Design optimization of liquid-phase flow patterns for microfabricated lung on a chip

Smart Sensors and Microtechnologies in the Precision Medicine Approach against Lung Cancer

BACKGROUND AND RATIONALE

The therapeutic interventions against lung cancer are currently based on a fully personalized approach to the disease with considerable improvement of patients' outcome. Alongside continuous scientific progresses and research investments, massive technologic efforts, innovative challenges, and consolidated achievements together with research investments are at the bases of the engineering and manufacturing revolution that allows a significant gain in clinical setting.

AIM AND METHODS

The scope of this review is thus to focus, rather than on the biologic traits, on the analysis of the precision sensors and novel generation materials, as semiconductors, which are below the clinical development of personalized diagnosis and treatment. In this perspective, a careful revision and analysis of the state of the art of the literature and experimental knowledge is presented.

RESULTS

Novel materials are being used in the development of personalized diagnosis and treatment for lung cancer. Among them, semiconductors are used to analyze volatile cancer compounds and allow early disease diagnosis. Moreover, they can be used to generate MEMS which have found an application in advanced imaging techniques as well as in drug delivery devices.

CONCLUSIONS

Overall, these issues represent critical issues only partially known and generally underestimated by the clinical community. These novel micro-technology-based biosensing devices, based on the use of molecules at atomic concentrations, are crucial for clinical innovation since they have allowed the recent significant advances in cancer biology deciphering as well as in disease detection and therapy. There is an urgent need to create a stronger dialogue between technologists, basic researchers, and clinicians to address all scientific and manufacturing efforts towards a real improvement in patients' outcome. Here, great attention is focused on their application against lung cancer, from their exploitations in translational research to their application in diagnosis and treatment development, to ensure early diagnosis and better clinical outcomes.

Human Organs-on-Chips: A Review of the State-of-the-Art, Current Prospects, and Future Challenges

New emerging technologies, remarkably miniaturized 3D organ models and microfluidics, enable simulation of the real in vitro microenvironment ex vivo more closely. There are many fascinating features of innovative organ-on-a-chip (OOC) technology, including the possibility of integrating semipermeable and/or stretchable membranes, creating continuous perfusion of fluids into microchannels and chambers (while maintaining laminar flow regime), embedding microdevices like microsensors, microstimulators, micro heaters, or different cell lines, along with other 3D cell culture technologies. OOC systems are designed to imitate the structure and function of human organs, ranging from breathing lungs to beating hearts. This technology is expected to be able to revolutionize cell biology studies, personalized precision medicine, drug development process, and cancer diagnosis/treatment. OOC systems can significantly reduce the cost associated with tedious drug development processes and the risk of adverse drug reactions in the body, which makes drug screening more effective. The review mainly focus on presenting an overview of the several previously developed OOC systems accompanied by subjects relevant to pharmacy-, cancer-, and placenta-on-a-chip. The challenging issues and opportunities related to these systems are discussed, along with a future perspective for this technology.

Breathing in vitro: Designs and applications of engineered lung models

The aim of this review is to provide a systematic design guideline to users, particularly engineers interested in developing and deploying lung models, and biologists seeking to identify a suitable platform for conducting in vitro experiments involving pulmonary cells or tissues. We first discuss the state of the art on lung in vitro models, describing the most simplistic and traditional ones. Then, we analyze in further detail the more complex dynamic engineered systems that either provide mechanical cues, or allow for more predictive exposure studies, or in some cases even both. This is followed by a dedicated section on microchips of the lung. Lastly, we present a critical discussion of the different characteristics of each type of system and the criteria which may help researchers select the most appropriate technology according to their specific requirements. Readers are encouraged to refer to the tables accompanying the different sections where comprehensive and quantitative information on the operating parameters and performance of the different systems reported in the literature is provided.

