Multi-Compartment 3D-Cultured Organ-on-a-Chip: Towards a Biomimetic Lymph Node for Drug Development

In vitro immunity: an overview of immunocompetent organ-on-chip models

Impressive advances have been made to replicate human physiology in vitro over the last few years due to the growth of the organ-on-chip (OoC) field in both industrial and academic settings. OoCs are a type of microphysiological system (MPS) that imitates functional and dynamic aspects of native human organ biology on a microfluidic device. Organoids and organotypic models, ranging in their complexity from simple single-cell to complex multi-cell type constructs, are being incorporated into OoC microfluidic devices to better mimic human physiology. OoC technology has now progressed to the stage at which it has received official recognition by the Food and Drug Administration (FDA) for use as an alternative to standard procedures in drug development, such as animal studies and traditional in vitro assays. However, an area that is still lagging behind is the incorporation of the immune system, which is a critical element required to investigate human health and disease. In this review, we summarise the progress made to integrate human immunology into various OoC systems, specifically focusing on models related to organ barriers and lymphoid organs. These models utilise microfluidic devices that are either commercially available or custom-made. This review explores the difference between the use of innate and adaptive immune cells and their role for modelling organ-specific diseases in OoCs. Immunocompetent multi-OoC models are also highlighted and the extent to which they recapitulate systemic physiology is discussed. Together, the aim of this review is to describe the current state of immune-OoCs, the limitations and the future perspectives needed to improve the field.

Lymph Node-on-Chip Technology: Cutting-Edge Advances in Immune Microenvironment Simulation

Organ-on-a-chip technology is attracting growing interest across various domains as a crucial platform for drug screening and testing and is set to play a significant role in precision medicine research. Lymph nodes, being intricately structured organs essential for the body's adaptive immune responses to antigens and foreign particles, are pivotal in assessing the immunotoxicity of novel pharmaceuticals. Significant progress has been made in research on the structure and function of the lymphatic system. However, there is still an urgent need to develop prospective tools and techniques to delve deeper into its role in various diseases' pathological and physiological processes and to develop corresponding immunotherapeutic therapies. Organ chips can accurately reproduce the specific functional areas in lymph nodes to better simulate the complex microstructure of lymph nodes and the interactions between different immune cells, which is convenient for studying specific biological processes. This paper reviews existing lymph node chips and their design approaches. It discusses the applications of the above systems in modeling immune cell motility, cell-cell interactions, vaccine responses, drug testing, and cancer research. Finally, we summarize the challenges that current research faces in terms of structure, cell source, and extracellular matrix simulation of lymph nodes, and we provide an outlook on the future direction of integrated immune system chips.

Mimicking blood and lymphatic vasculatures using microfluidic systems

The role of the circulatory system, containing the blood and lymphatic vasculatures, within the body, has become increasingly focused on by researchers as dysfunction of either of the systems has been linked to serious complications and disease. Currently, in vivo models are unable to provide the sufficient monitoring and level of manipulation needed to characterize the fluidic dynamics of the microcirculation in blood and lymphatic vessels; thus in vitro models have been pursued as an alternative model. Microfluidic devices have the required properties to provide a physiologically relevant circulatory system model for research as well as the experimental tools to conduct more advanced research analyses of microcirculation flow. In this review paper, the physiological behavior of fluid flow and electrical communication within the endothelial cells of the systems are detailed and discussed to highlight their complexities. Cell co-culturing methods and other relevant organ-on-a-chip devices will be evaluated to demonstrate the feasibility and relevance of the in vitro microfluidic model. Microfluidic systems will be determined as a noteworthy model that can display physiologically relevant flow of the cardiovascular and lymphatic systems, which will enable researchers to investigate the systems' prevalence in diseases and identify potential therapeutics.

Food allergen sensitization on a chip: the gut-immune-skin axis

The global population is growing, rapidly increasing the demand for sustainable, novel, and safe food proteins with minimal risks of food allergy. In vitro testing of allergy-sensitizing capacity is predominantly based on 2D assays. However, these lack the 3D environment and crosstalk between the gut, skin, and immune cells essential for allergy prediction. Organ-on-a-chip (OoC) technologies are promising to study type 2 immune activation required for sensitization, initiated in the small intestine or skin, in interlinked systems. Increasing the mechanistic understanding and, moreover, finding new strategies to study interorgan communication is of importance to recapitulate food allergen sensitization in vitro. Here, we outline recently developed OoC platforms and discuss the features needed for reliable prediction of sensitizing allergenicity of proteins.

