In Silico Design of Heterogeneous Microvascular Trees Using Generative Adversarial Networks and Constrained Constructive Optimization.

OBJECTIVE: Designing physiologically adequate microvascular trees is of crucial relevance for bioengineering functional tissues and organs. Yet, currently available methods are poorly suited to replicate the morphological and topological heterogeneity of real microvascular trees because the parameters used to control tree generation are too simplistic to mimic results of the complex angiogenetic and structural adaptation processes in vivo. METHODS: We propose a method to overcome this limitation by integrating a conditional deep convolutional generative adversarial network (cDCGAN) with a local fractal dimension-oriented constrained constructive optimization (LFDO-CCO) strategy. The cDCGAN learns the patterns of real microvascular bifurcations allowing for their artificial replication. The LFDO-CCO strategy connects the generated bifurcations hierarchically to form microvascular trees with a vessel density corresponding to that observed in healthy tissues. RESULTS: The generated artificial microvascular trees are consistent with real microvascular trees regarding characteristics such as fractal dimension, vascular density, and coefficient of variation of diameter, length, and tortuosity. CONCLUSIONS: These results support the adoption of the proposed strategy for the generation of artificial microvascular trees in tissue engineering as well as for computational modeling and simulations of microcirculatory physiology.

Simulation of angiogenesis in three dimensions: Application to cerebral cortex.

The vasculature is a dynamic structure, growing and regressing in response to embryonic development, growth, changing physiological demands, wound healing, tumor growth and other stimuli. At the microvascular level, network geometry is not predetermined, but emerges as a result of biological responses of each vessel to the stimuli that it receives. These responses may be summarized as angiogenesis, remodeling and pruning. Previous theoretical simulations have shown how two-dimensional vascular patterns generated by these processes in the mesentery are consistent with experimental observations. During early development of the brain, a mesh-like network of vessels is formed on the surface of the cerebral cortex. This network then forms branches into the cortex, forming a three-dimensional network throughout its thickness. Here, a theoretical model is presented for this process, based on known or hypothesized vascular response mechanisms together with experimentally obtained information on the structure and hemodynamics of the mouse cerebral cortex. According to this model, essential components of the system include sensing of oxygen levels in the midrange of partial pressures and conducted responses in vessel walls that propagate information about metabolic needs of the tissue to upstream segments of the network. The model provides insights into the effects of deficits in vascular response mechanisms, and can be used to generate physiologically realistic microvascular network structures.

Resilience of three-dimensional sinusoidal networks in liver tissue.

Can three-dimensional, microvasculature networks still ensure blood supply if individual links fail? We address this question in the sinusoidal network, a plexus-like microvasculature network, which transports nutrient-rich blood to every hepatocyte in liver tissue, by building on recent advances in high-resolution imaging and digital reconstruction of adult mice liver tissue. We find that the topology of the three-dimensional sinusoidal network reflects its two design requirements of a space-filling network that connects all hepatocytes, while using shortest transport routes: sinusoidal networks are sub-graphs of the Delaunay graph of their set of branching points, and also contain the corresponding minimum spanning tree, both to good approximation. To overcome the spatial limitations of experimental samples and generate arbitrarily-sized networks, we developed a network generation algorithm that reproduces the statistical features of 0.3-mm-sized samples of sinusoidal networks, using multi-objective optimization for node degree and edge length distribution. Nematic order in these simulated networks implies anisotropic transport properties, characterized by an empirical linear relation between a nematic order parameter and the anisotropy of the permeability tensor. Under the assumption that all sinusoid tubes have a constant and equal flow resistance, we predict that the distribution of currents in the network is very inhomogeneous, with a small number of edges carrying a substantial part of the flow-a feature known for hierarchical networks, but unexpected for plexus-like networks. We quantify network resilience in terms of a permeability-at-risk, i.e., permeability as function of the fraction of removed edges. We find that sinusoidal networks are resilient to random removal of edges, but vulnerable to the removal of high-current edges. Our findings suggest the existence of a mechanism counteracting flow inhomogeneity to balance metabolic load on the liver.

