Experimental Approach to Visualize Flow in a Stacked Hollow Fiber Bundle of an Artificial Lung With Particle Image Velocimetry

Coagulation and hemolysis complications in neonatal ECLS: Role of devices

Neonatal extracorporeal life support (ECLS) has enjoyed a long history of successful patient support for both cardiac and respiratory failure. The small size of this patient population has provided many technical challenges from cannulation to pumps and oxygenators. This is further complicated by the relatively meager commercial options for equipment owing to the relatively low utilization of neonatal ECLS compared to adults, which has exploded following the H1N1 epidemic and the availability of the polymethylpentene oxygenator. This paper focuses on the impact of equipment choices on thrombosis and hemolysis in neonatal ECLS and the underlying mechanisms behind them. Based upon the available evidence, it is clear neonatal ECLS requires careful attention to the selection and operation of all parts of the ECLS system. Practitioners should also be aware of the factors that increase blood cell fragility, which can impact decisions around equipment and subsequent operation.

Three-dimensional membranes for artificial lungs: Comparison of flow-induced hemolysis

BACKGROUND

Membranes based on triply periodic minimal surfaces (TPMS) have proven a superior gas transfer compared to the contemporary hollow fiber membrane (HFM) design in artificial lungs. The improved oxygen transfer is attributed to disrupting the laminar boundary layer adjacent to the membrane surface known as main limiting factor to mass transport. However, it requires experimental proof that this improvement is not at the expense of greater damage to the blood. Hence, the aim of this work is a valid statement regarding the structure-dependent hemolytic behavior of TPMS structures compared to the current HFM design.

METHODS

Hemolysis tests were performed on structure samples of three different kind of TPMS-based designs (Schwarz-P, Schwarz-D and Schoen's Gyroid) in direct comparison to a hollow fiber structure as reference.

RESULTS

The results of this study suggest that the difference in hemolysis between TPMS membranes compared to HFMs is small although slightly increased for the TPMS membranes. There is no significant difference between the TPMS structures and the hollow fiber design. Nevertheless, the ratio between the achieved additional oxygen transfer and the additional hemolysis favors the TPMS-based membrane shapes.

CONCLUSION

TPMS-shaped membranes offer a safe way to improve gas transfer in artificial lungs.

Microstructured Hollow Fiber Membranes: Potential Fiber Shapes for Extracorporeal Membrane Oxygenators

Extracorporeal membrane oxygenators are essential medical devices for the treatment of patients with respiratory failure. A promising approach to improve oxygenator performance is the use of microstructured hollow fiber membranes that increase the available gas exchange surface area. However, by altering the traditional circular fiber shape, the risk of low flow, stagnating zones that obstruct mass transfer and encourage thrombus formation, may increase. Finding an optimal fiber shape is therefore a significant task. In this study, experimentally validated computational fluid dynamics simulations were used to investigate transverse flow within fiber packings of circular and microstructured fiber geometries. A numerical model was applied to calculate the local Sherwood number on the membrane surface, allowing for qualitative comparison of gas exchange capacities in low-velocity areas caused by the microstructured geometries. These adverse flow structures lead to a tradeoff between increased surface area and mass transfer. Based on our simulations, we suggest an optimal fiber shape for further investigations that increases potential mass transfer by up to 48% in comparison to the traditional, circular hollow fiber shape.

Artificial lungs--Where are we going with the lung replacement therapy?

Lung transplantation may be a final destination therapy in lung failure, but limited donor organ availability creates a need for alternative management, including artificial lung technology. This invited review discusses ongoing developments and future research pathways for respiratory assist devices and tissue engineering to treat advanced and refractory lung disease. An overview is also given on the aftermath of the coronavirus disease 2019 pandemic and lessons learned as the world comes out of this situation. The first order of business in the future of lung support is solving the problems with existing mechanical devices. Interestingly, challenges identified during the early days of development persist today. These challenges include device-related infection, bleeding, thrombosis, cost, and patient quality of life. The main approaches of the future directions are to repair, restore, replace, or regenerate the lungs. Engineering improvements to hollow fiber membrane gas exchangers are enabling longer term wearable systems and can be used to bridge lung failure patients to transplantation. Progress in the development of microchannel-based devices has provided the concept of biomimetic devices that may even enable intracorporeal implantation. Tissue engineering and cell-based technologies have provided the concept of bioartificial lungs with properties similar to the native organ. Recent progress in artificial lung technologies includes continued advances in both engineering and biology. The final goal is to achieve a truly implantable and durable artificial lung that is applicable to destination therapy.

Toward a Long-Term Artificial Lung

Only a very small portion of end-stage organ failures can be treated by transplantation because of the shortage of donor organs. Although artificial long-term organ support such as ventricular assist devices provide therapeutic options serving as a bridge-to-transplantation or destination therapy for end-stage heart failure, suitable long-term artificial lung systems are still at an early stage of development. Although a short-term use of an extracorporeal lung support is feasible today, the currently available technical solutions do not permit the long-term use of lung replacement systems in terms of an implantable artificial lung. This is currently limited by a variety of factors: biocompatibility problems lead to clot formation within the system, especially in areas with unphysiological flow conditions. In addition, proteins, cells, and fibrin are deposited on the membranes, decreasing gas exchange performance and thus, limiting long-term use. Coordinated basic and translational scientific research to solve these problems is therefore necessary to enable the long-term use and implantation of an artificial lung. Strategies for improving the biocompatibility of foreign surfaces, for new anticoagulation regimes, for optimization of gas and blood flow, and for miniaturization of these systems must be found. These strategies must be validated by in vitro and in vivo tests, which remain to be developed. In addition, the influence of long-term support on the pathophysiology must be considered. These challenges require well-connected interdisciplinary teams from the natural and material sciences, engineering, and medicine, which take the necessary steps toward the development of an artificial implantable lung.

