Horizontal Capillary Research Articles

Wetting and pressure gradient performance in a lattice Boltzmann color gradient model

An accurate implementation of wetting and pressure drop is crucial to correctly reproduce fluid displacement processes in porous media. Although several strategies have been proposed in the literature, a systematic comparison of them is needed to determine the most suitable for practical applications. Here, we carried out numerical simulations to investigate the performance of two widely used wettability schemes in the lattice Boltzmann color gradient model, namely, the geometrical wetting scheme by Leclaire et al. [Phys. Rev. E 95(3), 033306 (2017)](scheme-I) and the modified direction of the color gradient scheme by Akai et al. [Adv. Water Resour. 116, 56–66 (2018)] (scheme-II). We showed that scheme-II was more accurate in simulating static contact angles of a fluid droplet on a solid surface. However, scheme-I was more accurate in simulating a dynamic case of a binary fluid flow in a horizontal capillary tube described by the Washburn equation. Moreover, we investigated the performance of two popular pressure gradient implementation types. Type-I used the so-called Zou–He pressure boundary conditions at the inlet and the outlet of the domain, while type-II used an external body force as a pressure gradient. We showed that the type-I implementation was slightly more accurate in simulating a neutrally wetting fluid in a horizontal capillary tube described by the Washburn equation. We also investigated the differences between the two types of pressure gradient implementation in simulating two fluid displacement processes in a Bentheimer sandstone rock sample: the primary drainage and the imbibition displacement processes.

Equilibrium shape of a bubble in a liquid-filled horizontal capillary

Bubbles in liquid-filled capillaries feature in many practical applications. Here we describe the equilibrium shape of a bubble in a horizontal capillary of circular cross section, as computed numerically using energy minimization. The data is presented in terms of empirical scaling laws for bubble extension along and perpendicular to the tube axis, over a large range of the ratio of cylinder to bubble diameter and Bond numbers. We also consider the limiting case of a bubble underneath a flat plate, for which approximate analytical solutions are available. Furthermore, we deduce an equation for the mean curvature of the gas–liquid interface and the variation of contact areas, the latter being of relevance also for estimating the wall drag forces of flowing bubbles.

Open-source high-performance software packages for direct and inverse solving of horizontal capillary flow

This work introduces Fronts, a set of open-source numerical software packages for nonlinear horizontal capillary-driven flow problems in unsaturated porous media governed by the Richards equation. The software uses the Boltzmann transformation to solve such problems in semi-infinite domains. The scheme adopted by Fronts allows it to be faster and easier to use than other tools, and provide continuous functions for all involved fields. The software is capable of solving problems that appear in hydrology, but also in other particular domains of interest such as paper-based microfluidics. As the first known open-source implementation to adopt this approach, Fronts has been validated against analytical solutions as well as existing software achieving remarkable results in terms of computational costs and numerical precision, and is meant to aid the study and modeling of capillary flow. Fronts can be freely downloaded and installed, and offers a friendly environment for new users with its complete documentation and tutorial cases. Cited as: Gerlero, G. S., Berli, C. L. A., Kler, P. A. Open-source high-performance software packages for direct and inverse solving of horizontal capillary flow. Capillarity, 2023, 6(2): 31-40. https://doi.org/10.46690/capi.2023.02.02

Effects of surface nanotexturing on the wickability of microtextured metal surfaces