Do body mass index and waist-to-height ratio over the preceding decade predict retinal microvasculature in 11-12 year olds and midlife adults?

BACKGROUND/OBJECTIVES: Microvascular changes may contribute to obesity-associated cardiovascular disease. We examined whether body mass index (BMI) and waist-to-height ratio (WHtR) (1) at multiple earlier time points and (2) decade-long trajectories predicted retinal microvascular parameters in mid-childhood/adulthood. METHODS: Participants/design: 1288 11-12 year olds (51% girls) and 1264 parents (87% mothers) in the population-based Child Health CheckPoint (CheckPoint) module within the Longitudinal Study of Australian Children (LSAC). LSAC exposure measures: biennial BMI z-score and WHtR for children at five time points from age 2-3 to 10-11 years and self-reported parent BMI at six time points from child age 0-1 years to 10-11 years. CheckPoint outcome measures: retinal arteriolar and venular caliber. ANALYSES: BMI/WHtR trajectories were identified by group-based trajectory modeling; linear regression models estimated associations between BMI/WHtR at each time point/trajectories and later retinal vascular caliber, adjusted for age, sex, and family socioeconomic status. RESULTS: In time point analyses, higher child BMI/WHtR from age 4 to 5 years was associated with narrower arteriolar caliber at the age of 11-12 years, but not venular caliber. For example, each standard deviation higher in BMI z-score at 4-5 years was associated with narrower arteriolar caliber at 11-12 years (standardized mean difference (SMD): -0.05, 95% confidence interval (CI): -0.10 to 0.01); by 10-11 years, associations had doubled to -0.10 (95% CI: -0.16 to -0.05). In adults, these finding were similar, except the magnitude of BMI and arteriolar associations were similar across all time points (SMD: -0.11 to -0.13). In child and adult BMI trajectory analyses, less favorable trajectories predicted narrower arteriolar (p-trend < 0.05), but not venular (p-trend > 0.1), caliber. Compared with those in the average BMI trajectory, SMDs in arterial caliber for children and adults in the highest trajectory were -0.25 (95% CI: -0.44 to -0.07) and -0.42 (95% CI: -0.73 to -0.10), respectively. Venular caliber showed late associations with child WHtR, but not with BMI in children or adults. CONCLUSIONS: Associations of decade-long high BMI trajectories with narrowed retinal arteriolar caliber emerge in children, and are clearly evident by midlife. Adiposity appears to exert its early adverse life course impacts on the microcirculation more via arteriolar than venular mechanisms.

Red blood cells stabilize flow in brain microvascular networks.

Capillaries are the prime location for oxygen and nutrient exchange in all tissues. Despite their fundamental role, our knowledge of perfusion and flow regulation in cortical capillary beds is still limited. Here, we use in vivo measurements and blood flow simulations in anatomically accurate microvascular network to investigate the impact of red blood cells (RBCs) on microvascular flow. Based on these in vivo and in silico experiments, we show that the impact of RBCs leads to a bias toward equating the values of the outflow velocities at divergent capillary bifurcations, for which we coin the term "well-balanced bifurcations". Our simulation results further reveal that hematocrit heterogeneity is directly caused by the RBC dynamics, i.e. by their unequal partitioning at bifurcations and their effect on vessel resistance. These results provide the first in vivo evidence of the impact of RBC dynamics on the flow field in the cortical microvasculature. By structural and functional analyses of our blood flow simulations we show that capillary diameter changes locally alter flow and RBC distribution. A dilation of 10% along a vessel length of 100 µm increases the flow on average by 21% in the dilated vessel downstream a well-balanced bifurcation. The number of RBCs rises on average by 27%. Importantly, RBC up-regulation proves to be more effective the more balanced the outflow velocities at the upstream bifurcation are. Taken together, we conclude that diameter changes at capillary level bear potential to locally change the flow field and the RBC distribution. Moreover, our results suggest that the balancing of outflow velocities contributes to the robustness of perfusion. Based on our in silico results, we anticipate that the bi-phasic nature of blood and small-scale regulations are essential for a well-adjusted oxygen and energy substrate supply.

