Role of Droplet Dynamics on Contact Line Depinning in Shearing Gas Flow.

Sessile droplets exposed to shearing gas flows resist depinning owing to surface tension and contact angle hysteresis. It is known that contact line depinning occurs when the shearing gas flow is large enough to deform the droplet beyond its contact angle hysteresis. This work explores the contact line depinning process by visualizing growing droplets on a porous layer in laminar shear gas flows. High-speed imaging of droplets revealed an oscillatory motion in droplets, which is speculated to originate from an interaction between the drag force and surface tension effects. This oscillatory motion creates an inertial force within the droplet which combines with the drag force when droplet acceleration is in the stream-wise direction. The combined effect competes against the droplet adhesion force, setting the depinning criteria. Analyzing droplet images revealed that droplet local velocity and acceleration (i.e., sessile droplet dynamics prior to detachment from the substrate) increase with the superficial gas velocity. At the same time, the contact line depinning occurs at a smaller droplet size for higher superficial gas velocities. This results in a "hill-like" variation of the inertial force as a function of the convective Weber number, Weconv, causing a local maximum in the inertial force data (Weconv scales the inertia effects of the shear flow to surface tension effects). For the experimental condition tested in the current study, the inertial force created in the droplet could reach up to half of the adhesion force, making the drag force only responsible for the other half to depin the droplet contact line. Even at low superficial gas velocities, which featured lower droplet oscillations, the inertial force created in the droplet was considerable with respect to the adhesion force, reaching around one-third of the adhesion force.

Enhancement of measurement accuracy of X-ray PIV in comparison with the micro-PIV technique.

The X-ray PIV (particle image velocimetry) technique has been used as a non-invasive measurement modality to investigate the haemodynamic features of blood flow. However, the extraction of two-dimensional velocity field data from the three-dimensional volumetric information contained in X-ray images is technically unclear. In this study, a new two-dimensional velocity field extraction technique is proposed to overcome technological limitations. To resolve the problem of finding a correction coefficient, the velocity field information obtained by X-ray PIV and micro-PIV techniques for disturbed flow in a concentric stenosis with 50% severity was quantitatively compared. Micro-PIV experiments were conducted for single-plane and summation images, which provide similar positional information of particles as X-ray images. The correction coefficient was obtained by establishing the relationship between velocity data obtained from summation images (VS) and centre-plane images (VC). The velocity differences between VS and VC along the vertical and horizontal directions were quantitatively analysed as a function of the geometric angle of the test model for applying the present two-dimensional velocity field extraction technique to a conduit of arbitrary geometry. Finally, the two-dimensional velocity field information at arbitrary positions could be successfully extracted from X-ray images by using the correction coefficient and several velocity parameters derived from VS.

Simultaneous measurement of bubble size, velocity and void fraction in two-phase bubbly flows with time-resolved X-ray imaging.

Key parameters of two-phase flows, such as void fraction and microscale bubble size, shape and velocity, were simultaneously measured using time-resolved X-ray imaging. X-ray phase-contrast imaging was employed to obtain those parameters on microbubbles. The void fraction was estimated from X-ray absorption. The radii of the measured microbubbles were mostly smaller than 20 µm, and the maximum velocity was 39.442 mm s(-1), much higher than that in previous studies. The spatial variations of the void fraction were consecutively obtained with a small time interval. This technique would be useful in the experimental analysis of bubbly flows in which microbubbles move at high speed.

Usage of CO2 microbubbles as flow-tracing contrast media in X-ray dynamic imaging of blood flows.