Multiorgan microfluidic platform with breathable lung chamber for inhalation or intravenous drug screening and development

Efficient and economical delivery of pharmaceuticals to patients is critical for effective therapy. Here we describe a multiorgan (lung, liver, and breast cancer) microphysiological system ("Body-on-a-Chip") designed to mimic both inhalation therapy and/or intravenous therapy using curcumin as a model drug. This system is "pumpless" and self-contained using a rocker platform for fluid (blood surrogate) bidirectional recirculation. Our lung chamber is constructed to maintain an air-liquid interface and contained a "breathable" component that was designed to mimic breathing by simulating gas exchange, contraction and expansion of the "lung" using a reciprocating pump. Three cell lines were used: A549 for the lung, HepG2 C3A for the liver, and MDA MB231 for breast cancer. All cell lines were maintained with high viability (>85%) in the device for at least 48 hr. Curcumin is used to treat breast cancer and this allowed us to compare inhalation delivery versus intravenous delivery of the drug in terms of effectiveness and potentially toxicity. Inhalation therapy could be potentially applied at home by the patient while intravenous therapy would need to be applied in a clinical setting. Inhalation therapy would be more economical and allow more frequent dosing with a potentially lower level of drug. For 24 hr exposure to 2.5 and 25 µM curcumin in the flow device the effect on lung and liver viability was small to insignificant, while there was a significant decrease in viability of the breast cancer (to 69% at 2.5 µM and 51% at 25 µM). Intravenous delivery also selectively decreased breast cancer viability (to 88% at 2.5 µM and 79% at 25 µM) but was less effective than inhalation therapy. The response in the static device controls was significantly reduced from that with recirculation demonstrating the effect of flow. These results demonstrate for the first time the feasibility of constructing a multiorgan microphysiological system with recirculating flow that incorporates a "breathable" lung module that maintains an air-liquid interface.

Lung on a Chip for Drug Screening and Design

Lung-on-a-chip is a micro device that combines the techniques of bioengineering, microbiology, polymer science and microfluidics disciplines in order to mimic physicochemical features and microenvironments, multicellular constructions, cell-cell interfaces of a human lung. Specifically, most novel lung on a chip designs consist of two micro-channeled outer parts, flexible and porous Polydimethylsiloxane (PDMS) membrane to create separation of air-blood chamber and subsidiary vacuum channels which enable stretching of the PDMS membrane to mimic movement mechanisms of the lung. Therefore, studies aim to emulate both tissue and organ functionality since it shall be creating great potential for advancing the studies about drug discovery, disease etiology and organ physiology compared with 2D (two dimensional) and 3D (three dimensional) cell culture models and current organoids. In this study, history of researches on lung anatomy and physiology, techniques of recreating lung functionality such as cell cultures in 2D and 3D models, organoids were covered and finally most advanced and recent state of the art technology product lung-on-a-chips' construction steps, advantages compared with other techniques, usage in lung modeling and diseases, present and future offers were analyzed in detail.

Sensor-free and Sensor-based Heart-on-a-chip Platform: A Review of Design and Applications

Drug efficacy and toxicity are key factors of drug development. Conventional 2D cell models or animal models have their limitations for the efficacy or toxicity assessment in preclinical assays, which induce the failure of candidate drugs or withdrawal of approved drugs. Human organs-on-chips (OOCs) emerged to present human-specific properties based on their 3D bioinspired structures and functions in the recent decade. In this review, the basic definition and superiority of OOCs will be introduced. Moreover, a specific OOC, heart-on-achip (HOC) will be focused. We introduce HOC modeling in the sensor-free and sensor-based way and illustrate the advantages of sensor-based HOC in detail by taking examples of recent studies. We provide a new perspective on the integration of HOC technology and biosensing to develop a new sensor-based HOC platform.