Immunity-on-a-Chip: Integration of Immune Components into the Scheme of Organ-on-a-Chip Systems

Studying the immune system in vitro aims to understand how, when, and where the immune cells migrate/differentiate and respond to the various triggering events and the decision points along the immune response journey. It becomes evident that organ-on-a-chip (OOC) technology has a superior capability to recapitulate the cell-cell and tissue-tissue interaction in the body, with a great potential to provide tools for tracking the paracrine signaling with high spatial-temporal precision and implementing in situ real-time, non-destructive detection assays, therefore, enabling extraction of mechanistic information rather than phenotypic information. However, despite the rapid development in this technology, integration of the immune system into OOC devices stays among the least navigated tasks, with immune cells still the major missing components in the developed models. This is mainly due to the complexity of the immune system and the reductionist methodology of the OOC modules. Dedicated research in this field is demanded to establish the understanding of mechanism-based disease endotypes rather than phenotypes. Herein, we systemically present a synthesis of the state-of-the-art of immune-cantered OOC technology. We comprehensively outlined what is achieved and identified the technology gaps emphasizing the missing components required to establish immune-competent OOCs and bridge these gaps.

Modeling immunity in microphysiological systems

There is a need for better predictive models of the human immune system to evaluate safety and efficacy of immunomodulatory drugs and biologics for successful product development and regulatory approvals. Current in vitro models, which are often tested in two-dimensional (2D) tissue culture polystyrene, and preclinical animal models fail to fully recapitulate the function and physiology of the human immune system. Microphysiological systems (MPSs) that can model key microenvironment cues of the human immune system, as well as of specific organs and tissues, may be able to recapitulate specific features of the in vivo inflammatory response. This minireview provides an overview of MPS for modeling lymphatic tissues, immunity at tissue interfaces, inflammatory diseases, and the inflammatory tumor microenvironment in vitro and ex vivo. Broadly, these systems have utility in modeling how certain immunotherapies function in vivo, how dysfunctional immune responses can propagate diseases, and how our immune system can combat pathogens.

Engineering prostate cancer in vitro: what does it take?

A key challenge in the clinical management and cause of treatment failure of prostate cancer (PCa) is its molecular, cellular and clinical heterogeneity. Modelling systems that fully recapitulate clinical diversity and resistant phenotypes are urgently required for the development of successful personalised PCa therapies. The advent of the three-dimensional (3D) organoid model has revolutionised preclinical cancer research through reflecting heterogeneity and offering genomic and environmental manipulation that has opened up unparalleled opportunities for applications in disease modelling, high-throughput drug screening and precision medicine. Despite these remarkable achievements of organoid technology, several shortcomings in emulating the complex tumor microenvironment and dynamic process of metastasis as well as the epigenome profile limit organoids achieving true in vivo functionality. Technological advances in tissue engineering have enabled the development of innovative tools to facilitate the design of improved 3D cancer models. In this review, we highlight the current in vitro 3D PCa models with a special focus on organoids and discuss engineering approaches to create more physiologically relevant PCa organoid models and maximise their translational relevance that ultimately will help to realise the transformational power of precision medicine.

Organ-on-chip systems as a model for nanomedicine

Nanomedicine is giving rise to increasing numbers of successful drugs, including cancer treatments, molecular imaging agents, and novel vaccine formulations. However, traditionally available model systems offer limited clinical translation and, compared to the number of preclinical studies, the approval rate of nanoparticles (NPs) for clinical use remains disappointingly low. A new paradigm of modeling biological systems on microfluidic chips has emerged in the last decade and is being gradually adopted by the nanomedicine community. These systems mimic tissues, organs, and diseases like cancer, on devices with small physical footprints and complex geometries. In this review, we report studies that used organ-on-chip approaches to study the interactions of NPs with biological systems. We present examples of NP toxicity studies, studies using biological NPs such as viruses, as well as modeling biological barriers and cancer on chip. Organ-on-chip systems present an exciting opportunity and can provide a renewed direction for the nanomedicine community.

