Low Flow Regions Research Articles

Application of operating scenarios and analysis of unstable flow characteristics at various angles of inlet guide vane.

In this study, we analyzed the performance characteristics of an axial flow pump with different angles of internally installed inlet guide vanes (IGVs). We predicted the pump's performance based on changes in the IGV angle and analyzed the impact of these angle variations on pump operation in the low-flow region. Additionally, we used real operational data from two sewage treatment plants to propose efficient operational scenarios. For turbulence flow analysis, the Reynolds-averaged Navier-Stokes equations were discretized based on the finite volume method. The grid formation was evaluated using the grid convergence index to select the optimal grid. Then, the internal flow was analyzed in detail through transient-state analysis. Through fast Fourier transform analysis, we confirmed that adjusting the IGV angle during pump operation in the low-flow region in response to load changes results in more stable operation compared with the existing method (valve control). Overall, our findings verified that energy reduction and efficient operation can be achieved through IGV angle adjustment compared with valve control.

Validity of the quasi-2D optimal variable density lattice for effective liquid cooling based on Darcy–Forchheimer theory

In this study, we investigate the validity of variable-lattice-density optimization based on the Darcy–Forchheimer theory for an effective liquid-cooling quasi-2D structure including experimental verification. The unit lattice features a simple cylinder shape, and its size distribution is optimized. Considering its anisotropy, we regard Darcy’s permeability, Forchheimer’s drag coefficient, and the effective thermal conductivity as tensors and calculate these effective properties using the representative-volume-element method. Two types of optimizations are performed, i.e., minimizing the surface temperature and maximizing the flow rate, using the gradient method. We examine the results using three methods: an approximate simulation based on the Brinkman–Forchheimer equation, a detailed simulation based on the Navier–Stokes equation, and an experiment. We focus primarily on the exact measurement of planar temperature distribution using thermocouples. The proposed methodology exhibits high accuracy in regions with a certain flow level, although the error can be significant in low-flow regions.

Effect of complex void structures on flow channeling and heterogeneous heat transfer in fractured rocks

Natural or hydraulic fractures in enhanced geothermal systems (EGS) typically have complex void structures due to the presence of surface contact. In this study, fluid flow and heat transfer processes in three-dimensional rough fractures with different contact ratios are investigated. Stronger flow channeling and heterogeneous heat transfer are observed in fracture voids with increasing surface contacts, and the fluid flow exhibits nonlinear characteristics due to the complex fracture void structures. Parts of fracture voids with large apertures and void areas contribute negligibly to the overall flow due to their weak connectivity to the main flow channels. Removing the low-flow regions does not significantly impact the flow channeling and heterogeneous heat transfer in the fracture voids. However, the heat exchange in the low-flow regions results in differences in the overall heat transfer coefficient and heat extraction rate between the reconstructed and original fractures. An empirical model is proposed to describe the overall heat transfer coefficient in fractures with complex void structures. Furthermore, the flow and heat transfer processes in the highly contacted fractures are not significantly affected by the change in flow direction, indicating that the anisotropic degree of the fracture void structures decreases as the contact areas increases. This study may further deepen the understanding of fluid flow and heat transfer in realistic fractured rocks at high temperatures, which is critical for geothermal energy extraction.

Low Volume Gas-Flow Seeding For Highly Resolved Velocimetry Of The Boundary Layer

