Monolithic integration of fine cylindrical glass microcapillaries on silicon for electrophoretic separation of biomolecules.
ABSTRACT: We demonstrate monolithic integration of fine cylindrical glass microcapillaries (diameter ∼1 μm) on silicon and evaluate their performance for electrophoretic separation of biomolecules. Such microcapillaries are achieved through thermal reflow of a glass layer on microstructured silicon whereby slender voids are moulded into cylindrical tubes. The process allows self-enclosed microcapillaries with a uniform profile. A simplified method is also described to integrate the microcapillaries with a sample-injection cross without the requirement of glass etching. The 10-mm-long microcapillaries sustain field intensities up to 90 kV/m and limit the temperature excursions due to Joule heating to a few degrees Celsius only.
Project description:We demonstrate a new method of fabricating in-plane cylindrical glass nanocapillaries (<100 nm) that does not require advanced patterning techniques but the standard coarse photolithography (>1 μm). These nanocapillaries are self-enclosed optically transparent and highly regular over large areas. Our method involves structuring μm-scale rectangular trenches in silicon, sealing the trenches into enclosed triangular channels by depositing phosphosilicate glass, and then transforming the channels into cylindrical capillaries through shape transformation by the reflow of annealed glass layer. Extended anneal has the structures shrunk into nanocapillaries preserving their cylindrical shape. Nanocapillaries ∼50 nm in diameter and effective stretching of digested λ-phage DNA in them are demonstrated.
Project description:The confined flow of red blood cells (RBCs) in microvasculature is essential for oxygen delivery to body tissues and has been extensively investigated in the literature, both in vivo and in vitro. One of the main problems still open in microcirculation is that flow resistance in microcapillaries in vivo is higher than that in vitro. This discrepancy has been attributed to the glycocalyx, a macromolecular layer lining the inner walls of vessels in vivo, but no direct experimental evidence of this hypothesis has been provided so far. Here, we investigate the flow behavior of RBCs in glass microcapillaries coated with a polymer brush (referred to as "hairy" microcapillaries as opposed to "bare" ones with no coating), an experimental model system of the glycocalyx. By high-speed microscopy imaging and image analysis, a velocity reduction of RBCs flowing in hairy microcapillaries as compared to bare ones is indeed found at the same pressure drop. Interestingly, such slowing down is larger than expected from lumen reduction due to the polymer brush and displays an on-off trend with a threshold around 70 nm of polymer brush dry thickness. Above this threshold, the presence of the polymer brush is associated with an increased RBC deformation, and RBC velocity is independent on polymer brush thickness (at the same pressure drop). In conclusion, this work provides direct support to the hypothesis that the glycocalyx is the main factor responsible of the higher flow resistance found in microcapillaries in vivo.
Project description:Phosphorous donors in silicon have an electronic structure that mimics the hydrogen atom, albeit on a larger length, smaller energy and smaller magnetic field scale. While the hydrogen atom is spherically symmetric, an applied magnetic field imposes cylindrical symmetry, and the solid-state analogue involves, in addition, the symmetry of the Si crystal. For one magnetic field direction, all six conduction-band valleys of Si:P become equivalent. New experimental data to high laboratory fields (30 T), supported by new calculations, demonstrate that this high symmetry field orientation allows the most direct comparison with free hydrogen.
Project description:We report on reversible electroporation of cells in a flow-through microfluidic device, whereby the required electric field is delivered through a set of integrated microcapillaries between a centre stream of cells and side streams of liquid electrolytes. The electrolytes are applied with a sine wave voltage and cells flow by the microcapillary openings encounter a burst of ac field with a duration and strength determined by their average speed and spatial proximity to the microcapillary openings, respectively. Effectiveness of the approach is presented through numerical simulations and empirical results on electroporation efficiency and cell viability against various flow rates (exposure time to the field) as well as frequencies and root-mean-square (rms) intensities of the field. High frequencies (80-400 kHz) and high intensities (e.g., 1.6 kV/cm, rms) are identified with increased electroporation efficiency 61% and viability 86% on average. These results suggest that the device demonstrated here with a simple design and robust operation offers a viable platform for flow-through electroporation.
Project description:We previously discovered a novel method for the preparation of polymer particles that have a cylindrical shape. Polystyrene (PS) or poly methyl methacrylate (PMMA) spherical particles were deformed into a cylindrical shape by stirring with a magnetic stirrer in a polyvinylpyrrolidone (PVP) aqueous solution. In this study, cylindrical "Janus" particles consisting of PS and PMMA were prepared by this stirring method. In the case of spherical Janus particles, cylindrical particles were obtained after stirring; however, the direction of the interface between the PS and PMMA phases was random. However, in the case of snowman-like Janus particles, cylindrical Janus particles with the interface at the center of the long axis were successfully prepared. This indicated that the extension direction can be controlled owing to the anisotropic shape and supported the proposed deformation mechanism of the cylindrical particles. Moreover, amphiphilic cylindrical Janus particles were also successfully prepared by hydrolysis of only one phase to introduce carboxy groups.
