Numerical modeling and experimental validation of passive microfluidic mixer designs for biological applications

The present work reports numerical simulation and experimental validation of novel designs of microfluidic mixers that can be employed for biological mixing applications. Numerical simulations involving various geometrical models were performed for design optimization. The effect of the presence of embedded obstacles was studied in detail, in order to understand the effect of channel occlusion on micromixing. The mixing performance of various channel designs was compared, and crossover in the mixing performance of the designs was observed in response to a change in the flow Reynolds number (Re). The improvement in micromixing efficiency was discussed in connection with the variations in local values of the Reynolds number and Dean number. It was observed that the presence of obstacles contributes to a significant increase in local Re in the vicinity of sharp-edged obstacles, thereby enhancing the efficiency of mixing. In addition, the local Dean number is observed to increase significantly inside spiral microfluidic designs. We validate the optimized microfluidic mixer designs by performing micromixing experiments and image analysis based on regions of interest along the length of the channels. Numerical predictions were observed to be in reasonable agreement with experimental results. Finally, we demonstrated the biological applicability of an optimized micromixer design for on-chip detection of calcium levels in blood serum. The passive mixing designs presented in this work are useful for chip-scale implementations of cell-drug biology, where some of the key cell signaling processes appear at second time scales

Transport and deposition of colloidal particles in microchannel flow

194 p.The emergence of Lab-on-a-Chip technologies has instilled an ever-growing interest in the design and analysis of microfluidic systems. During biochemical analyses involving microfluidic devices, particle deposition (surface fouling) can sometimes cause hindrance to the optical detection of the test particles. Also, when the particles and channels are of comparable size, the boundary effects on particle motion become significant. Even though many previous studies have been devoted to understanding particle deposition from pressure driven flows, limited efforts seem to have appeared in the modeling of transport, interaction and deposition of colloidal particles from electrokinetic flows. Hence, this dissertation is in pursuit to investigate the transport and deposition of colloidal particles from pressure driven and electrokinetic microfluidic flows, both theoretically and experimentally, with the objective of establishing the fundamental understanding of particle behavior in these flows, which could serve as useful input to the design and operation of microfluidic devices.DOCTOR OF PHILOSOPHY (MAE

Paper-based microfluidic platforms for osteoporosis diagnosis

We report a low-cost paper-based diagnostic device (Microfluidic paper based analytic device or muPAD) for diagnosing the biochemical risk factors associated with the onset of Osteoporosis. Photolithography is used to pattern the paper with hydrophilic channels and hydrophobic walls. Briefly, the analytes (serum Calcium and Alkaline Phosphatase) are measured by placing a drop of blood on the sample zone in the device. The serum flows to the test zones containing the immobilized reagents and produces a color reaction. The responses are then compared with the controls and the shift in analyte values from normal indicate normal or diseased state

Microfluidic design of tumor vasculature and nanoparticle uptake by cancer cells

The most challenging phase in the clinical translation of drugs is the complex process of screening various drugs and evaluating their therapeutic effects in vitro and in vivo. Microfluidic models have been recognized as an interesting alternative to animal models for drug screening. Enhanced permeation and retention (EPR) effect is one of the most widely used standard for drug delivery in solid tumors with high vascular density and active angiogenesis. The nascent blood vessels in the tumor vicinity have large gaps between the endothelial junctions which allow nanoparticles to pass through them, resulting in selective extravasation and passive accumulation in the tumor regions. In this study, an attempt has been made to mimic some of the physiological characteristics in solid tumors such as endothelial gap junctions, obstructed blood vessels and EPR using a microfluidic platform for drug screening under dynamic culture conditions. The microfluidic chip was fabricated using soft lithography technique. Numerical simulations were performed to analyze the flow patterns inside the chip. Fluorescent gold nanoclusters (Au NCs) were synthesized and their accumulation in the tumor cells cultured inside the microfluidic chip was studied. The experimental results showed an increased uptake of Au NCs in the cells near the endothelial gap junctions in comparison to the cells away from the junctions. The observations in the study correlated with the leaky nature of the tumor vasculature, owing to the enhancement of vascularization and thereby EPR effect. Hence, the fabricated microfluidic device has the potential of minimizing the number of pre-clinical trials using animal models, allowing easier drug screening

Microfluidic Protein Imaging Platform: Study of Tau Protein Aggregation and Alzheimer’s Drug Response

Tau protein aggregation is identified as one of the key phenomena associated with the onset and progression of Alzheimer’s disease. In the present study, we performed on-chip confocal imaging of tau protein aggregation and tau–drug interactions using a spiral-shaped passive micromixing platform. Numerical simulations and experiments were performed in order to validate the performance of the micromixer design. We performed molecular modeling of adenosine triphosphate (ATP)-induced tau aggregation in order to successfully validate the concept of helical tau filament formation. Tau aggregation and native tau restoration were realized using an immunofluorescence antibody assay. The dose–response behavior of an Alzheimer’s drug, methylthioninium chloride (MTC), was monitored on-chip for defining the optimum concentration of the drug. The proposed device was tested for reliability and repeatability of on-chip tau imaging. The amount of the tau protein sample used in our experiments was significantly less than the usage for conventional techniques, and the whole protein–drug assay was realized in less than two hours. We identified that intensity-based tau imaging could be used to study Alzheimer’s drug response. In addition, it was demonstrated that cell-free, microfluidic tau protein assays could be used as potential on-chip drug evaluation tools for Alzheimer’s disease

Characterization and separation of Cryptosporidium and Giardia cells using on-chip dielectrophoresis

Dielectrophoresis (DEP) has been shown to have significant potential for the characterization of cells and could become an efficient tool for rapid identification and assessment of microorganisms. The present work is focused on the trapping, characterization, and separation of two species of Cryptosporidium (C. parvum and C. muris) and Giardia lambia (G. lambia) using a microfluidic experimental setup. Cryptosporidium oocysts, which are 2-4 μm in size and nearly spherical in shape, are used for the preliminary stage of prototype development and testing. G. lambia cysts are 8–12 μm in size. In order to facilitate effective trapping, simulations were performed to study the effects of buffer conductivity and applied voltage on the flow and cell transport inside the DEP chip. Microscopic experiments were performed using the fabricated device and the real part of Clausius—Mossotti factor of the cells was estimated from critical voltages for particle trapping at the electrodes under steady fluid flow. The dielectric properties of the cell compartments (cytoplasm and membrane) were calculated based on a single shell model of the cells. The separation of C. muris and G. lambia is achieved successfully at a frequency of 10 MHz and a voltage of 3 Vpp (peak to peak voltage)