Ensuring fire safety in polymeric materials, which are inherently flammable but widely used in various industries, is of significant societal and economic importance. This study is part of a broader effort to understand polymer combustion and flame retardant effectiveness at a fundamental level. A major focus is the behavior of polymers burning along a vertical wall, a configuration chosen to study the release of flammable gases during pyrolysis, which contributes to the self-sustaining combustion reaction of a fire. This process occurs predominantly near the polymer surface within the boundary layer, requiring detailed analysis to evaluate flame retardant effectiveness. Our experimental setup replicates polymer pyrolysis using a flame-wall interaction burner with a vertical jet and a small inlet to mimic the release of flammable gases. The primary challenge in this setup is the introduction of seeding particles for Particle Image Velocimetry (PIV) measurements at low volume flow rates, which is complicated by reflections from the wall and the small flow scale relative to the main flow. To address this problem, we have developed a novel piezo-based ultrasonic seeder capable of controlled seeding at extremely low flow rates, thereby improving the accuracy of PIV measurements in non-reactive configurations. This seeder uses a piezo ring to excite a perforated metal membrane, forming uniform aerosol droplets. The design ensures a steady supply of particles, which is critical for evaluating boundary layer conditions. Our results demonstrate the seeder’s ability to maintain sufficient seeding density in the low volume flow region, facilitating detailed velocimetry analysis. The innovative seeder design proves effective in overcoming the limitations of conventional methods and provides new insights into polymer combustion processes and the role of flame retardants.

On the role of aortic valve architecture for physiological hemodynamics and valve replacement, Part I: Flow configuration and vortex dynamics

Aortic valve replacement has become an increasing concern due to the rising prevalence of aortic stenosis in an ageing population. Existing replacement options have limitations, necessitating the development of improved prosthetic aortic valves. In this study, flow characteristics during systole in a stenotic aortic valve case are compared with those downstream of two newly designed surgical bioprosthetic aortic valves (BioAVs). To do so, advanced three-dimensional fluid–structure interaction simulations are conducted and dedicated analysis methods to investigate jet flow configuration and vortex dynamics are developed. Our findings reveal that the stenotic case maintains a high jet flow eccentricity due to a fixed orifice geometry, resulting in flow separation and increased vortex stretching and tilting in the commissural low-flow regions. One BioAV design introduces non-axisymmetric leaflet motion, which reduces the maximum jet velocity and forms more vortical structures. The other BioAV design produces a fixed symmetric triangular jet shape due to non-moving leaflets and exhibits favourable vorticity attenuation, revealed by negative temporally and spatially averaged projected vortex stretching values, and significantly reduced drag. Therefore, this study highlights the benefits of custom-designed aortic valves in the context of their replacement through comprehensive and novel flow analyses. The results emphasise the importance of analysing jet flow, vortical structures, momentum balance and vorticity transport for thoroughly evaluating aortic valve performance.

Flow Exchange In Vegetated Environments: Integrating Experimental Insights Into Practical Engineering

Vegetation provides practical protective tools for estuarine and coastal regions. The roots, stems, and canopy systems of mangroves can divert and retard the flow field within and surrounding vegetation regions (Truong et al., 2019) and also absorb external forces from waves (Phan et al., 2015). The area within the vegetation is usually calmer compared to the unprotected region outside. Consequently, sediment tends to be deposited inside the vegetation region (Vargas Luna et al., 2015). The sediment deposited then may have feedback on the wave and flow field and the growth conditions of the vegetation (Truong et al., 2017). These mutual interactions between ecological area (vegetation), hydrodynamic conditsions (wave and flow field), and morphological conditions (sediment transport) are the crux of any proposed nature-based solutions (NbS). From a hydraulic engineering perspective, these dynamic interactions can translate into the momentum and mass exchange processes between vegetation and nearby areas. By observing the evolution of mangrove forests and associated with the rate of erosion/accretion of the shoreline, Phan, 2015 and Truong., 2017 proposed a hypothesis of “squeezed mangrove forest”, in which “the mangrove width” is considered a crucial length-scales that is related to the sustainable development of the mangroves. This length scale was physically interpreted and connected to the penetration of the mixing layer into the vegetation region (Truong., 2017; Truong et al., 2019). It is noted that whereas the characteristic of the incoming waves mainly controls the penetration of the mixing layer into the coastal mangroves, that of the estuarine mangroves is mainly governed by the characteristic of lateral flow. The latter is the primary focus of this study. Large vortex structures caused by the Kelvin-Helmholtz instability at the vegetation’s edge play an essential role in the transverse exchange of mass and momentum (White & Nepf, 2007; Truong et al., 2019). These structures are usually large compared to the water depths and are termed large horizontal coherent structures (LHCSs). The Reynolds Shear stresses (RSs) induced by LHCSs contribute more than 90% to the total turbulent shear stress at the edge of the floodplain vegetated region (Truong & Uijttewaal 2019). Nevertheless, our understanding of this topic often stems from small-scale laboratory experiments. Whether the presence and characteristic of vortex structures at the interface of the low flow and fast flow region obtained from small-scale physical models remain true for estuaries and coasts has not yet been determined. In order to obtain more insight into the physics of the exchange processes occurring at the vegetation interface at different scales, two unique physical models of vegetated channels have been conducted. One small-scale and another large-scale experiment, both with and without vegetation, were conducted at TU Delft Water Lab and the Korea Institute of Civil Engineering and Building Technology - River Experiment Center (KICT-REC), respectively. Two digital twin models of this flume were subsequently constructed using Delft3D, which were calibrated and validated using the collected datasets. In this study, recent findings pertaining to these experiments are presented

