Computational Simulations in Advanced Microfluidic Devices: A Review

Computational Fluid-Structure Interaction in Microfluidics

Micro elastofluidics is a transformative branch of microfluidics, leveraging the fluid-structure interaction (FSI) at the microscale to enhance the functionality and efficiency of various microdevices. This review paper elucidates the critical role of advanced computational FSI methods in the field of micro elastofluidics. By focusing on the interplay between fluid mechanics and structural responses, these computational methods facilitate the intricate design and optimisation of microdevices such as microvalves, micropumps, and micromixers, which rely on the precise control of fluidic and structural dynamics. In addition, these computational tools extend to the development of biomedical devices, enabling precise particle manipulation and enhancing therapeutic outcomes in cardiovascular applications. Furthermore, this paper addresses the current challenges in computational FSI and highlights the necessity for further development of tools to tackle complex, time-dependent models under microfluidic environments and varying conditions. Our review highlights the expanding potential of FSI in micro elastofluidics, offering a roadmap for future research and development in this promising area.

Advances in Microfluidic Systems and Numerical Modeling in Biomedical Applications: A Review

The evolution in the biomedical engineering field boosts innovative technologies, with microfluidic systems standing out as transformative tools in disease diagnosis, treatment, and monitoring. Numerical simulation has emerged as a tool of increasing importance for better understanding and predicting fluid-flow behavior in microscale devices. This review explores fabrication techniques and common materials of microfluidic devices, focusing on soft lithography and additive manufacturing. Microfluidic systems applications, including nucleic acid amplification and protein synthesis, as well as point-of-care diagnostics, DNA analysis, cell cultures, and organ-on-a-chip models (e.g., lung-, brain-, liver-, and tumor-on-a-chip), are discussed. Recent studies have applied computational tools such as ANSYS Fluent 2024 software to numerically simulate the flow behavior. Outside of the study cases, this work reports fundamental aspects of microfluidic simulations, including fluid flow, mass transport, mixing, and diffusion, and highlights the emergent field of organ-on-a-chip simulations. Additionally, it takes into account the application of geometries to improve the mixing of samples, as well as surface wettability modification. In conclusion, the present review summarizes the most relevant contributions of microfluidic systems and their numerical modeling to biomedical engineering.

Advancing Intelligent Organ-on-a-Chip Systems with Comprehensive In Situ Bioanalysis

In vitro models are essential to a broad range of biomedical research, such as pathological studies, drug development, and personalized medicine. As a potentially transformative paradigm for 3D in vitro models, organ-on-a-chip (OOC) technology has been extensively developed to recapitulate sophisticated architectures and dynamic microenvironments of human organs by applying the principles of life sciences and leveraging micro- and nanoscale engineering capabilities. A pivotal function of OOC devices is to support multifaceted and timely characterization of cultured cells and their microenvironments. However, in-depth analysis of OOC models typically requires biomedical assay procedures that are labor-intensive and interruptive. Herein, the latest advances toward intelligent OOC (iOOC) systems, where sensors integrated with OOC devices continuously report cellular and microenvironmental information for comprehensive in situ bioanalysis, are examined. It is proposed that the multimodal data in iOOC systems can support closed-loop control of the in vitro models and offer holistic biomedical insights for diverse applications. Essential techniques for establishing iOOC systems are surveyed, encompassing in situ sensing, data processing, and dynamic modulation. Eventually, the future development of iOOC systems featuring cross-disciplinary strategies is discussed.

Numerical evaluation and experimental validation of fluid flow behavior within an organ-on-a-chip model

BACKGROUND AND OBJECTIVE

By combining biomaterials, cell culture, and microfluidic technology, organ-on-a-chip (OoC) platforms have the ability to reproduce the physiological microenvironment of human organs. For this reason, these advanced microfluidic devices have been used to resemble various diseases and investigate novel treatments. In addition to the experimental assessment, numerical studies of biodevices have been performed aiming at their improvement and optimization. Despite considerable progress in numerical modeling of biodevices, the validation of these computational models through comparison with experimental assays remains a significant gap in the current literature. This step is critical to ensure the accuracy and reliability of numerical models, and consequently enhance confidence in their predictive results. The aim of the present work is to develop a numerical model capable of reproducing the fluid flow behavior within an OoC, for future investigations, encompassing the geometry optimization.

METHODS

In this study, the validation of a numerical model for an OoC microfluidic device was undertaken. This comprised both quantitative and qualitative assessments of trace microparticles flowing through a physical OoC model. High-speed microscopy images of the flow, using a blood analog fluid, were analyzed and compared with the numerical simulations run using the Ansys Fluent software. For a qualitative analysis, the particles' paths through the inlet and bifurcations were observed whereas, for a quantitative analysis, the particle velocities were measured. Furthermore, oxygen transport was simulated and evaluated for different Reynolds numbers.