Microfluidics for studying metastatic patterns of lung cancer

The incidence of lung cancer continues to rise worldwide. Because the aggressive metastasis of lung cancer cells is the major drawback of successful therapies, the crucial challenge of modern nanomedicine is to develop diagnostic tools to map the molecular mechanisms of metastasis in lung cancer patients. In recent years, microfluidic platforms have been given much attention as tools for novel point-of-care diagnostic, an important aspect being the reconstruction of the body organs and tissues mimicking the in vivo conditions in one simple microdevice. Herein, we present the first comprehensive overview of the microfluidic systems used as innovative tools in the studies of lung cancer metastasis including single cancer cell analysis, endothelial transmigration, distant niches migration and finally neoangiogenesis. The application of the microfluidic systems to study the intercellular crosstalk between lung cancer cells and surrounding tumor microenvironment and the connection with multiple molecular signals coming from the external cellular matrix are discussed. We also focus on recent breakthrough technologies regarding lab-on-chip devices that serve as tools for detecting circulating lung cancer cells. The superiority of microfluidic systems over traditional in vitro cell-based assays with regard to modern nanosafety studies and new cancer drug design and discovery is also addressed. Finally, the current progress and future challenges regarding printable and paper-based microfluidic devices for personalized nanomedicine are summarized.

Use of three-dimensional organoids and lung-on-a-chip methods to study lung development, regeneration and disease

Differences in lung anatomy between mice and humans, as well as frequently disappointing results when using animal models for drug discovery, emphasise the unmet need for in vitro models that can complement animal studies and improve our understanding of human lung physiology, regeneration and disease. Recent papers have highlighted the use of three-dimensional organoids and organs-on-a-chip to mimic tissue morphogenesis and function in vitro Here, we focus on the respiratory system and provide an overview of these in vitro models, which can be derived from primary lung cells and pluripotent stem cells, as well as healthy or diseased lungs. We emphasise their potential application in studies of respiratory development, regeneration and disease modelling.

Investigation of the effect of hepatic metabolism on off-target cardiotoxicity in a multi-organ human-on-a-chip system

Regulation of cosmetic testing and poor predictivity of preclinical drug studies has spurred efforts to develop new methods for systemic toxicity. Current in vitro assays do not fully represent physiology, often lacking xenobiotic metabolism. Functional human multi-organ systems containing iPSC derived cardiomyocytes and primary hepatocytes were maintained under flow using a low-volume pumpless system in a serum-free medium. The functional readouts for contractile force and electrical conductivity enabled the non-invasive study of cardiac function. The presence of the hepatocytes in the system induced cardiotoxic effects from cyclophosphamide and reduced them for terfenadine due to drug metabolism, as expected from each compound's pharmacology. A computational fluid dynamics simulation enabled the prediction of terfenadine-fexofenadine pharmacokinetics, which was validated by HPLC-MS. This in vitro platform recapitulates primary aspects of the in vivo crosstalk between heart and liver and enables pharmacological studies, involving both organs in a single in vitro platform. The system enables non-invasive readouts of cardiotoxicity of drugs and their metabolites. Hepatotoxicity can also be evaluated by biomarker analysis and change in metabolic function. Integration of metabolic function in toxicology models can improve adverse effects prediction in preclinical studies and this system could also be used for chronic studies as well.

Advanced Cell and Tissue Biomanufacturing

This position paper assesses state-of-the-art advanced biomanufacturing and identifies paths forward to advance this emerging field in biotechnology and biomedical engineering, including new research opportunities and translational and corporate activities. The vision for the field is to see advanced biomanufacturing emerge as a discipline in academic and industrial communities as well as a technological opportunity to spur research and industry growth. To navigate this vision, the paths to move forward and to identify major barriers were a focal point of discussions at a National Science Foundation-sponsored workshop focused on the topic. Some of the major needs include but are not limited to the integration of specific scientific and engineering disciplines and guidance from regulatory agencies, infrastructure requirements, and strategies for reliable systems integration. Some of the recommendations, major targets, and opportunities were also outlined, including some "grand challenges" to spur interest and progress in the field based on the participants at the workshop. Many of these recommendations have been expanded, materialized, and adopted by the field. For instance, the formation of an initial collaboration network in the community was established. This report provides suggestions for the opportunities and challenges to help move the field of advanced biomanufacturing forward. The field is in the early stages of effecting science and technology in biomanufacturing with a bright and important future impact evident based on the rapid scientific advances in recent years and industry progress.

