Electro-magneto-hydrodynamic peristaltic pumping of couple stress biofluids through a complex wavy micro-channel

Biomimetic propulsion mechanisms are increasingly being explored in engineering sciences. Peristalsis is one of the most efficient of these mechanisms and offers considerable promise in microscale fluidics. Electrokinetic peristalsis has recently also stimulated significant attention. Electrical and magnetic fields also offer an excellent mode for regulating flows. Motivated by novel applications in electro-conductive microchannel transport systems, the current article investigates analytically the electromagnetic pumping of non-Newtonian aqueous electrolytes via peristaltic waves in a two-dimensional microchannel with different peristaltic waves propagating at the upper and lower channel wall (complex wavy scenario). The Stokes couple stress model is deployed to capture micro-structural characteristics of real working fluids. The unsteady two-dimensional conservation equations for mass and momentum conservation, electro-kinetic and magnetic body forces, are formulated in two-dimensional Cartesian co-ordinates. The transport equations are transformed from the wave frame to the laboratory frame and the electrical field terms rendered into electrical potential terms via the Poisson-Boltzmann equation, Debye length approximation and ionic Nernst Planck equation. The dimensionless emerging linearized electro-magnetic boundary value problem is solved using integral methods. The influence of Helmholtz-Smoluchowski velocity (characteristic electro-osmotic velocity), couple stress length parameter (measure of the polarity of the fluid), Hartmann magnetic number, and electro-osmotic parameter on axial velocity, volumetric flow rate, time-averaged flow rate and streamline distribution are visualized and interpreted at length

A Controllable Flexible Micropump and a Semi-Active Vibration Absorber Using Magnetorheological Elastomers

This study is focused on magneto-fluid-solid interaction analysis of a soft magnetorheological elastomer (MRE) controllable flexible micropump. In addition, material characterizations of MRE, modeling, fabrication and testing of a MRE-based vibration absorber system are investigated.Theoretical modeling and analysis of a controllable flexible magnetically-actuated fluid transport system (CFMFTS) is presented. For the first time, soft magnetorheological elastomer (MRE) is proposed as an actuation element in a fluid transport system (micropump). The flexible micropump can propel fluid under a fluctuating magnetic field. Magnetic-fluid-solid interaction analysis is performed to determine deflection in the solid domain and velocity of the fluid under a magnetic field. The effects of key material and geometric system parameters are examined on the micropump performance. Two- and three-dimensional analyses are performed to model the asymmetric deflection of the channel under a magnetic field. It is successfully demonstrated that the proposed system can propel the fluid in one direction.In addition, a novel semi-active variable stiffness and damping absorber (VSDA) is modeled, built and tested. Magnetically induced mechanical properties of MRE and their controllability are investigated by quasi-static and dynamic experiments. The VSDA is modeled, using springs, dashpots and the Bouc-Wen hysteresis element, fabricated and implemented in a scaled building to assess performance. Experiments are performed on a single VSDA, integrated system of four VSDAs, and a scaled building supported by four VSDAs. To demonstrate feasibility, a scaled, two-story building is constructed and installed on a shake table supported by four prototype VSDAs. The properties of VSDAs are regulated in real time by varying the applied magnetic field through the controller. A scaled earthquake excitation is applied to the system, and the vibration mode is controlled by a Lyapunov-based control strategy. The control system is used to control displacement and acceleration of the floors. Results demonstrate that the proposed VSDA significantly reduces acceleration and relative displacement of the structure

Microfluidic Mixing: A Review

The aim of microfluidic mixing is to achieve a thorough and rapid mixing of multiple samples in microscale devices. In such devices, sample mixing is essentially achieved by enhancing the diffusion effect between the different species flows. Broadly speaking, microfluidic mixing schemes can be categorized as either “active”, where an external energy force is applied to perturb the sample species, or “passive”, where the contact area and contact time of the species samples are increased through specially-designed microchannel configurations. Many mixers have been proposed to facilitate this task over the past 10 years. Accordingly, this paper commences by providing a high level overview of the field of microfluidic mixing devices before describing some of the more significant proposals for active and passive mixers