Assessment of Electrospun Poly(ε-caprolactone) and Poly(lactic acid) Fiber Scaffolds to Generate 3D In Vitro Models of Colorectal Adenocarcinoma: A Preliminary Study

Three-dimensional scaffold-based culture has been increasingly gaining influence in oncology as a therapeutic strategy for tumors with a high relapse percentage. This study aims to evaluate electrospun poly(ε-caprolactone) (PCL) and poly(lactic acid) (PLA) scaffolds to create a 3D model of colorectal adenocarcinoma. Specifically, the physico-mechanical and morphological properties of PCL and PLA electrospun fiber meshes collected at different drum velocities, i.e., 500 rpm, 1000 rpm and 2500 rpm, were assessed. Fiber size, mesh porosity, pore size distribution, water contact angle and tensile mechanical properties were investigated. Caco-2 cells were cultured on the produced PCL and PLA scaffolds for 7 days, demonstrating good cell viability and metabolic activity in all the scaffolds. A cross-analysis of the cell-scaffold interactions with morphological, mechanical and surface characterizations of the different electrospun fiber meshes was carried out, showing an opposite trend of cell metabolic activity in PLA and PCL scaffolds regardless of the fiber alignment, which increased in PLA and decreased in PCL. The best samples for Caco-2 cell culture were PCL500 (randomly oriented fibers) and PLA2500 (aligned fibers). Caco-2 cells had the highest metabolic activity in these scaffolds, with Young's moduli in the range of 8.6-21.9 MPa. PCL500 showed Young's modulus and strain at break close to those of the large intestine. Advancements in 3D in vitro models of colorectal adenocarcinoma could move forward the development of therapies for this cancer.

A quantitative meta-analysis comparing cell models in perfused organ on a chip with static cell cultures

As many consider organ on a chip for better in vitro models, it is timely to extract quantitative data from the literature to compare responses of cells under flow in chips to corresponding static incubations. Of 2828 screened articles, 464 articles described flow for cell culture and 146 contained correct controls and quantified data. Analysis of 1718 ratios between biomarkers measured in cells under flow and static cultures showed that the in all cell types, many biomarkers were unregulated by flow and only some specific biomarkers responded strongly to flow. Biomarkers in cells from the blood vessels walls, the intestine, tumours, pancreatic island, and the liver reacted most strongly to flow. Only 26 biomarkers were analysed in at least two different articles for a given cell type. Of these, the CYP3A4 activity in CaCo2 cells and PXR mRNA levels in hepatocytes were induced more than two-fold by flow. Furthermore, the reproducibility between articles was low as 52 of 95 articles did not show the same response to flow for a given biomarker. Flow showed overall very little improvements in 2D cultures but a slight improvement in 3D cultures suggesting that high density cell culture may benefit from flow. In conclusion, the gains of perfusion are relatively modest, larger gains are linked to specific biomarkers in certain cell types.

Organoids and organs-on-chips: insights into predicting the efficacy of systemic treatment in colorectal cancer

Cancer heterogeneity has posed a great challenge to traditional cancer treatment, with the reappearance of cancer heterogeneity of inter and intra patients being especially critical. Based on this, personalized therapy has emerged as significant research focus in recent and even future years. Cancer-related therapeutic models are developing, including cell lines, patient-derived xenografts, organoids, etc. Organoids are three-dimensional in vitro models emerged in the past dozen years and are able to reproduce the cellular and molecular composition of the original tumor. These advantages demonstrate the great potential for patient-derived organoids to develop personalized anticancer therapies, including preclinical drug screening and the prediction of patient treatment response. The impact of microenvironment on cancer treatment cannot be underestimated, and the remodeling of microenvironment also allows organoids to interact with other technologies, among which organs-on-chips is a representative one. This review highlights the use of organoids and organs-on-chips as complementary reference tools in treating colorectal cancer from the perspective of clinical efficacy predictability. We also discuss the limitations of both techniques and how they complement each other well.

Lung-on-chip microdevices to foster pulmonary drug discovery

Respiratory diseases account for unprecedented mortality owing to a lack of personalized or insufficient therapeutic interventions. Fostering pulmonary research into managing pulmonary threat requires a potential alternative approach that can mimick the in vivo complexities of the human body. The in vitro miniaturized bionic simulation of the lung holds great potential in the quest for a successful therapeutic intervention. This review discusses the emerging roles of lung-on-chip microfluidic simulator devices in fostering translational pulmonary drug discovery and personalized medicine. This review also explicates how the lung-on-chip model emulates the breathing patterns, elasticity, and vascularization of lungs in creating a 3D pulmonary microenvironment.