Organs-on-a-Chip: A Fast Track for Engineered Human Tissues in Drug Development

Organs-on-a-chip (OOCs) are miniature tissues and organs grown in vitro that enable modeling of human physiology and disease. The technology has emerged from converging advances in tissue engineering, semiconductor fabrication, and human cell sourcing. Encompassing innovations in human stem cell technology, OOCs offer a promising approach to emulate human patho/physiology in vitro, and address limitations of current cell and animal models. Here, we review the design considerations for single and multi-organ OOCs, discuss remaining challenges, and highlight the potential impact of OOCs as a fast-track opportunity for tissue engineering to advance drug development and precision medicine.

Developmental pathways in lung regeneration

The key processes of lung development have been elucidated in the past several decades, helping to identify and characterize the resident progenitor cells that ultimately generate the mature organ. The adult lung is a complex organ consisting in scores of different cell lineages that are remarkably quiescent in the absence of injury. Despite low cellular turnover, the lung can respond quickly and dramatically to acute damage, with spatially restricted stem and progenitor cells re-entering the cell cycle and differentiating to promote repair. The findings from lung developmental biology are now being used to examine the mechanisms that underlie lung regeneration. The use of in vitro models such as pluripotent stem cells and new methods of gene editing have provided models for understanding lung disease and exploring the mechanisms of lung regeneration and have raised the prospect of correcting lung dysfunction. We outline the way that basic studies into lung developmental biology are now being applied to lung regeneration, opening up new avenues of research that may ultimately be harnessed for treatments of lung disease.

Modeling Barrier Tissues In Vitro: Methods, Achievements, and Challenges

Organ-on-a-chip devices have gained attention in the field of in vitro modeling due to their superior ability in recapitulating tissue environments compared to traditional multiwell methods. These constructed growth environments support tissue differentiation and mimic tissue-tissue, tissue-liquid, and tissue-air interfaces in a variety of conditions. By closely simulating the in vivo biochemical and biomechanical environment, it is possible to study human physiology in an organ-specific context and create more accurate models of healthy and diseased tissues, allowing for observations in disease progression and treatment. These chip devices have the ability to help direct, and perhaps in the distant future even replace animal-based drug efficacy and toxicity studies, which have questionable relevance to human physiology. Here, we review recent developments in the in vitro modeling of barrier tissue interfaces with a focus on the use of novel and complex microfluidic device platforms.

TEER measurement techniques for in vitro barrier model systems

Transepithelial/transendothelial electrical resistance (TEER) is a widely accepted quantitative technique to measure the integrity of tight junction dynamics in cell culture models of endothelial and epithelial monolayers. TEER values are strong indicators of the integrity of the cellular barriers before they are evaluated for transport of drugs or chemicals. TEER measurements can be performed in real time without cell damage and generally are based on measuring ohmic resistance or measuring impedance across a wide spectrum of frequencies. The measurements for various cell types have been reported with commercially available measurement systems and also with custom-built microfluidic implementations. Some of the barrier models that have been widely characterized using TEER include the blood-brain barrier (BBB), gastrointestinal (GI) tract, and pulmonary models. Variations in these values can arise due to factors such as temperature, medium formulation, and passage number of cells. The aim of this article is to review the different TEER measurement techniques and analyze their strengths and weaknesses, determine the significance of TEER in drug toxicity studies, examine the various in vitro models and microfluidic organs-on-chips implementations using TEER measurements in some widely studied barrier models (BBB, GI tract, and pulmonary), and discuss the various factors that can affect TEER measurements.

‘Body-on-a-Chip’ Technology and Supporting Microfluidics

In order to effectively streamline current drug development protocols, there is a need to generate high information content preclinical screens capable of generating data with a predictive power in relation to the activity of novel therapeutics in humans. Given the poor predictive power of animal models, and the lack of complexity and interconnectivity of standard in vitro culture methodologies, many investigators are now moving toward the development of physiologically and functionally accurate culture platforms composed of human cells to investigate cellular responses to drug compounds in high-throughput preclinical studies. The generation of complex, multi-organ in vitro platforms, built to recapitulate physiological dimensions, flow rates and shear stresses, is being investigated as the logical extension of this drive. Production and application of a biologically accurate multi-organ platform, or ‘body-on-a-chip’, would facilitate the correct modelling of the dynamic and interconnected state of living systems for high-throughput drug studies as well as basic and applied biomolecular research. This chapter will discuss current technologies aimed at producing ‘body-on-a-chip’ models, as well as highlighting recent advances and important challenges still to be met in the development of biomimetic single-organ systems for drug development purposes.

