Wall Shear Rate Research Articles

Pulmonary haemodynamic effects of interatrial shunt in heart failure with preserved ejection fraction: a preclinical study.

The aim of this study was to evaluate the effect of the creation of a left-to-right interatrial shunt on pulmonary haemodynamics in rats with heart failure with preserved ejection fraction (HFPEF). An interatrial communication (IAC) was created in 11 healthy rats (Lewis rats) and 11 rats which developed HFPEF (36-week-old spontaneously hypertensive rats [SHR]). Effects of the interatrial shunt were compared to 11 sham-operated Lewis and 11 sham-operated SHR. At 45 days post shunt, strain effect was observed in diastolic function (E/A ratio, p<0.001; isovolumetric relaxation time, p<0.001), left atrial volume (p=0.005) and pulmonary wall shear rate (WSR) (p=0.02) measured by Doppler echo. At sacrifice of the animals (60 days), a strain effect was also noted in elastin density (p=0.003) and eNOS protein expression (p=0.001). Interatrial shunt creation resulted in (i) an increase in pulmonary WSR (p=0.04) and a decrease in left atrial volume (p<0.001), (ii) an increase in elastin density (p<0.005), and (iii) an increase in eNOS protein expression (p=0.03). Creation of a left-to-right atrial shunt in rats with HFPEF was effective in improving pulmonary haemodynamics. In addition, this study provides preliminary evidence of the potential risk of right volume overload and pulmonary hypertension due to atrial shunting.

Pharmacological Blockade of Glycoprotein VI Promotes Thrombus Disaggregation in the Absence of Thrombin.

Atherothrombosis occurs upon rupture of an atherosclerotic plaque and leads to the formation of a mural thrombus. Computational fluid dynamics and numerical models indicated that the mechanical stress applied to a thrombus increases dramatically as a thrombus grows, and that strong inter-platelet interactions are essential to maintain its stability. We investigated whether GPVI (glycoprotein VI)-mediated platelet activation helps to maintain thrombus stability by using real-time video-microscopy. Approach and Results: We showed that GPVI blockade with 2 distinct Fab fragments promoted efficient disaggregation of human thrombi preformed on collagen or on human atherosclerotic plaque material in the absence of thrombin. ACT017-induced disaggregation was achieved under arterial blood flow conditions, and its effect increased with wall shear rate. GPVI regulated platelet activation within a growing thrombus as evidenced by the loss in thrombus contraction when GPVI was blocked, and the absence of the disaggregating effect of an anti-GPVI agent when the thrombi were fully activated with soluble agonists. The GPVI-dependent thrombus stabilizing effect was further supported by the fact that inhibition of any of the 4 key immunoreceptor tyrosine-based motif signalling molecules, src-kinases, Syk, PI3Kβ, or phospholipase C, resulted in kinetics of thrombus disaggregation similar to ACT017. The absence of ACT017-induced disaggregation of thrombi from 2 afibrinogenemic patients suggests that the role of GPVI requires interaction with fibrinogen. Finally, platelet disaggregation of fibrin-rich thrombi was also promoted by ACT017 in combination with r-tPA (recombinant tissue plasminogen activator). This work identifies an unrecognized role for GPVI in maintaining thrombus stability and suggests that targeting GPVI could dissolve platelet aggregates with a poor fibrin content.

Thermohydraulic Behavior of Minichannel Surface Simulated With Gaussian Function and Actual Roughness Data Generated Using Three-Dimensional Optical Surface Profilometer

Abstract The effect of surface roughness on the thermohydraulics in minichannels has been studied numerically. Fluid flow (at low Reynolds number) through a typical three-dimensional (3D) channel subjected to constant heat flux (at the bottom) is analyzed incorporating surface roughness on the solid–fluid interfaces characterized by its true random and nonperiodic nature. Two different approaches are adopted to model the rough channel surfaces. Topographic measurements have been performed on a stainless steel minichannel using an optical surface profilometer (OSP) to generate digital replica of the rough surface. Alternatively, the Gaussian function defined by two statistical parameters, namely average roughness (Ra) and correlation length (Cl), are employed to imitate the random nature of rough interface. At the outset, conjugate heat transfer simulations have been performed on the rough channel models and the results are validated against the experimental data. Finally, the effect of surface roughness on both local and global nondimensional performance parameters is analyzed and compared with findings from simulations performed on a similar smooth channel. The outcomes reveal an enhanced friction factor for flow over a rough surface, attributable to the near wall shear rate fluctuations experienced by the flow. Unlike smooth channels, the local Nusselt number (Nuy) exhibits continuous fluctuations along the channel axial length. The fully developed (Nufd) and the average (Nu¯) counterparts of the Nusselt number show enhanced magnitudes when compared to the theoretical predictions of the same in a smooth surface channel. This amplification can be attributed to two simultaneously acting factors: augmentation in heat transfer area and chaotic mixing due to flow perturbation. The magnitude of enhancement in terms of fully developed Nusselt number (Nufd) is roughly 1.3 times of its corresponding value in a smooth channel and the factor remains invariant of the supplied heat.

