Organ-on-chip technology: Opportunities and challenges

Bioprinting spatially guided functional 3D neural circuits with agarose-xanthan gum copolymer hydrogels

Engineered three-dimensional (3D) tissue models are being used as predictive human in vitro assays for drug discovery and development. Tissue engineering technologies such as bioprinting are now available which use mixtures of polymeric hydrogels and cells for the construction of biomimetic engineered 3D tissue models. Many of the polymeric hydrogels used for bioprinting require post-printing processing steps which might hinder their application directly in multi-well plate platforms, thus limiting their utility in a drug screening setting. Here we describe an agarose and xanthan gum copolymer hydrogel (AG-XG) that has optimal rheological properties for high shape fidelity with extrusion-based printing, has long term stability in cell culture conditions, and is "ready-to-use" after printing, not requiring post-printing processing treatments, making it ideal for applications in multi-well plate format. This AG-XG hydrogel is non-degradable and has non-cell permissive features which makes it ideal to create customized spatially guided cellular patterns to enhance relevant tissue geometry and function. As a proof-of-concept, we show that a bioprinted AG-XG hydrogel casting mold significantly enhances functional connectivity of an engineered 3D neural circuit model made using human iPSC-derived GABAergic and dopaminergic neurons and astrocytes. The bioprinted AG-XG mold promotes the formation of strong functional synaptic connections between two spatially separated neuronal regions, as measured with calcium and optogenetic-based fluorescent biosensors with a customized fiber photometry device. The high shape fidelity of the AG-XG hydrogels described here enables the biofabrication of precisely positioned and spatially designed cellular models, in muti well-based platforms used for drug screening. The process of printing these AG-XG hydrogels uses commercially available extrusion-based bioprinters and can therefore be easily implemented in translational laboratories doing tissue modeling and drug screening without the need of additional specialized bioengineering equipment.

Organ-on-a-chip: Quo vademus? Applications and regulatory status

Organ-on-a-chip systems, also referred to as microphysiological systems (MPS), represent an advance in bioengineering microsystems designed to mimic key aspects of human organ physiology and function. Drawing inspiration from the intricate and hierarchical architecture of the human body, these innovative platforms have emerged as invaluable in vitro tools with wide-ranging applications in drug discovery and development, as well as in enhancing our understanding of disease physiology. The facility to replicate human tissues within physiologically relevant three-dimensional multicellular environments empowers organ-on-a-chip systems with versatility throughout different stages of the drug development process. Moreover, these systems can be tailored to mimic specific disease states, facilitating the investigation of disease progression, drug responses, and potential therapeutic interventions. In particular, they can demonstrate, in early-phase pre-clinical studies, the safety and toxicity profiles of potential therapeutic compounds. Furthermore, they play a pivotal role in the in vitro evaluation of drug efficacy and the modeling of human diseases. One of the most promising prospects of organ-on-a-chip technology is to simulate the pathophysiology of specific subpopulations and even individual patients, thereby being used in personalized medicine. By mimicking the physiological responses of diverse patient groups, these systems hold the promise of revolutionizing therapeutic strategies, guiding them towards tailored intervention to the unique needs of each patient. This review presents the development status and evolution of microfluidic platforms that have facilitated the transition from cells to organs recreated on chips and some of the opportunities and applications offered by organ-on-a-chip technology. Additionally, the current potential and future perspectives of these microphysiological systems and the challenges this technology still faces are discussed.

Improve your success with fish cell lines-small things that matter

There is a drive towards reducing animal experiments and developing robust biologically relevant in vitro models based on cell lines, including those derived from fish. At the time of writing, Cellosaurus, the knowledge base of current cell lines used in research, listed more than 900 fish cell lines in its database. One of the key challenges facing fish cell biology is the lack of fundamental technical information regarding the isolation, culture, and application of cell lines. Researchers often work in silos, encountering similar technical challenges, each spending significant time and resources overcoming the same issues for which solutions may not be readily accessible. Here, we share some of the key considerations for the isolation, culture, maintenance, and application of fish cell lines in toxicology, which we have encountered over our collective decades of experience.

