Thin Capillaries Research Articles

A simple acoustofluidic device for on-chip fabrication of PLGA nanoparticles.

Miniaturization of systems and processes provides numerous benefits in terms of cost, reproducibility, precision, minimized consumption of chemical reagents, and prevention of contamination. The field of microfluidics successfully finds a place in a plethora of applications, including on-chip nanoparticle synthesis. Compared with the bulk approaches, on-chip methods that are enabled by microfluidic devices offer better control of size and uniformity of fabricated nanoparticles. However, these microfluidic devices generally require complex and expensive fabrication facilities that are not readily available in low-resourced laboratories. Here, a low-cost and simple acoustic device is demonstrated by generating acoustic streaming flows inside glass capillaries through exciting different flexural modes. At distinct frequencies, the flexural modes of the capillary result in different oscillation profiles that can insert harmonic forcing into the fluid. We explored these flexural modes and identified the modes that can generate strong acoustic streaming vortices along the glass capillary. Then, we applied these modes for fluid mixing using an easy-to-fabricate acoustofluidic device architecture. This device is applied in the fabrication of poly(d,l-lactide-co-glycolide) (PLGA) nanoparticles. The acoustic device consists of a thin glass capillary and two polydimethylsiloxane adaptors that are formed using three-dimensional printed molds. By controlling the flow rates of the polymer and water solutions, PLGA nanoparticles with diameters between 65 and 96 nm are achieved with polydispersity index values ranging between 0.08 and 0.18. Owing to its simple design and minimal fabrication requirements, the proposed acoustofluidic mixer can be applied for microfluidic fluid mixing applications in limited resource settings.

Destabilising persistent coal froth using silicone oil

Persistent froth is becoming more and more common in coal and mineral flotation plants and presents safety and operational challenges. No effective method has been developed to destabilise persistent froth. As a new initiative, this study examined the structural difference between persistent foam and coal froth, based on which a solution was developed to maximumly destabilise coal froth. Destabilisation test, oscillatory rheology measurement and scanning electron microscopy (SEM) analysis indicated that the coal froth was more stable than the foam due to the formation of thin capillaries and tightly arranged coal particles on bubble surfaces. Although 107 µm silicone oil droplet could completely destabilise the foam at 2 mmol/L concentration, it only destabilised less than 50% coal froth even at 6 mmol/L concentration. To maximumly destabilise the coal froth formed by −38 and −20 µm particles, 24 and 18 µm silicone oil droplets were required to pass through the thin capillaries and enter the bubble films, respectively. However, smaller silicone oil droplets could not bridge the bubble films to destabilise coal froth and therefore a critical droplet size occurred depending on the size of particles stabilising the froth.

Stereological Changes in Microvascular Parameters in Hippocampus of a Transgenic Rat Model of Alzheimer's Disease.

Background:Microcirculatory factors play an important role in amyloid-β (Aβ)-related neuropathology in Alzheimer’s disease (AD). Transgenic (Tg) rat models of mutant Aβ deposition can enhance our understanding of this microvascular pathology.Objective:Here we report stereology-based quantification and comparisons (between- and within-group) of microvessel length and number and associated parameters in hippocampal subregions in Tg model of AD in Fischer 344 rats and non-Tg littermates.Methods:Systematic-random samples of tissue sections were processed and laminin immunostained to visualize microvessels through the entire hippocampus in Tg and non-Tg rats. A computer-assisted stereology system was used to quantify microvessel parameters including total number, total length, and associated densities in dentate gyrus (DG) and cornu ammonis (CA) subregions.Results:Thin hair-like capillaries are common near Aβ plaques in hippocampal subregions of Tg rats. There are a 53% significant increase in average length per capillary across entire hippocampus (p≤0.04) in Tg compared to non-Tg rats; 49% reduction in capillary length in DG (p≤0.02); and, higher microvessel density in principal cell layers (p≤0.03). Furthermore, within-group comparisons confirm Tg but not non-Tg rats have significant increase in number density (p≤0.01) and potential diffusion distance (p≤0.04) of microvessels in principal cell layers of hippocampal subregions.Conclusion:We show the Tg deposition of human Aβ mutations in rats disrupts the wild-type microanatomy of hippocampal microvessels. Stereology-based microvascular parameters could promote the development of novel strategies for protection and the therapeutic management of AD.