X-ray imaging techniques have been employed to visualize various biofluid flow phenomena in a non-destructive manner. X-ray particle image velocimetry (PIV) was developed to measure velocity fields of blood flows to obtain hemodynamic information. A time-resolved X-ray PIV technique that is capable of measuring the velocity fields of blood flows under real physiological conditions was recently developed. However, technical limitations still remained in the measurement of blood flows with high image contrast and sufficient biocapability. In this study, CO2 microbubbles as flow-tracing contrast media for X-ray PIV measurements of biofluid flows was developed. Human serum albumin and CO2 gas were mechanically agitated to fabricate CO2 microbubbles. The optimal fabricating conditions of CO2 microbubbles were found by comparing the size and amount of microbubbles fabricated under various operating conditions. The average size and quantity of CO2 microbubbles were measured by using a synchrotron X-ray imaging technique with a high spatial resolution. The quantity and size of the fabricated microbubbles decrease with increasing speed and operation time of the mechanical agitation. The feasibility of CO2 microbubbles as a flow-tracing contrast media was checked for a 40% hematocrit blood flow. Particle images of the blood flow were consecutively captured by the time-resolved X-ray PIV system to obtain velocity field information of the flow. The experimental results were compared with a theoretically amassed velocity profile. Results show that the CO2 microbubbles can be used as effective flow-tracing contrast media in X-ray PIV experiments.

Detection of circulating tumor cells via an X-ray imaging technique.

Detailed information on the location and the size of tumor cells circulating through lymphatic and blood vessels is useful to cancer diagnosis. Metastasis of cancers to other non-adjacent organs is reported to cause 90% of deaths not from the primary tumors. Therefore, effective detection of circulating tumors cells (CTCs) related to metastasis is emphasized in cancer treatments. With the use of synchrotron X-ray micro-imaging techniques, high-resolution images of individual flowing tumor cells were obtained. Positively charged gold nanoparticles (AuNPs) which were inappropriate for incorporation into human red blood cells were selectively incorporated into tumor cells to enhance the image contrast. This approach enables images of individual cancer cells and temporal movements of CTCs to be captured by the high X-ray absorption efficiency of selectively incorporated AuNPs. This new technology for in vivo imaging of CTCs would contribute to improve cancer diagnosis and cancer therapy prognosis.

Time-resolved X-ray PIV technique for diagnosing opaque biofluid flow with insufficient X-ray fluxes.

X-ray imaging is used to visualize the biofluid flow phenomena in a nondestructive manner. A technique currently used for quantitative visualization is X-ray particle image velocimetry (PIV). Although this technique provides a high spatial resolution (less than 10 µm), significant hemodynamic parameters are difficult to obtain under actual physiological conditions because of the limited temporal resolution of the technique, which in turn is due to the relatively long exposure time (~10 ms) involved in X-ray imaging. This study combines an image intensifier with a high-speed camera to reduce exposure time, thereby improving temporal resolution. The image intensifier amplifies light flux by emitting secondary electrons in the micro-channel plate. The increased incident light flux greatly reduces the exposure time (below 200 µs). The proposed X-ray PIV system was applied to high-speed blood flows in a tube, and the velocity field information was successfully obtained. The time-resolved X-ray PIV system can be employed to investigate blood flows at beamlines with insufficient X-ray fluxes under specific physiological conditions. This method facilitates understanding of the basic hemodynamic characteristics and pathological mechanism of cardiovascular diseases.

Gold nanoparticle contrast agents in advanced X-ray imaging technologies.

Recently, there has been significant progress in the field of soft- and hard-X-ray imaging for a wide range of applications, both technically and scientifically, via developments in sources, optics and imaging methodologies. While one community is pursuing extensive applications of available X-ray tools, others are investigating improvements in techniques, including new optics, higher spatial resolutions and brighter compact sources. For increased image quality and more exquisite investigation on characteristic biological phenomena, contrast agents have been employed extensively in imaging technologies. Heavy metal nanoparticles are excellent absorbers of X-rays and can offer excellent improvements in medical diagnosis and X-ray imaging. In this context, the role of gold (Au) is important for advanced X-ray imaging applications. Au has a long-history in a wide range of medical applications and exhibits characteristic interactions with X-rays. Therefore, Au can offer a particular advantage as a tracer and a contrast enhancer in X-ray imaging technologies by sensing the variation in X-ray attenuation in a given sample volume. This review summarizes basic understanding on X-ray imaging from device set-up to technologies. Then this review covers recent studies in the development of X-ray imaging techniques utilizing gold nanoparticles (AuNPs) and their relevant applications, including two- and three-dimensional biological imaging, dynamical processes in a living system, single cell-based imaging and quantitative analysis of circulatory systems and so on. In addition to conventional medical applications, various novel research areas have been developed and are expected to be further developed through AuNP-based X-ray imaging technologies.