Hypothesis: Achieving spontaneous, rapid, and long-distance liquid transport is crucial for many practical applications such as phase change heat transfer and reactions at solid–liquid interfaces. Surface nanotexturing has been widely reported to improve the wickability of microtextured metal surfaces. Although surface nanotextures show high capillary pressure, the high fluid flow resistance through nanotextures prevents fluid transport. The underlying mechanisms responsible for the enhanced wickability of nanotextured surfaces are still unclear.Experiments: Herein, we prepared a variety of microtextures and nanotextures on copper surfaces by femtosecond laser micromachining and chemical oxidation, respectively. The wickability of these textured surfaces was quantitively compared by measuring wicking coefficient and capillary rise speed. We designed experiments to eliminate any possible effects of surface oxidation and metal composition on wickability. A theoretical model describing the vertical and horizontal capillary flow in V-shaped microgrooves was proposed and utilized to analyze the experimental results. The effects of time-dependent wettability on wickability were also examined.Findings: Surface nanotexturing can enhance surface wettability while altering the micrometer-scale structural characteristics. The greatly enhanced wickability of nanotextured surfaces can only be observed when the surface microtextures have a very small aspect ratio. Otherwise, for metal surfaces with fine microgrooves, the latter effect is more pronounced, and thus the surface wickability may deteriorate after preparing surface nanotextures; for surfaces with wide microgrooves, both effects are minimal, and the surface wickability enhances only marginally after surface nanotexturing. Furthermore, the wickability of microtextured surfaces will decay rapidly due to the adsorption of airborne organics, whereas adding surface nanotextures can significantly inhibit this degradation. The anti-contamination capability of surface nanotextures is considered likely to be a potential mechanism responsible for the greatly enhanced wickability of nanotextured surfaces noted in some studies.

Capillary washboarding during slow drainage of a frictional fluid.

Numerous natural and industrial processes involve the mixed displacement of liquids, gases and granular materials through confining structures. However, understanding such three-phase flows remains a formidable challenge, despite their tremendous economic and environmental impact. To unveil the complex interplay of capillary and granular stresses in such flows, we consider here a model configuration where a frictional fluid (an immersed sedimented granular layer) is slowly drained out of a horizontal capillary. Analyzing how liquid/air menisci displace particles from such granular beds, we reveal various drainage patterns, notably the periodic formation of dunes, analogous to road washboard instability. Considering the competitive role of friction and capillarity, a 2D theoretical approach supported by numerical simulations of a meniscus bulldozing a front of particles provides quantitative criteria for the emergence of those dunes. A key element is the strong increase of the frictional forces, as the bulldozed particles accumulate and bend the meniscus horizontally. Interestingly, this frictional enhancement with the attack angle is also crucial in small-legged animals' locomotion over granular media.

Capillary flow of water in tubes partially prefilled with oil

When water meets sunflower oil in a horizontal capillary tube, a water droplet can spontaneously form. The position of the breakup event can be manipulated by simply adjusting the oil content that prefills the capillary. For short length scales, the system advances with a constant velocity making it a good predictive tool for engineering applications.

Graphene Oxide Liquid Crystals Aligned in a Confined Configuration: Implications for Optical Materials

Orientation control of two-dimensional (2D) colloidal liquid crystals in both microscopic and macroscopic scales holds massive promise for improved multifield applications. In this respect, graphene oxide (GO) is used as a platform substance for 2D carbon-based lyotropic liquid crystal (LC) materials. Here, we design the directed alignment of aqueous GO-LC dispersion confined in a rectangular capillary tube. The isotropic GO dispersion is loaded into a horizontal capillary and subsequently concentrated to the LC phase by slow water evaporation at open ends of the tube. An obtained surprising result, GO layers organize normal to the inner surfaces of the capillary with a highly ordered orientation of the optic axis over tens of millimeters. Such transverse orientation of GO layers originates from the meniscus region and then moves toward the center, caused by the interfacial effect and the sequential isotropic-to-nematic transition. This aligned mesomorphic system is characterized via optical retardation, nematic order parameter, absorption, and modified Cauchy’s transmission equation about the dependency of both birefringence and wavelength with concentration. Finally, the aligned GO-LC layers are preserved in a polymer composite matrix by photopolymerizing the evaporation-aligned GO/acrylamide-LC dispersion confined in a capillary. This composite shows higher thermal stability than polyacrylamide until 500 °C of about 6.1%. Our experimental findings provide efficient advantages for controlling the orientation of GO-LC and 2D materials, beneficial for diverse optical applications due to their directional ordering.

Spontaneous Imbibition of Capillaries under the End Effect and Wetting Hysteresis.