Critical design parameters to develop biomimetic organ-on-a-chip models for the evaluation of the safety and efficacy of nanoparticles

INTRODUCTION

Organ-on-a-chip (OOC) models are based on microfluidics and can recapitulate the healthy and diseased microstructure of organs¹ and tissues and the dynamic microenvironment inside the human body. However, the use of OOC models to evaluate the safety and efficacy of nanoparticles (NPs) is still in the early stages.

AREAS COVERED

The different design parameters of the microfluidic chip and the mechanical forces generated by fluid flow play a pivotal role in simulating the human environment. This review discusses the role of different key parameters on the performance of OOC models. These include the flow pattern, flow rate, shear stress (magnitude, rate, and distribution), viscosity of the media, and the microchannel dimensions and shape. We also discuss how the shear stress and other mechanical forces affect the transport of NPs across biological barriers, cell uptake, and their biocompatibility.

EXPERT OPINION

We describe several good practices and design parameters to consider for future OOC research. We submit that following these recommendations will help realize the full potential of the OOC models in the preclinical evaluation of novel therapies, including NPs.

The T Cell Journey: A Tour de Force

T cells act as the puppeteers in the adaptive immune response, and their dysfunction leads to the initiation and progression of pathological conditions. During their lifetime, T cells experience myriad forces that modulate their effector functions. These forces are imposed by interacting cells, surrounding tissues, and shear forces from fluid movement. In this review, a journey with T cells is made, from their development to their unique characteristics, including the early studies that uncovered their mechanosensitivity. Then the studies pertaining to the responses of T cell activation to changes in antigen-presenting cells' physical properties, to their immediate surrounding extracellular matrix microenvironment, and flow conditions are highlighted. In addition, it is explored how pathological conditions like the tumor microenvironment can hinder T cells and allow cancer cells to escape elimination.

Organs-on-Chips Platforms Are Everywhere: A Zoom on Biomedical Investigation

Over the decades, conventional in vitro culture systems and animal models have been used to study physiology, nutrient or drug metabolisms including mechanical and physiopathological aspects. However, there is an urgent need for Integrated Testing Strategies (ITS) and more sophisticated platforms and devices to approach the real complexity of human physiology and provide reliable extrapolations for clinical investigations and personalized medicine. Organ-on-a-chip (OOC), also known as a microphysiological system, is a state-of-the-art microfluidic cell culture technology that sums up cells or tissue-to-tissue interfaces, fluid flows, mechanical cues, and organ-level physiology, and it has been developed to fill the gap between in vitro experimental models and human pathophysiology. The wide range of OOC platforms involves the miniaturization of cell culture systems and enables a variety of novel experimental techniques. These range from modeling the independent effects of biophysical forces on cells to screening novel drugs in multi-organ microphysiological systems, all within microscale devices. As in living biosystems, the development of vascular structure is the salient feature common to almost all organ-on-a-chip platforms. Herein, we provide a snapshot of this fast-evolving sophisticated technology. We will review cutting-edge developments and advances in the OOC realm, discussing current applications in the biomedical field with a detailed description of how this technology has enabled the reconstruction of complex multi-scale and multifunctional matrices and platforms (at the cellular and tissular levels) leading to an acute understanding of the physiopathological features of human ailments and infections in vitro.

3D microenvironment attenuates simulated microgravity-mediated changes in T cell transcriptome

Human space travel and exploration are of interest to both the industrial and scientific community. However, there are many adverse effects of spaceflight on human physiology. In particular, there is a lack of understanding of the extent to which microgravity affects the immune system. T cells, key players of the adaptive immune system and long-term immunity, are present not only in blood circulation but also reside within the tissue. As of yet, studies investigating the effects of microgravity on T cells are limited to peripheral blood or traditional 2D cell culture that recapitulates circulating blood. To better mimic interstitial tissue, 3D cell culture has been well established for physiologically and pathologically relevant models. In this work, we utilize 2D cell culture and 3D collagen matrices to gain an understanding of how simulated microgravity, using a random positioning machine, affects both circulating and tissue-resident T cells. T cells were studied in both resting and activated stages. We found that 3D cell culture attenuates the effects of simulated microgravity on the T cells transcriptome and nuclear irregularities compared to 2D cell culture. Interestingly, simulated microgravity appears to have less effect on activated T cells compared to those in the resting stage. Overall, our work provides novel insights into the effects of simulated microgravity on circulating and tissue-resident T cells which could provide benefits for the health of space travellers.