Clinical applications of aqueous angiography in glaucoma.

Aqueous humor outflow (AHO) pathways are the main site of resistance causing elevated intraocular pressure in glaucoma, especially primary open-angle glaucoma patients. With the recently introduced technique of aqueous angiography (AA); functional, real time assessment of AHO from proximal (trabecuar meshwork) to distal pathways under physiological conditions has been made possible. AHO pathways are segmental, and AA can identify high-flow region (increased angiographic signals) and low flow region (decreased angiographic signals) in an individual. With the introduction of canal-based minimally invasive glaucoma surgeries (MIGS), the assessment of AHO can help guide the placement of stents/incisions during MIGS procedures. This can allow individualized and targeted MIGS procedures in glaucoma patients for better results. Based on the density of AHO pathways visualized on AA, surgeons can decide whether to perform MIGS or conventional glaucoma surgery for improved outcomes for the patient. Immediate intraoperative assessment for functionality of the MIGS procedure performed is possible with AA, allowing for surgical adjustments of MIGS procedure in the same sitting, if needed. This review provides a summary of the studies performed with AA to date, with a special focus on Indian patients. It covers the basics and clinical applications of AA for improving surgical outcomes in glaucoma patients.

Surgical Modulation of Pulmonary Artery Shear Stress: A Patient-Specific CFD Analysis of the Norwood Procedure.

This study created 3D CFD models of the Norwood procedure for hypoplastic left heart syndrome (HLHS) using standard angiography and echocardiogram data to investigate the impact of shunt characteristics on pulmonary artery (PA) hemodynamics. Leveraging routine clinical data offers advantages such as availability and cost-effectiveness without subjecting patients to additional invasive procedures. Patient-specific geometries of the intrathoracic arteries of two Norwood patients were generated from biplane cineangiograms. "Virtual surgery" was then performed to simulate the hemodynamics of alternative PA shunt configurations, including shunt type (modified Blalock-Thomas-Taussig shunt (mBTTS) vs. right ventricle-to-pulmonary artery shunt (RVPAS)), shunt diameter, and pulmonary artery anastomosis angle. Left-right pulmonary flow differential, Qp/Qs, time-averaged wall shear stress (TAWSS), and oscillatory shear index (OSI) were evaluated. There was strong agreement between clinically measured data and CFD model output throughout the patient-specific models. Geometries with a RVPAS tended toward more balanced left-right pulmonary flow, lower Qp/Qs, and greater TAWSS and OSI than models with a mBTTS. For both shunt types, larger shunts resulted in a higher Qp/Qs and higher TAWSS, with minimal effect on OSI. Low TAWSS areas correlated with regions of low flow and changing the PA-shunt anastomosis angle to face toward low TAWSS regions increased TAWSS. Excellent correlation between clinically measured and CFD model data shows that 3D CFD models of HLHS Norwood can be developed using standard angiography and echocardiographic data. The CFD analysis also revealed consistent changes in PA TAWSS, flow differential, and OSI as a function of shunt characteristics.