Improvement of water harvesting performance through collector modification in industrial cooling tower.

Shortages of freshwater have become increasingly common around the world, and various studies have been conducted to solve this problem by collecting and reusing the water in nature or from factories and power plants that produce large fog plumes. Although the shape of a collection screen is strongly related to its harvesting performance, only flat meshes have been considered in previous studies, and research on the effects of collector structure shapes is severely lacking. In this study, we proposed modified collector structures improving harvesting performances in industrial cooling towers. The screen shape was modified in three steps. First, a concave shape was adopted for the mesh screen to increase the aerodynamic characteristics of the collection structure. Next, a sidewall was installed to collect additional fog from defected flows generated by the concave structure. Finally, to reduce loss during the draining of collected water droplets, the discharge direction of the fog flow was changed to follow the same direction as fog-laden flows in nature. Our results are expected to be useful for collector design in terms of increasing harvesting efficiency in various industrial fields in the future.

Effect of trichome structure of Tillandsia usneoides on deposition of particulate matter under flow conditions.

The removal of particulate matters (PM) has emerged as one of the most significant issues in public health and environment worldwide. Environmentalists have proposed the use of indoor air-purifying plants as an eco-friendly strategy to resolve PM-related problems and effectively remove fine particulate matter (PM2.5). Among air-purifying plants, Tillandsia usneoides (L.) L. (T. usneoides) has been used as a biomonitor for heavy metals and air pollutants. However, the PM removal effect of T. usneoides and its primary mechanism remain unclear. Here, we investigated the PM removal performance of T. usneoides in a closed chamber under flow conditions, the effects of trichomes, and the array density according to the different types of PM. The chamber with bulk T. usneoides under flow conditions exhibited 16.5 % and 9.2 % higher removal efficiency in PM2.5T. usneoides for incense and A1 rigid PM, respectively, than that without T. usneoides. T. usneoides with trichome structure exhibited larger removal efficiencies of 7% and 2% in PM2.5 and PM10, respectively, than without trichome for incense particles. In addition, the increase in total effective surface was effective for the deposition of both PM types. The increase in effective surface area by trichome structure and array density of T. usneoides is a crucial factor for the deposition of PM.

Microfluidic measurement for blood flow and platelet adhesion around a stenotic channel: Effects of tile size on the detection of platelet adhesion in a correlation map.

Platelet aggregation affects the surrounding blood flow and usually occurs where a blood vessel is narrowed as a result of atherosclerosis. The relationship between blood flow and platelet aggregation is not yet fully understood. This study proposes a microfluidic method to measure the velocity and platelet aggregation simultaneously by combining the micro-particle image velocimetry technique and a correlation mapping method. The blood flow and platelet adhesion procedure in a stenotic micro-channel with 90% severity were observed for a relatively long period of 4 min. In order to investigate the effect of tile size on the detection of platelet adhesion, 2D correlation coefficients were evaluated with binary images obtained by manual labeling and the correlation mapping method with different sizes of the square tile ranging from 3 to 50 pixels. The maximum 2D correlation coefficient occurred with the optimum tile size of 5 × 5 pixels. Since the blood flow and platelet aggregation are mutually influenced by each other, blood flow and platelet adhesion were continuously varied. When there was no platelet adhesion (t = 0 min), typical blood flow is observed. The blood flow passes through the whole channel smoothly, and jet-like flow occurs in the post-stenosis region. However, the flow pattern changes when platelet adhesion starts at the stenosis apex and after the stenosis. These adhesions induce narrow high velocity regions to become wider over a range of area from upstream to downstream of the stenosis. Separated jet-like flows with two high velocity regions are also created. The changes in flow patterns may alter the patterns of platelet adhesion. As the area of the plate adhesion increases, the platelets plug the micro-channel and there is only a small amount of blood flow, finally. The microfluidic method could provide new insights for better understanding of the interactions between platelet aggregation and blood flow in various physiological conditions.