Engineering complexity in human tissue models of cancer

Major progress in the understanding and treatment of cancer have tremendously improved our knowledge of this complex disease and improved the length and quality of patients' lives. Still, major challenges remain, in particular with respect to cancer metastasis which still escapes effective treatment and remains responsible for 90% of cancer related deaths. In recent years, the advances in cancer cell biology, oncology and tissue engineering converged into the engineered human tissue models of cancer that are increasingly recapitulating many aspects of cancer progression and response to drugs, in a patient-specific context. The complexity and biological fidelity of these models, as well as the specific questions they aim to investigate, vary in a very broad range. When selecting and designing these experimental models, the fundamental question is "how simple is complex enough" to accomplish a specific goal of cancer research. Here we review the state of the art in developing and using the human tissue models in cancer research and developmental drug screening. We describe the main classes of models providing different levels of biological fidelity and complexity, discuss their advantages and limitations, and propose a framework for designing an appropriate model for a given study. We close by outlining some of the current needs, opportunities and challenges in this rapidly evolving field.

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.

Studying metabolism with multi-organ chips: new tools for disease modelling, pharmacokinetics and pharmacodynamics

Non-clinical models to study metabolism including animal models and cell assays are often limited in terms of species translatability and predictability of human biology. This field urgently requires a push towards more physiologically accurate recapitulations of drug interactions and disease progression in the body. Organ-on-chip systems, specifically multi-organ chips (MOCs), are an emerging technology that is well suited to providing a species-specific platform to study the various types of metabolism (glucose, lipid, protein and drug) by recreating organ-level function. This review provides a resource for scientists aiming to study human metabolism by providing an overview of MOCs recapitulating aspects of metabolism, by addressing the technical aspects of MOC development and by providing guidelines for correlation with in silico models. The current state and challenges are presented for two application areas: (i) disease modelling and (ii) pharmacokinetics/pharmacodynamics. Additionally, the guidelines to integrate the MOC data into in silico models could strengthen the predictive power of the technology. Finally, the translational aspects of metabolizing MOCs are addressed, including adoption for personalized medicine and prospects for the clinic. Predictive MOCs could enable a significantly reduced dependence on animal models and open doors towards economical non-clinical testing and understanding of disease mechanisms.

Engineering in vitro immune-competent tissue models for testing and evaluation of therapeutics

Advances in 3D cell culture, microscale fluidic control, and cellular analysis have enabled the development of more physiologically-relevant engineered models of human organs with precise control of the cellular microenvironment. Engineered models have been used successfully to answer fundamental biological questions and to screen therapeutics, but these often neglect key elements of the immune system. There are immune elements in every tissue that contribute to healthy and diseased states. Including immune function will be essential for effective preclinical testing of therapeutics for inflammatory and immune-modulated diseases. In this review, we first discuss the key components to consider in designing engineered immune-competent models in terms of physical, chemical, and biological cues. Next, we review recent applications of models of immunity for screening therapeutics for cancer, preclinical evaluation of engineered T cells, modeling autoimmunity, and screening vaccine efficacy. Future work is needed to further recapitulate immune responses in engineered models for the most informative therapeutic screening and evaluation.

Multicompartment Hydrogels

Hydrogels belong to the most promising materials in polymer and materials science at the moment. As they feature soft and tissue-like character as well as high water-content, a broad range of applications are addressed with hydrogels, e.g. tissue engineering and wound dressings but also soft robotics, drug delivery, actuators and catalysis. Ways to tailor hydrogel properties are crosslinking mechanism, hydrogel shape and reinforcement, but new features can be introduced by variation of hydrogel composition as well, e.g. via monomer choice, functionalization or compartmentalization. Especially, multicompartment hydrogels drive progress towards complex and highly functional soft materials. In the present review the latest developments in multicompartment hydrogels are highlighted with a focus on three types of compartments, i.e. micellar/vesicular, droplets or multi-layers including various sub-categories. Furthermore, several morphologies of compartmentalized hydrogels and applications of multicompartment hydrogels will be discussed as well. Finally, an outlook towards future developments of the field will be given. The further development of multicompartment hydrogels is highly relevant for a broad range of applications and will have a significant impact on biomedicine and organic devices. This article is protected by copyright. All rights reserved.

