Sharif Digital Repository

Microfluidic is a science and technology in which they study the behavior of fluids, control them and design devices or systems with dimensions of tens to hundreds of micrometers. The technology has the ability to design and manufacture macro-scale and micro-scale equipment, such as micro-pumps, micro-valves, micro-filters, micro-mixers, micro-reactors, and other equipment. The benefits of this technology include the use of low sample size, low waste of energy, low power consumption, short response time, high system performance, portability and performance of several operating phases in a compressed piece such as production, isolation and analysis. Also, the very low amount of chemicals and... 

The advent of microfluidics as suitable environments for culturing cells is associated with some challenges such as shear stresses applied on the cells. In fact, hepatocytes lose their function as exposed to high shear stresses similar to other cell types. Moreover, among all factors needed for cell viability, feeding hepatocytes with adequate oxygen is of great importance due to their high demand for oxygen compared the other cells. In this thesis, different types of cultures including 2D and 3D has been used in order that shear stresses would be in allowed range and provision of hepatocytes with sufficient oxygen concentrations has been ensured as well. In addition to supplying hepatocytes... 

Lab-on-a-chip devices have gained a lot of attention in chemical and biomedical analyses during the past two decades. These devices employ microfluidics basics and fundamentals to combine multifold laboratory processes in one single portable chip. The electric field has been often used in most microfluidics applications for the ease of sample control as well as become easily integrated to other chip components. Instabilities in microflows would occur when two fluids of different electric properties are exposed to an adequately strong electric field. Studying these electrokinetic instabilities is not only important for the fundamental studies but also for practical applications in micromixers... 

Due to the increasing need of use of drugs and insufficient efficiency of conventional methods, drug delivery systems has gathered a lot of interests. There are different systems existing for controlled drug delivery, among which is implementation of hydrogel microparticles (microgels) as carriers with high potential. The most important factor in these systems is size distribution of drug-carrying microgels and a narrow size distribution leads to a controlled and suitable release. Due to unique characteristics of microfluidic systems, significant focus has been placed on them nowadays for production of microgels with suitable morphology and narrow size distribution. Therefore, in this study... 

The main goals of this research are design, simulation, and fabrication of a microfluidic system working based on dielectrophoresis. This research divided into two different parts, the first of which is the simulation of a microfluidic system, and second of which is an attempt for fabrication of microfluidic system. For the fabrication of the microfluidic system, different methods were used. In the simulation part, the enrichment of different particles was investigated, and the effects of different parameters on the enrichment were assessed. It was observed that as flow rate increases, the enrichment amount diminishes. Furthermore, as the microfluidic depth decreases, the enrichment amount... 

Recent developments in MEMS related areas have increased the demand for practical and novel pumping methods. Utilizing Electroosmotic force for flow generation in microchannels has become really popular recently, because of its reliable operation and control. One of potential applications of MEMS devices is biological and medical analysis which most samples are considered to be non-Newtonian; consequently, thermal transport characteristics of non-Newtonian electroosmotic flow of power-law fluids is investigated in this paper. In this study, thermal and hydrodynamic behavior of non-Newtonian electroosmotic flow of power-law model in a slit microchannel is analyzed. It is assumed that the flow... 

Electroosmosis is the predominant mechanism for flow generation in lab-on-a-chip devices. These microfluidic devices are microscale laboratories on a microchip that can perform clinical diagnoses. Since most biofluids encountered in these devices are considered to be non-Newtonian and the cross section of microchannels in these devices is close to a rectangular shape, In this study, the hydrodynamically and thermally fully developed combined electroosmotically and pressure driven flow of power-law fluids in rectangular microchannels is analyzed. The governing equations are first made dimensionless and then transformed into new ones based on the computational parameters which provide mesh... 

The lab-on-a-chip (LOC) devices utilizing electroosmosis for flow actuation are usually encountered with non-Newtonian behavior of working fluids. Hence, studying the flow of non-Newtonian fluids under an electroosmotic body force is of high importance for accurate design and active control of these devices. In this thesis, mixed electroosmotically and pressure driven flow of salivathrough a rectangular microchannel is examined utilizing two viscoelastic constitutive equations, namely PTT and FENE-P models. Since the hydrodynamic entry length is usually negligible for microflows, a hydrodynamically developed flow is considered in the analysis. The governing equations in dimensionless form... 

Microfluidics, employing fluids in structures with micrometer dimensions, is an emerging technology that has brought great opportunities to develop various devices including lab-on-a-chip systems. Lab-on-a-chip systems have the advantages of integrating several stages of different analytical methods, application in diverse fields, consumption of small volumes of samples, and portability. One of the crucial applications of lab-on-a-chip devices is sorting cells and biological particles, done by different methods. In separator devices, high separation efficiency and repeatability are critical. When a neutral particle is polarized in a non-uniform electric field, the dielectrophoresis force... 

Nowadays, microfluidic flow appears in many applications, such as medical, biological, and chemical industries. Where as, micromixing, which deals with mixing of microfluidic flow in micro channels, appears to be an important issue to many researchers. In such systems, molecular diffusion plays an important role. On the other hand, lattice Boltzmann method is a relatively new simulation technique for complex fluid systems and has become interesting to many researchers in computational physics. In this study, computational simulation of such mixing process, using LBM is the main objective. Different obstacle layouts inside a microchannel have been investigated. Chaotic advection and jet... 