Cutaneous vessel features of sensitive skin and its underlying functions.

BACKGROUND: Following the sufficient studies of the effects of skin barrier impairment and heightened neural reaction on sensitive skin (SS), many scholars have paid great attention to the roles of superficial microvasculature in SS. METHODS: By questionnaire survey, lactic acid sting test, and capsaicin test, eligible subjects were classified as normal skin, only lactic acid sting test positive (LASTP), only capsaicin test positive (CATP), and both positive (both LASTP and CATP). D-OCT was used to photograph images for evaluating the cutaneous vessels features each group. RESULTS: Totally 137 subjects completed the study. Compared with LASTN group, the vascular vessels were closer to epidermis in LASTP group. Mesh and branching vessels were more popular in SS than normal skin. High blood vessel density was more prevalent in SS, while low density frequently presented in normal skin. The vascular depth had a closely negative correlation with face flushing and SSS, and vascular shapes had a good positive correlation with face flushing and SSB. CONCLUSIONS: Our study indicates that there is a significant difference in vascular depth, shape, and density between SS and normal skin which is valuable to explore SS pathologic mechanism and to further investigate cutaneous microvasculature functions in SS.

Microvessel density, lipid chemistry and N2 solubility in human and pig adipose tissue.

Decompression sickness (DCS) occurs when nitrogen gas (N2) comes out of solution too quickly, forming bubbles in the blood and tissues. These bubbles can be a serious condition; thus it is of extreme interest in the dive community to model DCS risk. Diving models use tissue compartments to calculate tissue partial pressures, often using data obtained from other mammalian species (i.e., pigs). Adipose tissue is an important compartment in these models because N2 is five times more soluble in fat than in blood; at any blood/tissue interface N2 will diffuse into the fat and can lead to bubble formation on ascent. Little is known about many characteristics of adipose tissue relevant to diving physiology. Therefore, we measured microvessel density and morphology, lipid composition, and N2 solubility in adipose tissue from humans and pigs. Human adipose tissue has significantly higher microvascular density (1.79 ± 0.04 vs. 1.21 ± 0.30%), vessel diameter (10.25 ± 0.28 vs. 6.72 ± 0.60 µm), total monounsaturated fatty acids (50.1 vs. 41.2 mol%) and N2 solubility (0.061 ± 0.003 vs. 0.054 ± 0.004 mL N2 mL⁻ ¹ oil) compared to pig tissue. Pig adipose tissue has significantly higher lipid content (76.1 ± 4.9 vs. 64.6 ± 5.1%) and total saturated fatty acids (38.8 vs. 29.5 mol%). Though two important components in gas kinetics within adipose tissue during diving (blood flow rates and degree of perfusion) are not well understood, our results indicate differences between the adipose tissue of humans and pigs. This suggests data from swine may not exactly predict gas dynamics for estimating DCS in humans.

Dynamic Contrast Optical Coherence Tomography reveals laminar microvascular hemodynamics in the mouse neocortex in vivo.

Studies of flow-metabolism coupling often presume that microvessel architecture is a surrogate for blood flow. To test this assumption, we introduce an in vivo Dynamic Contrast Optical Coherence Tomography (DyC-OCT) method to quantify layer-resolved microvascular blood flow and volume across the full depth of the mouse neocortex, where the angioarchitecture has been previously described. First, we cross-validate average DyC-OCT cortical flow against conventional Doppler OCT flow. Next, with laminar DyC-OCT, we discover that layer 4 consistently exhibits the highest microvascular blood flow, approximately two-fold higher than the outer cortical layers. While flow differences between layers are well-explained by microvascular volume and density, flow differences between subjects are better explained by transit time. Finally, from layer-resolved tracer enhancement, we also infer that microvascular hematocrit increases in deep cortical layers, consistent with predictions of plasma skimming. Altogether, our results show that while the cortical blood supply derives mainly from the pial surface, laminar hemodynamics ensure that the energetic needs of individual cortical layers are met. The laminar trends reported here provide data that links predictions based on the cortical angioarchitecture to cerebrovascular physiology in vivo.

