Three-dimensional multidomain lattice Boltzmann grid refinement for passive scalar transport.

Simulations of passive scalar transport on a three-dimensional (3D) multiresolution grid are presented within the framework of single relaxation time lattice Boltzmann method. The combined modeling of the fluid flow and scalar transport is handled by a double distribution function approach in which the velocity in the fluid flow equation is solved first and then copied to the scalar equation to solve the corresponding scalar quantities. A 3D scaling technique, considering both external forces and scalar source terms, and two-dimensional bicubic interpolation scheme are developed for coupling nonequilibrium velocity and scalar distributions on the interfaces of different resolution grids. The proposed algorithm is validated for three benchmark cases, i.e., the forced convection in a 3D channel, natural convection in a cubical cavity, and turbulent channel flow with heat transfer. Good agreements are found between the present predictions and previous data, which confirms the capability of the proposed method for the computation of passive scalar transport in 3D domains.

Roller-Induced Bundling of Long Silver Nanowire Networks for Strong Interfacial Adhesion, Highly Flexible, Transparent Conductive Electrodes.

Silver nanowires (AgNWs) have been the most promising electrode materials for fabrication of flexible transparent touch panel, displays and many other electronics because of their excellent electrical properties, cost effectiveness, synthesis scalability, and suitability for mass production. Although a few literature reports have described the use of short Ag NWs in fabrication of randomly oriented Ag NW network-based electrode, their electrical conductivities are still far lower than that of Ag films. So far, no any literature report was able to provide any simple solution to fabrication of large-area and mass-manufactural ability to address the issues, such as, conductivity, transparency, electrical current withstand, bending stability, and interfacial adhesion. In the current work, we provide a simple solution to conquer the above-mentioned challenges, and report the development of long Ag NW bundle network electrodes on large area PET films that were coated, aligned, and bundled quickly and simply using a steel roller. Our developed AgNWs-bundle networks had superior performance in optoelectronic properties (sheet resistance 5.8 Ω sq-1; optical transmittance 89% at 550 nm wavelength), electrical current withstand up to 500 mA, and bending stability over 5000 bending cycles, and strong interfacial adhesion.

Influenza A virus-specific aptamers screened by using an integrated microfluidic system.

The influenza A virus is a notorious pathogen that causes high morbidity, high mortality, and even severe global pandemics. Early and rapid diagnosis of the virus is therefore crucial in preventing and controlling any influenza outbreaks. Recently, novel nucleic acid-based affinity reagents called aptamers have emerged as promising candidates for diagnostic assays as they offer several advantages over antibodies, including in vitro selection, chemical synthesis, thermal stability and relatively low costs. Aptamers with high sensitivity and specificity are generated via Systematic Evolution of Ligands by Exponential Enrichment (SELEX), a process that is currently time-consuming, as well as labor- and resource-intensive. In this study, an integrated microfluidic system was developed and was successfully applied to screen a specific aptamer for the influenza A/H1N1 (InfA/H1N1) virus in an automated and highly efficient manner. The selected aptamer was implemented in a magnetic-bead assay, which demonstrated specific and sensitive detection of the InfA/H1N1 virus, even in biological samples such as throat swabs. Consequently, this specific aptamer presents a promising affinity reagent for clinical diagnosis of InfA/H1N1. This is the first demonstration of screening influenza virus-specific aptamers using the microfluidic SELEX technology, which may be expanded for the rapid screening of aptamers against other pathogens for future biomedical applications.

Hemodynamics altered by placing helix stents in an aneurysm at a 45 degrees angle to the curved vessel.

Flow visualization, particle image velocimetry and numerical computation have been complementarily performed to study the fluid flow inside a stented lateral aneurysm. The curved afferent vessel had an inner diameter of 5 mm. The diameters of the aneurysmal orifice, neck and fundus were 7 mm, 5 mm and 7.5 mm, respectively, and the distance between the orifice and dome measured 10 mm. Stents with various porosities were examined. A volume-flow rate waveform of the internal carotid artery was reconstructed with a Wormersley number of 4 and Reynolds number ranging from 202 to 384 in a cardiac cycle. Results are presented in terms of the main and secondary flow velocity vector fields, the inflow rates into the aneurysm and the intra-aneurysmal wall shear stress and pressure. Some comparisons of the computed results with the experimental results and the data available from the literature are also made. It is found that the placement of stents for endovascular treatment is more critical for an unstented parent vessel with curvature than without since the maximum inflow rate of the former is 15 times the latter. The critical porosity of 70% below which an inhibition of intra-aneurysmal thrombus formation will not occur is identified for the first time.