Microfluidic systems based on electroactive polymers technology

Dielectric elastomer actuators (DEAs) have been widely investigated for more than 30 years. Lately, several fabrication methods have successfully allowed the creation of very thin elastomer and electrode layers. The development of attractive applications, in which DEAs offer advantages over conventional technologies, is thus necessary for the advance of the technology. In this work, new biocompatible microfluidic devices based on DEAs are developed. In the first part of this thesis, several prototypes of peristaltic pumps of single layer dielectric elastomer actuators are designed, manufactured and characterized. Although these prototypes were not able to produce fluid flow, novel insights into the capabilities of Electroactive Polymer technology were gained. In the second part of this work, a pumping micromixer as a novel application of dielectric elastomer stacked actuators is manufactured. The pumping micromixer is based on peristaltic movements, which gently act as a mixer and a pump for microfluidics. Experimental data show a maximal flow rate of 21.5 µL/min at 10 Hz. Image analysis at the outlet proves a 50/50 mixing when all actuators are functioning at the same pace and voltage. The performance of the pumping micromixer is further studied with the Finite Element Method, using the COMSOL Multiphysics® software. Simulations demonstrate the versatility of the pumping characteristics of such a microdevice, from very few µL/min to mL/min, and from a very low pressure in the range of Pa to hundreds of kPa, by only changing the duty cycle, phase shift and actuation frequency

A Novel Propeller Design for Micro-Swimming robot

The applications of a micro-swimming robot such as minimally invasive surgery, liquid pipeline robot etc. are widespread in recent years. The potential application fields are so inspiring, and it is becoming more and more achievable with the development of microbiology and Micro-Electro-Mechanical Systems (MEMS). The aim of this study is to improve the performance of micro-swimming robot through redesign the structure. To achieve the aim, this study reviewed all of the modelling methods of low Reynolds number flow including Resistive-force Theory (RFT), Slender Body Theory (SBT), and Immersed Boundary Method (IBM) etc. The swimming model with these methods has been analysed. Various aspects e.g. hydrodynamic interaction, design, development, optimisation and numerical methods from the previous researches have been studied. Based on the previous design of helix propeller for micro-swimmer, this study has proposed a novel propeller design for a micro-swimming robot which can improve the velocity with simplified propulsion structure. This design has adapted the coaxial symmetric double helix to improve the performance of propulsion and to increase stability. The central lines of two helical tails overlap completely to form a double helix structure, and its tail radial force is balanced with the same direction and can produce a stable axial motion. The verification of this design is conducted using two case studies. The first one is a pipe inspection robot which is in mm scale and swims in high viscosity flow that satisfies the low Reynolds number flow condition. Both simulation and experiment analysis are conducted for this case study. A cross-development method is adopted for the simulation analysis and prototype development. The experiment conditions are set up based on the simulation conditions. The conclusion from the analysis of simulation results gives suggestions to improve design and fabrication for the prototype. Some five revisions of simulation and four revisions of the prototype have been completed. The second case study is the human blood vessel robot. For the limitations of fabrication technology, only simulation is conducted, and the result is compared with previous researches. The results show that the proposed propeller design can improve velocity performance significantly. The main outcomes of this study are the design of a micro-swimming robot with higher velocity performance and the validation from both simulation and experiment

Proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress

Published proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress, hosted by York University, 27-30 May 2018

The Fluid Dynamics of Heart Development: The effect of morphology on flow at several stages