Project description:Antimicrobial peptides (AMPs) are small, usually cationic peptides, which permeabilize biological membranes. Their mechanism of action is still not well understood. Here we investigate the preference of alamethicin and melittin for pores of different shapes, using molecular dynamics (MD) simulations of the peptides in pre-formed toroidal and cylindrical pores. When an alamethicin hexamer is initially embedded in a cylindrical pore, at the end of the simulation the pore remains cylindrical or closes if glutamines in the N-termini are not located within the pore. On the other hand, when a melittin tetramer is embedded in toroidal pore or in a cylindrical pore, at the end of the simulation the pore is lined both with peptides and lipid headgroups, and, thus, can be classified as a toroidal pore. These observations agree with the prevailing views that alamethicin forms barrel-stave pores whereas melittin forms toroidal pores. Both alamethicin and melittin form amphiphilic helices in the presence of membranes, but their net charge differs; at pH approximately 7, the net charge of alamethicin is -1 whereas that of melittin is +5. This gives rise to stronger electrostatic interactions of melittin with membranes than those of alamethicin. The melittin tetramer interacts more strongly with lipids in the toroidal pore than in the cylindrical one, due to more favorable electrostatic interactions.
Project description:We use template stripping to integrate metallic nanostructures onto flexible, stretchable, and rollable substrates. Using this approach, high-quality patterned metals that are replicated from reusable silicon templates can be directly transferred to polydimethylsiloxane (PDMS) substrates. First we produce stretchable gold nanohole arrays and show that their optical transmission spectra can be modulated by mechanical stretching. Next we fabricate stretchable arrays of gold pyramids and demonstrate a modulation of the wavelength of light resonantly scattered from the tip of the pyramid by stretching the underlying PDMS film. The use of a flexible transfer layer also enables template stripping using a cylindrical roller as a substrate. As an example, we demonstrate roller template stripping of metallic nanoholes, nanodisks, wires, and pyramids onto the cylindrical surface of a glass rod lens. These nonplanar metallic structures produced via template stripping with flexible and stretchable films can facilitate many applications in sensing, display, plasmonics, metasurfaces, and roll-to-roll fabrication.
Project description:Intravital microscopy is an essential tool that reveals behaviours of live cells under conditions close to natural physiological states. So far, although various approaches for imaging cells in vivo have been proposed, most require the use of labelling and also provide only qualitative imaging information. Holographic imaging approach based on measuring the refractive index distributions of cells, however, circumvent these problems and offer quantitative and label-free imaging capability. Here, we demonstrate in vivo two- and three-dimensional holographic imaging of circulating blood cells in intact microcapillaries of live mice. The measured refractive index distributions of blood cells provide morphological and biochemical properties including three-dimensional cell shape, haemoglobin concentration, and haemoglobin contents at the individual cell level. With the present method, alterations in blood flow dynamics in live healthy and sepsis-model mice were also investigated.
Project description:Surface integrity has attracted the attention of researchers for improving the functional performance of engineering products. Improvement in surface finish, one of the important parameters in surface integrity, has been attempted by researchers through different processes. Grinding has been widely used for final machining of components requiring smooth surfaces coupled with precise tolerances. Proper selection of grinding wheel material and grade with grinding parameters can result in an improved surface finish and improved surface characteristics. The present work reports the study of the effect of grinding parameters on surface finish of EN8 steel. Experiments were performed on surface grinding and cylindrical grinding for optimization of grinding process parameters for improved surface finish. Grinding wheel speed, depth of cut, table feed, grinding wheel material and table travel speed for surface grinding operation, and work speed for cylindrical grinding operation were taken as the input parameters with four types of grinding wheels (Al2O3 of grades K and L, and white alumina of grades J and K). The surface roughness was taken as an output parameter for experimentation. The grinding wheel material and grade have been observed to be the most significant variables for both cylindrical grinding and surface grinding. Surface roughness in the case of surface grinding is better compared to that of cylindrical grinding, which can be attributed to vibrations produced in the cylindrical grinding attachment. Surface roughness (Ra) values of 0.757 µm in cylindrical grinding and 0.66 µm in surface grinding have been achieved.
Project description:Three models are considered for describing the dynamics of a pulsating cylindrical bubble. A linear solution is derived for a cylindrical bubble in an infinite compressible liquid. The solution accounts for losses due to viscosity, heat conduction, and acoustic radiation. It reveals that radiation is the dominant loss mechanism, and that it is 22 times greater than for a spherical bubble of the same radius. The predicted resonance frequency provides a basis of comparison for limiting forms of other models. The second model considered is a commonly used equation in Rayleigh-Plesset form that requires an incompressible liquid to be finite in extent in order for bubble pulsation to occur. The radial extent of the liquid becomes a fitting parameter, and it is found that considerably different values of the parameter are required for modeling inertial motion versus acoustical oscillations. The third model was developed by V. K. Kedrinskii [Hydrodynamics of Explosion (Springer, New York, 2005), pp. 23-26] in the form of the Gilmore equation for compressible liquids of infinite extent. While the correct resonance frequency and loss factor are not recovered from this model in the linear approximation, it provides reasonable agreement with observations of inertial motion.