Bamboo-Inspired Porous Scaffolds for Advanced Orthopedic Implants: Design, Mechanical Properties, and Fluid Characteristics.

In orthopedic implant development, incorporating a porous structure into implants can reduce the elastic modulus to prevent stress shielding but may compromise yield strength, risking prosthesis fracture. Bamboo's natural structure, with its exceptional strength-to-weight ratio, serves as inspiration. This study explores biomimicry using bamboo-inspired porous scaffolds (BISs) resembling cortical bone, assessing their mechanical properties and fluid characteristics. The BIS consists of two 2D units controlled by structural parameters α and β. The mechanical properties, failure mechanisms, energy absorption, and predictive performance are investigated. BIS exhibits mechanical properties equivalent to those of natural bone. Specifically, α at 4/3 and β at 2/3 yield superior mechanical properties, and the destruction mechanism occurs layer by layer. Besides, the Gibson-Ashby models with different parameters are established to predict mechanical properties. Fluid dynamics analysis reveals two high-flow channels in BISs, enhancing nutrient delivery through high-flow channels and promoting cell adhesion and proliferation in low-flow regions. For wall shear stress below 30 mPa (ideal for cell growth), α at 4/3 achieves the highest percentage (99.04%), and β at 2/3 achieves 98.46%. Permeability in all structural parameters surpasses that of human bone. Enhanced performance of orthopedic implants through a bionic approach that enables the creation of pore structures suitable for implants.

Segmental Unconventional Outflow in Mouse Eyes.

To investigate the flow pattern in unconventional outflow and its correlation with conventional outflow in mouse eyes. Fluorescent microspheres were injected into the anterior chamber of one eye of anesthetized C57BL/6J mice (n = 4), followed by perfused fixation with 4% paraformaldehyde in situ after 45minutes. Post-euthanasia, the injected eyes were enucleated, further immersion fixed, and dissected into 12 equal radial segments. Both sides of each segment were imaged using a confocal microscope after nuclear counterstaining. Both unconventional and conventional outflow patterns of each eye were analyzed by ImageJ and ZEN 2.3 imaging software. Segmental outflow patterns were observed in both the ciliary body (CB) and the supraciliary space and suprachoroidal space (SCS). In the CB, the tracer intensity was the lowest at 12 o'clock and highest at 9 o'clock, whereas in the SCS it was the lowest at 2 o'clock and the highest at 10 o'clock. Consequently, a segmental unconventional outflow was observed, with the lowest and highest flow regions in the superior and temporal quadrants, respectively. The overall segmental uveoscleral outflow has no correlation with trabecular outflow (P > 0.05). Four different outflow patterns were observed: (1) low-flow regions in both outflows, (2) primarily a high-flow region in conventional outflow, (3) primarily a high-flow region in unconventional outflow, and (4) high-flow regions in both outflows. Uveoscleral outflow is segmental and unrelated to the trabecular segmental outflow. These findings will lead to future studies to identify the best location for the placement of drainage devices and drug delivery.

Segmental biomechanics of the normal and glaucomatous human aqueous outflow pathway