Proper cardiogenesis requires a delicate balance between genetic and environmental (epigenetic) signals, and mechanical forces. While many cellular biologists and geneticists have extensively studied heart morphogenesis using various experimental techniques, only a few scientists have begun using mathematical modeling as a tool for studying cardiogenic events. Hemodynamic processes, such as vortex formation, are important in the generation of shear at the endothelial surface layer and strains at the epithelial layer, which aid in proper morphology and functionality. The purpose of this thesis is to study the underlying fluid dynamics in various stages on heart development, in particular, the morphogenic stages when the heart is a linear heart tube as well as during the onset of ventricular trabeculation. Previous mathematical models of the linear heart tube stage have focused on mechanisms of valveless pumping, whether dynamic suction pumping (impedance pumping) or peristalsis; however, they all have neglected hematocrit. The impact of blood cells was examined by fluid-structure interaction simulations, via the immersed boundary method. Moreover, electrophysiology models were incorporated into an immersed boundary framework, and bifurcations within the morphospace were studied that give rise to a spectrum of pumping regimes, with peristaltic-like waves of contraction and impedance pumping at the extremes. Lastly, effects of resonant pumping, damping, and boundary inertial effects (added mass) were studied for dynamic suction pumping. The other stage of heart development considered here is during the onset of ventricular trabeculation. This occurs after the heart has undergone the cardiac looping stage and now is a multi-chambered pumping system with primitive endocardial cushions, which act as precursors to valve leaflets. Trabeculation introduces complex morphology onto the inner lining of the endocardium in the ventricle. This transition of a smooth endocardium to one with complex geometry, may have significant effect on the intracardial fluid dynamics and stress distribution within emrbyonic hearts. Previous studies have not included these geometric perturbations along the ventricular endocardium. The role of trabeculae on intracardial (and intertrabecular) flows was studied using two different mathematical models implemented within an immersed boundary framework. It is shown that the trabecular geometry and number density have a significant effect on such flows. Furthermore this thesis also focused attention to the creation of software for scientists and engineers to perform fluid-structure interaction simulations at an accelerated rate, in user-friendly environments for beginner programmers, e.g., MATLAB or Python 3.5. The software, IB2d, performs fully coupled fluid-structure interaction problems using Charles Peskin's immersed boundary method. IB2d is capable of running a vast range of biomechanics models and contains multiple options for constructing material properties of the fiber structure, advection-diffusion of a chemical gradient, muscle mechanics models, Boussinesq approximations, and artificial forcing to drive boundaries with a preferred motion. The software currently contains over 50 examples, ranging from rubber-bands oscillating to flow past a cylinder to a simple aneurysm model to falling spheres in a chemical gradient to jellyfish locomotion to a heart tube pumping coupled with electrophysiology, muscle, and calcium dynamics modelsDoctor of Philosoph

Fluid Mixing Online and In Microdevices

Microfluidics and polymer MEMS are the most promising technologies to realize biochemical analysis systems on a chip with low cost, tiny fluid sample, fast chemical/biochemical reaction, and high detection accuracy capabilities. Sample processing, chemical/biochemical reaction, and sample detection are considered as the three major tasks required for lab-on-a-chips. Micropumps, microvalves and micromixers are also considered as key components in handling microfluidics in the lab- on-a-chips. There have been numerous efforts to develop on-chip active micropumps and microvalves. However, the realization of active microfluidic components in an on-chip disposable platform has been considered as one of the most difficult tasks in terms of fabrication, system integration, reliability, and cost. Consequently, the development of passive microfluidic components is a good alternative to the active components if they can provide the same level of functionality. In this research, passive mixing using geometric and initial conditions variations in microchannels were studied due to its advantages over active mixing in terms of simplicity and ease of fabrication. Because of the nature of laminar flow in a microchannel, the geometric variations were designed to improve lateral convection to increase cross-stream diffusion. Previous research using this approach was limited, and a detailed research program using computational fluid dynamic (CFD) solvers, various shapes, sizes and layouts of geometric structures was undertaken for the first time. Mixing efficiency was evaluated by using mass fraction distributions. Different types of geometric and initial conditions variations were researched. First, Structures were used to investigate the effect channel geometry on fluid mixing and flow patterns. Secondly, we applied different initial velocity in each inlet to see the effect of Reynolds number applied on mixing behavior. Third, we applied different kind of fluid in each inlet to visualize the effect of viscosity and finally we create new split and stair geometries to enhance the mixing efficiency

Droplet motion on miniaturized ratchets

The main objective of this study is to evaluate the feasibility of using miniaturized asymmetric structures to move liquid droplets and understand the driving mechanism. We developed the fabrication process for large area topological ratchets with the period ranging from millimeter down to sub-micrometer using micromachining techniques. Non-wetting superhydrophobic surfaces were successfully fabricated using soft UV or thermal nanoimprint lithography, reactive ion etching by oxygen plasma, and chemical surface modification by fluorinated silane vapor deposition. An accurate and reproducible experimental setup equipped with high speed camera and automatic injection system was established. Image processing tools allowed us to obtain various critical information related droplet motion and behavior along the ratchets surface. Various influences on the motion such as the surface temperature, ratchets dimension, surface wettability, droplet volume, kind of liquid, initial impact speed of droplet, polymer additive, and surface slope were systematically investigated for miniaturized non-wetting asymmetric ratchets. It is observed that the droplet motion on the ratchets is strongly dependent on the ratchets dimensions as well as the surface temperature. Extremely fast water droplet motion was achieved from the sub-micrometer ratchets near the Leidenfrost temperature. Even though the Leidenfrost-miniaturized ratchets system can be considered as an efficient pumping and cooling component, further intensive study to reduce the operating temperature and drive the liquid motion within microchannel is required for the broad range of applications