Selection of laser pulse width for efficient generation of photoacoustic signals in liquid-filled thin capillary embedded in soft material

To design an instrumentation system for evaluating contrast agents of photoacoustic imaging, the optimal pulse width of the excitation laser is discussed in this paper. A pulsed semiconductor laser with a moderate pulse width (15–129 ns) and low peak power (1 W) is adopted in the proposed system. Black ink is selected as the reference sample, which is filled in a glass capillary embedded in a soft phantom. Our aim is that the pulse width matches the acoustic resonance of the target and the center frequency of the receiving transducer (5 MHz) to obtain sufficient strength of the ultrasonic signal with minimal laser power. A series of experiments reveal a clear relationship between the laser pulse width and the maximal amplitude of the resonance mode. Acoustic resonance occurs inside the capillary whose frequencies can be precisely predicted as the radial eigen mode. The laser pulse width and concentration of the sample showed little influence on these resonance frequencies as expected. To efficiently utilize the signal enhancement effect due to the resonance, several resonance mode candidates are investigated and discussed. It then becomes clear that the second angular and zeroth radial order mode is useful for capillaries with sub-millimeter inner diameters. It was demonstrated that the concentration of samples had very limited influence on the frequencies. Finally, consideration based on two delayed attenuating vibrations is successfully conducted to explain the experimental results.

Enhancement of UV-visible transmission characteristics in wet-etched hollow core anti-resonant fibers.

We report on the feasibility of short-wavelength transmission window modification in anti-resonant hollow core fibers using post-processing by hydrofluoric (HF) acid etching. Direct drawing of stacked anti-resonant hollow core fibers with sub-micron thin cladding capillary membranes is technologically challenging, but so far this has been the only proven method of assuring over an octave-spanning transmission windows across the visible and UV wavelengths. In this study we revealed that low HF concentration allows us to reduce the thickness of the cladding capillary membranes from the initial 760 nm down to 180 nm in a controlled process. The glass etching rates have been established for different HF concentrations within a range non-destructive to the anti-resonant cladding structure. Etching resulted in spectral blue-shifting and broadening of anti-resonant transmission windows in all tested fiber samples with lengths between 15 cm and 75 cm. Spectrally continuous transmission, extending from around 200 nm to 650 nm was recorded in 75 cm long fibers with cladding membranes etched down to thickness of 180 nm. The experiment allowed us to verify the applicability and feasibility of controlling a silica fiber post-processing technique, aimed at broadening of anti-resonant transmission windows in hollow core fibers. A practical application of the processed fiber samples is demonstrated with their simple butt-coupling to light-emitting diodes centered at various ultraviolet wavelengths between 265 nm and 365 nm.

Histopathological analysis of zebrafish after introduction of non-biodegradable polyelectrolyte microcapsules into the circulatory system.

Polyelectrolyte microcapsules are among the most promising carriers of various sensing substances for their application inside the bloodstream of vertebrates. The long-term effects of biodegradable microcapsules in mammals are relatively well studied, but this is not the case for non-biodegradable microcapsules, which may be even more generally applicable for physiological measurements. In the current study, we introduced non-biodegradable polyelectrolyte microcapsules coated with polyethylene glycol (PMs-PEG) into the circulatory system of zebrafish to assess their long-term effects on fish internal organs with histopathologic analysis. Implantation of PMs-PEG was not associated with the formation of microclots or thrombi in thin capillaries; thus, the applied microcapsules had a low aggregation capacity. The progression of the immune response to the implant depended on the time and the abundance of microparticles in the tissues. We showed that inflammation originated from recognition and internalization of PMs-PEG by phagocytes. These microcapsule-filled immune cells have been found to migrate through the intestinal wall into the lumen, demonstrating a possible mechanism for partial microparticle elimination from fish. The observed tissue immune response to PMs-PEG was local, without a systemic effect on the fish morphology. The most pronounced chronic severe inflammatory reaction was observed near the injection site in renal parenchyma and within the abdominal cavity since PMs-PEG were administered with kidney injection. Blood clots and granulomatosis were noted at the injection site but were not found in the kidneys outside the injection site. Single microcapsules brought by blood into distal organs did not have a noticeable effect on the surrounding tissues. The severity of noted pathologies of the gills was insufficient to affect respiration. No statistically significant alterations in hepatic morphology were revealed after PMs-PEG introduction into fish body. Overall, our data demonstrate that despite they are immunogenic, non-biodegradable PMs-PEG have low potential to cause systemic effects if applied in the minimal amount necessary for detection of fluorescent signal from the microcapsules.