Modeling Thrombin Generation in Plasma under Diffusion and Flow

We investigate the capacity of published numerical models of thrombin generation to reproduce experimentally observed threshold behavior under conditions in which diffusion and/or flow are important. Computational fluid dynamics simulations incorporating species diffusion, fluid flow, and biochemical reactions are compared with published data for thrombin generation in vitro in 1) quiescent plasma exposed to patches of tissue factor and 2) plasma perfused through a capillary coated with tissue factor. Clot time is correctly predicted in individual cases, and some models qualitatively replicate thrombin generation thresholds across a series of tissue factor patch sizes or wall shear rates. Numerical results suggest that there is not a genuine patch size threshold in quiescent plasma—clotting always occurs given enough time—whereas the shear rate threshold observed under flow is a genuine physical limit imposed by flow-mediated washout of active coagulation factors. Despite the encouraging qualitative results obtained with some models, no single model robustly reproduces all experiments, demonstrating that greater understanding of the underlying reaction network, and particularly of surface reactions, is required. In this direction, additional simulations provide evidence that 1) a surface-localized enzyme, speculatively identified as meizothrombin, is significantly active toward the fluorescent thrombin substrate used in the experiments or, less likely, 2) thrombin is irreversibly inhibited at a faster-than-expected rate, possibly explained by a stimulatory effect of plasma heparin on antithrombin. These results highlight the power of simulation to provide novel mechanistic insights that augment experimental studies and build our understanding of complex biophysicochemical processes. Further validation work is critical to unleashing the full potential of coagulation models as tools for drug development and personalized medicine.

Src family kinases inhibition by dasatinib blocks initial and subsequent platelet deposition on collagen under flow, but lacks efficacy with thrombin generation

Kinase inhibitors can pose bleeding risks as platelet signaling evolves during clotting. Using microfluidics (200 s−1 wall shear rate) to perfuse Factor XIIa-inhibited or thrombin-inhibited whole blood (WB) over collagen ± tissue factor (TF), we explored the potency of the Src family kinase (SFK) inhibitor dasatinib or the spleen tyrosine kinase (Syk) inhibitor GS-9973 present at clot initiation or added after 90 s (via rapid switch to inhibitor-pretreated WB). When initially present, dasatinib potently inhibited platelet deposition on collagen (no TF). Furthermore, dasatinib immediately inhibited subsequent platelet deposition when introduced 90 s after clot initiation. However, when thrombin was generated, dasatinib was markedly less potent against platelet deposition on collagen/TF (but blocked fibrin deposition) and had no effect when added 90 s after clot initiation. Similarly, dasatinib added at 90 s had no effect on clotting on collagen/TF when fibrin was also blocked with Gly-Pro-Arg-Pro, indicating that strong thrombin-induced signaling (but not fibrin-induced signaling) can bypass the SFK inhibition at later times. The Syk inhibitor GS-9973 was less potent than dasatinib when present initially, but inhibited clot growth when added at 90 s, even in the presence of thrombin (±fibrin). Interestingly, the active form (R-406) of fostamatinib inhibits platelet function in only 2 0f 5 healthy blood samples. SFK-inhibitors may have reduced antithrombotic activity and reduced bleeding risks in settings of high TF and local thrombin generation. For oncology patients, SFK-inhibitors like dasatinib may have reduced antithrombotic activity and reduced bleeding risk in settings of local thrombin generation.

