Jeongeun Ryu

Label-free viscosity measurement of complex fluids using reversal flow switching manipulation in a microfluidic channel

The accurate viscosity measurement of complex fluids is essential for characterizing fluidic behaviors in blood vessels and in microfluidic channels of lab-on-a-chip devices. A microfluidic platform that accurately identifies biophysical properties of blood can be used as a promising tool for the early detections of cardiovascular and microcirculation diseases. In this study, a flow-switching phenomenon depending on hydrodynamic balancing in a microfluidic channel was adopted to conduct viscosity measurement of complex fluids with label-free operation. A microfluidic device for demonstrating this proposed method was designed to have two inlets for supplying the test and reference fluids, two side channels in parallel, and a junction channel connected to the midpoint of the two side channels. According to this proposed method, viscosities of various fluids with different phases (aqueous, oil, and blood) in relation to that of reference fluid were accurately determined by measuring the switching flow-rate ratio between the test and reference fluids, when a reverse flow of the test or reference fluid occurs in the junction channel. An analytical viscosity formula was derived to measure the viscosity of a test fluid in relation to that of the corresponding reference fluid using a discrete circuit model for the microfluidic device. The experimental analysis for evaluating the effects of various parameters on the performance of the proposed method revealed that the fluidic resistance ratio ( R J L / R L , fluidic resistance in the junction channel ( R J L ) to fluidic resistance in the side channel ( R L )) strongly affects the measurement accuracy. The microfluidic device with smaller R J L / R L values is helpful to measure accurately the viscosity of the test fluid. The proposed method accurately measured the viscosities of various fluids, including single-phase (Glycerin and plasma) and oil-water phase (oil vs. deionized water) fluids, compared with conventional methods. The proposed method was also successfully applied to measure viscosities of blood with varying hematocrits, chemically fixed RBCS, and channel sizes. Based on these experimental results, the proposed method can be effectively used to measure the viscosities of various fluids easily, without any fluorescent labeling and tedious calibration procedures.

Direct observation of local xylem embolisms induced by soil drying in intact Zea mays leaves

Highlight Direct X-ray micro-imaging reveals localized xylem embolism under water stress conditions in the leaves of intact maize, with a specific spatial distribution of embolism in terms of xylem structure.

How the change of contact angle occurs for an evaporating droplet: effect of impurity and attached water films

On a hydrophobic surface, the contact angle of an evaporating droplet decreases with time and becomes much smaller than its receding contact angle; the rate of decrease is accelerated with time. When we use impurity-concentrated water produced by partial distillation, the decrease in contact angle is remarkably accelerated with time. In contrast, for purified water, the decrease in contact angle is significantly reduced and the start of stage 3 is delayed. These results indicate that the submicron-sized impurities cause the decrease in contact angle. Also, we found that a number of attached thin films of water are generated around the periphery of impure droplets. We derived the contact angle equation under the Cassie–Baxter model by regarding the water film as a heterogeneous layer. We compared the theoretical model to the experimental data, and these results suggest that the attached film should be considered as one of the direct causes for the large deviation from the Youngs angle of evaporating droplets.

Nearly Perfect Durable Superhydrophobic Surfaces Fabricated by a Simple One-Step Plasma Treatment

Fabrication of superhydrophobic surfaces is an area of great interest because it can be applicable to various engineering fields. A simple, safe and inexpensive fabrication process is required to fabricate applicable superhydrophobic surfaces. In this study, we developed a facile fabrication method of nearly perfect superhydrophobic surfaces through plasma treatment with argon and oxygen gases. A polytetrafluoroethylene (PTFE) sheet was selected as a substrate material. We optimized the fabrication parameters to produce superhydrophobic surfaces of superior performance using the Taguchi method. The contact angle of the pristine PTFE surface is approximately 111.0° ± 2.4°, with a sliding angle of 12.3° ± 6.4°. After the plasma treatment, nano-sized spherical tips, which looked like crown-structures, were created. This PTFE sheet exhibits the maximum contact angle of 178.9°, with a sliding angle less than 1°. As a result, this superhydrophobic surface requires a small external force to detach water droplets dripped on the surface. The contact angle of the fabricated superhydrophobic surface is almost retained, even after performing an air-aging test for 80 days and a droplet impacting test for 6 h. This fabrication method can provide superb superhydrophobic surface using simple one-step plasma etching.

Interactive Ion-Mediated Sap Flow Regulation in Olive and Laurel Stems: Physicochemical Characteristics of Water Transport via the Pit Structure

Sap water is distributed and utilized through xylem conduits, which are vascular networks of inert pipes important for plant survival. Interestingly, plants can actively regulate water transport using ion-mediated responses and adapt to environmental changes. However, ionic effects on active water transport in vascular plants remain unclear. In this report, the interactive ionic effects on sap transport were systematically investigated for the first time by visualizing the uptake process of ionic solutions of different ion compositions (K+/Ca2+) using synchrotron X-ray and neutron imaging techniques. Ionic solutions with lower K+/Ca2+ ratios induced an increased sap flow rate in stems of Olea europaea L. and Laurus nobilis L. The different ascent rates of ionic solutions depending on K+/Ca2+ ratios at a fixed total concentration increases our understanding of ion-responsiveness in plants from a physicochemical standpoint. Based on these results, effective structural changes in the pit membrane were observed using varying ionic ratios of K+/Ca2+. The formation of electrostatically induced hydrodynamic layers and the ion-responsiveness of hydrogel structures based on Hofmeister series increase our understanding of the mechanism of ion-mediated sap flow control in plants.