Melissa officinalis L. Aqueous Extract Exerts Antioxidant and Antiangiogenic Effects and Improves Physiological Skin Parameters

Melissa officinalis (MO) is a medicinal plant well-known for its multiple pharmacological effects, including anti-inflammatory, anticancer and beneficial effects on skin recovery. In this context, the present study was aimed to investigate the in vitro and in vivo safety profile of an MO aqueous extract by assessing cell viability on normal (HaCaT—human keratinocytes) and tumor (A375—human melanoma) cells and its impact on physiological skin parameters by a non-invasive method. In addition, the antioxidant activity and the antiangiogenic potential of the extract were verified. A selective cytotoxic effect was noted in A375 cells, while no toxicity was noticed in healthy cells. The MO aqueous extract safety profile after topical application was investigated on SKH-1 mice, and an enhanced skin hydration and decreased erythema and transepidermal water loss levels were observed. The in ovo CAM assay, performed to investigate the potential modulating effect on the angiogenesis process and the blood vessels impact, indicated that at concentrations of 100 and 500 µg/mL, MO aqueous extract induced a reduction of thin capillaries. No signs of vascular toxicity were recorded at concentrations as high as 1000 μg/mL. The aqueous extract of MO leaves can be considered a promising candidate for skin disorders with impaired physiological skin parameters.

Direct comparison of wire, foil, and hybrid X-pinches on a 200 kA, 150 ns current driver

Wire X-pinches (WXPs) have been studied comprehensively as fast (∼1 ns pulse width), small (∼1 μm) x-ray sources, created by twisting two or more fine wires into an “X” to produce a localized region of extreme magnetic pressure at the cross-point. Recently, two alternatives to the traditional WXP have arisen: the hybrid X-pinch (HXP), composed of two conical electrodes bridged by a thin wire or capillary, and the laser-cut foil X-pinch (LCXP), cut from a thin foil using a laser. We present a comparison of copper wire, hybrid, and laser-cut foil X-pinches on a single experimental platform: UC San Diego’s ∼200 kA, 150 ns rise time GenASIS driver. All configurations produced 1–2 ns pulse width, ≤5 μm soft x-ray (Cu L-shell, ∼1 keV) sources (resolutions diagnostically limited) with comparable fluxes. WXP results varied with linear mass and wire count, but consistently showed separate pinch and electron-beam-driven sources. LCXPs produced the brightest (∼1 MW), smallest (≤5 μm) Cu K-shell sources, and spectroscopic data showed both H-like Cu Kα lines indicative of source temperatures ≥2 keV, and cold Kα (∼8050 eV) characteristic of electron beam generated sources, which were not separately resolved on other diagnostics (within 1–2 ns and ≤200 μm). HXPs produced minimal K-shell emission and reliably single, bright, and small L-shell sources after modifications to shape the early current pulse through them. Benefits and drawbacks for each configuration are discussed to provide potential X-pinch users with the information required to choose the configuration best suited to their needs.

Nematic Phase of Plate-like Semicrystalline Block Copolymer Single Crystals in Solution Studied by Small-Angle X-Ray Scattering.