Note: development of a compact x-ray particle image velocimetry for measuring opaque flows. II. Three-dimensional velocity field reconstruction.

An x-ray particle image velocimetry (PIV) system using a cone-beam type x-ray was developed. The field of view and the spatial resolution are 36 × 24.05 mm(2) and 20 µm, respectively. The three-dimensional velocity field was reconstructed by adopting the least squares minimum residue and simultaneous multiplicative algebraic reconstruction techniques. According to a simulation study with synthetic images, the reconstructions were acceptable with 7 projections and 50 iterations. The reconstructed and supplied flow rates differed by only about 6.49% in experimental verification. The x-ray tomographic PIV system would be useful for 3D velocity field information of opaque flows.

In vivo measurements of blood flow in a rat using X-ray imaging technique.

To measure instantaneous velocity fields of venous blood flow in a rat using X-ray particle tracking method. Gold nanoparticles (AuNPs) incorporated chitosan microparticles were applied as biocompatible flow tracers. After intravenous injection of the AuNP-chitosan particles into 7- to 9-week-old male rat vein, X-ray images of particle movement inside the cranial vena cava were consecutively captured. Individual AuNP-chitosan particles in the venous blood flow were clearly observed, and the corresponding velocity vectors were successfully extracted. The measured velocity vectors are in good agreement with the theoretical velocity profile suggested by Casson. This is the first trial to measure blood flow in animals under in vivo conditions with X-ray imaging technique. The results show that X-ray particle tracking technique has a great potential for in vivo measurements of blood flow, which can extend to various biomedical applications related with the diagnosis of circulatory vascular diseases.

Chitosan microparticles incorporating gold as an enhanced contrast flow tracer in dynamic X-ray imaging.

In situ monitoring of a biofluid can provide important information on circulatory disorders and a basic understanding on the metabolic mechanisms of living organisms. X-ray imaging has significant advantages as one of the most popular diagnostic tools to seethrough various biological systems. Particle traced velocity field measurement is one of the most popular methods for quantitative analysis of dynamic flow motion. In this study we have developed chitosan microparticles incorporating gold nanoparticles (AuNP) as a new enhanced contrast flow tracer for dynamic X-ray imaging. Gold is a useful material possessing high X-ray absorption ability and also biocompatibility. We chose chitosan as an AuNP delivery system because it can effectively trap AuNPs at high yield. In particular, the unique gold ion reduction ability of and compatibility with surface-modified chitosans are effectively utilized. The physical properties of the Au-chitosan microparticles can be controlled by varying the molecular weight of the chitosan employed and the AuNP incorporation methodology. The environment of the particles and the type of applied X-ray essentially determine the imaging efficiency. The designed chitosan microparticles incorporating Au have been successfully applied to track the digestive mechanisms occurring in delicate insects such as live mosquitoes.

Properties of iopamidol-incorporated poly(vinyl alcohol) microparticle as an X-ray imaging flow tracer.