A 96-well microplate bioreactor platform supporting individual dual perfusion and high-throughput assessment of simple or biofabricated 3D tissue models

Traditional 2D monolayer cell cultures and submillimeter 3D tissue construct cultures used widely in tissue engineering are limited in their ability to extrapolate experimental data to predict in vivo responses due to their simplistic organization and lack of stimuli. The rise of biofabrication and bioreactor technologies has sought to address this through the development of techniques to spatially organize components of a tissue construct, and devices to supply these tissue constructs with an increasingly in vivo-like environment. Current bioreactors supporting both parenchymal and barrier tissue constructs in interconnected systems for body-on-a-chip platforms have chosen to emphasize study throughput or system/tissue complexity. Here, we report a platform to address this disparity in throughput and both system complexity (by supporting multiple in situ assessment methods) and tissue complexity (by adopting a construct-agnostic format). We introduce an ANSI/SLAS-compliant microplate and docking station fabricated via stereolithography (SLA), or precision machining, to provide up to 96 samples (Ø6 × 10 mm) with two individually-addressable fluid circuits (192 total), loading access, and inspection window for imaging during perfusion. Biofabricated ovarian cancer models were developed to demonstrate the in situ assessment capabilities via microscopy and a perfused resazurin-based metabolic activity assay. In situ microscopy highlighted flexibility of the sample housing to accommodate a range of sample geometries. Utility for drug screening was demonstrated by exposing the ovarian cancer models to an anticancer drug (doxorubicin) and generating the dose-response curve in situ, while achieving an assay quality similar to static wellplate culture. The potential for quantitative analysis of temporal tissue development and screening studies was confirmed by imaging soft- (gelatin) and hard-tissue (calcium chloride) analogs inside the bioreactor via spectral computed tomography (CT) scanning. As a proof-of-concept for particle tracing studies, flowing microparticles were visualized to inform the design of hydrogel constructs. Finally, the ability for mechanistic yet high-throughput screening was demonstrated in a vascular coculture model adopting endothelial and mesenchymal stem cells (HUVEC-MSC), encapsulated in gelatin-norbornene (gel-NOR) hydrogel cast into SLA-printed well inserts. This study illustrates the potential of a scalable dual perfusion bioreactor platform for parenchymal and barrier tissue constructs to support a broad range of multi-organ-on-a-chip applications.

Artificial Organs 2017: A Year in Review

In this Editor's Review, articles published in 2017 are organized by category and summarized. We provide a brief reflection of the research and progress in artificial organs intended to advance and better human life while providing insight for continued application of these technologies and methods. Artificial Organs continues in the original mission of its founders "to foster communications in the field of artificial organs on an international level." Artificial Organs continues to publish developments and clinical applications of artificial organ technologies in this broad and expanding field of organ Replacement, Recovery, and Regeneration from all over the world. Peer-reviewed Special Issues this year included contributions from the 12th International Conference on Pediatric Mechanical Circulatory Support Systems and Pediatric Cardiopulmonary Perfusion edited by Dr. Akif Undar, Artificial Oxygen Carriers edited by Drs. Akira Kawaguchi and Jan Simoni, the 24th Congress of the International Society for Mechanical Circulatory Support edited by Dr. Toru Masuzawa, Challenges in the Field of Biomedical Devices: A Multidisciplinary Perspective edited by Dr. Vincenzo Piemonte and colleagues and Functional Electrical Stimulation edited by Dr. Winfried Mayr and colleagues. We take this time also to express our gratitude to our authors for offering their work to this journal. We offer our very special thanks to our reviewers who give so generously of time and expertise to review, critique, and especially provide meaningful suggestions to the author's work whether eventually accepted or rejected. Without these excellent and dedicated reviewers the quality expected from such a journal could not be possible. We also express our special thanks to our Publisher, John Wiley & Sons for their expert attention and support in the production and marketing of Artificial Organs. We look forward to reporting further advances in the coming years.

Experimental quantification of the fluid dynamics in blood-processing devices through 4D-flow imaging: A pilot study on a real oxygenator/heat-exchanger module

The performance of blood-processing devices largely depends on the associated fluid dynamics, which hence represents a key aspect in their design and optimization. To this aim, two approaches are currently adopted: computational fluid-dynamics, which yields highly resolved three-dimensional data but relies on simplifying assumptions, and in vitro experiments, which typically involve the direct video-acquisition of the flow field and provide 2D data only. We propose a novel method that exploits space- and time-resolved magnetic resonance imaging (4D-flow) to quantify the complex 3D flow field in blood-processing devices and to overcome these limitations. We tested our method on a real device that integrates an oxygenator and a heat exchanger. A dedicated mock loop was implemented, and novel 4D-flow sequences with sub-millimetric spatial resolution and region-dependent velocity encodings were defined. Automated in house software was developed to quantify the complex 3D flow field within the different regions of the device: region-dependent flow rates, pressure drops, paths of the working fluid and wall shear stresses were computed. Our analysis highlighted the effects of fine geometrical features of the device on the local fluid-dynamics, which would be unlikely observed by current in vitro approaches. Also, the effects of non-idealities on the flow field distribution were captured, thanks to the absence of the simplifying assumptions that typically characterize numerical models. To the best of our knowledge, our approach is the first of its kind and could be extended to the analysis of a broad range of clinically relevant devices.