Search

Mechanical loads on the polymeric fibers of oxygenating bundles are commonly present due to bundle press-fitting during device assembly and blood pressure load. However, computational fluid dynamics (CFD) simulations for fiber bundle optimization neglect possible changes in microstructure due to such deformations. The aim of this study is to investigate the impact of fiber deformability on bundle microstructure and fluid dynamics mainly in terms of permeability. Fibers from commercial mats typically used for blood oxygenators were mechanically tested and based on these experimental data, a material model was developed to simulate the structural deformations the fibers undergo under press-fitting and blood pressure loads. Then, CFD simulations were performed on deformed bundle repetitive units to investigate permeability under varying loading conditions. The effects of different bundle geometric parameters on the variation of bundle permeability due to press-fitting were evaluated. Bundle press-fitting results in significant changes in microstructure that are reflected in a bundle permeability more than halved for a 15% press-fitting. This impact on permeability is present in all the simulated fiber bundles and becomes more pronounced as the pitch between fibers and thus bundle porosity decreases. Instead, the analyses on pressurized bundle show only small deformations caused by pressure load, with permeability changes below 1%. While blood pressure effects could be neglected, bundle press-fitting turns out to have a significant impact on bundle microstructure and permeability. Neglecting such microstructure variations during CFD simulations could also lead to incorrect assessment of the local fluid dynamics within the bundle. [ABSTRACT FROM AUTHOR]

We demonstrate a methodology which both improves oxygen transport and reduces or eliminates bubble formation in a novel hyperbaric membrane oxygenator catheter model system. Angular oscillations were introduced to a bundle of hollow fiber membranes (HFMs) supplied with hyperbaric 100% oxygen at average gauge pressures up to 0.35 barg. Oscillating bundles enabled delivery of an oxygen flux of up to 400 mL min−1 m−2 in an aqueous solution, a doubling over a previous non-oscillating setup. Similarly, the addition of angular oscillations facilitated a five-fold reduction in pressure to achieve similar oxygen flux. The increased angular speed of oscillation improved flux, while the addition of angular micro-oscillation variations resulted in flux reductions of 7–20% compared to continuous macro-oscillation only, depending on mixing conditions. However, semi-quantitative visual observation demonstrated that angular oscillations reduced or eliminated the instance of oxygen bubble formation on the HFMs. The modeled mass transfer coefficients indicated a quasi linear relationship between rotational velocity and flux, suggesting that faster oscillation speeds could further improve oxygen mass transport allowing for HFM bundles to maintain high oxygen fluxes while eliminating bubble formation. This encourages further development of our compact oxygenating catheter that could be used intravascularly. [ABSTRACT FROM AUTHOR]

Purpose: Blood is commonly treated as single-phase homogeneous fluid in numerical simulations of blood flow within fiber bundles of blood oxygenators. However, microfluidics tests revealed the presence of hematocrit heterogeneity in blood flowing across such geometries. Given the significant role of red blood cells (RBCs) in the oxygenation process, this study aims to propose a multiphase blood model able to correctly describe the experimental evidence and computationally investigate hematocrit heterogeneities inside fiber bundles., Methods: The experimental results of microfluidics tests performed in a previous study were processed and based on quantitative data of image intensity, a two-phase blood model following the Eulerian-Eulerian approach was calibrated and evaluated in its predictive ability against the experimental data. The two-phase model was then used to study the RBCs distribution inside different fiber bundles at average hematocrit values of 25% and 35%, representative of hemodilution in extracorporeal blood circulation., Results: The numerical model proved to be able to describe and predict the experimental phase separation between plasma and RBCs within the microchannel geometry at different test conditions. Moreover, blood flow simulation in commercial fiber bundles revealed the presence of specific patterns in hematocrit distribution and their dependence on variations in bundle microstructure., Conclusion: The two-phase blood model proposed in this study provides a tool for advanced evaluation of local fluid dynamics and identification of optimal bundle microstructure allowing further gas transfer simulations to account for a reliable heterogeneous distribution of RBCs around the oxygenating fibers., Competing Interests: Declarations Conflict of interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024. The Author(s) under exclusive licence to Biomedical Engineering Society.)