3D cell culture models: how to obtain and characterize the main models

For many years, the gold standard in the study of malignant tumors has been the in vitro culture of tumor cells, in vivo xenografts or genetically modified animal models. Meanwhile, three-dimensional cell models (3D cultures) have been added to the arsenal of modern biomedical research. 3D cultures reproduce tissue-specific features of tissue topology. This makes them relevant tissue models in terms of cell differentiation, metabolism and the development of drug resistance. Such models are already being used by many research groups for both basic and translational research, and may substantially reduce the number of animal studies, for example in the field of oncological research. In the current literature, 3D cultures are classified according to the technique of their formation (with or without a scaffold), cultivation conditions (static or dynamic), as well as their cellular organization and function. In terms of cellular organization, 3D cultures are divided into "spheroid models", "organoids", "organs-on-a-chip" and "microtissues". Each of these models has its own unique features, which should be taken into account when using a particular model in an experiment. The simplest 3D cultures are spheroid models which are floating spherical cell aggregates. An organoid is a more complex 3D model, in which a self-organizing 3D structure is formed from stem cells (SCs) capable of self-renewal and differentiation within the model. Organ-on-a-chip models are chips of microfluidic systems that simulate dynamic physical and biological processes found in organs and tissues in vitro. By combining different cell types into a single structure, spheroids and organoids can act as a basis for the formation of a microtissue - a hybrid 3D model imitating a specific tissue phenotype and containing tissue-specific extracellular matrix (ECM) components. This review presents a brief history of 3D cell culture. It describes the main characteristics and perspectives of the use of "spheroid models", "organoids", "organ-on-a-chip" models and "microtissues" in immune oncology research of solid tumors.

Automated electrochemical oxygen sensing using a 3D-printed microfluidic lab-on-a-chip system

Dissolved oxygen is crucial for metabolism, growth, and other complex physiological and pathological processes; however, standard physiological models (such as organ-on-chip systems) often use ambient oxygen levels, which do not reflect the lower levels that are typically found in vivo. Additionally, the local generation of reactive oxygen species (ROS; a key factor in physiological systems) is often overlooked in biology-mimicking models. Here, we present a microfluidic system that integrates electrochemical dissolved oxygen sensors with lab-on-a-chip technology to monitor the physiological oxygen concentrations and generate hydrogen peroxide (H2O2; a specific ROS). This microfluidic lab-on-a-chip system was fabricated using high-resolution 3D printing technology in a one-step process. It incorporates a micromixer, an on-chip bubble-trap, an electrochemical cell with fabricated gold or platinum black-coated working electrodes as well as an Ag/AgCl reference electrode, and a commercial optical oxygen sensor for validation. This device enables an automated variation of the oxygen levels as well as sensitive electrochemical oxygen monitoring (limit of detection = 11.9 ± 0.3 μM), with a statistically significant correlation with the optical sensor. The proposed system can serve as a tool to characterize and evaluate custom-made electrodes. Indeed, we envision that in the future it will be used to regulate dissolved oxygen levels and oxygen species in real time in organ-on-chip systems.

Evaluation of Drug Permeation Enhancement by Using In Vitro and Ex Vivo Models

Drugs administered by means of extravascular routes of drug administration must be absorbed into the systemic circulation, which involves the movement of the drug molecules across biological barriers such as epithelial cells that cover mucosal surfaces or the stratum corneum that covers the skin. Some drugs exhibit poor permeation across biological membranes or may experience excessive degradation during first-pass metabolism, which tends to limit their bioavailability. Various strategies have been used to improve drug bioavailability. Absorption enhancement strategies include the co-administration of chemical permeation enhancers, enzymes, and/or efflux transporter inhibitors, chemical changes, and specialized dosage form designs. Models with physiological relevance are needed to evaluate the efficacy of drug absorption enhancement techniques. Various in vitro cell culture models and ex vivo tissue models have been explored to evaluate and quantify the effectiveness of drug permeation enhancement strategies. This review deliberates on the use of in vitro and ex vivo models for the evaluation of drug permeation enhancement strategies for selected extravascular drug administration routes including the nasal, oromucosal, pulmonary, oral, rectal, and transdermal routes of drug administration.