Advantages and challenges of microfluidic cell culture in polydimethylsiloxane devices

Culture of cells using various microfluidic devices is becoming more common within experimental cell biology. At the same time, a technological radiation of microfluidic cell culture device designs is currently in progress. Ultimately, the utility of microfluidic cell culture will be determined by its capacity to permit new insights into cellular function. Especially insights that would otherwise be difficult or impossible to obtain with macroscopic cell culture in traditional polystyrene dishes, flasks or well-plates. Many decades of heuristic optimization have gone into perfecting conventional cell culture devices and protocols. In comparison, even for the most commonly used microfluidic cell culture devices, such as those fabricated from polydimethylsiloxane (PDMS), collective understanding of the differences in cellular behavior between microfluidic and macroscopic culture is still developing. Moving in vitro culture from macroscopic culture to PDMS based devices can come with unforeseen challenges. Changes in device material, surface coating, cell number per unit surface area or per unit media volume may all affect the outcome of otherwise standard protocols. In this review, we outline some of the advantages and challenges that may accompany a transition from macroscopic to microfluidic cell culture. We focus on decisive factors that distinguish macroscopic from microfluidic cell culture to encourage a reconsideration of how macroscopic cell culture principles might apply to microfluidic cell culture.

Microfluidic approaches for epithelial cell layer culture and characterisation

In higher eukaryotes, epithelial cell layers line most body cavities and form selective barriers that regulate the exchange of solutes between compartments. In order to fulfil these functions, the cells assume a polarised architecture and maintain two distinct plasma membrane domains, the apical domain facing the lumen and the basolateral domain facing other cells and the extracellular matrix. Microfluidic biochips offer the unique opportunity to establish novel in vitro models of epithelia in which the in vivo microenvironment of epithelial cells is precisely reconstituted. In addition, analytical tools to monitor biologically relevant parameters can be directly integrated on-chip. In this review we summarise recently developed biochip designs for culturing epithelial cell layers. Since endothelial cell layers, which line blood vessels, have similar barrier functions and polar organisation as epithelial cell layers, we also discuss biochips for culturing endothelial cell layers. Furthermore, we review approaches to integrate tools to analyse and manipulate epithelia and endothelia in microfluidic biochips; including methods to perform electrical impedance spectroscopy; methods to detect substances undergoing trans-epithelial transport via fluorescence, spectrophotometry, and mass spectrometry; techniques to mechanically stimulate cells via stretching and fluid flow-induced shear stress; and methods to carry out high-resolution imaging of vesicular trafficking using light microscopy. Taken together, this versatile microfluidic toolbox enables novel experimental approaches to characterise epithelial monolayers.

How multi-organ microdevices can help foster drug development

Multi-organ microdevices can mimic tissue-tissue interactions that occur as a result of metabolite travel from one tissue to other tissues in vitro. These systems are capable of simulating human metabolism, including the conversion of a pro-drug to its effective metabolite as well as its subsequent therapeutic actions and toxic side effects. Since tissue-tissue interactions in the human body can play a significant role in determining the success of new pharmaceuticals, the development and use of multi-organ microdevices present an opportunity to improve the drug development process. The devices have the potential to predict potential toxic side effects with higher accuracy before a drug enters the expensive phase of clinical trials as well as to estimate efficacy and dose response. Multi-organ microdevices also have the potential to aid in the development of new therapeutic strategies by providing a platform for testing in the context of human metabolism (as opposed to animal models). Further, when operated with human biopsy samples, the devices could be a gateway for the development of individualized medicine. Here we review studies in which multi-organ microdevices have been developed and used in a ways that demonstrate how the devices' capabilities can present unique opportunities for the study of drug action. We will also discuss challenges that are inherent in the development of multi-organ microdevices. Among these are how to design the devices, and how to create devices that mimic the human metabolism with high authenticity. Since single organ devices are testing platforms for tissues that can later be combined with other tissues within multi-organ devices, we will also mention single organ devices where appropriate in the discussion.

