Blood viscosity associated with stroke mechanism and early neurological deterioration in middle cerebral artery atherosclerosis.

Blood viscosity may affect the mechanisms of stroke and early neurological deterioration (END). We aimed to investigate the relationship between blood viscosity, stroke mechanisms, and END in patients with middle cerebral artery (MCA) infarction. Patients with symptomatic MCA atherosclerosis (≥ 50% stenosis) were recruited. Blood viscosity was compared across patients with different mechanisms of symptomatic MCA disease: in situ thrombo-occlusion (sMCA-IST), artery-to-artery embolism (sMCA-AAE), and local branch occlusion (sMCA-LBO). END was defined as four points increase in the National Institutes of Health Stroke Scale score from baseline during the first week. The association between blood viscosity and END was also evaluated. A total of 360 patients (76 with sMCA-IST, 216 with sMCA-AAE, and 68 with sMCA-LBO) were investigated. Blood viscosity was highest in patients with sMCA-IST, followed by sMCA-AAE and sMCA-LBO (P < 0.001). Blood viscosity was associated with END in patients with MCA disease. Low shear viscosity was associated with END in patients with sMCA- LBO (adjusted odds ratio, aOR 1.524; 95% confidence interval, CI 1.035-2.246), sMCA- IST (aOR 1.365; 95% CI 1.013-1.839), and sMCA- AAE (aOR 1.285; 95% CI 1.010-1.634). Blood viscosity was related to END in patients with stroke caused by MCA disease.

Wall Shear Stress Associated with Stroke Occurrence and Mechanisms in Middle Cerebral Artery Atherosclerosis.

BACKGROUND AND PURPOSE: Various mechanisms are involved in the etiology of stroke caused by atherosclerosis of the middle cerebral artery (MCA). Here, we compared differences in plaque nature and hemodynamic parameters according to stroke mechanism in patients with MCA atherosclerosis. METHODS: Consecutive patients with asymptomatic and symptomatic MCA atherosclerosis (≥50% stenosis) were enrolled. MCA plaque characteristics (location and plaque enhancement) and wall shear stress (WSS) were measured using high-resolution vessel wall and four-dimensional flow magnetic resonance imaging, respectively, at five points (initial, upstream, minimal lumen, downstream, and terminal). These parameters were compared between patients with asymptomatic and symptomatic MCA atherosclerosis with infarctions of different mechanisms (artery-to-artery embolism vs. local branch occlusion). RESULTS: In total, 110 patients (46 asymptomatic, 32 artery-to-artery embolisms, and 32 local branch occlusions) were investigated. Plaques were evenly distributed in the MCA of patients with asymptomatic MCA atherosclerosis, more commonly observed in the distal MCA of patients with artery-to-artery embolism, and in the middle MCA of patients with local branch occlusion. Maximum WSS and plaque enhancement were more prominent in the minimum lumen area of patients with asymptomatic MCA atherosclerosis or those with local branch occlusion, and were more prominent in the upstream area in those with artery-to-artery embolism. The elevated variability in the maximum WSS was related to stroke caused by artery-to-artery embolism. CONCLUSION: Stroke caused by artery-to-artery embolism was related to plaque enhancement and the highest maximum WSS at the upstream point of the plaque, and was associated with elevated variability of maximum WSS.

Pixelated Microsized Quantum Dot Arrays Using Surface-Tension-Induced Flow.

Quantum dots (QDs) are semiconducting nanoparticles that exhibit unique fluorescent characteristics when excited by an ultraviolet light source. Owing to their highly saturated emissions, display panels using QDs as pixels have been presented. However, the complications of the nanofabrication procedure limit the industrial application of QDs. This study suggests a method to arrange high-aspect-ratio QD pixels by inducing both Laplace-pressure-driven capillary flow and thermally driven Marangoni flow. The evaporation of colloidal QDs induces a capillary flow that drives the QDs toward the inner tips of V-shaped structures. Additionally, the Marangoni flow arranges the gathered QDs at the tip; thus, they could form a high dune, overcoming the limitations of the existing capillary assembly method using evaporation. Using these phenomena, clover-shaped (assembly of V-shaped edges) templates were made to gather numerous QDs, and the clover with a 30° angle afforded the highest brightness among all the angle structures. Finally, by demonstrating a 100-cm2-sized QD microarray with high uniformity (98.6%), our method shows the feasibility of large-area fabrication, which has extensive application in manufacturing QD displays, anti-counterfeiting labels, and other QD-based optical devices.

