Electro-kinetically driven peristaltic transport of viscoelastic physiological fluids through a finite length capillary : mathematical modelling

Analytical solutions are developed for the electro-kinetic flow of a viscoelastic biological liquid in a finite length cylindrical capillary geometry under peristaltic waves. The Jefferys’ non-Newtonian constitutive model is employed to characterize rheological properties of the fluid. The unsteady conservation equations for mass and momentum with electro-kinetic and Darcian porous medium drag force terms are reduced to a system of steady linearized conservation equations in an axisymmetric coordinate system. The long wavelength, creeping (low Reynolds number) and Debye–Hückel linearization approximations are utilized. The resulting boundary value problem is shown to be controlled by a number of parameters including the electro-osmotic parameter, Helmholtz-Smoluchowski velocity (maximum electro-osmotic velocity), and Jefferys’ first parameter (ratio of relaxation and retardation time), wave amplitude. The influence of these parameters and also time on axial velocity, pressure difference, maximum volumetric flow rate and streamline distributions (for elucidating trapping phenomena) is visualized graphically and interpreted in detail. Pressure difference magnitudes are enhanced consistently with both increasing electro-osmotic parameter and Helmholtz-Smoluchowski velocity, whereas they are only elevated with increasing Jefferys’ first parameter for positive volumetric flow rates. Maximum time averaged flow rate is enhanced with increasing electro-osmotic parameter, Helmholtz-Smoluchowski velocity and Jefferys’ first parameter. Axial flow is accelerated in the core (plug) region of the conduit with greater values of electro-osmotic parameter and Helmholtz-Smoluchowski velocity whereas it is significantly decelerated with increasing Jefferys’ first parameter. The simulations find applications in electro-osmotic (EO) transport processes in capillary physiology and also bio-inspired EO pump devices in chemical and aerospace engineering

Non-Newtonian Microfluidics

Microfluidics has seen a remarkable growth over recent decades, with its extensive applications in engineering, medicine, biology, chemistry, etc. Many of these real applications of microfluidics involve the handling of complex fluids, such as whole blood, protein solutions, and polymeric solutions, which exhibit non-Newtonian characteristics—specifically viscoelasticity. The elasticity of the non-Newtonian fluids induces intriguing phenomena, such as elastic instability and turbulence, even at extremely low Reynolds numbers. This is the consequence of the nonlinear nature of the rheological constitutive equations. The nonlinear characteristic of non-Newtonian fluids can dramatically change the flow dynamics, and is useful to enhance mixing at the microscale. Electrokinetics in the context of non-Newtonian fluids are also of significant importance, with their potential applications in micromixing enhancement and bio-particles manipulation and separation. In this Special Issue, we welcomed research papers, and review articles related to the applications, fundamentals, design, and the underlying mechanisms of non-Newtonian microfluidics, including discussions, analytical papers, and numerical and/or experimental analyses

SENSORS: Detecting Microbial Pathogens with Novel Surface Acoustic Wave Devices in Liquid Environments