Effects of stent porosity on hemodynamics in a sidewall aneurysm model.

Computation and experiment have been complementarily performed to study the fluid flow inside a stented lateral aneurysm anchored on the straight parent vessel. The implicit solver was based on the time-dependent incompressible Navier-Stokes equations of laminar flow. Solutions were generated by a cell-center finite-volume method that used second-order upwind and second-order center flux difference splitting for the convection and diffusion term, respectively. The second-order Crank-Nicolson method was used in the time integration term. Experimental techniques used were flow visualization (FV) and particle tracking velocimetry (PTV). Experimentally, the straight afferent vessel had an inner diameter 10mm. The diameters of the aneurysmal orifice, neck, and fundus were 14, 10, and 15 mm, respectively, and the distance between the orifice and dome measured 20mm. A 30 mm long helix-shaped stent was tested. Four stent porosities of 100%, 70%, 50%, and 25% were examined. Volume-flow rate waveform of a cerebral artery was considered with a maximum Reynolds number of 250 and Womersley number of 3.9. Results are presented in terms of the pulsatile main and secondary flow velocity vector fields, the volume inflow rates into the aneurysm, and the wall shear stress (WSS) and wall pressure at the aneurysm dome. Some comparisons of computed results with the present FV and PTV results and with the data available from the literature are also made. The maximum flow velocity inside the aneurysm ostium and the WSS in the dome region at the peak flow can, respectively, be suppressed to less than 5% of the parent vessel bulk velocity (or 20% of the unstented case) and 8% of the unstented case if the stent porosity is smaller than 40% (about the porosity of the two-layer stents). In general, the three-layer stents seem not as effective as the two-layer stents in reducing the magnitude of aneurysm inflow rate and WSS.

Numerical and experimental studies on pulsatile flow in aneurysms arising laterally from a curved parent vessel at various angles.

Both numerical and experimental studies have been performed to characterize the fluid flow inside the lateral aneurysms arising from the curved parent vessels at various angles gamma. The implicit solver was based on the time-dependent Navier-Stokes equations of incompressible laminar flow. Solutions were generated by a cell-center finite-volume method that used second order upwind and second order center flux difference splitting for the convection and diffusion term, respectively. The second order Crank-Nicolson method was used in the time integration term while the SIMPLEC algorithm was adopted to handle the pressure-velocity coupling. Complementarily, the particle tracking velocimetry (PTV) was used to measure the velocity fields. The conditions selected were to simulate an internal carotid artery with a diameter of 5 mm by similarity rules. The values of gamma explored were 0 degrees, 45 degrees, 90 degrees, and 135 degrees. Pulsatile flow with Wormersley number 3.9 and Reynolds numbers varying from 350 to 850 was considered. The computed results are firstly verified by the PTV measured ones. Discussion of the results is in terms of pulsatile main and secondary velocity vector fields, inflow rates into the aneurysm, and the distributions of wall shear stress and static pressure. It is found that among the angles examined gamma=45( composite function) is the riskiest angle from a fluid dynamics point of view and the aneurysmal dome is at risk.

Intra-aneurysmal flow with helix and mesh stent placement across side-wall aneurysm pore of a straight parent vessel.

Pulsatile flow fields in a cerebrovascular side-wall aneurysm model with a wide ostium after stenting are presented in terms of particle tracking velocimetry measurements and flow visualization. Among the stent parameters the shape, helix versus mesh, was selected to study its effect on the changes of intraaneurysmal hemodynamics for the reference of minimally invasive endovascular aneurysm treatment. The blocking ratio of the stents was fixed at 30%. The Womersley number was 3.9 and the mean, peak, and minimal Reynolds numbers based on the bulk average velocity and diameter of the parent vessel were 600, 850, and 300, respectively. Four consecutive flow-rate phases were selected to characterize the intra-aneurysmal flow. The results are characterized in terms of velocity vector field, regional average velocity, and intra-aneurysmal vorticity/circulation/wall shear stress. It is found that the hemodynamic features inside the aneurysm alter markedly with the shape of the stent and the size of the orifice. Both stents investigated induce favorable changes in the intra-aneurysmal flow stasis as well as direction and undulation of wall shear stresses. A comparison of the results of the helix to mesh stent shows that the former is more favorable for endovascular treatment.