Evaporation-Crystallization Method to Promote Coalescence-Induced Jumping on Superhydrophobic Surfaces.

Biphilic surfaces exhibit outstanding condensation efficiency compared to surfaces having homogeneous wettability. Especially, hydrophilic patterns on a superhydrophobic substrate significantly promote the coalescence-induced jumping of condensed droplets by increasing the nucleation rate of condensation, thus enhancing the condensation efficiency drastically. However, the application of biphilic surfaces in practical industries remains challenging because controlling the size and spacing of the hydrophilic spots on large and complex surfaces is difficult. In this study, we have achieved heterogeneous wettability using the evaporation-crystallization method, which can be applied to various surfaces as required by industries. The crystals generated using the evaporation-crystallization process drastically increased the number density of condensed droplets on a superhydrophobic surface (SHS), so the developed biphilic surface increased the cumulative volume of jumping droplets by up to 63% compared to that on a conventional superhydrophobic surface. Furthermore, the condensation dynamics on the biphilic surface were analyzed with the classical nucleation theory and the Ohnesorge number. The analysis results indicated that the generated hydrophilic crystals can reduce the nucleation energy barrier and decrease the available excessive surface energy of coalesced droplets on the biphilic surface; this implies that the size distribution of the crystals determines the condensation dynamics. In sum, this study not only introduced an effective surface tailoring approach for enhancing condensation but also provided insights into the design of optimum biphilic surfaces for various conditions, creating new opportunities to widen the applicability of biphilic surfaces in practical industries that exploit condensation.

Loss of superhydrophobicity of hydrophobic micro/nano structures during condensation.

Condensed liquid behavior on hydrophobic micro/nano-structured surfaces is a subject with multiple practical applications, but remains poorly understood. In particular, the loss of superhydrophobicity of hydrophobic micro/nanostructures during condensation, even when the same surface shows water-repellant characteristics when exposed to air, requires intensive investigation to improve and apply our understanding of the fundamental physics of condensation. Here, we postulate the criterion required for condensation to form from inside the surface structures by examining the grand potentials of a condensation system, including the properties of the condensed liquid and the conditions required for condensation. The results imply that the same hydrophobic micro/nano-structured surface could exhibit different liquid droplet behavior depending on the conditions. Our findings are supported by the observed phenomena: the initiation of a condensed droplet from inside a hydrophobic cavity, the apparent wetted state changes, and the presence of sticky condensed droplets on the hydrophobic micro/nano-structured surface.

Enhanced heat transfer is dependent on thickness of graphene films: the heat dissipation during boiling.

Boiling heat transfer (BHT) is a particularly efficient heat transport method because of the latent heat associated with the process. However, the efficiency of BHT decreases significantly with increasing wall temperature when the critical heat flux (CHF) is reached. Graphene has received much recent research attention for applications in thermal engineering due to its large thermal conductivity. In this study, graphene films of various thicknesses were deposited on a heated surface, and enhancements of BHT and CHF were investigated via pool-boiling experiments. In contrast to the well-known surface effects, including improved wettability and liquid spreading due to micron- and nanometer-scale structures, nanometer-scale folded edges of graphene films provided a clue of BHT improvement and only the thermal conductivity of the graphene layer could explain the dependence of the CHF on the thickness. The large thermal conductivity of the graphene films inhibited the formation of hot spots, thereby increasing the CHF. Finally, the provided empirical model could be suitable for prediction of CHF.

Nucleate boiling performance on nano/microstructures with different wetting surfaces.

A study of nucleate boiling phenomena on nano/microstructures is a very basic and useful study with a view to the potential application of modified surfaces as heating surfaces in a number of fields. We present a detailed study of boiling experiments on fabricated nano/microstructured surfaces used as heating surfaces under atmospheric conditions, employing identical nanostructures with two different wettabilities (silicon-oxidized and Teflon-coated). Consequently, enhancements of both boiling heat transfer (BHT) and critical heat flux (CHF) are demonstrated in the nano/microstructures, independent of their wettability. However, the increment of BHT and CHF on each of the different wetting surfaces depended on the wetting characteristics of heating surfaces. The effect of water penetration in the surface structures by capillary phenomena is suggested as a plausible mechanism for the enhanced CHF on the nano/microstructures regardless of the wettability of the surfaces in atmospheric condition. This is supported by comparing bubble shapes generated in actual boiling experiments and dynamic contact angles under atmospheric conditions on Teflon-coated nano/microstructured surfaces.