Comparison on experimental and numerical results for helical swimmers inside channels

Swimming micro robots are becoming feasible in biomedical applications such as targeted drug delivery, opening clogged arteries and diagnosis owing to recent developments in micro and nano manufacturing technologies. It has been demonstrated at various scales that micro helices with magnetic coating or attached to a magnet can move in fluids with the application of external rotating magnetic fields. The motion of micro swimmers interacting with flow inside channels needs to be well understood especially for medical applications where the motion of micro robots inside arteries and conduits in the body become pertinent. In this work, swimming of helical micro robots with magnetic heads inside tubes is modeled with the resistive force theory (RFT) and validated with experiments conducted in glycerin filled mini glass channels placed in rotational magnetic fields. The time-averaged forward velocities of magnetically driven micro swimmers that are calculated by the RFT model agree very well with experimental results

Bio-inspired micro robots swimming in channels

Swimming micro robots that mimic micro organisms have a huge potential in biomedical applications such as opening clogged hard-to-reach arteries, targeted drug delivery and diagnostic operations. Typically, a micro swimmer that consists of a magnetic bead as its body, which is attached to a rigid helical tail, is actuated by a rotating external magnetic field and moved forward in the direction of the rotation in fluids. Understanding of hydrodynamic effects has utmost importance for modeling and prediction of the trajectory of the robot. In this work, a computational fluid dynamics (CFD) model is presented for the mm-long swimmer with the helical tail; the swimmer is used in our previous experiments on the effect of the confinement of the robot in a liquid filled channel. Forward velocity, fluid forces and torques on the micro swimmer are studied with respect to robot’s radial position in the channel and the number of waves on the helical tail. Forward velocities from the CFD model for the robots swimming near the wall agree reasonably well with experimental measurements

In-channel experiments on vertical swimming with bacteria-like robots

Bio-inspired micro-robots are of great importance as to implement versatile microsystems for a variety of in vivo and in vitro applications in medicine and biology. Accurate models are necessary to understand the swimming and rigidbody dynamics of such systems. In this study, a series of experiments are conducted with a two-link cm-scale bioinspired robot moving vertically without a tether, in siliconefilled narrow cylindrical glass channels. Swimming velocities are obtained for a set of varying tail and wave geometries, and employed to validate a resistive force theory (RFT) model using modified resistance coefficients based on measured forward velocity and body rotation rates

Experiment-based kinematic validation of numeric modeling and simulated control of an untethered biomimetic microrobot in channel

Modeling and control of swimming untethered microrobots are important for future therapeutic medical applications. Bio-inspired propulsion methods emerge as realistic substitutes for hydrodynamic thrust generation in micro realm. Accurate modeling, power supply, and propulsion-means directly affect microrobot motility and maneuverability. In this work, motility of bacteria-like untethered helical microrobots in channels is modeled with the resistive force theory coupled with motor dynamics. Results are validated with private experiments conducted on cm-scale prototypes fully submerged in Si-oil filled glass channel. Li-Po battery is utilized as the onboard power supply. Helical tail rotation is triggered by an IR remote control. It is observed that time-averaged velocities calculated by the model agree well with experimental results. Finally, time-dependent performance of a hypothetical model-based position control scheme is simulated with upstream flow as disturbance

Experiments on in-channel swimming of an untethered biomimetic robot with different helical tails

Experiments are carried out with a cm-scale bio-mimetic swimming robot, which consists of a body and a rigid helical tail and mimics typical eukaryotic micro organisms, inside circular channels filled with viscous fluids. The body of the robot is made of a cylindrical capsule, which includes an onboard power supply, a dedicated DC-motor, and a driving circuitry with IR-receiver for remote control purposes. In experiments geometric parameters of the helical tail, wavelength and amplitude, and the diameter of the circular channels are varied to understand the effect of those parameters on the swimming speed of the robots. Models, based on slender body theory (SBT) and resistive force theory (RFT), are implemented to predict the swimming speeds, which are then compared with experimentally measured values. A simple model for the DC-motor dynamics is included to account for the contact friction effects on the body rotation rates. Model results agree reasonably well with experimental measurements

Improved kinematic models for two-link helical micro/nano-swimmers

Accurate prediction of the three-dimensional trajectories of micro/nano-swimmers is a key element as to achieve high precision motion control in therapeutic applications. Rigid-body kinematics of such robotic systems is dominated by viscous forces. The induced flow field around a two-link swimmer is investigated with a validated computational fluid dynamics (CFD) model. Force-free-swimming constraints are employed in order to simulate motion of bacteria-like swimmers in viscous medium. The fluid resistance exerted on the body of the swimmer is quantified by an improved resistance matrix, which is embedded in a validated resistive force theory (RFT) model, based on complex-impedance approach. Parametric studies confirmed that the hydrodynamic interaction between body and tail are of great importance in predicting the trajectories for such systems

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

Computational and microhydrodynamic modeling and experiments with bio-inspired swimming robots in cylindrical channels

Modeling and control of swimming untethered micro robots are important for future therapeutic medical applications. Bio-inspired propulsion methods emerge as realistic substitutes for hydrodynamic thrust generation in micro realm. Accurate modeling, power supply, and propulsion-means directly affect the mobility and maneuverability of swimming micro robots with helical or planar wave propagation. Flow field around a bio-inspired micro swimmer comprised of a spherical body and a rotating helical tail is studied with time-dependent three-dimensional computational fluid dynamics (CFD) model. Analytical hydrodynamic studies on the bodies of well known geometries submerged in viscous flows reported in literature do not address the effect of hydrodynamic interactions between the body and the tail of the robot in unbounded viscous fluids. Hydrodynamic interactions are explained qualitatively and quantitatively with the help of CFD-model. A cm-scale powered bio-inspired swimmer robot with helical tails is manufactured including a payload and a replaceable rigid helical tail. The payload includes on-board power supply and remote-control circuitry. A number of helical tails with parameterized wave geometry are used. Swimmer performed in cylindrical channels of different diameters while fully submerged in an oil-bath of high viscosity. A real-time six degrees-of-freedom microhydrodynamic model is developed and implemented to predict the rigid-body motion of the swimming robots with helical and traveling-plane-wave tails. Results of microhydrodynamic models with alternative resistance coefficients are compared against CFD simulations and in-channel swimming experiments with different tails. Validated microhydrodynamic model is further employed to study efficient geometric designs with different wave propagation methods within a predefined design space