce the force-free swimming and obtain forward, lateral and angular velocities that satisfy the constraints. Effects of the number of helical waves, wave amplitude, relative size of the cylindrical head of micro swimmer and the radial position on angular and linear velocity vectors of micro swimmer are presented