Crystalline block copolymers have been used to prepare plate-like colloidal systems with well-controlled size, shape, and size distribution. The isotropic-to-nematic (I-N) phase transition of the novel plate-like colloidal particle suspensions has been reported previously. In this work, we focus on the characterization of the solution structure of the crystals and the N-phase using small- and ultrasmall-angle X-ray scattering techniques (SAXS/USAXS). The system has polystyrene-block-poly(l-lactide) (PS-b-PLLA) block copolymer single crystals (BCSCs) with different sizes dispersed in p-xylene. These crystals are truncated lozenge in shape and have effective diameters ranging from 550 to 4000 nm with a uniform dry thickness of 18.0 nm. Scattering of the individual crystal in solution can be simplified using a disc model with a core layer of 9-10 nm due to the lower contrast of the tethered PS layer. BCSC suspensions filled in thin quartz capillaries are prepared for monitoring the structural information. SAXS measurements of the isotropic phase show a strong face-to-face correlation, indicating that platelets form small stacked clusters in solutions. The isotropic phase is thus a coexistence of single crystals and the stacked multiple-layered clusters. The face-to-face spacing, d, in the N phases is around 75-90 nm, which increases slightly upon increasing the size of crystals. For a given system, the spacing does not change with increasing concentration under the current experimental conditions. Finally, the possible formation of lamellar domains within the N phase is also discussed due to the lateral attraction of this system. These results demonstrate the importance of the lateral attraction between the polar crystalline PLLA blocks on the formation of the N phase: the BCSCs self-assemble into larger sheets via the lateral attraction, which further enhances the I-N transition.

Low-loss micro-machining of anti-resonant hollow-core fiber with focused ion beam for optofluidic application

Hollow-core fiber (HCF) is a promising candidate for optofluidic applications because it can act as a gas-cell, permitting intense fluid-light interaction over extended lengths with low optical loss and inherent flexibility. Such a platform could pave the way for an all-fiberized, compact, robust and practical system for sensing applications. To facilitate this, we report a high-precision and repeatable micro-machining technique using focused ion beam (FIB) milling on a nodeless anti-resonant hollow-core fiber (ARHCF). Ga+ ions are bombarded on a 43 µm thick outer cladding of ARHCF for 30 minutes, to create a 50 µm deep fluidic channel, that has a negligible influence on the guiding properties of the fiber. The milled channel, followed by the 2.8 µm gap between adjacent 500 nm thin capillary tubes, provides direct access for liquid/gas to diffuse into the hollow-core region. The novel design presented here will allow ARHCFs to be spliced with solid-core fibers while preserving the fluidic channel. Corroborating results from simulation of such a structure are presented to demonstrate that no additional loss is induced by the milled hole.

Erratum to: Separation of Binary Alloys in Thin Capillaries

Erratum to: Separation of Binary Alloys in Thin Capillaries

The mesopancreas and pancreatic head plexus: morphological, developmental, and clinical perspectives.

Total mesopancreas excision has been found to be helpful for increasing no residual tumor resection rate and improving the prognosis of pancreatic cancer. This study analyzed the relationships among the mesopancreas and pancreatic head plexus from the morphological, developmental, and clinical perspectives. Twenty-four cadavers were employed. The upper abdominal viscera were resected en-bloc with the hepatoduodenal ligament, abdominal aorta, and nerve plexuses, and the innervation of the pancreas was dissected. Ten additional cadavers were used for histological examination of the pancreatic head and neck, part of the duodenum, the superior mesenteric artery (SMA) and its surrounding tissues, and the related arteries and veins. As results, cross-sections of the SMA revealed 6-9 layers of membranous structures resembling the layers of an onion, and the nerve fibers of the superior mesenteric plexus ran between the layers. Loose areolar tissue, adipose tissue, and lymphatics existed between the SMA and the pancreatic head/uncinate process, along with abundant thin blood vessels and capillaries, but very few nerves were found approaching the pancreas. Several parallel layers of collagen fibers (so-called Treitz's fusion fascia) existed between the dorsal aspect of the pancreatic head and the aortocaval plane. The mesopancreas was continuous and connected with the para-aortic area. It may be better termed the mesopancreatoduodenum than the mesopancreas, as the duodenum-pancreas-SMA forms a complex morphological, developmental, functional, and pathological structure.