A Mathematical Description of the Flow in a Spherical Lymph Node

The motion of the lymph has a very important role in the immune system, and it is influenced by the porosity of the lymph nodes: more than 90% takes the peripheral path without entering the lymphoid compartment. In this paper, we construct a mathematical model of a lymph node assumed to have a spherical geometry, where the subcapsular sinus is a thin spherical shell near the external wall of the lymph node and the core is a porous material describing the lymphoid compartment. For the mathematical formulation, we assume incompressibility and we use Stokes together with Darcy-Brinkman equation for the flow of the lymph. Thanks to the hypothesis of axisymmetric flow with respect to the azimuthal angle and the use of the stream function approach, we find an explicit solution for the fully developed pulsatile flow in terms of Gegenbauer polynomials. A selected set of plots is provided to show the trend of motion in the case of physiological parameters. Then, a finite element simulation is performed and it is compared with the explicit solution.

Lymph Nodes-On-Chip: Promising Immune Platforms for Pharmacological and Toxicological Applications

Organs-on-chip are gaining increasing attention as promising platforms for drug screening and testing applications. However, lymph nodes-on-chip options remain limited although the lymph node is one of the main determinants of the immunotoxicity of newly developed pharmacological drugs. In this review, we describe existing biomimetic lymph nodes-on-chip, their design, and their physiological relevance to pharmacology and shed the light on future directions associated with lymph node-on-chip design and implementation in drug discovery and development.

May the Force Be with You (Or Not): The Immune System under Microgravity

All terrestrial organisms have evolved and adapted to thrive under Earth's gravitational force. Due to the increase of crewed space flights in recent years, it is vital to understand how the lack of gravitational forces affects organisms. It is known that astronauts who have been exposed to microgravity suffer from an array of pathological conditions including an impaired immune system, which is one of the most negatively affected by microgravity. However, at the cellular level a gap in knowledge exists, limiting our ability to understand immune impairment in space. This review highlights the most significant work done over the past 10 years detailing the effects of microgravity on cellular aspects of the immune system.

Organ-on-a-chip technology for nanoparticle research

The last two decades have witnessed explosive growth in the field of nanoengineering and nanomedicine. In particular, engineered nanoparticles have garnered great attention due to their potential to enable new capabilities such as controlled and targeted drug delivery for treatment of various diseases. With rapid progress in nanoparticle research, increasing efforts are being made to develop new technologies for in vitro modeling and analysis of the efficacy and safety of nanotherapeutics in human physiological systems. Organ-on-a-chip technology represents the most recent advance in this effort that provides a promising approach to address the limitations of conventional preclinical models. In this paper, we present a concise review of recent studies demonstrating how this emerging technology can be applied to in vitro studies of nanoparticles. The specific focus of this review is to examine the use of organ-on-a-chip models for toxicity and efficacy assessment of nanoparticles used in therapeutic applications. We also discuss challenges and future opportunities for implementing organ-on-a-chip technology for nanoparticle research.

Application of lung microphysiological systems to COVID-19 modeling and drug discovery: a review

There is a pressing need for effective therapeutics for coronavirus disease 2019 (COVID-19), the respiratory disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus. The process of drug development is a costly and meticulously paced process, where progress is often hindered by the failure of initially promising leads. To aid this challenge, in vitro human microphysiological systems need to be refined and adapted for mechanistic studies and drug screening, thereby saving valuable time and resources during a pandemic crisis. The SARS-CoV-2 virus attacks the lung, an organ where the unique three-dimensional (3D) structure of its functional units is critical for proper respiratory function. The in vitro lung models essentially recapitulate the distinct tissue structure and the dynamic mechanical and biological interactions between different cell types. Current model systems include Transwell, organoid and organ-on-a-chip or microphysiological systems (MPSs). We review models that have direct relevance toward modeling the pathology of COVID-19, including the processes of inflammation, edema, coagulation, as well as lung immune function. We also consider the practical issues that may influence the design and fabrication of MPS. The role of lung MPS is addressed in the context of multi-organ models, and it is discussed how high-throughput screening and artificial intelligence can be integrated with lung MPS to accelerate drug development for COVID-19 and other infectious diseases.