The conventional aqueous outflow pathway, encompassing the trabecular meshwork (TM), juxtacanalicular connective tissue (JCT), and inner wall endothelium of Schlemm's canal (SC), governs intraocular pressure (IOP) regulation. This study targets the biomechanics of low-flow (LF) and high-flow (HF) regions within the aqueous humor outflow pathway in normal and glaucomatous human donor eyes, using a combined experimental and computational approach. LF and HF TM/JCT/SC complex tissues from normal and glaucomatous eyes underwent uniaxial tensile testing. Dynamic motion of the TM/JCT/SC complex was recorded using customized green-light optical coherence tomography during SC pressurization in cannulated anterior segment wedges. A hyperviscoelastic model quantified TM/JCT/SC complex properties. A fluid-structure interaction model simulated tissue-aqueous humor interaction. FluoSpheres were introduced into the pathway via negative pressure in the SC, with their motion tracked using two-photon excitation microscopy. Tensile test results revealed that the elastic moduli of the LF and HF regions in glaucomatous eyes are 3.5- and 1.5-fold stiffer than the normal eyes, respectively. The FE results also showed significantly larger shear moduli in the TM, JCT, and SC of the glaucomatous eyes compared to the normal subjects. The LF regions in normal eyes demonstrated larger elastic moduli compared to the HF regions in glaucomatous eyes. The resultant strain in the outflow tissues and velocity of the aqueous humor in the FSI models were in good agreement with the digital volume correlation and 3D particle image velocimetry data, respectively. This study uncovers stiffer biomechanical responses in glaucomatous eyes, with LF regions stiffer than HF regions in both normal and glaucomatous eyes. Statement of significanceThis study delves into the biomechanics of the conventional aqueous outflow pathway, a crucial regulator of intraocular pressure and ocular health. By analyzing mechanical differences in low-flow and high-flow regions of normal and glaucomatous eyes, this research unveils the stiffer response in glaucomatous eyes. The distinction between regions' properties offers insights into aqueous humor outflow regulation, while the integration of experimental and computational methods enhances credibility. These findings have potential implications for disease management and present a vital step toward innovative ophthalmic interventions. This study advances our understanding of glaucoma's biomechanical basis and its broader impact on ocular health.

Effects of Topological Properties with Local Variable Apertures on Solute Transport through Three-Dimensional Discrete Fracture Networks

In this study, the effects of topological properties with local variable apertures on fluid flow and solute transport through three-dimensional (3D) discrete fracture networks (DFNs) were investigated. A series of 3D DFNs with different fracture density, length, and aperture distribution were generated. The fluid flow and solute transport through the models were simulated by combining the MATLAB code and COMSOL Multiphysics. The effects of network topology and aperture heterogeneity on fluid flow and transport process were analyzed. The results show that the fluid flow and solute transport exhibit a strong channeling effect even in the DFNs with identical aperture, in which the areas of fast and slow migration fit well with the high- and low-flow regions, respectively. More obvious preferential paths of flow and migration are observed in individual fractures for the DFN with heterogeneous aperture than the model with identical aperture. Increasing the fracture length exponent reduces the available flow and transport paths for sparse fracture networks but does not significantly change the flow and transport channels for dense fracture networks. The breakthrough curves (BTCs) shift towards the right and slightly lag behind as the fracture density decreases or the aperture heterogeneity increases. The advection–diffusion equation (ADE) model cannot properly capture the evolution of BTCs for 3D DFNs, especially the long tails of BTCs. Compared to the ADE model, the mobile-immobile model (MIM) model separating the liquid phase into flowing and stagnate regions is proven to better fit the BTCs of 3D DFNs with heterogeneous aperture.

Optimal placement of flexible ureteral access sheath in retrograde intrarenal surgery

This study aims to explore the optimal location of flexible ureteral access sheath (f-UAS) in retrograde intrarenal lithotripsy (RIRS). RIRS model was built by AutoCAD 2011 software, and imported COMSOL 5.6 software to computer simulation. An RIRS model was constructed in vitro to analyze the distribution pattern of stone fragments and compare the weight of stone fragments carried out by the irrigation fluid when the f-UAS is in different positions. Computer simulation showed that the highest flow of irrigation fluid was in the channel of flexible ureteroscopy (f-URS) and in the lumen of f-UAS. From the f-URS to the renal collection system and then to the f-UAS, the velocity of irrigation fluid changes gradually from high-flow to low-flow and then to high-flow. When the f-URS and the f-UAS are at the same level, the irrigation fluid is always at a state of high flow during the process from f-URS to f-UAS. When the f-URS and the f-UAS are at the same level, it can increase the local intrarenal pressure (IRP) at the front of f-URS. The stone fragments are mainly sediment in the low-flow region of irrigation fluid. More stone fragments could follow the irrigation fluid out of the body when the tip of f-URS and the tip of f-UAS are at the same level (P < 0.001). The f-UAS should be brought closer to the stone in RIRS. And more stone fragments can be taken out of the body by the effect of irrigation fluid.