Effects of elapsed time on downstream platelet adhesion following transient exposure to elevated upstream shear forces

Transient exposure to elevated shear forces is known to prime platelets for enhanced downstream adhesion, but how far downstream these priming effects persist is not known. In the present study, the platelet capture regions, prepared by immobilizing fibrinogen, collagen, or von Willebrand factor, were placed at three different distances from the upstream stenotic region to vary the elapsed time of circulating platelets downstream. Platelet adhesion increased with the increase of upstream wall shear rates from 1620 s−1 to 11,560 s−1 for all three downstream proteins, but only the adhesion to fibrinogen increased significantly with the distance between the upstream stenotic region and the downstream capture region. In contrast, platelet adhesion to downstream collagen remained essentially independent on the distance and the adhesion to von Willebrand factor marginally increased with the distance after transient platelet exposure to upstream wall shear rates of 2145 s−1 and 11,560 s−1. The results implied that the activation of fibrinogen receptor GPIIb/IIIa by transient exposure to high upstream wall shear rates progresses in a time-dependent manner during the downstream flow of platelets. The highly elevated upstream wall shear rate of 11,560 s−1 altered the morphology of many platelets adhered to downstream fibrinogen from their native ellipsoidal to spread circular form. The platelet shape analysis showed that longer periods of post-stenotic flow increased the surface coverage fraction of ellipsoidal platelet population and decreased the surface coverage fraction of fully spread platelets on fibrinogen for both transiently elevated upstream wall shear rates.

Melt rheology and extrudate swell properties of talc filled polyethylene compounds

An experimental study of high-density polyethylene (HDPE) composites filled with talc (0–15 wt.%) was carried out to investigate the rheological properties. The apparent melt viscosity, melt density, and die-swell ratio (B) of the composites were measured at constant shear stress and constant shear rate by using a melt flow indexer and capillary rheometer. The experimental conditions were set to a temperature range from 190 to 220 °C for both apparatuses whereas a load range from 5 to 12.16 kg was selected for melt flow indexer and shear rate range from 1 to 10000 s−1 for capillary rheometer. The initial study showed that the talc particulates did not influence the melt viscosity compared with the neat HDPE but decreased the elasticity of the polymer system. The HDPE/talc systems obeyed power-law model in shear stress–shear rate variations and were shear thinning, meanwhile, the die-swell increased with an increased wall shear rate and shear stress. The melt density of the composites increased linearly with an increase of the filler weight fraction and decreased with the increase of the testing temperature. The talc-HDPE composites showed compressible in the molten state.

Improvement of transfer phenomena rates in open chaotic flow of nanofluid under the effect of magnetic field: Application of a combined method

Numerical investigation is carried out in the present research in order to assess the effects of a combined technique on heat transfer and fluid motion. A linking between three promoting ways to enhance transfer phenomena presented in terms of regime flow (chaotic flow), the fluid type (nanofluid) along with a non-intrusive means (magnetic induction) is considered throughout the current study. In this project, magnetohydrodynamic MHD field is applied with two different manners; either on the full geometry or partially on selected portions of the channel. Moreover, evolutions of local and average Nusselt numbers, thermal and velocity fields, average wall shear rate in addition to the flow patterns are examined for Hartmann number, Reynolds number and different scenarios of the MHD field application and direction. Findings illustrate that Nusselt number and therefore heat transfer is an increasing function with Ha number in the case of partial mode and transversal orientation of the MHD field. While it is either a constant, decreasing or slightly augmented function with Ha in the other applications. An amelioration of about 13% in heat transfer is recorded for the optimum case compared to the standard situation (without magnetic field). Besides, it is shown that Re number grows heat exchanges with an existing critical value of Re for the transversal orientation case, where the effect of the MHD mode on the average Nu number is differently.

Investigation on the impact of thermal performance of fluid due to hybrid nano-structures

This article explores the role of hybrid nano-particles in enhancing the thermal performance of Sutterby fluid over a two-dimensional body of variable thickness. Copper and aluminum oxides are dispersed in the Sutterby liquid simultaneously. The models for effective thermal properties of hybrid nano-fluids (a mixture of copper oxide, aluminum oxide, and Sutterby fluid) are used to model the transport of heat which results in a set of complex mathematical equations for momentum and energy conservation. These equations are solved numerically by finite element method (FEM). FEM methodology is tested and validated. An excellent agreement between the present and the published benchmarks is found. The parametric investigation is carried out, and a significant improvement in the thermal performance of Sutterby fluid due to hybrid nano-particles (copper oxide and aluminum trioxide) is observed. The wall heat flux for hybrid nano-Sutterby fluid (a mixture of cupper oxide, aluminum trioxide and Sutterby fluid) is significantly found to be greater than the thermal performance of a mixture of aluminum trioxide and the Sutterby fluid. The present work is a generalization of already published works. Therefore, the present work is retrieved into the previous special cases and the results are validated by comparing it with already published works. A good agreement between the present and the already published work is found. The wall shear stress and rate of heat transport increase when the Reynolds and the Deborah numbers are increased.