Modeling Impregnation of Porous Materials in a Force Field with Account of the Diffusion of Trapped Gases

It has been shown that a nonuniform electric field can have a significant effect on the kinetics of diffusion capillary imbibition of liquids into thin dead-end capillaries that are a model of pore strictures. The results of calculations are in satisfactory agreement with experimental data.

New textile-based hybrid photovoltaic/thermal (PV/T) system

This paper introduces a new textile-based hybrid PV/T system utilizing a spacer fabric treated with phase change material (PCM). The PCM absorbs excess heat from the PV modules, which keeps the modules in their optimal temperature range so that their power output is enhanced. The thermal energy stored in the PCM is then used for hot water generation. Cold water, which is pumped through thin capillaries integrated into the spacer fabric, absorbs the heat stored in the PCM and is heated up. The warm water can be used immediately or stored in an intermediate storage tank. Comparing the proposed textile-based hybrid PV/T system to conventional hybrid PV/T systems, the proposed system is less expensive and provides a higher overall efficiency. The textile-based collector is lightweight, thin and flexible.

Thin hybrid capillary two-phase cooling system

A novel hybrid two-phase cooling system was developed that integrated a mechanically pumped two-phase loop with a capillary-driven two-phase cooling device. The latter cooling mechanism was based on evaporation/boiling from wick structures made by sintering copper particles on the interior surfaces of a copper cold plate. The cold plate provided cooling to two surfaces and each of them included four heaters in series. The novelty of the developed technology was preventing flooding of the evaporator wicks by isolating the evaporation surface from the pumped liquid flow that fed them. This arrangement allowed for a high liquid feed flow rate much greater than would be allowed by a capillary pumped system while maintaining a low thermal resistance at the evaporation surface. Using this approach, the cooling system removed over 850 W with a low pumping power below 1.0 W while using R245fa as the working fluid. The equivalent heat fluxes exceeded 970 W/cm2 over areas less than 0.12 cm2. The measured thermal resistance was as low as 0.09 K-cm2/W. The presented thermal management solution enables an increase in the power of high heat flux electronic devices beyond the state-of-the-art.

Micro‐computed tomography for the investigation of stationary liquid–liquid and liquid–gas interfaces in capillaries

AbstractFor better understanding and optimization of multiphase flow in miniaturized devices, micro‐computed tomography (μCT) is a promising visualization tool, as it is nondestructive, three‐dimensional, and offers a high spatial resolution. Today, computed tomography (CT) is a standard imaging technique. However, using CT in microfluidics is still challenging, since X‐ray related artifacts, low phase contrast, and limited spatial resolution complicate the exact localization of interfaces. We apply μCT for the characterization of stationary interfaces in thin capillaries. The entire workflow for imaging stationary interfaces in capillaries, from image acquisition to the analysis of interfaces, is presented. Special emphasis is given to an in‐house developed segmentation routine. For demonstration purposes, contact angles of water, liquid polydimethylsiloxane, and air in FEP, glass, and PMMA are determined and the influence of gravity on interface formation is discussed. This work comprises the first steps for a systematic 3D investigation of multiphase flows in capillaries using μCT.

Crystallinity and grain distributions of fiber-formed nanostructure on tungsten surface with helium plasma exposure

Growth mechanisms of complex tungsten (W) fuzzy nanostructure on helium-plasma-irradiated W surface have been extensively studied since the discovery of the phenomenon in 2006. However, the growth process of complicated W nano-fibers from the atomistic and crystal structure standpoints is not well understood. In this study, the X-ray diffraction (XRD) and transmission electron microscopy (TEM) were performed to investigate complexity of nano-fibers as well as their crystallinity. Small-angle-incident XRD on the substrate with fuzz and He-defected bulk surface was used to determine grain distribution among contributions of different crystal orientation families, showing the difference in grain distribution of surface fuzz layer and the basing W bulk surface with helium defects compared with the distribution of pristine powder metallurgy W (PM-W). Peak shifts and broadenings of X-ray diffracted spectra with respect to pristine PM-W substrate and TEM observations were discussed in terms of crystallinity and He-bubbles induced strain. It is speculated that the grain distribution of the He-defected W with nano-fibers would be very similar to that of bulk α-phase W globally. Moreover, the scraped-off fuzz aggregate without basing plate makes it possible to conduct XRD using a thin glass capillary tube. The grain distribution of pure fuzz aggregate was found to be very similar to natural α-phase W with intensification of high grain orientation modes. The process of such high modes may bring morphological complexity to nano-fibers because grain boundaries play a role of turning surfaces along nano-fibers.