This SENSORS proposal integrates research and education to exploit the sensitivity of a new family of LGX crystal devices operated in novel Shear Horizontal Surface Acoustic Wave (SH-SAW) propagation directions by combining them with highly selective molecular padlock probes to detect specific nucleic acid sequences associated with bacteria such as Escherichia coli O157:H7, Salmonella typhi, and Vibrio cholerae in aqueous solutions. The anticipated fundamental advances in sensor science and engineering will be relevant to numerous applications, including rapid response to bioterrorism, healthcare, epidemiology, agriculture, food safety, and pollution avoidance and mitigation. This SENSORS program builds upon the initial proof-of-concept results provided by an NSF SGER project funded by the divisions of Electrical and Communication Systems, and Bioengineering and Environmental Systems. The intellectual merit of this proposal rests in the creative, integrated research and education activities related to combining the recently identified LGX SH-SAW devices with molecular padlock probe technology to permit the design, fabrication, testing, and optimization of prototype biosensors. The specific research objectives of this SENSORS program are to: (i) Identify the surface density chemistry for increased sensitivity; (ii) Investigate and identify the optimal LGX SH-SAW orientation and device design for operation with the padlock technology; (iii) Study and develop the molecular padlock probe system to operate effectively in conjunction with the LGX SH-SAW device; (iv) Fabricate and test the prototype SH-SAW liquid biosensors; (v) Identify and optimize a procedure for sensor regeneration; and (vi) Characterize and optimize the sensor\u27s dynamic range and cross-effects due to temperature and other physical and chemical factors. The educational objective of this SENSORS program is to provide a multidisciplinary learning experience to students ranging from high school to graduate student level in the area of sensors in general, and biosensors in particular. Broader impacts will be achieved through the following programs and activities to: (i) Train and interact with high school audiences through two major ongoing programs at University of Maine (UMaine), NSF Research Experiences for Teachers (RET) and the GK-12 Sensors; (ii) Involve undergraduates from Maine and other institutions directly into the research project under the umbrella of the ongoing NSF Research Experience for Undergraduates (REU) program at the UMaine; (iii) Expand existing undergraduate Sensor Technology and Instrumentation and Biochemical Engineering Engineering courses at the UMaine by adding modules relating to biosensors devices and systems; (iv) Identify appropriate Capstone projects for undergraduates involving cross-disciplinary research and design projects; (v) Enhance existing graduate level courses Microscale Bioengineering and Design and Fabrication of Acoustic Wave Devices by incorporating research results into the course; (vi) Contribute to the new interdisciplinary multi-institutional NSF Integrative Graduate Education and Research Traineeship (IGERT) program in functional genomics, which involves UMaine, the Jackson Laboratory, and the Maine Medical Center Research Institute; (vi) Provide a experimental and/or theoretical thesis topics for Masters and Ph.D. students; (vii) Disseminate the research and educational material on a project website, and through conferences and printed literature. The SENSORS project proposed here is designed to result in tangible research and educational benefits. It will provide a knowledge base critical to creation of the next generation of biosensors for single unit production and future integration into arrays. It also seeks to establish a model program whereby cross-disciplinary education is integrated with a state-of-the-art research program, providing a rich learning experience for students ranging from high school to graduate student level. Finally, the project will help to strengthen U.S. research and educational capabilities in an area of high technology that currently is in need of highly trained industry and academic professionals

Compact laser-assisted tools for high-resolution additive manufacturing

Micro-additive manufacturing has become an enabling technology in biomedical research as it allows for instance creating functional microstructures or studying cellular interactions at the microscale. Among the various manufacturing techniques laser-actuation offers a versatile control means for microprinting applications since it both enables jetting liquids and curing photoresists to form three-dimensional microstructures. In the first part of this thesis, the potential of laser-actuation for embedded three-dimensional printing was studied. In conventional embedded three-dimensional printing, soft microstructures are built by directly depositing ink filaments with a microextruder into a gel-like support material. As microextruders produce continuous ink filaments, they do not allow optimally mimicking the complex three-dimensional micro-architectures of tissues. Thus, to improve the resolution of three-dimensional embedded printing, laser-induced forward transfer, a high-velocity liquid jetting technique, was employed to achieve depth-controlled liquid delivery within a gel-like support substrate. Interestingly, controlling the deposition depth of liquid droplets adds a degree of freedom to laser-induced forward transfer, turning this conventional two-dimensional patterning technique into a direct three-dimensional printing technique. In the second part of this thesis, the potential of laser-actuation to build a compact laser- assisted toolkit for high-resolution manufacturing was further studied. The fabrication of advanced functional parts with multi-material and multi-resolution features stills remains challenging. Existing microfabrication techniques rely on complex and bulky devices, which prevent processing parts with several manufacturing tools on a single platform due to space constraints. Hence, to enable multiprocess additive manufacturing, miniaturized laser-assisted drop-on-demand and direct writing tools were developed in this thesis. In the first component of this compact toolkit, a laser-induced flow focusing phenomenon was studied to generate viscous micro-droplets through a 300-µm glass microcapillary, thus paving the way for a compact drop-on-demand device operating on a wider range of printable liquids than standard inkjet printers. The second component of the miniaturized toolkit is based on oxygen-inhibited single-photon photopolymerization. This non-linear photopolymerization process was investigated and then implemented through a 70-µm multimode fiber to demonstrate three-dimensional microfabrication through an endoscope-like tool. This curing probe provides a compact and affordable alternative to conventional direct laser writing devices, which rely on two-photon absorption, a non-linear absorption phenomenon that entails using femtosecond lasers. Such a miniature additive manufacturing toolkit could also open up possibilities for the fabrication of microstructures in areas otherwise inaccessible, for instance in in vivo applications