Rheological analysis of Newtonian and non‐Newtonian fluids using Marsh funnel: Experimental study and computational fluid dynamics modeling

AbstractIn the drilling industry, Marsh funnel viscosity is only a dynamic viscosity and cannot characterize actual rheology. Thus, measuring rheology using a Marsh funnel has been drawing considerable attention. In this study, we develop simplified mathematical models for wall shear rate, wall shear stress, and their consistency plots. Moreover, we propose mathematical models for the rheological parameters of Newtonian and non‐Newtonian fluids. We compare the results of the present model with those of a ZNN‐6 viscometer, a computational fluid dynamics (CFD) model, and other analytical models. According to the quantitative analysis results, the average systematic error of the Newtonian, apparent, and plastic viscosities between the present model and the ZNN‐6 viscometer measurements is 1.35%, 8.18%, and 5.42%, respectively. The average systematic error of the yield stress is 21.43%, which is under the controllable scope. Meanwhile, results of the qualitative analysis reveal that the present model for the wall shear rate and stress agrees with the CFD model. Moreover, the flow field inside the Marsh funnel is axisymmetric and has a component velocity in the horizontal direction. In summary, the proposed model is accurate, concise, available for field applications, and beneficial for a successful and safe drilling operation. Furthermore, the CFD approach is a necessary complement to exploring the actual field flow inside the Marsh funnel.

Platelet Adhesion and Thrombus Formation in Microchannels: The Effect of Assay-Dependent Variables.

Microfluidic flow chambers (MFCs) allow the study of platelet adhesion and thrombus formation under flow, which may be influenced by several variables. We developed a new MFC, with which we tested the effects of different variables on the results of platelet deposition and thrombus formation on a collagen-coated surface. Methods: Whole blood was perfused in the MFC over collagen Type I for 4 min at different wall shear rates (WSR) and different concentrations of collagen-coating solutions, keeping blood samples at room temperature or 37 °C before starting the experiments. In addition, we tested the effects of the antiplatelet agent acetylsalicylic acid (ASA) (antagonist of cyclooxygenase-1, 100 µM) and cangrelor (antagonist of P2Y12, 1 µM). Results: Platelet deposition on collagen (I) was not affected by the storage temperature of the blood before perfusion (room temperature vs. 37 °C); (II) was dependent on a shear rate in the range between 300/s and 1700/s; and (III) was influenced by the collagen concentration used to coat the microchannels up to a value of 10 µg/mL. ASA and cangrelor did not cause statistically significant inhibition of platelet accumulation, except for ASA at low collagen concentrations. Conclusions: Platelet deposition on collagen-coated surfaces is a shear-dependent process, not influenced by the collagen concentration beyond a value of 10 µg/mL. However, the inhibitory effect of antiplatelet drugs is better observed using low concentrations of collagen.

Effects of Elapsed Time on Downstream Platelet Adhesion Following Exposure to Transiently Elevated Upstream Shear Forces

Transient exposure to elevated shear forces pre-activates platelets for enhanced downstream adhesion, but how far downstream these priming effects persist is not known. We found that platelet adhesion to downstream capture region containing one of the three immobilized platelet binding proteins: fibrinogen, collagen, or von Willebrand factor, changed after platelets flowed through an upstream stenotic region. These platelet capture regions were placed at three different distances from the upstream stenotic region. Platelet adhesion increased with the increase of upstream wall shear rates from 1620 s-1 to 11560 s-1 for all three proteins, but only the adhesion to fibrinogen increased significantly with the distance between the upstream stenotic region and downstream capture region. Platelet adhesion to collagen remained essentially independent on the distance and adhesion to von Willebrand factor marginally increased with the distance after transient platelet exposure to higher upstream shear rates. The results implied that the activation of fibrinogen receptor GPIIb/IIIa by transient exposure to high upstream wall shear rates progresses in a time-dependent manner during the flow of platelets to the downstream capture regions. The highly elevated upstream wall shear rate of 11560 s-1 altered the morphology of many platelets adhered to downstream fibrinogen from their native ellipsoidal to spread circular form. The platelet shape analysis showed that longest periods of post-stenotic flow increased the surface coverage fraction of ellipsoidal platelet population and decreased the surface coverage fraction of fully spread platelets on fibrinogen after both elevated upstream wall shear rates.