Separation of Binary Alloys in Thin Capillaries

A direct numerical simulation of the process of binary alloy separation in a thin nonuniformly heated circular capillary is carried out. The key point of this process is the assumption of the existence of a thin gas layer between the melt and the boundary of the reservoir due to the non-wetting conditions. This effect was described using the equations of interphase hydrodynamics, which made it possible to construct a phenomenological model of the processes at the melt-solid interface for mixtures of liquid metals. The problem was solved by the finite difference method in combination with an explicit scheme on the PGNIU-Kepler supercomputer at the Research and Education Center “Parallel and Distributed Computing” of the Perm State National Research University. The velocity and temperature fields, as well as the concentration of melt components in the bulk and on the surface, were determined through numerical simulation. The dynamics of the separation process is described. It is shown that the longitudinal temperature gradient and the non-wetting conditions on the lateral surface create a downward motion of the melt along the boundary, which, together with the adsorption and desorption effects, leads to the formation of volumetric nonuniformity of the concentration of the mixture components along the capillary. The experimentally observed time dependence of the difference in the volume concentrations of the components at the ends of the capillary is reproduced. The distribution of volume concentrations of the components and the surface phase along the capillary is analyzed at various values of the adsorption and desorption coefficients and the Marangoni number. The dependence of the concentration difference for the melt components at the ends of the capillary as function of its length is studied. It is found that the separation effect intensifies with an increase in the capillary length. A qualitative and quantitative comparison of most of the characteristics demonstrates a good correlation of the calculation results with the data previously obtained for the plane problem and the available experimental data. A numerical experiment shows that the motion in the surface layer is rather intense. The heavy component is transported by the convective flow to the lower part of the capillary so that its concentration increases by almost an order of magnitude on 1/8 of the capillary surface.

Flow-Induced Precipitation in Thin Capillaries Creates Helices, Lamellae, and Tubes.

Precipitation reactions under flow in confined media are relevant to the control of pathological biomineralization, processes affecting aquifers, and challenges in the petroleum industry. Here we show that for a simple geometry, such conditions create macroscopic structures including helices, tubes, lamellae, slugs, and disordered patterns. All structures emerge when salt solution is slowly injected into thin capillaries filled with hydroxide solution. For the helices, the pitch is proportional to the pump rate revealing a constant period of 0.63 s. Different morphologies of the insoluble metal hydroxide can co-exist causing random transitions along the capillary. On average, 15 % of the final system contains residual hydroxide solution. While mechanically stable for flow speeds above 25 mm min-1 , structures collapse and sediment for slower injection speeds. Some of the observed features share similarities with precipitate tubes in chemical gardens and the dynamics of liquid-liquid pipe flow.

Gas Hydrate Crystallization in Thin Glass Capillaries: Roles of Supercooling and Wettability.

We designed and implemented an experimental methodology to investigate gas hydrate formation and growth around a water-guest meniscus in a thin glass capillary, thus mimicking pore-scale processes in sediments. The glass capillary acts as a high-pressure optical cell in a range of supercooling conditions from 0.1 °C, i.e., very close to hydrate dissociation conditions, to ∼35 °C, very near the metastability limit. Liquid or gaseous CO2 is the guest phase in most of the experiments reported in this paper, and N2 in a few of them. The setup affords detailed microscopic observation of the roles of the key parameters on hydrate growth and interaction with the substrate: supercooling and substrate wettability. At low supercooling (less than 0.5 °C), a novel hydrate growth process is discovered, which consists of a hollow crystal originating from the meniscus and advancing on the guest side along the glass, fed by a thick water layer sandwiched between the glass and this crystal.