RESULTS

In both qualitative and quantitative analyses, the results predicted by the numerical model and the ones outputted by the experimental model were in good agreement. These findings underscore the capability and potential of the developed numerical model. The examination of oxygen transport at various vertical positions within the organoid has revealed that for lower positions, oxygen transport predominantly occurs through diffusion, leading to a symmetric distribution of oxygen. Contrastingly, the convection phenomenon becomes more evident in the upper region of the organoid.

CONCLUSIONS

The successful validation of the numerical model against experimental data shows its accuracy and reliability in simulating the fluid flow within the OoC, which consequently can expedite the OoC design process by reducing the need for prototypes' fabrication and costly laboratory experiments.

Computational Modeling as a Tool to Drive the Development of a Novel, Chemical Device for Monitoring the Injured Brain and Body

Real-time measurement of dynamic changes, occurring in the brain and other parts of the body, is useful for the detection and tracked progression of disease and injury. Chemical monitoring of such phenomena exists but is not commonplace, due to the penetrative nature of devices, the lack of continuous measurement, and the inflammatory responses that require pharmacological treatment to alleviate. Soft, flexible devices that more closely match the moduli and shape of monitored tissue and allow for surface microdialysis provide a viable alternative. Here, we show that computational modeling can be used to aid the development of such devices and highlight the considerations when developing a chemical monitoring probe in this way. These models pave the way for the development of a new class of chemical monitoring devices for monitoring neurotrauma, organs, and skin.

Microfluidic-based skin-on-chip systems for safety assessment of nanomaterials

The skin is the body's largest organ, continuously exposed to and affected by natural and anthropogenic nanomaterials (materials with external and internal dimensions in the nanoscale range). This broad spectrum of insults gives rise to irreversible health effects (from skin corrosion to cancer). Organ-on-chip systems can recapitulate skin physiology with high fidelity and potentially revolutionize the safety assessment of nanomaterials. Here, we review current advances in skin-on-chip models and their potential to elucidate biological mechanisms. Further, strategies are discussed to recapitulate skin physiology on-chip, improving control over nanomaterials exposure and transport across cells. Finally, we highlight future opportunities and challenges from design and fabrication to acceptance by regulatory bodies and industry.

Establishment of a gut-on-a-chip device with controllable oxygen gradients to study the contribution of Bifidobacterium bifidum to inflammatory bowel disease

Supplemental Bifidobacterium has been shown to aid in the prevention, alleviation, and treatment of inflammatory bowel disease (IBD), but the progression and mechanisms are largely unstudied, partly because of a lack of appropriate models. In vitro human gut models must accurately recreate oxygen concentration gradients consistent with those in vivo to mimic gene expression, metabolism, and host-microbiome interactions. A non-equipment-intensive and inexpensive method for constructing the gut-on-a-chip with physiological oxygen concentration gradients remains challenging. Here, we propose a simple strategy using numerical simulations in a dual-channel gut-on-a-chip to guide chip design and achieve controllable oxygen gradients. By varying the size of microchannels, blocking the oxygen penetration of the polydimethylsiloxane layer at a given location, and controlling the flow of hypoxic/aerobic media, this strategy creates steep gradients across the intestinal epithelium. IBD symptoms were induced on the chip by tumor necrosis factor-α and lipopolysaccharide treatment. Bifidobacterium bifidum has been validated to contribute to the stability of the intestinal epithelial barrier, including preventing epithelial barrier disruption and promoting the repair of damaged intestinal epithelial cell monolayers. These effects may be associated with the co-localization of Bifidobacterium bifidum and ZO-1. This simple but robust approach for designing microfluidic devices is applicable to various organs-on-chips in which fluid dynamics and concentration profiles between different media must be considered. With the customized chip, the integration of activated Bifidobacterium bifidum provides an initial step toward developing a multi-factorial IBD platform. The approach could be scaled up for disease modeling, high-throughput drug screening and personalized medicine.

Editorial for the Special Issue on Micro/Nanofluidic and Lab-on-a-Chip Devices for Biomedical Applications

Micro/Nanofluidic and lab-on-a-chip devices have been increasingly used in biomedical research [...].

Diagnosis Methods for COVID-19: A Systematic Review

At the end of 2019, the coronavirus appeared and spread extremely rapidly, causing millions of infections and deaths worldwide, and becoming a global pandemic. For this reason, it became urgent and essential to find adequate tests for an accurate and fast diagnosis of this disease. In the present study, a systematic review was performed in order to provide an overview of the COVID-19 diagnosis methods and tests already available, as well as their evolution in recent months. For this purpose, the Science Direct, PubMed, and Scopus databases were used to collect the data and three authors independently screened the references, extracted the main information, and assessed the quality of the included studies. After the analysis of the collected data, 34 studies reporting new methods to diagnose COVID-19 were selected. Although RT-PCR is the gold-standard method for COVID-19 diagnosis, it cannot fulfill all the requirements of this pandemic, being limited by the need for highly specialized equipment and personnel to perform the assays, as well as the long time to get the test results. To fulfill the limitations of this method, other alternatives, including biological and imaging analysis methods, also became commonly reported. The comparison of the different diagnosis tests allowed to understand the importance and potential of combining different techniques, not only to improve diagnosis but also for a further understanding of the virus, the disease, and their implications in humans.