The phenomenon of spontaneous imbibition is widely present in the development process of tight oil/gas reservoirs. To further explore the spontaneous imbibition behavior of capillary tubes to provide theoretical and methodological references for the study of microscopic porous media imbibition phenomena, the capillaries that can be observed with the naked eye on the order of 10–100 μm were selected as research objects. Based on the theory of interface chemistry, the capillary end effect, and wetting hysteresis, the influence of the additional pressures generated by the two-phase interface on the spontaneous absorption of the horizontal capillary was studied. Some of the capillaries were processed for wettability, and then the water wettability of different capillaries was measured by the introduced concept, which is the conversion height of the self-absorption phase in the capillary. The capillaries were horizontally placed in the liquid for a spontaneous imbibition experiment, and the air–liquid two-phase menisci behavior was observed at the same time, and then the influence of water wettability, surfactant, and capillary diameter on spontaneous imbibition was discussed. It was found that in the equal diameter capillaries, the spontaneous air–liquid imbibition behavior of capillary tubes with different water wetting properties is different in sensitivity to surfactants and tube diameters; when surfactants are used to improve capillary water wettability to increase spontaneous imbibition efficiency, the initial water wettability of the capillary and the comprehensive changes in the capillary pressure caused by interfacial tension should be considered.

Computational Fluid Dynamics of Two-Phase Flow Pressure Gradient of Air-Sodium Chloride and Glucose in Horizontal Capillary Channels

One of the problems in the two-phase flow is investigating the type of flow pattern that occurs in a mini channel without experimenting first. Computational Fluid Dynamics (CFD) is one way that can be used to predict pressure drop, flow pattern, void fraction, other parameters in fluid flow through a channel of a specific size. This research used the CFD simulations to predict the pressure gradient in a two-phase flow of air-sodium chloride 0.9% and glucose in a horizontal capillary tube with a diameter of 1.6 mm, and length of 70 mm. This research aims to obtain the simulation results of 2D and 3D pressure gradients to validate the experimental data. The simulation was carried out with a variation of the superficial gas velocity 0.1 - 8.3 m / s against the superficial velocity of the liquid constant 0.207 m / s. Simulations were carried out using the Volume of Fluid (VOF) model with the "ANSYS Fluent 2020 R1" software. In 2D and 3D simulations, the gradient values of pressure gradients tend to increase as JG increases. The pressure gradient fluctuates linearly at first, then exponentially from mid-to-end. The findings demonstrate that simulations may properly model physical processes like pattern creation and phase interactions. However, due to several physical elements considered in 3D simulation but missed in 2D simulation, the findings of the 2D and 3D simulations were dramatically different when looking at the pressure gradient values.

Accelerated mass transfer enhancement by density-driven natural convection

ABSTRACT The prolonged heat and mass transfer can be enhanced by orders of magnitude that originate from the natural convection. This work examines the mass transfer enhancement in the fluid motion inside a horizontal capillary. In the experimental setup, dye or polystyrene (PS) in aqueous sucrose is taken on one side, and water is on the other side. The main purpose of employing two different systems (i.e. dye and PS) is that it can confirm whether the enhanced mass transfer is with only nanoparticles or it can be possible without nanoparticles in the presence of solute concentration gradients in a fluid. It is demonstrated that the induced flow is due to natural convection attributed to the density-driven flow. The induced flow in the present setup may open up various additional applications for the systems where rapid mixing is important, for instance, rapid formation of drug carriers.

Hydrodynamics of a completely wetting isolated liquid plug oscillating inside a square capillary tube