Bridging silicon and carbon worlds with digital twins and on-chip systems in drug discovery

This perspective discusses the convergence of digital twin (DT) technology and on-the-chip systems as pivotal innovations in precision medicine, substantially advancing drug discovery. DT leverages extensive health data to create dynamic virtual patient models, enabling predictive insights and optimized treatment strategies. Concurrently, on-the-chip systems from the Carbon world replicate human biological processes on microfluidic platforms, providing detailed insights into disease mechanisms and pharmacological interactions. The convergence of these technologies promises to revolutionize drug development by enhancing therapeutic precision, accelerating discovery timelines, and reducing costs. Specifically, it assesses their role in drug development, from refining therapeutic precision to expediting discovery timelines and reducing the final price. Nevertheless, integrating these technologies faces challenges, including data collection and privacy concerns, technical intricacies, and clinical adoption barriers. This manuscript argues for interdisciplinary cooperation to navigate these challenges, positing DTs and on-the-chip technologies as foundational elements in personalized healthcare and drug discovery.

Organ-on-a-Chip Models-New Possibilities in Experimental Science and Disease Modeling

'Organ-on-a-chip' technology is a promising and rapidly evolving model in biological research. This innovative microfluidic cell culture device was created using a microchip with continuously perfused chambers, populated by living cells arranged to replicate physiological processes at the tissue and organ levels. By consolidating multicellular structures, tissue-tissue interfaces, and physicochemical microenvironments, these microchips can replicate key organ functions. They also enable the high-resolution, real-time imaging and analysis of the biochemical, genetic, and metabolic activities of living cells in the functional tissue and organ contexts. This technology can accelerate research into tissue development, organ physiology and disease etiology, therapeutic approaches, and drug testing. It enables the replication of entire organ functions (e.g., liver-on-a-chip, hypothalamus-pituitary-on-a-chip) or the creation of disease models (e.g., amyotrophic lateral sclerosis-on-a-chip, Parkinson's disease-on-a-chip) using specialized microchips and combining them into an integrated functional system. This technology allows for a significant reduction in the number of animals used in experiments, high reproducibility of results, and the possibility of simultaneous use of multiple cell types in a single model. However, its application requires specialized equipment, advanced expertise, and currently incurs high costs. Additionally, achieving the level of standardization needed for commercialization remains a challenge at this stage of development.

In Vitro Models for Peripheral Nerve Regeneration

Peripheral nerve injury (PNI) resulting in lesions is highly prevalent clinically, but current therapeutic approaches fail to provide satisfactory outcomes in many patients. While peripheral nerves have intrinsic regenerative capacity, the regenerative capabilities of peripheral nerves are often insufficient to restore full functionality. This highlights an unmet need for developing more effective strategies to repair damaged peripheral nerves and improve regenerative success. Consequently, researchers are actively exploring a variety of therapeutic strategies, encompassing the local delivery of trophic factors or bioactive molecules, the design of advanced biomaterials that interact with regenerating axons, and augmentation with nerve guidance conduits or complex prostheses. However, clinical translation of these technologies remains limited, emphasizing the need for continued research on peripheral nerve regeneration modalities that can enhance functional restoration. Experimental models that accurately recapitulate key aspects of peripheral nerve injury and repair biology can accelerate therapeutic development by enabling systematic testing of new techniques. Advancing regenerative therapies for PNI requires bridging the gap between basic science discoveries and clinical application. This review discusses different in vitro models of peripheral nerve injury and repair, including their advantages, limitations, and potential applications.