Immunocompetent cancer-on-chip models to assess immuno-oncology therapy

The advances in cancer immunotherapy come with several obstacles, limiting its widespread use and benefits so far only to a small subset of patients. One of the underlying challenges remains to be the lack of representative nonclinical models that translate to human immunity and are able to predict clinical efficacy and safety outcomes. In recent years, immunocompetent Cancer-on-Chip models emerge as an alternative human-based platform that enables the integration and manipulation of complex tumor microenvironment. In this review, we discuss novel opportunities offered by Cancer-on-Chip models to advance (mechanistic) immuno-oncology research, ranging from design flexibility to multimodal analysis approaches. We then exemplify their (potential) applications for the research and development of adoptive cell therapy, immune checkpoint therapy, cytokine therapy, oncolytic virus, and cancer vaccines.

Dendritic cell immune potency on 2D and in 3D collagen matrices

Dendritic cells (DCs) are antigen-presenting cells capable of either activating the immune response or inducing and maintaining immune tolerance. Understanding how biophysical properties affect DC behaviors will provide insight into the biology of a DC and its applications. In this work, we studied how cell culture dimensionality (two-dimensional (2D) and three-dimensional (3D)), and matrix density of 3D collagen matrices modulate differentiation and functions of DCs. Besides, we aimed to point out the different conceptual perspectives in modern immunological research, namely tissue-centric and cell-centric perspectives. The tissue-centric perspective intends to reveal how specific microenvironments dictate DC differentiation and in turn modulate DC functionalities, while the cell-centric perspective aims to demonstrate how pre-differentiated DCs behave in specific microenvironments. DC plasticity was characterized in terms of cell surface markers and cytokine secretion profiles. Subsequently, antigen internalization and T cell activation were quantified to demonstrate the cellular functions of immature DCs (iDCs) and mature DCs (mDCs), respectively. In the tissue-centric perspective, we found that expressed surface markers and secreted cytokines of both iDCs and mDCs are generally higher in 2D culture, while they are regulated by matrix density in 3D culture. In contrast, in the cell-centric perspective, we found enhanced expression of cell surface markers as well as distinct cytokine secretion profiles in both iDCs and mDCs. By analyzing cellular functions of cells in the tissue-centric perspective, we found matrix density dependence in antigen uptake by iDCs, as well as on mDC-mediated T cell proliferation in 3D cell culture. On the other hand, in the cell-centric perspective, both iDCs and mDCs appeared to lose their functional potentials to internalization antigen and T cell stimulation. Additionally, mDCs from tissue- and cell-centric perspectives modulated T cell differentiation by their distinct cytokine secretion profiles towards Th1 and Th17, respectively. In sum, our work emphasizes the importance of dimensionality, as well as collagen fibrillar density in the regulation of the immune response of DCs. Besides this, we demonstrated that the conceptual perspective of the experimental design could be an essential key point in research in immune cell-material interactions and biomaterial-based disease models of immunity.

Human lung-on-chips: Advanced systems for respiratory virus models and assessment of immune response

Respiratory viral infections are leading causes of death worldwide. A number of human respiratory viruses circulate in all age groups and adapt to person-to-person transmission. It is vital to understand how these viruses infect the host and how the host responds to prevent infection and onset of disease. Although animal models have been widely used to study disease states, incisive arguments related to poor prediction of patient responses have led to the development of microfluidic organ-on-chip models, which aim to recapitulate organ-level physiology. Over the past decade, human lung chips have been shown to mimic many aspects of the lung function and its complex microenvironment. In this review, we address immunological responses to viral infections and elaborate on human lung airway and alveolus chips reported to model respiratory viral infections and therapeutic interventions. Advances in the field will expedite the development of therapeutics and vaccines for human welfare.

Modeling the Human Body on Microfluidic Chips

Animals often fail to faithfully mimic human diseases and drug toxicities, and most in vitro models are not complex enough to recapitulate human body function and pathophysiology. Organ-on-chip culture technology, however, offers a promising tool for the study of tissue development and homeostasis, which has brought us one step closer to performing human experimentation in vitro. To recapitulate the complex functionality of multiple organs at once, their respective on-chip models can be linked to create a functional human body-on-chip platform. Here, we highlight the advantages and translational potentials of body-on-chip platforms in disease modeling, therapeutic development, and personalized medicine. We provide the reader with current limitations of the body-on-chip approach and new ideas to address the pending issues moving forwards.

