The effect of particle seeding on the rheological properties of blood Analog fluid used during laser Doppler velocimetry.

It is generally assumed that blood behaves strictly as a particle-free fluid and not as a suspension in arterial sized vessels (> 1 mm). However, we have previously demonstrated a biphasic deviation of pressure gradients(PG) of blood from a particle-free fluid of equal viscosity in straight tubes, with the blood PG being greater than the particle-free fluid at low flowrates and lower at high flowrates. Since this behavior may affect velocity-derived PG, we addressed the hypothesis that PG across a BT shunt would show significant deviation from that of a particle-free blood analog fluid (BAF). Methods: The in vitro BT shunt model consisted of two arterial sections connected by a physiologically sized shunt (D = 5 mm, L = 9 cm). PG across the shunt were obtained by measuring pressure 10 cm proximal and distal to the inlet and outlet respectively. For a given flow rate the PG across the shunt was recorded for both blood and an equal viscosity BAF(aqueous glycerin solution, 3.8 cP). PG differences were plotted vs. Reynolds number (Re = ratio of inertial to viscous forces) and divided into laminar and turbulent flow regimes, with a transition Re of 2100 (the approximate transition from laminar to turbulent flow in tubes). Differences in PG between blood and BAF were considered significant at a level of 0.01 using a paired t-test for both the laminar and turbulent regimes. Results: For Re 0.5). However, for Re > 2100, the PG for blood were consistently lower than that of BAF and the differences were significant (mean difference = 9.9 mmHg, p < 0.01). Conclusions: Blood PG across BT shunts deviate from BAF PG. This effect is especially pronounced in the turbulent regime and is consistent with our previous investigations using straight tubes, suggesting Re-dependent phenomena may account for this behavior. These findings may have important implications in the noninvasive assessment of pulmonary artery pressure in patients with BT shunts.

This study represents a pioneering work on the extensional magnetorheological properties of human blood analogue fluids loaded with magnetic microparticles. Dynabeads M-270 particles were dispersed in Newtonian and viscoelastic blood analogue fluids at 5% wt. Capillary breakup experiments were performed, with and without the influence of an external magnetic field aligned with the flow direction. The presence of the particles increased the viscosity of the fluid, and that increment was larger when embedded within a polymeric matrix. The application of an external magnetic field led to an even larger increment of the viscosity of the working fluids, as the formation of small aggregates induced an increment in the effective volume fraction of particles. Regarding the liquid bridge stability, the Newtonian blood analogue fluid remained as a Newtonian liquid exhibiting a pinch-off at the breakup time in any circumstance. However, in the case of the viscoelastic blood analogue fluid, the presence of the particles and the simultaneous application of the magnetic field enhanced the formation of the beads-on-a-string structure, as the Ohnesorge number remained basically unaltered, whereas the time of the experiment increased due to its larger viscosity, which resulted in a decrease in the Deborah Number. This result was confirmed with fluids containing larger concentrations of xanthan gum.

Flexible PDMS microparticles to mimic RBCs in blood particulate analogue fluids

Four commonly used refractive-index (RI)-matched Newtonian blood-analog fluids are reviewed, and different non-Newtonian blood-analogs, with RI of 1.372–1.495, are investigated. Sodium iodide (NaI), sodium thiocyanate (NaSCN) and potassium thiocyanate are used to adjust the RI of blood-analogs to that of test sections for minimizing optical distortions in particle image velocimetry data, and xanthan gum (XG) is added to the fluids to give them non-Newtonian properties (shear thinning and viscoelasticity). Our results support the general belief that adding NaI to Newtonian fluids matches the RI without changing the kinematic viscosity. However, in contrast to claims made in a few studies that did not measure rheology, our investigation revealed that adding NaI or NaSCN to XG-based non-Newtonian fluids changes the viscosity of the fluids considerably and reduces the shear-thinning property. Therefore, the RI of non-Newtonian blood-analog fluids with XG cannot be adjusted easily by varying the concentration of NaI or NaSCN and needs more careful rheological study.

