Microphysiological systems: analysis of the current status, challenges and commercial future

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.

A Progress Report and Roadmap for Microphysiological Systems and Organ-On-A-Chip Technologies to Be More Predictive Models in Human (Knee) Osteoarthritis

Osteoarthritis (OA), a chronic debilitating joint disease affecting hundreds of million people globally, is associated with significant pain and socioeconomic costs. Current treatment modalities are palliative and unable to stop the progressive degeneration of articular cartilage in OA. Scientific attention has shifted from the historical view of OA as a wear-and-tear cartilage disorder to its recognition as a whole-joint disease, highlighting the contribution of other knee joint tissues in OA pathogenesis. Despite much progress in the field of microfluidic systems/organs-on-a-chip in other research fields, current in vitro models in use do not yet accurately reflect the complexity of the OA pathophenotype. In this review, we provide: 1) a detailed overview of the most significant recent developments in the field of microsystems approaches for OA modeling, and 2) an OA-pathophysiology-based bioengineering roadmap for the requirements of the next generation of more predictive and authentic microscale systems fit for the purpose of not only disease modeling but also of drug screening to potentially allow OA animal model reduction and replacement in the near future.

3D in vitro morphogenesis of human intestinal epithelium in a gut-on-a-chip or a hybrid chip with a cell culture insert

Human intestinal morphogenesis establishes 3D epithelial microarchitecture and spatially organized crypt-villus characteristics. This unique structure is necessary to maintain intestinal homeostasis by protecting the stem cell niche in the basal crypt from exogenous microbial antigens and their metabolites. Also, intestinal villi and secretory mucus present functionally differentiated epithelial cells with a protective barrier at the intestinal mucosal surface. Thus, re-creating the 3D epithelial structure is critical to building in vitro intestine models. Notably, an organomimetic gut-on-a-chip can induce spontaneous 3D morphogenesis of an intestinal epithelium with enhanced physiological function and biomechanics. Here we provide a reproducible protocol to robustly induce intestinal morphogenesis in a microfluidic gut-on-a-chip as well as in a Transwell-embedded hybrid chip. We describe detailed methods for device fabrication, culture of Caco-2 or intestinal organoid epithelial cells in conventional setups as well as on microfluidic platforms, induction of 3D morphogenesis and characterization of established 3D epithelium using multiple imaging modalities. This protocol enables the regeneration of functional intestinal microarchitecture by controlling basolateral fluid flow within 5 d. Our in vitro morphogenesis method employs physiologically relevant shear stress and mechanical motions, and does not require complex cellular engineering or manipulation, which may be advantageous over other existing techniques. We envision that our proposed protocol may have a broad impact on biomedical research communities, providing a method to regenerate in vitro 3D intestinal epithelial layers for biomedical, clinical and pharmaceutical applications.

[Current challenges and future perspectives of pharmacological testing using new approach methodologies]

The mission of regulatory science is to promote human longevity by providing safer and more effective drugs and ensuring human health. At present, various in vitro and in vivo evaluation methods are used for drug development, and no major problems have been observed. However, there is still room for improvement in terms of risk prediction in humans. Thus, new approaches and methodologies (NAMs) have recently been developed to predict adverse events in humans more accurately. Based on the animal alternative methods and the current COVID-19 pandemic, in vitro methods, such as human iPS cells, and computational approach are accelerated to improve the efficiency of drug development, ensure the patients' safety and speed up the review process. In this review, we would like to summarize the current status and future perspectives of pharmacological assay system using NAM in drug development.

Patient-Specific Organoid and Organ-on-a-Chip: 3D Cell-Culture Meets 3D Printing and Numerical Simulation

The last few decades have witnessed diversified in vitro models to recapitulate the architecture and function of living organs or tissues and contribute immensely to advances in life science. Two novel 3D cell culture models: 1) Organoid, promoted mainly by the developments of stem cell biology and 2) Organ-on-a-chip, enhanced primarily due to microfluidic technology, have emerged as two promising approaches to advance the understanding of basic biological principles and clinical treatments. This review describes the comparable distinct differences between these two models and provides more insights into their complementarity and integration to recognize their merits and limitations for applicable fields. The convergence of the two approaches to produce multi-organoid-on-a-chip or human organoid-on-a-chip is emerging as a new approach for building 3D models with higher physiological relevance. Furthermore, rapid advancements in 3D printing and numerical simulations, which facilitate the design, manufacture, and results-translation of 3D cell culture models, can also serve as novel tools to promote the development and propagation of organoid and organ-on-a-chip systems. Current technological challenges and limitations, as well as expert recommendations and future solutions to address the promising combinations by incorporating organoids, organ-on-a-chip, 3D printing, and numerical simulation, are also summarized.