Diabetic microaneurysms detected by fluorescein angiography spatially correlate with regions of macular ischemia delineated by optical coherence tomography angiography.

To characterize the relationship between diabetic macular ischemia (DMI) delineated by optical coherence tomography angiography (OCTA) and microaneurysms (MAs) identified by fundus fluorescein angiography (FFA). Patients with diabetic retinopathy (DR) who underwent OCTA and FFA were retrospectively identified. FFA images were cropped and aligned with their respective OCTA images using i2k Align Retina software (Dual-Align, Clifton Park, NY, USA). Foveal avascular zone (FAZ) and ischemic areas were manually delineated on OCTA images, and MAs were marked on the corresponding FFA images before overlaying paired scans for analysis (ImageJ; National Institutes of Health, Bethesda, MD, USA). Twenty-eight eyes of 20 patients were included. The average number of MAs identified in cropped FFA images was 127 ± 42. More DMI was noted in the superficial capillary plexus (SCP; 36 ± 13%) compared to the deep capillary plexus (DCP; 28 ± 14%, P < 0.001). Similarly, more MAs were associated with ischemic areas in SCP compared to DCP (92.0 ± 35.0 vs. 76.8 ± 36.5, P < 0.001). Most MAs bordered ischemic areas; fewer than 10% localized inside these regions. As DMI area increased, so did associated MAs (SCP: r = 0.695, P < 0.001; DCP: r = 0.726, P < 0.001). Density of MAs surrounding FAZ (7.7 ± 6.0 MAs/mm2) was similar to other DMI areas (SCP: 7.0 ± 4.0 MAs/mm2, P = 0.478; DCP: 9.2 ± 10.9 MAs/mm2, P = 0.394). MAs identified in FFA strongly associate with, and border areas of, DMI delineated by OCTA. Although more MAs are localized to SCP ischemia, the concentration of MAs associated with DCP ischemia is greater. By contrast, few MAs are present inside low-flow regions, likely because capillary loss is associated with their regression.

Characterization of extracellular matrix deposited by segmental trabecular meshwork cells

PurposeBiophysical and biochemical attributes of the extracellular matrix are major determinants of cell fate in homeostasis and disease. Ocular hypertension and glaucoma are diseases where the trabecular meshwork tissue responsible for aqueous humor egress becomes stiffer accompanied by changes in its matrisome in a segmental manner with regions of high or low flow. Prior studies demonstrate these alterations in the matrix are dynamic in response to age and pressure changes. The underlying reason for segmentation or differential response to pressure and stiffening are unknown. This is largely due to a lack of appropriate models (in vitro or ex vivo) to study this phenomena. MethodsPrimary trabecular meshwork cells were isolated from segmental flow regions, and cells were cultured for 4 weeks in the presence or absence or dexamethasone to obtain cell derived matrices (CDM). The biomechanical attributes of the CDM, composition of the matrisome, and incidence of crosslinks were determined by atomic force microscopy and mass spectrometry. ResultsData demonstrate that matrix deposited by cells from low flow regions are stiffer and exhibit a greater number of immature and mature crosslinks, and that these are exacerbated in the presence of steroid. We also show a differential response of high or low flow cells to steroid via changes observed in the matrix composition. However, no correlations were observed between elastic moduli and presence or absence of mature and immature crosslinks in the CDMs. ConclusionRegardless of a direct correlation between matrix stiffness and crosslinks, we observed distinct differences in the composition and mechanics of the matrices deposited by segmental flow cells. These results suggest distinct differences in cellular identify and likely a basis for mechanical memory post isolation and culture. Nevertheless, we conclude that although a mechanistic basis for matrix stiffness was undetermined in this study, it is a viable tool to study cell-matrix interactions and further our understanding of trabecular meshwork pathobiology.