The effect of imposed flow oscillations on the local hydrodynamics of a completely wetting isolated liquid plug (of silicone oil) placed inside a horizontal square glass capillary tube (1 mm × 1 mm) is studied. A known volume of liquid (plug with a given L/D ratio) is made to harmonically oscillate inside the capillary tube by the action of air pressure on one of its menisci, while the other meniscus interacts freely with the atmosphere. The effect of plug length, imposed oscillation frequency and amplitude, on the net pressure drop and menisci shapes, in terms of normalized radii of curvature, is addressed. A hydrodynamic model, based on Bretherton's theory, coupled with Tanner's law is reviewed and simplified for oscillatory flows, which shows excellent correlation with the experimental data, via a single universal fitting parameter. This parameter manifests the combined effect of wall shear stress and additional dissipation due to the dynamically deforming menisci. During oscillations of the liquid plug, the contact lines of both menisci stay pinned and the plug slides over a thin liquid film laid down during its motion, exhibiting dynamic hysteresis at both the respective menisci. The system parameter that governs the hydrodynamics of oscillating liquid plug is the instantaneous capillary number, which depends on both, the imposed frequency and amplitude, the former having an overbearing effect on the dynamic menisci shapes. The study clearly brings forward the fact that capillary induced dissipation at the menisci is much more prominent than the wall induced shear.

Designed Electroosmotic Polymer for an Anti-Drying Contact Lens Device

A smart contact lens (CL) is an attractive wearable device that could enable noninvasive monitoring of physiological information and augmented reality display in addition to vision correction. Whereas, the CL is one of the causes of dry eye syndrome due to more rapid moisture evaporation through the CLs than that from the normal tear film covered by a lipid layer. Conventional rehydration by regular eye drops takes time and efforts. The only example so far of a smart CL for maintaining the moisture is that of Lee et al., who developed a CL coated with single layer of graphene which decreases the evaporation. Hence, there is still a high demand to develop a CL equipped with an anti-dehydration function. We here designed a charge-fixed soft CL generating electroosmotic flow (EOF) under an electric field for maintaining the moisture of the lens (Figure 1a) [1]. The CL supplies tears via EOF from the tear meniscus (temporary tear reservoir) behind the lower eyelid. EOF is the motion of water induced by an applied electric field across a fluid conduit like a capillary tube or a porous material such as hydrogels. When the fluid conduit contains fixed electrical charges, the dominant electromigration of the mobile counter ions produces net water flow.The soft CL made of negatively charged hydrogel were fabricated by copolymerizing methacrylic acid (MA, 0 – 15 wt%), 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA). At First, we evaluated the efficiency of EOF generation for each of the 0.2 mm thick hydrogel films. DC currents of 1.0, 2.0, and 3.0 mA were applied to the films sandwiched by the side-by-side Franz cell with a horizontal capillary, and the flow velocity of EOF was calculated from the movement of the water surface in the horizontal capillary. These results indicate that a hydrogel with a high MA content is suitable for effective EOF generation in hydrogels. Secondly, compression tests were performed to the films to evaluate the indentation fracture toughness. The larger MA content tends to make the hydrogel become brittle and the hydrogel with 15 wt% MA was easily broken by folding. By considering both the results of the EOF strength and the fracture toughness, we mainly used the 10 wt% MA hydrogel in subsequent experiments. The water content and the conductance of the films were separately monitored at 100 kHz during the slow drying under 75% humidity. This result supports that the change in water content in the hydrogel film can be traced by the conductance measurement (Figure 1b). Finally, the EOF-based moisturization for the battery-mounted CL was demonstrated using an enzymatic fructose–oxygen fuel cell [2], in which the CL was put on a hemispherical jig (ocular model) equipped with printed Ag/AgCl electrodes for conductance measurements (Figure 1c). The lower end (≈3 mm) of the CL was dipped in a buffer solution containing D-fructose to imitate a tear meniscus. Figure 1d shows the observed changes in conductance (moisture) of CLs without EOF (gray, natural drying) and with upward EOF generated by an enzymatic fuel cell (red). The results demonstrated that applying an upward EOF through the CL reduced the moisture loss of the lens compared to natural drying. Since the demonstration was conducted at a relatively dry condition (40% humidity) for the hanging CLs, it can be expected that the moisturization would be more effective in situations where CLs are put onto eye. From these results, we believe that the proposed hydrogel will promise development of a contact lens devices with an anti-drying function.Reference[1] S. Kusama, K. Sato, S. Yoshida, and M. Nishizawa, “Self-Moisturizing Smart Contact Lens Employing Electroosmosis”, Adv. Mater. Technol. 5, 1, 1–9 (2020)[2] Y. Ogawa, K. Kato, T. Miyake, K. Nagamine, T. Ofuji, S. Yoshino, and M. Nishizawa, “Organic Transdermal Iontophoresis Patch with Built-in Biofuel Cell,” Adv. Healthc. Mater. 4, 506–510 (2015). Figure 1