Radiotherapy on-chip: microfluidics for translational radiation oncology

The clinical importance of radiotherapy in the treatment of cancer patients justifies the development and use of research tools at the fundamental, pre-clinical, and ultimately clinical levels, to investigate their toxicities and synergies with systemic agents on relevant biological samples. Although microfluidics has prompted a paradigm shift in drug discovery in the past two decades, it appears to have yet to translate to radiotherapy research. However, the materials, dimensions, design versatility and multiplexing capabilities of microfluidic devices make them well-suited to a variety of studies involving radiation physics, radiobiology and radiotherapy. This review will present the state-of-the-art applications of microfluidics in these fields and specifically highlight the perspectives offered by radiotherapy on-a-chip in the field of translational radiobiology and precision medicine. This body of knowledge can serve both the microfluidics and radiotherapy communities by identifying potential collaboration avenues to improve patient care.

Design and Modeling of a Microfluidic Coral Polyps Culture Chip with Concentration and Temperature Gradients

Traditional methods of cultivating polyps are costly and time-consuming. Microfluidic chip technology makes it possible to study coral polyps at the single-cell level, but most chips can only be analyzed for a single environmental variable. In this work, we addressed these issues by designing a microfluidic coral polyp culture chip with a multi-physical field for multivariable analyses and verifying the feasibility of the chip through numerical simulation. This chip used multiple serpentine structures to generate the concentration gradient and used a circuit to form the Joule effect for the temperature gradient. It could generate different temperature gradients at different voltages for studying the growth of polyps in different solutes or at different temperatures. The simulation of flow field and temperature showed that the solute and heat could be transferred evenly and efficiently in the chambers, and that the temperature of the chamber remained unchanged after 24 h of continuous heating. The thermal expansion of the microfluidic chip was low at the optimal culture temperature of coral polyps, which proves the feasibility of the use of the multivariable microfluidic model for polyp culture and provides a theoretical basis for the actual chip processing.

Organ-on-a-Chip: Design and Simulation of Various Microfluidic Channel Geometries for the Influence of Fluid Dynamic Parameters

Shear stress, pressure, and flow rate are fluid dynamic parameters that can lead to changes in the morphology, proliferation, function, and survival of many cell types and have a determinant impact on tissue function and viability. Microfluidic devices are promising tools to investigate these parameters and fluid behaviour within different microchannel geometries. This study discusses and analyses different designed microfluidic channel geometries regarding the influence of fluid dynamic parameters on their microenvironment at specified fluidic parameters. The results demonstrate that in the circular microchamber, the velocity and shear stress profiles assume a parabolic shape with a maximum velocity occurring in the centre of the chamber and a minimum velocity at the walls. The longitudinal microchannel shows a uniform velocity and shear stress profile throughout the microchannel. Simulation studies for the two geometries with three parallel microchannels showed that in proximity to the micropillars, the velocity and shear stress profiles decreased. Moreover, the pressure is inversely proportional to the width and directly proportional to the flow rate within the microfluidic channels. The simulations showed that the velocity and wall shear stress indicated different values at different flow rates. It was also found that the width and height of the microfluidic channels could affect both velocity and shear stress profiles, contributing to the control of shear stress. The study has demonstrated strategies to predict and control the effects of these forces and the potential as an alternative to conventional cell culture as well as to recapitulate the cell- and organ-specific microenvironment.

Integrative lymph node-mimicking models created with biomaterials and computational tools to study the immune system

The lymph node (LN) is a vital organ of the lymphatic and immune system that enables timely detection, response, and clearance of harmful substances from the body. Each LN comprises of distinct substructures, which host a plethora of immune cell types working in tandem to coordinate complex innate and adaptive immune responses. An improved understanding of LN biology could facilitate treatment in LN-associated pathologies and immunotherapeutic interventions, yet at present, animal models, which often have poor physiological relevance, are the most popular experimental platforms. Emerging biomaterial engineering offers powerful alternatives, with the potential to circumvent limitations of animal models, for in-depth characterization and engineering of the lymphatic and adaptive immune system. In addition, mathematical and computational approaches, particularly in the current age of big data research, are reliable tools to verify and complement biomaterial works. In this review, we first discuss the importance of lymph node in immunity protection followed by recent advances using biomaterials to create in vitro/vivo LN-mimicking models to recreate the lymphoid tissue microstructure and microenvironment, as well as to describe the related immuno-functionality for biological investigation. We also explore the great potential of mathematical and computational models to serve as in silico supports. Furthermore, we suggest how both in vitro/vivo and in silico approaches can be integrated to strengthen basic patho-biological research, translational drug screening and clinical personalized therapies. We hope that this review will promote synergistic collaborations to accelerate progress of LN-mimicking systems to enhance understanding of immuno-complexity.