Ultrasound patterning technologies for studying vascular morphogenesis in 3D.

Investigations in this report demonstrate the versatility of ultrasound-based patterning and imaging technologies for studying determinants of vascular morphogenesis in 3D environments. Forces associated with ultrasound standing wave fields (USWFs) were employed to non-invasively and volumetrically pattern endothelial cells within 3D collagen hydrogels. Patterned hydrogels were composed of parallel bands of endothelial cells located at nodal regions of the USWF and spaced at intervals equal to one half wavelength of the incident sound field. Acoustic parameters were adjusted to vary the spatial dimensions of the endothelial bands, and effects on microvessel morphogenesis were analyzed. High-frequency ultrasound imaging techniques were used to image and quantify the spacing, width and density of initial planar cell bands. Analysis of resultant microvessel networks showed that vessel width, orientation, density and branching activity were strongly influenced by the initial 3D organization of planar bands and, hence, could be controlled by acoustic parameters used for patterning. In summary, integration of USWF-patterning and high-frequency ultrasound imaging tools enabled fabrication of vascular constructs with defined microvessel size and orientation, providing insight into how spatial cues in 3D influence vascular morphogenesis.

Electroosmosis modulated transient blood flow in curved microvessels: Study of a mathematical model.

The flow through curved microvessels has more realistic applications in physiological transport phenomena especially in blood flow through capillary and microvessels. Motivated by the biomicrofluidics applications, a mathematical model is developed to describe the blood flow inside a curved microvessel driven by electroosmosis. In addition to this flow, the channel experiences electric double layer phenomenon due to zeta potential about -25 mV. Lubrication theory and Debye-Hückel approximation are employed to obtain an analytical solution for electric potential function. Computations of stream function, axial velocity, volume flow rate, and pressure rise are computed through low zeta potentials. The electroosmotic flow behaviour is governed by two dimensionless parameters: Helmholtz-Smoluchowski velocity and Debye-Hückel parameter. It is also examined that, how curvature affects the blood flow driven by the electroosmosis. Furthermore, the salient features of flow characteristics and trapping phenomena are presented. The results indicate that pressure gradient and wall shear stress reduce with increasing the curvature effects however the trapping is more with high curvature of the microvessel. The observations also indicate promising features of micromixer, micro-peristaltic pumps, and organ-on-a-chip devices. They may further be exploited in diagnosis/mixing of samples, and haemodialysis respectively.

Cadaveric Specimen Study of Prostate Microvasculature: Implications for Arterial Embolization.

PURPOSE: To describe the prostatic microvasculature anatomy and to measure the diameter of the intraprostatic vessels from human cadaveric specimens. MATERIAL AND METHODS: The prostates of 18 white males (35-68 years of age; mean prostate volume, 60.11 mL) were fixed in a solution of phosphate-buffered 10% formaldehyde and processed histologically with hematoxylin and eosin stain, Masson trichrome stain, immune peroxidase, and immunofluorescence. Fluorescence-conjugated antibodies (anti-CD34 and anti-actin smooth muscle) were used to mark the endothelium and the fibromuscular stroma, respectively. Each slide was digitally scanned and photographed under microscopy to measure the intraprostatic arterial diameters using image analysis software. RESULTS: In 28 hemipelvises (77.8%) a single dominant prostate artery was found (mean diameter, 1.96 mm). The microvasculature study identified 3 types of intraprostatic arterial distributions: internodal (IT), perinodal (PN), and intranodal (IN). The IT arteries are located at the trabeculae of the hyperplastic stroma between the nodules. The PN arteries were located at the periphery of each hyperplastic nodule before entering into it. The IN vessels were located inside the hyperplastic nodules as terminal arteries to the glands. The mean IT artery diameter was 317 µm (min-max range, 155-555 µm), mean PN artery diameter was 150 µm (min-max range, 59-266 µm), and the mean IN artery was 56 µm (min-max range, 24-104 µm). The diameters of intraprostatic arteries did not correlate with prostate volume (IT arteries, P = .303; PN arteries, P = .686; and IN arteries, P = .413). CONCLUSIONS: The description of the prostate microvasculature anatomy, as described by this cadaveric study, may provide useful information for prostate artery embolization.