Evaluation of Electroosmotic Flow Promoted By a Porous Microneedle Array

A transdermal drug delivery (TDD) system has been an attractive method to delivery needed drug into our bodies directly with few side effect, and electroosmotic flow (EOF) is known as the method to enhance TDD and even the extraction of interstitial fluid (ISF) which contains biomarkers such as glucose. The limitation of these transdermal penetration / extraction arises from stratum corneum (SC), an outermost layer of skin. SC is highly resistive and functions as a barrier for harmful molecules, which makes it difficult to apply direct currents to the skin by mild and safe voltage and to deliver larger molecular drugs (>600 Da) into the skin1. The microneedle array (MNA) is one of the promising approaches to break through SC without pain, and solve problems of the electrical and the drug pass. Recently, we have realized organic polymer-based porous microneedles (PMN) made of poly(glycidyl methacrylate) (PGMA) which were prepared by the combination of molding process and the porogen method 2. In this study, we developed a PMN inducing the EOF for efficient TDD and extraction of ISF (Figure 1a). Furthermore, in order to enhance efficiency in the induction of the EOF, negatively-charged hydrogel was embedded in the porous channels of the PMN.The modified PMN was prepared by the following steps. Briefly, naked PMN was prepared by the step described in the report2. After that, the naked PMN chips were immersed in an aqueous solution containing 0.05 M of AMPS, 0.10 M of MBAAm, ammonium persulfate and tetramethylenediamine at 4 ℃ for more than 8 h, followed by thermal copolymerization at 70 ℃ for more than 8 h.First, we evaluated the property of water transport by EOF. A chip of PAMPS-modified PGMA was bound with side-by-side Franz cells with a horizontal capillary, and constant DC currents were applied by a source meter. McIlvaine buffer (pH 7.0) was used as the electrolyte. Flow velocity was calculated from the moving of the water surface in the capillary. The flow velocity of the EOF increased by the modification with AMPS (Figure 1b). The reason was that the negative charge was increased by the AMPS modification and that promoted the EOF.In order to evaluate the property of large molecule transport, the same system as water transport was employed as well. The Franz cells were poured with McIlvaine buffer (pH 6.0) and 0.75 mg/mL FITC-dextran (10,000 Da, pKa 6.4) was added to the donor chamber. We applied a constant DC current in direction from the donor side to the receptor side, and a 100 µL portion was collected from the receptor chamber every hour for analysis by a fluorescence spectrophotometer. From the result, we found that PAMPS significantly contributes to transport for the large molecule transport (Figure 1c). This might be due to dense polymer chains of PMAPS capturing large molecules such as dextran.Finally, the transdermal injection was demonstrated by enzymatic fructose / O2 battery into pig’s skin (Figure 1d). The injection of FITC-dextran at an anode was evaluated the PMN modified with 0.05 M AMPS and the cotton with 0.3 mL McIlvaine buffer (pH 6.0) containing 0.2 M D-fructose and 0.75 mg/mL FITC-dextran. The cross-sectional fluorescence image of the skin was observed after the application of the current around 0.2 mA/cm2 for 1 hour. These results showed that this novel PMN with negatively charged hydrogel can be a desirable tool for enhancing the injection of large molecules such as drugs and nutrients.Reference[1] Brown, M. B, Martin, G. P., Jones, S. A. & Akomeah, F. K. Dermal and transdermal drug delivery system: Current and future prospects. Drug Deliv. J. Deliv. Target. Ther. Agents 13, 175-187 (2006).[2] Liu, L., Kai, H., Nagamine, K., Ogawa, Y. & Nishizawa, M. Porous polymer microneedles with interconnecting microchannels for rapid fluid transport. RSC Adv. 6, 48630-48635 (2016). Figure 1