The influence of the non-Newtonian properties of blood on the flow in large arteries: steady flow in a carotid bifurcation model

The objective of inspection, testing and supervision of medical devices is to ensure the effectiveness and safety of medical devices in use. Leachables are substances that are leached from medical devices or materials during their clinical use. Leachables are important factors for the safety risks of medical devices. The analysis, detection, and safety evaluation of leachables are important parts of the safety evaluation of medical devices. The allowable limits for leachable substances which are established on the toxicological research provide a scientific basis for the judgment of qualitative and quantitative analysis results. Obtaining more detailed, rigorous and sufficient toxicological research data is of great significance to set highly enforceable product technical indicators. For the establishment of allowable limits for leachable substances, its role in the safety evaluation of medical devices is summarized, and the relevant standards and their implementation status in the testing of medical devices are introduced.

A long-term durability test was conducted on a newly developed axial-flow ventricular assist device (VAD) with hydrodynamic bearings. The mock circulatory loop consisted of a diaphragm pump with a mechanical heart valve, a reservoir, a compliance tank, a resistance valve, and flow paths made of polymer or titanium. The VAD was installed behind the diaphragm pump. The blood analog fluid was a saline solution with added glycerin at a temperature of 37°C. A pulsatile flow was introduced into the VAD over a range of flow rates to realize a positive flow rate and a positive pressure head at a given impeller rotational speed, yielding a flow rate of 5L/min and a pressure of 100mmHg. Pulsatile flow conditions were achieved with the diastolic and systolic flow rates of ~0 and 9.5L/min, respectively, and an average flow rate of ~5L/min at a pulse rate of 72bpm. The VAD operation was judged by not only the rotational speed of the impeller, but also the diastolic, systolic, and average flow rates and the average pressure head of the VAD. The conditions of the mock circulatory loop, including the pulse rate of the diaphragm pump, the fluid temperature, and the fluid viscosity were maintained. Eight VADs were tested with testing periods of 2years, during which they were continuously in operation. The VAD performance factors, including the power consumption and the vibration characteristics, were kept almost constant. The long-term durability of the developed VAD was successfully demonstrated.

A number of common eye diseases are associated with ocular perfusion abnormalities. The present study aimed to investigate whether systemically administered moxaverine improves ocular blood flow. Sixteen healthy volunteers were studied in this randomized, double-masked, placebo-controlled, two-way crossover study. Moxaverine in a dose of 150 mg was administered i.v. Ocular haemodynamic parameters were measured before and after drug administration. Retinal arterial and venous diameters were measured with a retinal vessel analyser. Retinal blood velocity was assessed using laser Doppler velocimetry and choroidal and optic nerve head blood flow was measured with laser Doppler flowmetry. Moxaverine increased choroidal blood flow (22.6 ± 27.9%), an effect which was significant versus placebo (p = 0.015). Red blood cell velocity in retinal veins tended to increase by 13.6 ± 13.3% after infusion of moxaverine, but this effect was not significant compared with placebo (p = 0.25). In the optic nerve head moxaverine also tended to increase blood flow (11.8 ± 12.7%), but, again, this effect was not significant versus placebo (p = 0.12). Neither moxaverine nor placebo had an effect on retinal arterial diameters. In retinal veins moxaverine tended to induce vasodilation (2.6 ± 2.8%) and to increase blood flow (19.6 ± 16.5%), but these effects were not significant (both p = 0.12). The present study indicates an increase in choroidal blood flow after systemic infusion of a single dose of moxaverine in healthy subjects. Further studies are warranted to investigate whether these effects are also seen after longterm treatment in patients with ocular vascular disease.