Comparison of the functional features of the pump organs of Anopheles sinensis and Aedes togoi

Mosquitoes act as vectors for severe tropical diseases. Mosquito-borne diseases are affected by various factors such as environmental conditions, host body susceptibility, and mosquito feeding behavior. Among these factors, feeding behavior is affected by the feeding pump system located inside the mosquito head and also depends on the species of mosquito. Therefore, the 3D morphological structures of the feeding pumps of Aedes togoi and Anopheles sinensis were comparatively investigated using synchrotron X-ray microscopic computed tomography. In addition, the feeding behaviors of their pumping organs were also investigated using a 2D X-ray micro-imaging technique. An. sinensis, a malarial vector mosquito, had a larger feeding pump volume than Ae. togoi in the static or resting position. Interestingly, the two species of mosquitoes exhibited different feeding behaviors. Ae. togoi had a higher feeding frequency and expansion ratio than An. sinensis. Ae. togoi also exhibited F-actin localization more clearly. These distinctive variations in feeding volumes and behaviors provide essential insight into the blood-feeding mechanisms of female mosquitoes as vectors for tropical diseases.

Vulnerability of Protoxylem and Metaxylem Vessels to Embolisms and Radial Refilling in a Vascular Bundle of Maize Leaves

Regulation of water flow in an interconnected xylem vessel network enables plants to survive despite challenging environment changes that can cause xylem embolism. In this study, vulnerability to embolisms of xylem vessels and their water-refilling patterns in vascular bundles of maize leaves were experimentally investigated by employing synchrotron X-ray micro-imaging technique. A vascular bundle in maize consisted of a protoxylem vessel with helical thickenings between two metaxylem vessels with single perforation plates and nonuniformly distributed pits. When embolism was artificially induced in excised maize leaves by exposing them to air, protoxylem vessels became less vulnerable to dehydration compared to metaxylem vessels. After supplying water into the embolized vascular bundles, when water-refilling process stopped at the perforation plates in metaxylem vessels, discontinuous radial water influx occurred surprisingly in the adjacent protoxylem vessels. Alternating water refilling pattern in protoxylem and metaxylem vessels exhibited probable correlation between the incidence location and time of water refilling and the structural properties of xylem vessels. These results imply that the maintenance of water transport and modulation of water refilling are affected by hydrodynamic roles of perforation plates and radial connectivity in a xylem vascular bundle network.

SPECT/CT analysis of splenic function in genistein-treated malaria-infected mice

Spleen traps malaria-infected red blood cells, thereby leading to splenomegaly. Splenomegaly induces impairment in splenic function, i.e., rupture. Therefore, splenomegaly inhibition is required to protect the spleen. In our previous study, genistein was found to have an influence on malaria-induced splenomegaly. However, the effect of genistein in malaria-induced splenomegaly, especially on the function of spleen, has not been fully investigated. In this study, hematoxylin and eosin (H&E) staining images show that genistein partially prevents malaria-induced architectural disruption of spleen. In addition, genistein decreases transgenic Plasmodium parasites accumulation in the spleen. Genistein treatment can protect splenic function from impairment caused by malaria infection. To examine the functions of malaria-infected spleen, we employed single-photon emission computed tomography/computed tomography (SPECT/CT) technology. Red blood cells are specifically radiolabeled with Technetium-99m pertechnetate (99mTcO4-) and trapped inside the spleen. The standardized uptake values (SUVs) in the spleen of infected mice are higher than those of naive and genistein-treated mice. However, genistein reduces the malaria-induced trapping capacity of spleen for heat-damaged radiolabeled RBCs, while exhibiting a protective effect against malaria. Considering these results, we suggested that genistein could be effectively used in combination therapy for malaria-induced splenic impairment.

Functional Water Flow Pathways and Hydraulic Regulation in the Xylem Network of Arabidopsis

In vascular plants, the xylem network constitutes a complex microfluidic system. The relationship between vascular network architecture and functional hydraulic regulation during actual water flow remains unexplored. Here, we developed a method to visualize individual xylem vessels of the 3D xylem network of Arabidopsis thaliana, and to analyze the functional activities of these vessels using synchrotron X-ray computed tomography with hydrophilic gold nanoparticles as flow tracers. We show how the organization of the xylem network changes dynamically throughout the plant, and reveal how the elementary units of this transport system are organized to ensure both long-distance axial water transport and local lateral water transport. Xylem vessels form distinct clusters that operate as functional units, and the activity of these units, which determines water flow pathways, is modulated not only by varying the number and size of xylem vessels, but also by altering their interconnectivity and spatial arrangement. Based on these findings, we propose a regulatory model of water transport that ensures hydraulic efficiency and safety.

Three-dimensional structures of the tracheal systems of Anopheles sinensis and Aedes togoi pupae

Mosquitoes act as a vector for the transmission of disease. The World Health Organization has recommended strict control of mosquito larvae because of their “few, fixed, and findable” features. The respiratory system of mosquito larvae and pupae in the water has a weak point. As aquatic organisms, mosquito larvae and pupae inhale atmosphere oxygen. However, the mosquito pupae have a non-feeding stage, unlike the larvae. Therefore, detailed study on the tracheal system of mosquito pupae is helpful for understanding their survival strategy. In this study, the three-dimensional (3D) structures of the tracheal systems of Anopheles sinensis and Aedes togoi pupae were comparatively investigated using synchrotron X-ray microscopic computed tomography. The respiratory frequencies of the dorsal trunks were also investigated. Interestingly, the pupae of the two mosquito species possess special tracheal systems of which the morphological and functional features are distinctively different. The respiratory frequency of Ae. togoi is higher than that of An. sinensis. These differences in the breathing phenomena and 3D structures of the respiratory systems of these two mosquito species provide an insight into the tracheal systems of mosquito pupae.