ANALYSIS OF THE NORMAL PERIPHERAL RETINAL VASCULAR PATTERN AND ITS CORRELATION WITH MICROVASCULAR ABNORMALITIES USING ULTRA-WIDEFIELD FLUORESCEIN ANGIOGRAPHY.

PURPOSE: To describe the retinal peripheral vascular morphology and to elucidate its relationship to microvascular abnormalities in normal fundus using ultra-widefield fluorescein angiography. METHODS: A total of 242 eyes from 167 consecutive patients were categorized into 3 groups: bilateral normal (n = 64), normal with contralateral eye affected with vascular disease (n = 82), and early diabetic eyes (n = 96). Peripheral vascular morphology was described and classified according to the shape. Microvascular abnormalities such as capillary telangiectasia, microaneurysm, or vascular leakage were documented, and the relationship between those abnormalities in each groups were analyzed. RESULTS: There were two distinctive peripheral vascular morphologies-loop and branching patterns. Microvascular abnormalities were more frequently found as loop patterns; this difference was most prominent when both eyes were normal. In case of normal eyes with contralateral eye affected with vascular disease or diabetic eyes, branching pattern microvascular abnormalities were relatively increased, whereas loop pattern still showed a large degree of microvascular abnormalities. CONCLUSION: In normal retinal periphery, we observed microvascular abnormalities and their relationship with vascular morphology, which could be influenced by the condition of the contralateral eye or systemic disease such as diabetes mellitus.

Numerical simulation of heat transfer in blood flow altered by electroosmosis through tapered micro-vessels.

A numerical simulation is presented to study the heat and flow characteristics of blood flow altered by electroosmosis through the tapered micro-vessels. Blood is assumed as non-Newtonian (micropolar) nanofluids. The flow regime is considered as asymmetric diverging (tapered) microchannel for more realistic micro-vessels which is produced by choosing the peristaltic wave train on the walls to have different amplitudes and phase. The Rosseland approximation is employed to model the radiation heat transfer and temperatures of the walls are presumed constants. The mathematical formulation of the present problem is simplified under the long-wavelength, low-Reynolds number and Debye-Hückel linearization approximations. The influence of various dominant physical parameters are discussed for axial velocity, microrotation distribution, thermal temperature distribution and nanoparticle volume fraction field. However, our foremost emphasis is to determine the effects of thermal radiation and coupling number on the axial velocity and microrotation distribution beneath electroosmotic environment. This analysis places a significant observation on the thermal radiation and coupling number which plays an influential role in hearten fluid velocity. This study is encouraged by exploring the nanofluid-dynamics in peristaltic transport as symbolized by heat transport in biological flows and also in novel pharmacodynamics pumps and gastro-intestinal motility enhancement.

Vascular architecture in free flaps: Analysis of vessel morphology and morphometry in murine free flaps.

The aim of this study was to analyze the development of vascular architecture as well as vascular morphometry and morphology of anastomosed microvascular free flaps. Free pectoral skin flaps were raised in 25 rats and anastomosed to the femoral vessels in the groin region. CD31 immunohistology was performed after 3, 7 and 12 d (each 5 animals each) to analyze microvessel density (MVD), microvessel area (MVA) and microvessel size (MVS). Microvascular corrosion casting was performed after 7 and 12 d (5 animals each) to analyze vessel diameter (VD), intervascular distance (IVD), interbranching distance (IBD), and branching angle (BA). Further on, sprout and pillar density as hallmarks of sprouting and intussusceptive angiogenesis were analyzed. Pectoral skin isles from the contralateral side served as controls. A significantly increased MVD was found after 7 and 12 d (p each <0.001). MVA was significantly increased after 3, 7 and 12 d (p each <0.001) and a significantly increased MVS was analyzed after 3 and 7 d (p each <0.001). VD and IVD were significantly increased after 7 and 12 d (p each <0.001). For IBD, a significantly increase was measured after 7 d (p < 0.001). For IBA, sprout and pillar density, no significant differences were found (p each ≥0.05). Significant changes in the vascular architecture of free flaps after successful microvascular anastomosis were seen. Since there was no evidence for sprout and pillar formation within the free flaps, the increased MVD and flap revascularization might be induced by the receiving site.