Revolutionizing IBD research with on-chip models of disease modeling and drug screening

Inflammatory bowel disease (IBD) comprises chronic inflammatory conditions with complex mechanisms and diverse manifestations, posing significant clinical challenges. Traditional animal models and ethical concerns in human studies necessitate innovative approaches. This review provides an overview of human intestinal architecture in health and inflammation, emphasizing the role of microfluidics and on-chip technologies in IBD research. These technologies allow precise manipulation of cellular and microbial interactions in a physiologically relevant context, simulating the intestinal ecosystem microscopically. By integrating cellular components and replicating 3D tissue architecture, they offer promising models for studying host-microbe interactions, wound healing, and therapeutic approaches. Continuous refinement of these technologies promises to advance IBD understanding and therapy development, inspiring further innovation and cross-disciplinary collaboration.

Brain-on-a-chip: an emerging platform for studying the nanotechnology-biology interface for neurodegenerative disorders

Neurological disorders have for a long time been a global challenge dismissed by drug companies, especially due to the low efficiency of most therapeutic compounds to cross the brain capillary wall, that forms the blood-brain barrier (BBB) and reach the brain. This has boosted an incessant search for novel carriers and methodologies to drive these compounds throughout the BBB. However, it remains a challenge to artificially mimic the physiology and function of the human BBB, allowing a reliable, reproducible and throughput screening of these rapidly growing technologies and nanoformulations (NFs). To surpass these challenges, brain-on-a-chip (BoC) - advanced microphysiological platforms that emulate key features of the brain composition and functionality, with the potential to emulate pathophysiological signatures of neurological disorders, are emerging as a microfluidic tool to screen new brain-targeting drugs, investigate neuropathogenesis and reach personalized medicine. In this review, the advance of BoC as a bioengineered screening tool of new brain-targeting drugs and NFs, enabling to decipher the intricate nanotechnology-biology interface is discussed. Firstly, the main challenges to model the brain are outlined, then, examples of BoC platforms to recapitulate the neurodegenerative diseases and screen NFs are summarized, emphasizing the current most promising nanotechnological-based drug delivery strategies and lastly, the integration of high-throughput screening biosensing systems as possible cutting-edge technologies for an end-use perspective is discussed as future perspective.

Tiny Organs, Big Impact: How Microfluidic Organ-on-Chip Technology Is Revolutionizing Mucosal Tissues and Vasculature

Organ-on-chip (OOC) technology has gained importance for biomedical studies and drug development. This technology involves microfluidic devices that mimic the structure and function of specific human organs or tissues. OOCs are a promising alternative to traditional cell-based models and animals, as they provide a more representative experimental model of human physiology. By creating a microenvironment that closely resembles in vivo conditions, OOC platforms enable the study of intricate interactions between different cells as well as a better understanding of the underlying mechanisms pertaining to diseases. OOCs can be integrated with other technologies, such as sensors and imaging systems to monitor real-time responses and gather extensive data on tissue behavior. Despite these advances, OOCs for many organs are in their initial stages of development, with several challenges yet to be overcome. These include improving the complexity and maturity of these cellular models, enhancing their reproducibility, standardization, and scaling them up for high-throughput uses. Nonetheless, OOCs hold great promise in advancing biomedical research, drug discovery, and personalized medicine, benefiting human health and well-being. Here, we review several recent OOCs that attempt to overcome some of these challenges. These OOCs with unique applications can be engineered to model organ systems such as the stomach, cornea, blood vessels, and mouth, allowing for analyses and investigations under more realistic conditions. With this, these models can lead to the discovery of potential therapeutic interventions. In this review, we express the significance of the relationship between mucosal tissues and vasculature in organ-on-chip (OOC) systems. This interconnection mirrors the intricate physiological interactions observed in the human body, making it crucial for achieving accurate and meaningful representations of biological processes within OOC models. Vasculature delivers essential nutrients and oxygen to mucosal tissues, ensuring their proper function and survival. This exchange is critical for maintaining the health and integrity of mucosal barriers. This review will discuss the OOCs used to represent the mucosal architecture and vasculature, and it can encourage us to think of ways in which the integration of both can better mimic the complexities of biological systems and gain deeper insights into various physiological and pathological processes. This will help to facilitate the development of more accurate predictive models, which are invaluable for advancing our understanding of disease mechanisms and developing novel therapeutic interventions.