Cyclo olefin polymer-based solvent-free mass-productive microphysiological systems

A microphysiological system (MPS) holds great promise for drug screening and toxicological testing as an alternative to animal models. However, this platform faces several challenges in terms of the materials used (e.g., polydimethylsiloxane; PDMS). For instance, absorption of drug candidates and fluorescent dyes into PDMS, as well as the effect elicited by materials on cultured cells, can cause inaccurate or misleading results in cell assays. The use of PDMS also poses challenges for mass production and long-term storage of fabricated MPSs. Hence, to circumvent these issues, herein we describe the development of a cyclo olefin polymer (COP)-based MPS using photobonding processes and vacuum ultraviolet (VUV), designated as COP-VUV-MPS. COP is an amorphous polymer with chemical/physical stability, high purity and optical clarity. Due to the thermostability and high modulus of COP, the metal molding processes was applied for mass production of MPSs without deformation of microstructures and with quick fabrication cycle time (approx. 10 min/cycle). Moreover, VUV photobonding process with an excimer light at a 172-nm wavelength allowed assembling COP materials without the use of additional solvents and tapes, which might cause cell damages. In comparison with the conventional MPS made of PDMS (PDMS-MPS), COP-VUV-MPS showed improved chemical resistance without causing molecule absorption. Moreover, COP-VUV-MPS maintained the stemness of environmentally sensitive human-induced pluripotent stem cells without causing undesired cellular phenotypes or gene expression. These results suggest that COP-VUV-MPS may be broadly applicable for the advancement of MPS and applications in drug development, as well as in vitro toxicological testing.

Strategies for using mathematical modeling approaches to design and interpret multi-organ microphysiological systems (MPS)

Recent advances in organ-on-a-chip technology have resulted in numerous examples of microscale systems that faithfully mimic the physiology and pathology of human organs and diseases. The next step in this field, which has already been partially demonstrated at a proof-of-concept level, would be integration of organ modules to construct multiorgan microphysiological systems (MPSs). In particular, there is interest in "body-on-a-chip" models, which recapitulate complex and dynamic interactions between different organs. Integration of multiple organ modules, while faithfully reflecting human physiology in a quantitative sense, will require careful consideration of factors such as relative organ sizes, blood flow rates, cell numbers, and ratios of cell types. The use of a mathematical modeling platform will be an essential element in designing multiorgan MPSs and interpretation of experimental results. Also, extrapolation to in vivo will require robust mathematical modeling techniques. So far, several scaling methods and pharmacokinetic and physiologically based pharmacokinetic models have been applied to multiorgan MPSs, with each method being suitable to a subset of different objectives. Here, we summarize current mathematical methodologies used for the design and interpretation of multiorgan MPSs and suggest important considerations and approaches to allow multiorgan MPSs to recapitulate human physiology and disease progression better, as well as help in vitro to in vivo translation of studies on response to drugs or chemicals.

Harnessing Human Microphysiology Systems as Key Experimental Models for Quantitative Systems Pharmacology

Two technologies that have emerged in the last decade offer a new paradigm for modern pharmacology, as well as drug discovery and development. Quantitative systems pharmacology (QSP) is a complementary approach to traditional, target-centric pharmacology and drug discovery and is based on an iterative application of computational and systems biology methods with multiscale experimental methods, both of which include models of ADME-Tox and disease. QSP has emerged as a new approach due to the low efficiency of success in developing therapeutics based on the existing target-centric paradigm. Likewise, human microphysiology systems (MPS) are experimental models complementary to existing animal models and are based on the use of human primary cells, adult stem cells, and/or induced pluripotent stem cells (iPSCs) to mimic human tissues and organ functions/structures involved in disease and ADME-Tox. Human MPS experimental models have been developed to address the relatively low concordance of human disease and ADME-Tox with engineered, experimental animal models of disease. The integration of the QSP paradigm with the use of human MPS has the potential to enhance the process of drug discovery and development.