Vascular morphology in normal skin studied with dynamic optical coherence tomography.

Dynamic optical coherence tomography (D-OCT) is a non-invasive imaging technique, suitable for the study of structural and dynamic features of cutaneous microvasculature. Studies with D-OCT have primarily focused on non-melanoma skin cancer (NMSC), and a reference description of healthy skin is lacking. The aim of the study was to describe the prevalence of standard microvascular features in normal skin. A total of 280 participants without skin disease were D-OCT-scanned on four body locations: three sun-exposed areas and one unexposed: forehead, back of the neck, back of the hand and medial side of the upper arm. Frequencies of standard vascular features were reported, and relations to anatomical location and demographic data were investigated. "Dots," "lines" and "curves" were the most frequent shapes at 150 µm, 300 µm and 500 µm. "Mottle" was the predominant pattern at 150 µm and 300 µm. "Mesh" was found from 300 µm and primarily found at 500 µm. Regional differences in vascular characteristics were primarily found comparing the medial side of the arm with the other body locations. In normal skin, the most frequent shapes were "dots," "lines" and "curves," and "mottle" was present more superficially than "mesh." In conclusion, regional anatomical differences should be taken into account when evaluating D-OCT images.

Optimal occlusion uniformly partitions red blood cells fluxes within a microvascular network.

In animals, gas exchange between blood and tissues occurs in narrow vessels, whose diameter is comparable to that of a red blood cell. Red blood cells must deform to squeeze through these narrow vessels, transiently blocking or occluding the vessels they pass through. Although the dynamics of vessel occlusion have been studied extensively, it remains an open question why microvessels need to be so narrow. We study occlusive dynamics within a model microvascular network: the embryonic zebrafish trunk. We show that pressure feedbacks created when red blood cells enter the finest vessels of the trunk act together to uniformly partition red blood cells through the microvasculature. Using mathematical models as well as direct observation, we show that these occlusive feedbacks are tuned throughout the trunk network to prevent the vessels closest to the heart from short-circuiting the network. Thus occlusion is linked with another open question of microvascular function: how are red blood cells delivered at the same rate to each micro-vessel? Our analysis shows that tuning of occlusive feedbacks increase the total dissipation within the network by a factor of 11, showing that uniformity of flows rather than minimization of transport costs may be prioritized by the microvascular network.

Analysis of vascular homogeneity and anisotropy on high-resolution primate brain imaging.

Using a systematic investigation of brain blood volume, in high-resolution synchrotron 3D images of microvascular structures within cortical regions of a primate brain, we challenge several basic questions regarding possible vascular bias in high-resolution functional neuroimaging. We present a bilateral comparison of cortical regions, where we analyze relative vascular volume in voxels from 150 to 1000 µm side lengths in the white and grey matter. We show that, if voxel size reaches a scale smaller than 300 µm, the vascular volume can no longer be considered homogeneous, either within one hemisphere or in bilateral comparison between samples. We demonstrate that voxel size influences the comparison between vessel-relative volume distributions depending on the scale considered (i.e., hemisphere, lobe, or sample). Furthermore, we also investigate how voxel anisotropy and orientation can affect the apparent vascular volume, in accordance with actual fMRI voxel sizes. These findings are discussed from the various perspectives of high-resolution brain functional imaging. Hum Brain Mapp 38:5756-5777, 2017. © 2017 Wiley Periodicals, Inc.