Ultrasound Assessment of the Relation Between Local Hemodynamic Parameters and Plaque Morphology

Mechanical factors, especially wall shear stress (WSS) and circumferential strain (CS), play an important role in the progression and rupture of atherosclerotic plaques. Previous studies have shown that the temporal phase angle between WSS and CS, referred to as the stress phase angle (SPA) may be a biomarker for plaque development and vulnerability. Since the SPA is influenced by the severity and length of the stenosis, a multifactorial relationship between local hemodynamic variables and plaque morphology can be hypothesized. However, due to ethical restrictions and the difficulty of developing animal models, there is little experimental data to support such a hypothesis about the biomarker function of SPA. In this study, a novel non-invasive ultrasound-based method for investigating the relationship between local hemodynamics and plaque morphology is developed and investigated in-vitro and in-vivo with an apolipoprotein deficient mouse model. In the in-vitro experiments, using polyvinyl alcohol cryogel (PVA-c) phantoms, we have observed that the SPA becomes more negative and the wall shear rate (WSR) rises, as the severity of the stenosis increases. Conversely, SPA becomes more positive and WSR falls with increasing plaque length. These changes in plaque morphology have little effect on CS. The in-vivo experiments show that, as the severity of the plaque increases, the SPA becomes more negative and WSR tends to more positive values; whereas, the CS drops. We conclude that these local hemodynamic parameters such as SPA, WSR and CS, as suggested by others, can be regarded as prognostic markers for the assessment of plaque vulnerability.

Flow and wall shear rate analysis for a cruciform jet impacting on a plate at short distance

There are numerous turbulence models that have been developed in the past years, many of them being used in predicting flows, turbulence, mass and/or heat transfer. The particular case of an impinging jet implies all of the above. The performance of eight highly used Reynolds averaged Navier-Stokes turbulence models is examined in simulating a very sheared lobed impinging jet. The study is based on the investigation of an orthogonally lobed jet, impinging on a flat surface that flows out from a nozzle having a cruciform cross-section at a Reynolds number of 5620. Two experimental methods were implied for the comparison with numerical results. For the measurement of the wall shear rate an electrodiffusion method was employed. The velocity flow fields were measured using particle image velocimetry technique. The relative strengths and drawbacks of the SST k-ω, k-ω, TransSST, k-e realisable, RNG k-e, k-e, k-kl-ω and RSM turbulence models are compared.

Microfluidic hemophilia models using blood from healthy donors

BackgroundMicrofluidic clotting assays permit drug action studies for hemophilia therapeutics under flow. However, limited availability of patient samples and Inter‐donor variability limit the application of such assays, especially with many patients on prophylaxis. ObjectiveTo develop approaches to phenocopy hemophilia using modified healthy blood in microfluidic assays. MethodsCorn trypsin inhibitor (4 µg/mL)‐treated healthy blood was dosed with either anti–factor VIII (FVIII; hemophilia A model) or a recombinant factor IX (FIX) missense variant (FIX‐V181T; hemophilia B model). Treated blood was perfused at 100 s−1 wall shear rate over collagen/tissue factor (TF) or collagen/factor XIa (FXIa). ResultsAnti‐FVIII partially blocked fibrin production on collagen/TF, but completely blocked fibrin production on collagen/FXIa, a phenotype reversed with 1 µmol/L bispecific antibody (emicizumab), which binds FIXa and factor X. As expected, emicizumab had no significant effect on healthy blood (no anti‐FVIII present) perfused over collagen/FXIa. The efficacy of emicizumab in anti‐FVIII‐treated healthy blood phenocopied the action of emicizumab in the blood of a patient with hemophilia A perfused over collagen/FXIa. Interestingly, a patient‐derived FVIII‐neutralizing antibody reduced fibrin production when added to healthy blood perfused over collagen/FXIa. For low TF surfaces, reFIX‐V181T (50 µg/mL) fully blocked platelet and fibrin deposition, a phenotype fully reversed with anti‐TFPI. ConclusionTwo new microfluidic hemophilia A and B models demonstrate the potency of anti‐TF pathway inhibitor, emicizumab, and a patient‐derived inhibitory antibody. Using collagen/FXIa‐coated surfaces resulted in reliable and highly sensitive hemophilia models.