We have recently reported on poly(vinyl alcohol) microparticles containing X-ray contrast agent, iopamidol, designed as a flow tracer working in synchrotron X-ray imaging ( Biosens. Bioelectron. 2010 , 25 , 1571 ). Although iopamidol is physically encapsulated in the microparticles, it displays a great contrast enhancement and stable feasibility in in vitro human blood pool. Nonetheless, a direct relation between the absolute amount of incorporated iopamidol and the enhancement in imaging efficiency was not observed. In this study, physical properties of the designed microparticle are systematically investigated experimentally with theoretical interpretation to correlate an enhancement in X-ray imaging efficiency. The compositional ratio of X-ray contrast agent in polymeric microparticle is controlled as 1/1 and 10/1 [contrast agent/polymer microparticle (w/w)] with changed degree of cross-linkings. Flory-Huggins interaction parameter (χ), retractive force (τ) and degree of swelling of the designed polymeric microparticles are investigated. In addition, the hydrodynamic size (D(H)) and ζ-potential are evaluated in terms of environment responsiveness. The physical properties of the designed flow tracer microparticles under a given condition are observed to be strongly related with the X-ray absorption efficiency, which are also supported by the Beer-Lambert-Bouguer law. The designed microparticles are almost nontoxic with a reasonable concentration and time period, enough to be utilized as a flow tracer in various biomedical applications. This study would contribute to the basic understanding on the physical property connected with the imaging efficiency of contrast agents.

Imaging efficiency of an X-ray contrast agent-incorporated polymeric microparticle.

Biocompatible polymeric encapsulants have been widely used as a delivery vehicle for a variety of drugs and imaging agents. In this study, X-ray contrast agent (iopamidol) is encapsulated into a polymeric microparticle (polyvinyl alcohol) as a particulate flow tracer in synchrotron X-ray imaging system. The physical properties of the designed microparticles are investigated and correlated with enhancement in the imaging efficiency by experimental observation and theoretical interpretation. The X-ray absorption ability of the designed microparticle is assessed by Beer-Lambert-Bouguer law. Particle size, either in dried state or in solvent, primarily dominates the X-ray absorption ability under the given condition, thus affecting imaging efficiency of the designed X-ray contrast flow tracers.

Gold nanoparticle-incorporated human red blood cells (RBCs) for X-ray dynamic imaging.

Time-resolved dynamic imaging of bio-fluids can provide valuable information for clinical diagnosis and treatment of circulatory disorders. Quantitative information on non-transparent blood flows can be directly obtained by particle-tracing dynamic X-ray imaging, which needs better spatial resolution and enhanced image contrast compared to static imaging. For that use, tracer particles tagging along the flow streams are critically required. In this study, taking the advantage of high X-ray absorption, gold nanoparticles (AuNPs) are incorporated into human red blood cells (RBC) to produce contrast-enhanced tracers designed for dynamic X-ray imaging of blood flows. RBCs are advantageous tracers for blood flow measurements since they are natural and primary components of blood. The loading efficiency of AuNPs into RBCs is investigated in terms of the surface properties of the AuNPs. The AuNP-incorporated RBC provides a potential in the dynamic X-ray imaging of blood flows which can be used for clinical applications.

Visual genome-wide RNAi screening to identify human host factors required for Trypanosoma cruzi infection.

The protozoan parasite Trypanosoma cruzi is the etiologic agent of Chagas disease, a neglected tropical infection that affects millions of people in the Americas. Current chemotherapy relies on only two drugs that have limited efficacy and considerable side effects. Therefore, the development of new and more effective drugs is of paramount importance. Although some host cellular factors that play a role in T. cruzi infection have been uncovered, the molecular requirements for intracellular parasite growth and persistence are still not well understood. To further study these host-parasite interactions and identify human host factors required for T. cruzi infection, we performed a genome-wide RNAi screen using cellular microarrays of a printed siRNA library that spanned the whole human genome. The screening was reproduced 6 times and a customized algorithm was used to select as hits those genes whose silencing visually impaired parasite infection. The 162 strongest hits were subjected to a secondary screening and subsequently validated in two different cell lines. Among the fourteen hits confirmed, we recognized some cellular membrane proteins that might function as cell receptors for parasite entry and others that may be related to calcium release triggered by parasites during cell invasion. In addition, two of the hits are related to the TGF-beta signaling pathway, whose inhibition is already known to diminish levels of T. cruzi infection. This study represents a significant step toward unveiling the key molecular requirements for host cell invasion and revealing new potential targets for antiparasitic therapy.