Multi-Compartment Lymph-Node-on-a-Chip Enables Measurement of Immune Cell Motility in Response to Drugs

Organs On-a-Chip represent novel platforms for modelling human physiology and disease. The lymph node (LN) is a relevant immune organ in which B and T lymphocytes are spatially organized in a complex architecture, and it is the place where the immune response initiates. The present study addresses the utility of a recently designed LN-on-a-chip to dissect and understand the effect of drugs delivered to cells in a fluidic multicellular 3D setting that mimics the human LN. To do so, we analyzed the motility and viability of human B and T cells exposed to hydroxychloroquine (HCQ). We show that the innovative LN platform, which operates at a microscale level, allows real-time monitoring of co-cultured B and T cells by imaging, and supports cellular random movement. HCQ delivered to cells through a constant and continuous flow induces a reduction in T cell velocity while promotes persistent rotational motion. We also find that HCQ increases the production of reactive oxygen species in T cells. Taken together, these results highlight the potential of the LN-on-a-chip to be applied in drug screening and development, and in cellular dynamics studies.

Graph Theory for Modeling and Analysis of the Human Lymphatic System

The human lymphatic system (HLS) is a complex network of lymphatic organs linked through the lymphatic vessels. We present a graph theory-based approach to model and analyze the human lymphatic network. Two different methods of building a graph are considered: the method using anatomical data directly and the method based on a system of rules derived from structural analysis of HLS. A simple anatomical data-based graph is converted to an oriented graph by quantifying the steady-state fluid balance in the lymphatic network with the use of the Poiseuille equation in vessels and the mass conservation at vessel junctions. A computational algorithm for the generation of the rule-based random graph is developed and implemented. Some fundamental characteristics of the two types of HLS graph models are analyzed using different metrics such as graph energy, clustering, robustness, etc.

The Importance of Poly(ethylene glycol) and Lipid Structure in Targeted Gene Delivery to Lymph Nodes by Lipid Nanoparticles

Targeted delivery of nucleic acids to lymph nodes is critical for the development of effective vaccines and immunotherapies. However, it remains challenging to achieve selective lymph node delivery. Current gene delivery systems target mainly to the liver and typically exhibit off-target transfection at various tissues. Here we report novel lipid nanoparticles (LNPs) that can deliver plasmid DNA (pDNA) to a draining lymph node, thereby significantly enhancing transfection at this target organ, and substantially reducing gene expression at the intramuscular injection site (muscle). In particular, we discovered that LNPs stabilized by 3% Tween 20, a surfactant with a branched poly(ethylene glycol) (PEG) chain linking to a short lipid tail, achieved highly specific transfection at the lymph node. This was in contrast to conventional LNPs stabilized with a linear PEG chain and two saturated lipid tails (PEG-DSPE) that predominately transfected at the injection site (muscle). Interestingly, replacing Tween 20 with Tween 80, which has a longer unsaturated lipid tail, led to a much lower transfection efficiency. Our work demonstrates the importance of PEGylation in selective organ targeting of nanoparticles, provides new insights into the structure-property relationship of LNPs, and offers a novel, simple, and practical PEGylation technology to prepare the next generation of safe and effective vaccines against viruses or tumours.

Novel Strategies in Artificial Organ Development: What Is the Future of Medicine?

The technology of tissue engineering is a rapidly evolving interdisciplinary field of science that elevates cell-based research from 2D cultures through organoids to whole bionic organs. 3D bioprinting and organ-on-a-chip approaches through generation of three-dimensional cultures at different scales, applied separately or combined, are widely used in basic studies, drug screening and regenerative medicine. They enable analyses of tissue-like conditions that yield much more reliable results than monolayer cell cultures. Annually, millions of animals worldwide are used for preclinical research. Therefore, the rapid assessment of drug efficacy and toxicity in the early stages of preclinical testing can significantly reduce the number of animals, bringing great ethical and financial benefits. In this review, we describe 3D bioprinting techniques and first examples of printed bionic organs. We also present the possibilities of microfluidic systems, based on the latest reports. We demonstrate the pros and cons of both technologies and indicate their use in the future of medicine.