In the concept of a biohybrid lung, endothelial cells seeded on gas exchange membranes form a non-thrombogenic an anti-inflammatory surface to overcome the lacking hemocompatibility of today's oxygenators during extracorporeal membrane oxygenation. To evaluate this concept, the long-term stability and gas exchange performance of endothelialized RGD-conjugated polydimethylsiloxane (RGD-PDMS) membranes was evaluated. Human umbilical vein endothelial cells (ECs) were cultured on RGD-PDMS in a model system under physiological wall shear stress (WSS) of 0.5 Pa for up to 33 days. Gas exchange performance was tested with three biological replicates under elevated WSS of 2.5 Pa using porcine blood adjusted to venous values following ISO 7199 and blood gas analysis. EC morphology was assessed by immunocytochemistry (n = 3). RGD-PDMS promoted endothelialization and stability of endothelialized membranes was shown for at least 33 days and for a maximal WSS of 2.5 Pa. Short-term exposure to porcine blood did not affect EC integrity. The gas transfer tests provided evidence for the oxygenation and decarboxylation of the blood across endothelialized membranes with a decrease of transfer rates over time that needs to be addressed in further studies with larger sample sizes. Our results demonstrate the general suitability of RGD-PDMS for biohybrid lung applications, which might enable long-term support of patients with chronic lung failure in the future. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics (CFD) is a useful tool in characterizing artificial lung designs by providing predictions of device performance through analyses of pressure distribution, perfusion dynamics, and gas transport properties. Validation of numerical results in membrane oxygenators has been predominantly based on experimental pressure measurements with little emphasis placed on confirmation of the velocity fields due to opacity of the fiber membrane and limitations of optical velocimetric methods. Biplane X-ray digital subtraction angiography was used to visualize flow of a blood analogue through a commercial membrane oxygenator at 1-4.5 L/min. Permeability and inertial coefficients of the Ergun equation were experimentally determined to be 180 and 2.4, respectively. Numerical simulations treating the fiber bundle as a single momentum sink according to the Ergun equation accurately predicted pressure losses across the fiber membrane, but significantly underestimated velocity magnitudes in the fiber bundle. A scaling constant was incorporated into the numerical porosity and reduced the average difference between experimental and numerical values in the porous media regions from 44 ± 4% to 6 ± 5%. [ABSTRACT FROM AUTHOR]

Intravascular oxygenation and carbon dioxide removal remains a potentially attractive means for respiratory support in patients with acute or chronic respiratory failure. Our group has been developing an intravascular hollow fiber artificial lung that uses a pulsating balloon located within the fiber bundle to augment gas transfer. We previously reported on a simple compartmental model for simulating O2 exchange in pulsating intravascular artificial lungs. In this study we evaluate the O2 exchange model with gas exchange and PO2 measurements performed on an idealized intravascular artificial lung (IIVAL) tested in a water perfusion loop. The IIVAL has well-defined bundle geometry and can be operated in balloon pulsation mode, or a steady perfusion mode for determining the mass transfer correlation required by the model. The O2 exchange rates and compartmental O2 tensions measured with balloon pulsation in the IIVAL are within 10% of model predictions for flow and pulsation conditions relevant to intravascular oxygenation. The experiments confirmed that a significant buildup of PO2 occurs within the fiber bundle, which reduces the O2 exchange rate. The agreement between experiments and predictions suggests that the model captures the cardinal processes dictating gas transfer in pulsating intravascular artificial lungs. © 2000 Biomedical Engineering Society. PAC00: 8780-y, 8710+e [ABSTRACT FROM AUTHOR]

Acute respiratory distress syndrome (ARDS) is a pulmonary edemic condition which reduces respiratory exchange in 150,000 people per year in the United States. The currently available therapies of mechanical ventilation and extracorporeal membrane oxygenation are associated with high mortality rates, so intravenous oxygenation represents an attractive, alternative support modality. We are developing an intravenous membrane oxygenator (IMO) device intended to provide 50% of basal oxygen and carbon dioxide exchange requirements for ARDS patients. A unique aspect of the IMO is its use of an integral balloon to provide active mixing. This paper describes a mathematical model which was developed to quantify and optimize the gas exchange performance of the IMO. The model focuses on balloon activated mixing, uses a lumped compartment approach, and approximates the blood-side mass transfer coefficients with cross-flow correlations. IMO gas exchange was simulated in water and blood, for a variety of device geometries and balloon pulsation rates. The modeling predicts the following: (1) gas exchange efficiency is reduced by a buildup of oxygen in the fluid near the fibers; (2) the IMO gas exchange rate in blood is normally about twice that in water under comparable conditions; (3) a balloon diameter of about 1.5 cm leads to optimal gas exchange performance; and (4) in vivo positioning can affect gas exchange rates. The numerically predicted gas transfer rates correlate closely with those experimentally measured in vitro for current IMO prototypes. © 1998 Biomedical Engineering Society. PAC98: 8710+e, 8790+y, 8265Fr [ABSTRACT FROM AUTHOR]