Microfabricated quantum dot linked immuno-diagnostic assay (QLIDA) biosensor with electrothermally accelerated biomolecular binding

Optically transduced microfluidic immunoassays have proven to be a highly sensitive and rapid method to assess the concentrations of analytes in a biological fluid. Although microfluidic immunoassays facilitate higher throughput and automation than standard microtiter plates, the immunoreaction within such devices remains diffusion-limited unless the analyte concentration is high enough to compensate the diffusion limit. We aim to circumvent this issue and accelerate the immunoreaction by developing a microfluidic immunosensor with an integrated set of electrodes to facilitate perpendicular electrothermal flow due to joule heating. In this work, 1) particle behaviors under AC electrohydrodynamic conditions, especially eletrothermal effect (ETE), has been studied, and 2) microfluidic biosensor devices with electrothermal mixing elements have been designed and developed. The Maxwell stress tensor method was used to understand dielectrophoretic particle-particle interactions. We applied the results of this to the interpretation of particle behaviors under dielectrophoresis (DEP) and electrothermal effect (ETE) conditions. Distinct particle behaviors ETE are presented and analyzed. Moreover, diverse particle-particle interactions are observed in experiments. These include particle clustering wherein particles keep a certain distance from each other, chain formation, and disc formation. These behaviors are explained by numerical simulation data (COMSOL Multiphysics v3.5a). After studying fluid motion under AC electrohydrodynamic condition, microelectrodes, the key elements to generate ETE, was integrated into microfluidic immune-biosensor using microfabrication technique. Microfluidic channels serve as solid phase in immunoassay, that were fabricated on inexpensive poly methylmethacrylate (PMMA) sheets by a solvent-based polymer imprinting and binding method. The microfluidic biosensors take advantage of quantum dots (QDs) as fluorescence probes. A low cost UV-LED was used as an excitation source, and data were collected by a CCD camera. Electrothermal effect increases the possibility of antibody-antigen binding by actively transporting analyte to the sensing part. With the enhancement of ETE, the time spent on the core part of immunoassay has been significantly reduced from 3.5 hours to 30 minutes.M.S., Biomedical Engineering -- Drexel University, 201