Evaluation of viscosity and surface tension of low-volume samples using glass capillary

In this paper, methods for measuring the viscosity and surface tension of low-volume liquid samples are proposed. Viscosity is measured by recording the motion of a liquid driven by surface tension through a horizontal glass capillary tube. Surface tension is determined by connecting a container of a constant volume to the distal end of the capillary tube and measuring the penetration distance of the liquid entering via the proximal end. Sucrose solutions of various concentrations (0–50 wt%) were measured as samples, and the determined viscosities were confirmed to be consistent with the tabulated values provided in the Handbook of Chemistry. The surface tension was found to be constant within the measurement sensitivity of the device regardless of the sucrose concentration.

Capillary imbibition of non-Newtonian fluids in a microfluidic channel: analysis and experiments

We have presented an experimental analysis on the investigations of capillary filling dynamics of inelastic non-Newtonian fluids in the regime of surface tension dominated flows. We use the Ostwald–de Waele power-law model to describe the rheology of the non-Newtonian fluids. Our analysis primarily focuses on the experimental observations and revisits the theoretical understanding of the capillary dynamics from the perspective of filling kinematics at the interfacial scale. Notably, theoretical predictions of the filling length into the capillary largely endorse our experimental results. We study the effects of the shear-thinning nature of the fluid on the underlying filling phenomenon in the capillary-driven regime through a quantitative analysis. We further show that the dynamics of contact line motion in this regime plays an essential role in advancing the fluid front in the capillary. Our experimental results on the filling in a horizontal capillary re-establish the applicability of the Washburn analysis in predicting the filling characteristics of non-Newtonian fluids in a vertical capillary during early stage of filling (Digilov 2008 Langmuir 24 , 13 663–13 667 ( doi:10.1021/la801807j )). Finally, through a scaling analysis, we suggest that the late stage of filling by the shear-thinning fluids closely follows the variation x ~ t . Such a regime can be called the modified Washburn regime (Washburn 1921 Phys. Rev. 17 , 273–283 ( doi:10.1103/PhysRev.17.273 )).

Self-powered microfluidic pump using evaporation from diatom biosilica thin films

In recent years, researchers have successfully applied diatom biosilica to molecular detection platforms including Surface-Enhanced Raman Scattering (SERS) optofluidic sensors that are currently capable of detecting a variety of biological and chemical molecules at concentrations as low as 10−10 M. This study investigates the feasibility of an SERS device that couples the sensing and pumping capabilities of diatom biosilica thin films by determining flow rate limitations and stability. In this paper, we quantify the ability of porous diatom biosilica thin films to continuously pump deionized (DI) water from a reservoir via wicking flow by utilizing the strong capillary forces of the porous film coupled with evaporation. Our microfluidic device is comprised of a narrow horizontal reservoir fixed to a horizontal capillary whose end contacts a diatom biosilica film. Flow rates were controlled by altering the size and/or temperature of the biosilica porous film, determined by tracking the liquid meniscus displacement in the reservoir, and correlated with a modified laminar boundary-layer model. System stability was observed by tracking flow rates over the course of a given experiment, image analysis of the meniscus contacting the film, and a flow duration study. We found that for untreated DI water bubbles begin to form in the capillary tube at temperatures above 40 °C, but degassed water remains stable at temperatures of 90 °C and below. The pumping capabilities of the films ranged from 0.11 to 10.46 µL/min, matched theoretical predictions, demonstrated stable flow trends, and maintained flow for over 48 h.

Numerical simulation of the thermal and fluid-dynamic behavior of a cryogenic capillary tube

A 2D numerical model based on an axisymmetric geometry has been developed to simulate the behavior of the two-phase working fluid in a horizontal capillary tube. Numerical results have been compared with experimental results to validate the model. Fluid flow characteristics related to the liquid film and the bubbles shape have been reproduced and evaporation and condensation processes in the liquid film have been simulated. Furthermore, the heat transfer from the evaporator to the condenser through fluid oscillations has been verified and specific thermodynamic instabilities of the working fluid in pulsating heat pipes have been reproduced. Conversely, it appears that only thermal instabilities are not sufficient to maintain an oscillating two-phase flow in horizontal capillary tubes. Nevertheless, the model represents accurately the overall heat transfer phenomena and constitutes a first step for future 2D numerical simulations of horizontal pulsating heat pipes.