Greater Outflow Facility Increase After Targeted Trabecular Bypass in Angiographically Determined Low-low Regions

To investigate the impact of trabecular bypass surgery targeted to angiographically determined high- vs. low-aqueous humor outflow areas on outflow facility (C) and intraocular pressure (IOP). Exvivo comparative study. Postmortem exvivo porcine and human eyes. Porcine (n=14) and human (n=13) whole globes were acquired. In both species, anterior segments were dissected, mounted onto a perfusion chamber, and perfused using Dulbecco's phosphate buffered solution containing glucose in a constant flow paradigm to achieve a stable baseline. Fluorescein was perfused into the anterior chamber and used to identify baseline segmental high- and low-flow regions of the conventional outflow pathways. The anterior segments were divided into 2 groups, and a 5 mm needle goniotomy was performed in either a high- or low-flow area. Subsequently, C and IOP were quantitatively reassessed and compared between surgery in baseline "high-flow" and "low-flow" region eyes followed by indocyanine green angiography. Outflow facility. In all eyes, high- and low-flow segments could be identified. Performing a 5-mm goniotomy increased outflow facility to a variable extent depending on baseline flow status. In the porcine high-flow group, C increased from 0.31±0.09 to 0.39±0.09 μL/mmHg/min (P=0.12). In the porcine low-flow group, C increased from 0.29±0.03 to 0.56±0.10 μL/mmHg/min (P<0.001). In the human high-flow group, C increased from 0.38±0.20 to 0.41±0.20 μL/mmHg/min (P=0.02). In the human low-flow group, C increased from 0.25±0.11 to 0.32±0.11 μL/mmHg/min (<0.001). There was statistically significant greater increase in C for eyes where surgery was targeted to baseline low-flow regions in both porcine (0.07±0.09 vs. 0.27±0.13, P=0.007 μL/mmHg/min, high vs low flow) and human eyes (0.03±0.03 vs. 0.07±0.02, P=0.03 μL/mmHg/min, high vs. low flow). Targeting surgery to low-flow areas of the trabecular meshwork yields higher overall facility increase and IOP reduction compared to surgery in high-flow areas. Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Necrosis reduction efficacy of subdermal biomaterial mediated oxygen delivery in ischemic skin flaps

Inadequate tissue blood supply as may be found in a wound or a poorly vascularised graft, can result in tissue ischemia and necrosis. As revascularization is a slow process relative to the proliferation of bacteria and the onset of tissue necrosis, extensive tissue damage and loss can occur before healing is underway. Necrosis can develop rapidly, and treatment options are limited such that loss of tissue following necrosis onset is considered unavoidable and irreversible.Oxygen delivery from biomaterials exploiting aqueous decomposition of peroxy-compounds has shown some potential in overcoming the supply limitations by creating oxygen concentration gradients higher than can be attained physiologically or by air saturated solutions.We sought to test whether subdermal oxygen delivery from a material composite that was buffered and contained a catalyst, to reduce hydrogen peroxide release, could ameliorate necrosis in a 9 × 2 cm flap in a rat model that reliably underwent 40 % necrosis if untreated. Blood flow in this flap reduced from near normal to essentially zero, along its 9 cm length and subdermal perforator vessel anastomosis was physically prevented by placement of a polymer sheet. In the middle, low blood flow region of the flap, treatment significantly reduced necrosis based on measurements from photographs and histological micrographs. No change was observed in blood vessel density but significant differences in HIF1-α, inducible nitric oxide synthase and liver arginase were observed with oxygen delivery.

Impacts of hydrodynamic conditions and microscale surface roughness on the critical shear stress to develop and thickness of early-stage Pseudomonas putida biofilms.