Microphysiological systems and low-cost microfluidic platform with analytics

A multiorgan, functional, human in vitro assay system or 'Body-on-a-Chip' would be of tremendous benefit to the drug discovery and toxicology industries, as well as providing a more biologically accurate model for the study of disease as well as applied and basic biological research. Here, we describe the advances our team has made towards this goal, as well as the most pertinent issues facing further development of these systems. Description is given of individual organ models with appropriate cellular functionality, and our efforts to produce human iterations of each using primary and stem cell sources for eventual incorporation into this system. Advancement of the 'Body-on-a-Chip' field is predicated on the availability of abundant sources of human cells, capable of full differentiation and maturation to adult phenotypes, for which researchers are largely dependent on stem cells. Although this level of maturation is not yet achievable in all cell types, the work of our group highlights the high level of functionality that can be achieved using current technology, for a wide variety of cell types. As availability of functional human cell types for in vitro culture increases, the potential to produce a multiorgan in vitro system capable of accurately reproducing acute and chronic human responses to chemical and pathological challenge in real time will also increase.

Creating living cellular machines

Development of increasingly complex integrated cellular systems will be a major challenge for the next decade and beyond, as we apply the knowledge gained from the sub-disciplines of regenerative medicine, synthetic biology, micro-fabrication and nanotechnology, systems biology, and developmental biology. In this prospective, we describe the current state-of-the-art in the assembly of source cells, derived from pluripotent cells, into populations of a single cell type to produce the components or building blocks of higher order systems and finally, combining multiple cell types, possibly in combination with scaffolds possessing specific physical or chemical properties, to produce higher level functionality. We also introduce the issue, questions and ample research opportunities to be explored by others in the field. As these "living machines" increase in capabilities, exhibit emergent behavior and potentially reveal the ability for self-assembly, self-repair, and even self-replication, questions arise regarding the ethical implications of this work. Future prospects as well as ways of addressing these complex ethical questions will be discussed.

Microfabricated mammalian organ systems and their integration into models of whole animals and humans

While in vitro cell based systems have been an invaluable tool in biology, they often suffer from a lack of physiological relevance. The discrepancy between the in vitro and in vivo systems has been a bottleneck in drug development process and biological sciences. The recent progress in microtechnology has enabled manipulation of cellular environment at a physiologically relevant length scale, which has led to the development of novel in vitro organ systems, often termed 'organ-on-a-chip' systems. By mimicking the cellular environment of in vivo tissues, various organ-on-a-chip systems have been reported to reproduce target organ functions better than conventional in vitro model systems. Ultimately, these organ-on-a-chip systems will converge into multi-organ 'body-on-a-chip' systems composed of functional tissues that reproduce the dynamics of the whole-body response. Such microscale in vitro systems will open up new possibilities in medical science and in the pharmaceutical industry.

A functional system for high-content screening of neuromuscular junctions in vitro

High-content phenotypic screening systems are the logical extension of the current efficient, yet low information content, pre-clinical screens for drug discovery. A physiologically accurate in vitro neuromuscular junction (NMJ) screening system would therefore be of tremendous benefit to the study of peripheral neuropathies as well as for basic and applied neuromuscular research. To date, no fully-defined, selective assay system has been developed which would allow investigators to determine the functional output of cultured muscle fibers (myotubes) when stimulated via the NMJ in real time for both acute and chronic applications. Here we present the development of such a phenotypic screening model, along with evidence of NMJ formation and motoneuron initiated neuromuscular transmission in an automated system. Myotubes assembled on silicon cantilevers allowed for measurement of substrate deflection in response to contraction and provided the basis for monitoring the effect of controlled motoneuron stimulation on the contractile behavior. The effect was blocked by treatment with D-tubocurarine, confirming NMJ functionality in this highly multiplexed assay system.