In this study, we show the importance of extensional rheology, in addition to the shear rheology, in the choice of blood analog solutions intended to be used in vitro for mimicking the microcirculatory system. For this purpose, we compare the flow of a Newtonian fluid and two well-established viscoelastic blood analog polymer solutions through microfluidic channels containing both hyperbolic and abrupt contractions∕expansions. The hyperbolic shape was selected in order to impose a nearly constant strain rate at the centerline of the microchannels and achieve a quasihomogeneous and strong extensional flow often found in features of the human microcirculatory system such as stenoses. The two blood analog fluids used are aqueous solutions of a polyacrylamide (125 ppm w∕w) and of a xanthan gum (500 ppm w∕w), which were characterized rheologically in steady-shear flow using a rotational rheometer and in extension using a capillary breakup extensional rheometer (CaBER). Both blood analogs exhibit a shear-thinning behavior similar to that of whole human blood, but their relaxation times, obtained from CaBER experiments, are substantially different (by one order of magnitude). Visualizations of the flow patterns using streak photography, measurements of the velocity field using microparticle image velocimetry, and pressure-drop measurements were carried out experimentally for a wide range of flow rates. The experimental results were also compared with the numerical simulations of the flow of a Newtonian fluid and a generalized Newtonian fluid with shear-thinning behavior. Our results show that the flow patterns of the two blood analog solutions are considerably different, despite their similar shear rheology. Furthermore, we demonstrate that the elastic properties of the fluid have a major impact on the flow characteristics, with the polyacrylamide solution exhibiting a much stronger elastic character. As such, these properties must be taken into account in the choice or development of analog fluids that are adequate to replicate blood behavior at the microscale.

In order to simulate hemodynamics within centrifugal blood pumps and to predict pump hemolysis, CFD simulations must be thoroughly validated against experimental data. They must also account for and accurately model the specific working fluid in the pump, whether that is a blood-analog solution to match an experimental PIV study or animal blood in a hemolysis experiment. Therefore, the Food and Drug Administration (FDA) benchmark centrifugal blood pump and its database of experimental PIV and hemolysis data were used to thoroughly validate CFD simulations of the same blood pump. A Newtonian blood model was first used to compare to the PIV data with a blood analog fluid while hemolysis data were compared using a power-law hemolysis model fit to porcine blood data. A viscoelastic blood model was then incorporated into the CFD solver to investigate the importance of modeling blood's viscoelasticity in centrifugal pumps. The established computational framework, including a dynamic rotating mesh, animal blood-specific fluid properties and hemolysis modeling, and a k-ω SST turbulence model, was shown to more accurately predict pump pressure heads, velocity fields, and hemolysis compared to previously published CFD studies of the FDA centrifugal pump. The CFD simulations were able to match the FDA pressure and hemolysis data for multiple pump operating conditions, with the CFD results being within the standard deviations of the experimental results. While CFD radial velocity profiles between the impeller blades also compared well to the PIV velocity results, more work is still needed to address the large variability among both experimental and computational predictions of velocity in the diffuser outlet jet. Small differences were observed between the Newtonian and viscoelastic blood models in pressure head and hemolysis at the higher flow rate cases (FDA Conditions 4 and 5) but were more significant at lower flow rate and pump impeller speeds (FDA Condition 1). These results suggest that the importance of accounting for blood's viscoelasticity may be dependent on the specific blood pump operating conditions. This detailed computational framework with improved modeling techniques and an extensive validation procedure will be used in future CFD studies of centrifugal blood pumps to aid in device design and predictions of their biological responses.

Prediction of the effects of refractive index (RI) mismatch on laser Doppler anemometer (LDA) measurements within a curvilinear cavity (an artificial ventricle) was achieved by developing a general technique for modelling the paths of the convergent beams of the LDA system using 3D vector geometry. Validated by ray tracing through CAD drawings, the predicted maximum tolerance in RI between the solid model and the working fluid was +/- 0.0005, equivalent to focusing errors commensurate with the geometric and alignment uncertainties associated with the flow model and the LDA arrangement. This technique supports predictions of the effects of refraction within a complex geometry. Where the RI mismatch is unavoidable but known, it is possible not only to calculate the true position of the measuring volume (using the probe location and model geometry), but also to estimate degradation in signal quality arising from differential displacement and refraction of the laser beams.