Flow tracing microparticle sensors designed for enhanced X-ray contrast.

In applying the X-ray particle image velocimetry (PIV) technique to biofluid flows, the most pivotal prerequisite is suitable flow tracing sensors which should be detected effectively by the X-ray imaging system. In this study, to design those flow tracing sensors, X-ray contrast agent Iopamidol was encapsulated into the poly(vinyl alcohol) (PVA) microparticles crosslinked by glutaraldehyde (GA). The characteristics of the fabricated particle sensors were determined by optical microscopy, scanning electron microscopy, dynamic light scattering, laser Doppler electrophoresis and nuclear magnetic resonance spectroscopy ((1)H NMR). The amount of Iopamidol in the microparticles was measured using the energy dispersive X-ray spectroscopy (EDS) and (1)H NMR. The physical properties of the PVA microparticles are effectively controlled in terms of the average particle size, degree of crosslinking, degree of swelling and encapsulation efficiency of Iopamidol. By changing the amount of crosslinker, the degree of crosslinking and the efficiency of the Iopamidol encapsulation reached to the optimal. To some extent, the zeta-potential of the PVA microparticles is increased in less ionic media where the particles can effectively repel each other prohibiting aggregation. The X-ray absorption ability of the designed tracing sensors was examined by a synchrotron X-ray imaging technique. The X-ray absorption coefficients of the particle sensors were expressed by an exponential law assuming the spherical shape of the microparticles. The X-ray contrast agent, Iopamidol, was successfully encapsulated into the bio-compatible and bio-degradable PVA. With the controlled physical properties of the flow tracing sensors designed in this study, the particle sensors exhibit excellent X-ray absorption contrast fairly applicable in biological systems.

Gold nanoparticle flow sensors designed for dynamic X-ray imaging in biofluids.

X-ray-based imaging is one of the most powerful and convenient methods in terms of versatility in applicable energy and high performance in use. Different from conventional nuclear medicine imaging, contrast agents are required in X-ray imaging especially for effectively targeted and molecularly specific functions. Here, in contrast to much reported static accumulation of the contrast agents in targeted organs, dynamic visualization in a living organism is successfully accomplished by the particle-traced X-ray imaging for the first time. Flow phenomena across perforated end walls of xylem vessels in rice are monitored by a gold nanoparticle (AuNP) (approximately 20 nm in diameter) as a flow tracing sensor working in nontransparent biofluids. AuNPs are surface-modified to control the hydrodynamic properties such as hydrodynamic size (DH), zeta-potential, and surface plasmonic properties in aqueous conditions. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray nanoscopy (XN), and X-ray microscopy (XM) are used to correlate the interparticle interactions with X-ray absorption ability. Cluster formation and X-ray contrast ability of the AuNPs are successfully modulated by controlling the interparticle interactions evaluated as flow-tracing sensors.

Development of a compact x-ray particle image velocimetry for measuring opaque flows.

A compact x-ray particle image velocimetry (PIV) system employing a medical x-ray tube as a light source was developed to measure quantitative velocity field information of opaque flows. The x-ray PIV system consists of a medical x-ray tube, an x-ray charge coupled device camera, a programmable shutter for a pulse-type x ray, and a synchronization device. Through performance tests, the feasibility of the developed x-ray PIV system as a flow measuring device was verified. To check the feasibility of the developed system, we tested a tube flow at two different mean velocities of 1 and 2 mm/s. The x-ray absorption of tracer particles must be quite different from that of working fluid to have a good contrast in x-ray images. All experiments were performed under atmospheric pressure condition. This system is unique and useful for investigating various opaque flows or flows inside opaque conduits.