Capillary Filling Dynamics of Electromagnetohydrodynamic Flow of Non-Newtonian Fluids

Abstract In this work, we aim to develop a mathematical model for capillary filling dynamics of electromagnetohydrodynamic flow of non-Newtonian fluids. An axially applied electric field and a transverse magnetic field are considered to elucidate the electromagnetohydrodynamic transport through the microcapillary. Assuming a non-Newtonian power-law obeying fluids, we analyze the transient evolution of the electromagnetohydrodynamic capillary positions by considering the magnitude of the total force balance via finite volume-based numerical formalism. We have highlighted the various rheological regimes in the horizontal capillary through a scaling analysis. For the Newtonian fluids, corresponding inviscid linear Washburn regime is also analyzed and compared with the power-law obeying fluids. Furthermore, we have also derived closed-form analytical expressions for the electromagnetohydrodynamic velocity, pressure gradient, and transient evolution of the capillary positions by using couple stress parameter model to characterize the fluid rheological behaviors. We perform a comparison test of the coupled stress parameter model with the results from the literature for a similar set of fluid rheological parameters. The comparison results are found to be in good agreement.

Real-time capillary convective PCR based on horizontal thermal convection

A real-time, capillary, convective polymerase chain reaction (PCR) system based on horizontal convection is developed and analyzed. The capillary tube reactor is heated at one end in a pseudo-isothermal manner to achieve efficient thermal cycling based on horizontal thermal convection. Mathematical modeling and the in silico simulations indicate that, once consistent temperature gradient along the horizontal capillary tube has been established, a repeatable and continuous circulatory flow in the horizontal directions is created. The formed convection is able to transport PCR reagents through different temperature zones inside the horizontal capillary tube for different reaction stages, that is, DNA denaturing, annealing, and extension in a typical PCR cycle. Furthermore, the effectiveness and efficiency of the horizontal convection for PCR thermal cycling in a capillary tube is confirmed by experimentation. To evaluate the concept of horizontal convective PCR, a compact system, which is able to heat the capillary tube from one end and monitor the fluorescence in situ with a smartphone camera, is developed for real-time amplification. With horizontal thermal convection, influenza A (H1N1) virus nucleic acid targets with a limit of detection (LOD) of 1.0 TCID50/mL can be successfully amplified and detected in 30 min, which is promising for efficient nucleic acid analysis in point-of-care testing.

Borosilicate nozzles manufactured by reproducible fire shaping

Borosilicate glass nozzles are used by researchers in many fields. They are mainly manufactured by two methods: (i) heating and drawing (or pulling), and (ii) fire shaping (or fire polishing). The latter produces the nozzle by heating one capillary end with a flame, and nozzles are typically much shorter than those obtained by pulling, what may be necessary for some applications. In this work, we built an experimental setup and we evaluated the performance and reproducibility of two different approaches to fire shaping. The first approach heats the tip of a horizontal capillary on the side of the flame. The resulting nozzles are very short and have very good symmetry at the neck. However, there is a small but significant misalignment angle between the nozzle neck and the capillary axes that may be unacceptable for its use in some experimental setups. The second fire shaping approach heats a vertical capillary at the top of the flame. The resulting nozzles show very good symmetry and a very low, and acceptable, misalignment angle between the nozzle neck and the capillary axes. As the phenomena involved in the process are complex, the diameter variability for the same experimental conditions (heating position and time) is high. Results show that using the nozzle shortening to control the neck diameter may be an alternative to produce nozzles of a desired size. However, the shape reproducibility is very good, as nozzles of the same diameter have the same shape, even when they have been produced in different conditions.