Insights in thixotropic concrete pumping by a Poiseuille flow extension

AbstractThixotropy is a reversible time-dependent phenomenon in fluids, in which an internal structure grows due to flocculation and breaks down under shear action. Numerous fluids are thixotropic,e.g.concretes and cementitious suspensions. Pumping of concrete is an important application. Since current approaches omit thixotropic effects, we aim to develop a simple theoretical model to evaluate or understand the significance of thixotropy on the concrete pumping behaviour. We therefore extended Poiseuille flow for thixotropic concretes and reformulated it in a dimensionless form to gain insights. After a validation, the results and significance are elaborated and concluded.Results showed that for increasing thixotropy and decreasing flow rates, the plug radius, wall shear rate and pumping pressure loss increase. Even though all thixotropy mechanisms may not be covered, a simple model is delivered to interpret or predict the effect of thixotropy on the pumping behaviour of cementitious suspensions. The dimensionless formulations via the Bingham numberBnand related discharge diagrams are sufficiently elegant for computational implementation and very insightful to distinguish a thixotropic flow regime. The model could be extended for more complicated thixotropies, irreversible time-dependent effects or even other pumping related phenomena.

Flow and wall shear rate analysis for a cruciform jet impacting on a plate at short distance

Flow and wall shear rate analysis for a cruciform jet impacting on a plate at short distance

Engineering a Bi-Conical Microchip as Vascular Stenosis Model.

Vascular stenosis is always associated with hemodynamic changes, especially shear stress alterations. Herein, bi-conical shaped microvessels were developed through flexibly and precisely controlled templated methods for hydrogel blood-vessel-like microchip. The blood-vessel-like microvessels demonstrated tunable dimensions, perfusable ability, and good cytocompatibility. The microchips showed blood-vessel-like lumens through fine embeddedness of human umbilical vein endothelial cells (HUVECs) on the interior surface of hydrogel microchannels, which closely reproduced the morphology and functions of human blood vessels. In the gradual narrowing region of bi-conical shape, fluid flow generated wall shear stress, which caused cell morphology variations. Wall shear rates at the gradual narrowing region were simulated by FLUENT software. The results showed that our microchannels qualified for performance as a vascular stenosis-like model in evaluating blood hydrodynamics. In general, our blood-vessel-on-a-chip could offer potential applications in the prevention, diagnosis, and therapy of arterial thrombosis.

Whole Blood Based Multiparameter Assessment of Thrombus Formation in Standard Microfluidic Devices to Proxy In Vivo Haemostasis and Thrombosis.

Microfluidic assays are versatile tests which, using only small amounts of blood, enable high throughput analyses of platelet function in several minutes. In combination with fluorescence microscopy, these flow tests allow real-time visualisation of platelet activation with the possibility of examining combinatorial effects of wall shear rate, coagulation and modulation by endothelial cells. In particular, the ability to use blood and blood cells from healthy subjects or patients makes this technology promising, both for research and (pre)clinical diagnostic purposes. In the present review, we describe how microfluidic devices are used to assess the roles of platelets in thrombosis and haemostasis. We place emphasis on technical aspects and on experimental designs that make the concept of “blood-vessel-component-on-a-chip” an attractive, rapidly developing technology for the study of the complex biological processes of blood coagulability in the presence of flow.

Rapid Electrostatic Capture of Rod-Shaped Particles on Planar Surfaces: Standing up to Shear.

We compare the electrostatically driven capture of flowing rod-shaped and spherical silica particles from dilute solutions onto a flow chamber wall that carries the opposite electrostatic charge from the particles. Particle accumulation and orientation are measured in time at a fixed region on the wall of a shear flow chamber. Rod-shaped particle aspect ratios are 2.5-3.2 and particle lengths are 1.3 and 2.67 μm for two samples, while sphere diameters were 0.72, 0.96, and 2.0 μm for three samples. At a moderate wall shear rate of 22 s-1, the particle accumulation for both rods and spheres is well described by diffusion-limited kinetics, demonstrating the limiting effect of particle diffusion in the near-wall boundary layer for electrostatically driven capture in this particle shape and size range. The significance of this finding is demonstrated in a calculation that shows that for delivery applications, nearly the same (within 10%) particle volume or mass is delivered to a surface at the diffusion-limited rate by rods and spheres. Therefore, in the absence of other motivating factors, the expense of developing rod-shaped microscale delivery packages to enhance capture from flow in the diffusion-limited simple shear regime is unwarranted. It is also interesting that the captured orientations of the larger rods, 2.6 μm in average length, were highly varied and insensitive to flow: a substantial fraction of rods were trapped in standing and slightly leaning orientations, touching the surface by their ends. Additionally, for particles that were substantially tipped over, there was only modest orientation in the flow direction. Taken together, these findings suggest that on the time scale of near-surface particle rotations, adhesion events are fast, trapping particles in orientations that do not necessarily maximize their favored adhesive contact or reduce hydrodynamic drag.