Biofilms can increase pathogenic contamination of drinking water, cause biofilm-related diseases, alter the sediment erosion rate, and degrade contaminants in wastewater. Compared with mature biofilms, biofilms in the early-stage have been shown to be more susceptible to antimicrobials and easier to remove. Mechanistic understanding of physical factors controlling early-stage biofilm growth is critical to predict and control biofilm development, yet such understanding is currently incomplete. Here, we reveal the impacts of hydrodynamic conditions and microscale surface roughness on the development of early-stage Pseudomonas putida biofilm through a combination of microfluidic experiments, numerical simulations, and fluid mechanics theories. We demonstrate that early-stage biofilm growth is suppressed under high flow conditions and that the local velocity for early-stage P. putida biofilms (growth time < 14 h) to develop is about 50 μm/s, which is similar to P. putida's swimming speed. We further illustrate that microscale surface roughness promotes the growth of early-stage biofilms by increasing the area of the low-flow region. Furthermore, we show that the critical average shear stress, above which early-stage biofilms cease to form, is 0.9 Pa for rough surfaces, three times as large as the value for flat or smooth surfaces (0.3 Pa). The important control of flow conditions and microscale surface roughness on early-stage biofilm development, characterized in this study, will facilitate future predictions and managements of early-stage P. putida biofilm development on the surfaces of drinking water pipelines, bioreactors, and sediments in aquatic environments.

Differences in Outflow Facility Between Angiographically Identified High- Versus Low-Flow Regions of the Conventional Outflow Pathways in Porcine Eyes.

To investigate differences in outflow facility between angiographically determined high- and low-flow segments of the conventional outflow pathway in porcine eyes. Porcine anterior segments (n = 14) were mounted in a perfusion chamber and perfused using Dulbecco's phosphate buffered solution with glucose. Fluorescein angiography was performed to determine high- and low-flow regions of the conventional outflow pathways. The trabecular meshwork (TM) was occluded using cyanoacrylate glue, except for residual 5-mm TM areas that were either high or low flow at baseline, designating these eyes as "residual high-flow" or "residual low-flow" eyes. Subsequently, outflow was quantitatively reassessed and compared between residual high-flow and residual low-flow eyes followed by indocyanine green angiography. Fluorescein aqueous angiography demonstrated high-flow and low-flow regions. Baseline outflow facilities were 0.320 ± 0.08 and 0.328 ± 0.10 µL/min/mmHg (P = 0.676) in residual high-flow and residual low-flow eyes before TM occlusion, respectively. After partial trabecular meshwork occlusion, outflow facility decreased to 0.209 ± 0.07 µL/min/mmHg (-32.66% ± 19.53%) and 0.114 ± 0.08 µL/min/mmHg (-66.57% ± 23.08%) in residual high- and low-flow eyes (P = 0.035), respectively. There was a significant difference in the resulting IOP increase (P = 0.034). Angiographically determined high- and low-flow regions in the conventional outflow pathways differ in their segmental outflow facility; thus, there is an uneven distribution of local outflow facility across different parts of the TM.

Dispersion of motile bacteria in a porous medium

Understanding flow and transport of bacteria in porous media is crucial to technologies such as bioremediation, biomineralization and enhanced oil recovery. While physicochemical bacteria filtration is well documented, recent studies showed that bacterial motility plays a key role in the transport process. Flow and transport experiments performed in microfluidic chips containing randomly placed obstacles confirmed that the distributions of non-motile bacteria stays compact, whereas for the motile strains, the distributions are characterized by both significant retention as well as fast downstream motion. For motile bacteria, the detailed microscopic study of individual bacteria trajectories reveals two salient features: (i) the emergence of an active retention process triggered by motility, (ii) enhancement of dispersion due to the exchange between fast flow channels and low flow regions in the vicinity of the solid grains. We propose a physical model based on a continuous time random walk approach. This approach accounts for bacteria dispersion via variable pore-scale flow velocities through a Markov model for equidistant particle speeds. Motility of bacteria is modelled by a two-rate trapping process that accounts for the motion towards and active trapping at the obstacles. This approach captures the forward tails observed for the distribution of bacteria displacements, and quantifies an enhanced hydrodynamic dispersion effect that originates in the combined effect of pore-scale flow variability and bacterial motility. The model reproduces the experimental observations, and predicts bacteria dispersion and transport at the macroscale.