Nanoliter sample preparation for electron microscopy and single-cell analysis

Proteins belong to the most fascinating macromolecules found in living systems. These natural nanomachines are involved in virtually all biological processes. Among others, they provide mechanical stability, transport molecules, and catalyze countless chemical reactions. This ubiquity also makes them a major drug target. The function of proteins is directly linked to their three-dimensional structure. Hence, high-resolution protein structures are essential for understanding protein function, and they are a fundamental part of structure based drug design. Structure determination has long been dominated by X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy. Until recently, electron microscopy (EM) at cryogenic temperatures (cryo-EM) has played a minor role in high-resolution structure determination due to technical reasons. However, with the advent of direct electron detection cameras, and the ability to record high frame rate movies, instead of single long-exposure images, cryo-EM has quickly caught up and is now recognized as a full-fledged method for structural analysis. In contrast to X-ray crystallography, cryo-EM does not require protein crystals, which are difficult, or sometimes even impossible to grow. On the contrary, cryo-EM allows to image individual protein particles in a nearly physiological, frozen-hydrated environment. And unlike NMR spectroscopy, cryo-EM works well with large protein complexes and requires only a few thousand to million particles to be imaged for structural analysis. This allows, at least theoretically, the structure determination of a protein from extremely low sample volumes. However, EM sample preparation has almost been excluded from the recent advances in the field. It is still dependent on filter paper blotting, a method used to remove excess sample during preparation. This blotting step consumes high amounts of sample, and is often responsible for many problems observed in EM sample preparation, such as reproducibility issues, and loss or degradation of sample. Sample preparation is now widely recognized as the largest remaining bottleneck in the EM structural analysis pipeline. EM is, in principle, a quantitative and highly sensitive method that can detect single particles and provide structural information in parallel. These qualities can be used for approaches other than structure determination, such as single-cell visual proteomics. Visual proteomics aims at spreading the lysate of a single cell on an electron transparent support and imaging it by EM. Visually distinguishable protein particles are then detected and counted. This, however, requires (i) the lossless preparation of single-cell lysate samples, and (ii) the complete imaging of the prepared sample by EM. Such biological experiments with single-cell resolution have become a major field of research. The main reason for single-cell analysis lies in the heterogeneity of cell populations. Due to the stochastic nature of biological processes, seemingly identical cells can develop different phenotypes. Some of these variations can lead to serious disorders. Tumor heterogeneity, for example, is limiting the efficiency of medical treatments. And the selective vulnerability of certain neurons could be the basis of many neurodegenerative diseases. A main goal of this thesis was to extend single-cell analysis to electron microscopy, thus enabling future visual proteomics studies. The major work consisted of developing novel EM sample preparation methods. The focus was laid on minimum sample volume requirements and lossless preparation. Both are a prerequisite for single-cell analysis by electron microscopy. First, a single-cell lysis instrument was built that allowed live-cell imaging and targeted lysis of individual cells from a mammalian tissue culture through a microcapillary electrode. Subsequently, liquid handling was continually improved, until sample volumes as low as three nanoliters could be controlled by the instrument. Such low volumes demanded new approaches for EM sample preparation. Nanoliter sample conditioning inside a microcapillary tip was developed to transport negative stain in, and salt ions out of the sample plug by diffusion. With this method, nanoliter samples of protein particles, protein nanocrystals, and single-cell lysate were successfully prepared for negative stain EM. To benefit from the most recent developments in cryo-EM, including high-resolution imaging, the instrument was further developed to perform cryogenic sample preparation. Therefore, a dew point stage and plunge-freezing mechanism was invented. The invention allowed to control the temperature of the EM grid, to apply a thin sample film, estimate its thickness through an optical detection, and to quickly plunge-freeze the sample for vitrification. A 5 Å structure of the protein urease was solved by collecting a few thousand imaged particles, prepared from 20 nanoliters of sample. The ability to lyse and extract single cells from tissue culture, without diluting the sample more than a thousandfold, created alternative opportunities for single-cell analysis. Arrays of single-cell lysate were deposited on nitrocellulose, forming a miniaturized dot-blot, or reverse-phase protein array experiment. This single-cell microarray technology was further investigated and optimized, and different housekeeping proteins were detected at single-cell level. At last, single-cell sampling was interfaced with liquid chromatography-mass spectrometry (LC-MS) to explore the potential for single-cell metabolite analysis. Therefore, arrays of nanoliter-sized sample spots were applied to plastic slides. These slides served as carriers to transfer the samples to the MS facility, where a thin-film chromatography device was used to elute the dried sample spots from the carrier surface and introduce them into the LC-MS instrument. Proof-of-concept experiments compared this new method with conventional sample injection and validated its usability