The increased adoption of endovascular neurosurgery procedures to treat cerebrovascular pathologies has led to the commercialization of a wide array of medical devices which, in turn, necessitates a more sophisticated training environment for physicians and fellows than the traditional “see one, do one, teach one” concept. Improvements in simulation technology and a changing healthcare culture are facilitating a wider assimilation of benchtop simulation models in lieu of cadaver or animal models in physician training as well as treatment planning. Medical device manufacturers as well as regulators are also increasingly utilizing such simulators for device development and assessment of efficacy. Low-fidelity physical simulacra in the form of simplistic vascular replicas with or without coarse pumping systems have been available for basic neuroendovascular simulations for several years. Additive manufacturing, or 3D printing, has ushered in the use of anatomically accurate vascular replicas derived from patient imaging. Other considerations that improve the fidelity of simulating the neuroendovascular compartment include flows and pressures, catheter friction, blood-analog fluid, X-ray attenuation, etc. This chapter briefly describes these components of high-fidelity physical simulators, called replicators, for endovascular neurosurgery training.

Application of Enhanced oil recovery methods (EOR) in offshore oil fields are getting more popular with the advancement in technology and chemicals used. Polymer flooding is one of the most successful projects to improve water mobility by increasing the viscosity. Application of polymers promises to improve areal sweep efficiency and consequently recovery factor. However the main concern associated with injection of chemicals in offshore oil fields is the possibility of leakage and pollution of marine systems affecting biodiversity and environment. The following study focuses on rheological properties of three bio-polymers: Xanthan gum, Wulan gum and Potato starch in laboratory conditions as viscosifying agents. The study involved characterization of each polymer at different concentrations from 500 ppm to 5,000 ppm dosage. Sensitivity analysis on various reservoir temperatures were also performed from 25°C to 55°C to fit Kazakhstan reservoirs along with sea water salinity to simulate Kazakhstan reservoir conditions. Results from rheological studies showed that 3,000 ppm is considered as the optimum concentration from Xanthan and Wulan gums, Potato starch did not show any good results as viscosifying agent. Further temperature effect studies showed that both Xanthan and Wulan gums have a strong temperature resistance and does not experience dramatic viscosity drop at reservoir temperatures in a range of 8-14% of loss. However, salinity effect showed that Wulan gum tends to lose rheological properties in high salinity environment and high viscosity drop. Rheological studies showed that Xanthan gum is highly resistant to salinity and temperature changes, while Wulan is only temperature resistant. The obtained rheological data were correlated with the Ostwald–de Waele power-law model to characterize fluid flow parameters, shear thinning behavior and identify n, k values. The correlations affirmed the shear-thinning properties of Xanthan and Wulan gums, a critical attribute for effective oil displacement in offshore reservoirs Core flooding experiments were performed for each polymer at the optimum concentration, salinity and temperature. Carbonate cores were used to simulate reservoir conditions and assess the effectiveness of natural polymers in improving oil recovery. Core flooding experiments with Xanthan and Wulan gums showed incremental oil recovery of 30 and 20% respectively. In the context of Kazakhstan's Caspian Sea, these findings herald a promising future for enhanced oil recovery, leveraging the robustness of natural polymers in challenging offshore conditions. Overall, these polymers demonstrated impressive results in displacing oil under harsh offshore reservoir conditions

In this work, we have fabricated physiologically relevant polydimethylsiloxane microfluidic phantoms to investigate the fluid-structure interaction that arises from the interaction between a non-Newtonian fluid and the deformable wall. A shear thinning fluid (Xanthan gum solution) is used as the blood analog fluid. We have systematically analyzed the steady flow characteristics of the microfluidic phantom using pressure drop, deformation, and flow visualization using micro-PIV (Particle Image Velocimetry) to identify the intricate aspects of the pressure as well as the velocity field. A simple mathematical formulation is introduced to evaluate the flow induced deformation. These results will aid in the design and development of deformable microfluidic systems and provide a deeper understanding of the fluid-structure interaction in microchannels with special emphasis on biomimetic in-vitro models for lab-on-a-chip applications.

Experimental Investigation of the Overall Efficiency of a Centrifugal Blood Pump Using Glycerin Solution and Xanthan Gum Solutions as Blood Analog Fluid