Dissemination of an analyte under the laminar flows plays a major role in measuring and assessment of biological fluids such as sample preparation in the context of microfluidic systems. Due to the development of manufacturing technology in the Lab-on-a-chip devices, the production of rectangular microchannels with finite aspect ratios and micron and submicron sizes has been provided by which the effect of electrokinetic phenomena on concentration distribution will be magnified in these systems. On the other hand, these biofluids are viscoelastic and show extraordinary flow behaviors, not existing in Newtonian fluids and adopting appropriate constitutive equations these exotic flow behaviors... 

Continuous separation processes in microfluidic devices experienced a steep rise in attention during the last two decades. Among the different separation processes, liquid-liquid extraction especially benefits from the short molecular diffusion distance and large specific interfacial area, as these are advantageous for effective mass transport. In the present study, glass-based microfluidic devices have been fabricated utilizing laser ablation and wet chemical etching methods then experiments and numerical simulation were carried out to investigate hydrodynamic behavior of fluid flow in Y-junction microfluidic. In order to achieve phase separation at the end of the microchannel, a phase... 

Diabetes is one of the most catastrophic diseases in the world. There will be an end to patients’ problems if scientists can invent the artificial pancreas, but there is no implantable sensing core available. All of the sensors used for measuring blood glucose level were based on an electrochemical sensor which will generate a glucose level dependent electric current. The chemical structure of that sensor will deny its usability for in vivo applications. By exploring several biological and electrical literatures we introduced a fully electrical method for sensing the blood glucose level by impedance measurement. In this thesis we introduced a new method for sensing the blood glucose... 

Circulating tumor cells (CTCs) are cancer cells which shed from the primary tumor, enter circulation and spread cancer all over the body. CTCs give valuable information about cancer and can help diagnosis and prognosis. Hence separating and isolating CTCs from blood is a necessity for cancer therapeutics. CTCs are separated from blood cells by their different physical or biochemical properties. Many groups have attempted different methods for separation of CTCs. Inertial microfluidics is one of the newest approaches in CTC separation technologies which separates CTCs based on their size. Current inertial microfluidic systems containing straight, spiral, serpentine and contraction expansion... 

The first attempt of this study was theoretical and experimental investigations of bioelectrochemical processes in microfluidic systems. Besides, novel applications of this technology as a powerful platform for maximum usage of bioenergy were introduced. The feasibility of a microfluidic microbial fuel cell (MFC) as an efficient power generator for production of bioelectricity for implantable medical devices (IMDs) and fabrication of microfluidic microbial electrolysis cell (MEC) for hydrogen medicine were investigated. For the glucose-fed microfluidic MFC, the maximum power density of 5.2 µW cm-2 obtained in this study is 13 fold greater than the power density reported previously for... 

All the biological diagnostic devices that are introduced to the consumers, must meet WHO criteria. Some of these criteria include being affordable, sensitive and deliverable to the user. In the last twenty years, there have been lots of efforts to use microfluidic devices for biological assay. Due to their expensive price and requirement of complex equipment for their fabrication, polymer-based microfluidic devices have not been able to be used in developing countries. It is to be hoped that introduction of paper for fabrication of microfluidic devices could make microfluidic devices meet WHO criteria. μPADs are divided into well-based and channel-based devices. In the present work, both... 

Recent advances in micro-technology are finding important applications especially in chemical and biological processes. In these applications, mixing has a profound importance. Due to the inherent low Reynold’s number flow in micro systems, diffusion mixing is the dominant mixing mechanism at these scales. This is in contrary to the high Reynold’s number ordinary applications where turbulent mixing plays the major role. There are two major classes of micro-mixers: passive and active. Passive micro-mixers rely on geometric features to enhance mixing. Active micro-mixers on the other hand, use external excitation to promote and control the rate of mixing. In this work, using numerical tools,... 

The accurate assessment of biomarkers likes proteins, hormones or other biomolecules that amount of them changes with state of disease or level of treatment and gives diagnostic information is a difficult duty. In these samples, pathogens exist in small quantity compared to other background molecules. Therefore, appropriate sampling process for concentrating and separating pathogens from the matrix should be developed in order to provide rapid and accurate pathogen detection test. In this thesis design and fabrication of microfluidic biosensors based on the modified nanofibrous membranes were investigated and explained. PES nanofibrous membrane with carboxyl functional groups for covalent... 

Microfluidics is a novel technology that brought a revolution in the field of chemistry and biology. This technology allows precise control and manipulation of fluids and particles in sub-millimeter bio-compatible channels. This makes microfluidics a powerful tool to study and examine bio-particles and bio-processes. One of the most prominent areas in microfluidics is the integration of developed measurement tools and devices of the electrical engineering field, with microfluidic chips. The purpose of this thesis is to measure the electrical impedance spectrum of bio-particles with high precision and in a wide bandwidth. These valuable spectrums are useful in many applications such as... 

The main purposes of this project are simulation, design, and fabrication of a microfluidic system based on dielectrophoresis (DEP) exploiting AC voltages for separation of microparticles. Generally, this project can be divided into two parts. First, the engineering section including design and fabrication of microchip, and second biological samples preparation for investigating the system performance. The main advantages of proposed system are eliminating joule heating, a significant problem in insulating based dielectrophoresis systems, overcoming problems related to metal contamination in biological samples, the main problem of conventional dielectrophoresis platforms, and removing...