Model-based inference from microvascular measurements: Combining experimental measurements and model predictions using a Bayesian probabilistic approach.

OBJECTIVE: In vivo imaging of the microcirculation and network-oriented modeling have emerged as powerful means of studying microvascular function and understanding its physiological significance. Network-oriented modeling may provide the means of summarizing vast amounts of data produced by high-throughput imaging techniques in terms of key, physiological indices. To estimate such indices with sufficient certainty, however, network-oriented analysis must be robust to the inevitable presence of uncertainty due to measurement errors as well as model errors. METHODS: We propose the Bayesian probabilistic data analysis framework as a means of integrating experimental measurements and network model simulations into a combined and statistically coherent analysis. The framework naturally handles noisy measurements and provides posterior distributions of model parameters as well as physiological indices associated with uncertainty. RESULTS: We applied the analysis framework to experimental data from three rat mesentery networks and one mouse brain cortex network. We inferred distributions for more than 500 unknown pressure and hematocrit boundary conditions. Model predictions were consistent with previous analyses, and remained robust when measurements were omitted from model calibration. CONCLUSION: Our Bayesian probabilistic approach may be suitable for optimizing data acquisition and for analyzing and reporting large data sets acquired as part of microvascular imaging studies.

Computer modelling of electro-osmotically augmented three-layered microvascular peristaltic blood flow.

A theoretical study is presented here for the electro-osmosis modulated peristaltic three-layered capillary flow of viscous fluids with different viscosities in the layers. The layers considered here are the core layer, the intermediate layer and the peripheral layer. The analysis has been carried out under a number of physical restrictions viz. Debye-Hückel linearization (i.e. wall zeta potential ≤25mV) is assumed sufficiently small, thin electric double layer limit (i.e. the peripheral layer is much thicker than the electric double layer thickness), low Reynolds number and large wavelength approximations. A non-dimensional analysis is used to linearize the boundary value problem. Fluid-fluid interfaces, peristaltic pumping characteristics, and trapping phenomenon are simulated. Present study also evaluates the responses of interface, pressure rise, time-averaged volume flow rate, maximum pressure rise, and the influence of Helmholtz-Smoluchowski velocity on the mechanical efficiency (with two different cases of the viscosity of fluids between the intermediate and the peripheral layer). Trapping phenomenon along with bolus dynamics evolution with thin EDL effects are analyzed. The findings of this study may ultimately be useful to control the microvascular flow during the fractionation of blood into plasma (in the peripheral layer), buffy coat (intermediate layer) and erythrocytes (core layer). This work may also contributes in electrophoresis, hematology, electrohydrodynamic therapy and, design and development of biomimetic electro-osmotic pumps.

Microvasculature of the California sea lion (Zalophus californianus) eye and its functional significance.

OBJECTIVE: To examine the ocular circulation in California sea lions (Zalophus californianus). ANIMALS STUDIED: Eyes were obtained postmortem from three sea lions that died while in captivity. PROCEDURES: Specimens from sea lions were investigated using scanning electron microscopy (SEM) of vascular corrosion casts. The thermal characteristics of live animal eyes were measured using an infrared imaging system. RESULTS: The major orbital artery of the sea lion was the ophthalmic artery. The artery was remarkably thick in diameter, showed a marked convolution and formed an ophthalmic rete around the optic nerve at the posterior pole of the eyeball. The long posterior ciliary artery terminates to form a prominent inner arterial circle at the pupillary margin. The iridial arteries originated from the arterial circle showing either a crimped or somewhat coiled course, extending toward the root of the iris and formed a root supplying a large amount of blood to the iris and ciliary bodies. The venules in the conjunctiva formed a well-developed venous plexus. The vortex veins showed a dilation and constriction at the site passing through the sclera. Thermographic examination revealed that the eye showed a higher degree of thermal emission than adjacent skin areas. CONCLUSIONS: These characteristics suggest that the ocular vasculature might play roles in thermoregulation as well as in hemodynamics by draining a large amount of blood so that the appropriate operating temperature for the eye can be maintained in a deep and cold aquatic environment.