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.

A brief history of organoids.

In vitro cell cultures are crucial research tools for modeling human development and diseases. Although the conventional monolayer cell cultures have been widely used in the past, the lack of tissue architecture and complexity of such model fails to inform the true biological processes in vivo. Recent advances in the organoid technology have revolutionized the in vitro culture tools for biomedical research by creating powerful three-dimensional (3D) models to recapitulate the cellular heterogeneity, structure, and functions of the primary tissues. Such organoid technology enables researchers to recreate human organs and diseases in a dish and thus holds great promises for many translational applications such as regenerative medicine, drug discovery, and precision medicine. In this review, we provide an overview of the organoid history and development. We discuss the strengths and limitations of organoids as well as their potential applications in the laboratory and the clinic.

Bioinspired Engineering of Organ-on-Chip Devices.

The human body can be viewed as an organism consisting of a variety of cellular and non-cellular materials interacting in a highly ordered manner. Its complex and hierarchical nature inspires the multi-level recapitulation of the human body in order to gain insights into the inner workings of life. While traditional cell culture models have led to new insights into the cellular microenvironment and biological control in vivo, deeper understanding of biological systems and human pathophysiology requires the development of novel model systems that allow for analysis of complex internal and external interactions within the cellular microenvironment in a more relevant organ context. Engineering organ-on-chip systems offers an unprecedented opportunity to unravel the complex and hierarchical nature of human organs. In this chapter, we first highlight the advances in microfluidic platforms that enable engineering of the cellular microenvironment and the transition from cells-on-chips to organs-on-chips. Then, we introduce the key features of the emerging organs-on-chips and their proof-of-concept applications in biomedical research. We also discuss the challenges and future outlooks of this state-of-the-art technology.

[Establishment and application of gastric and gastric cancer organoids].

Gastric organoid is the organotypic cultures of gastric stem cells or pluripotent stem cells. Gastric organoid is comprised of all major types of gastric epithelial cells and represent the architecture and function remarkably similar to those of the gastric epithelium, faithfully recapitulating the functional gastric epithelium ex vivo. As ideal basic experimental model, gastric organoid has advantages over animal models and conventional cell model in many aspects. Gastric organoid derived from human gastric tissue, in particular, allows the investigation of the function of human stomach in the ex vivo setting. It has now been applied in the field of formation and physiology of the stomach, Helicobacter pylori infection-associated diseases, research of the pathogenic gene, screening and development of drugs, and regenerative medicine. What is more, as an innovative pre-clinical cancer model, gastric cancer organoid has provided important insights in the development of gastric cancer and screening of antitumor drugs, such as simulating the occurrence and development of gastric cancer, screening and development of antitumor drugs, personalized medication and targeted therapy for gastric cancer, and combined application with patient-derived xenograft. In this review, we summarize the establishment and application of gastric and gastric cancer organoids, especially in modeling gastric cancer, basic research and drug development.

Developmentally inspired human 'organs on chips'.

Although initially developed to replace animal testing in drug development, human 'organ on a chip' (organ chip) microfluidic culture technology offers a new tool for studying tissue development and pathophysiology, which has brought us one step closer to carrying out human experimentation in vitro In this Spotlight article, I discuss the central role that developmental biology played in the early stages of organ-chip technology, and how these models have led to new insights into human physiology and disease mechanisms. Advantages and disadvantages of the organ-chip approach relative to organoids and other human cell cultures are also discussed.

Integrated biocircuits: engineering functional multicellular circuits and devices.

OBJECTIVE: Implantable neurotechnologies have revolutionized neuromodulatory medicine for treating the dysfunction of diseased neural circuitry. However, challenges with biocompatibility and lack of full control over neural network communication and function limits the potential to create more stable and robust neuromodulation devices. Thus, we propose a platform technology of implantable and programmable cellular systems, namely Integrated Biocircuits, which use only cells as the functional components of the device. APPROACH: We envision the foundational principles for this concept begins with novel in vitro platforms used for the study and reconstruction of cellular circuitry. Additionally, recent advancements in organoid and 3D culture systems account for microenvironment factors of cytoarchitecture to construct multicellular circuits as they are normally formed in the brain. We explore the current state of the art of these platforms to provide knowledge of their advancements in circuit fabrication and identify the current biological principles that could be applied in designing integrated biocircuit devices. MAIN RESULTS: We have highlighted the exemplary methodologies and techniques of in vitro circuit fabrication and propose the integration of selected controllable parameters, which would be required in creating suitable biodevices. SIGNIFICANCE: We provide our perspective and propose new insights into the future of neuromodulaion devices within the scope of living cellular systems that can be applied in designing more reliable and biocompatible stimulation-based neuroprosthetics.

The promise of organ and tissue preservation to transform medicine.

The ability to replace organs and tissues on demand could save or improve millions of lives each year globally and create public health benefits on par with curing cancer. Unmet needs for organ and tissue preservation place enormous logistical limitations on transplantation, regenerative medicine, drug discovery, and a variety of rapidly advancing areas spanning biomedicine. A growing coalition of researchers, clinicians, advocacy organizations, academic institutions, and other stakeholders has assembled to address the unmet need for preservation advances, outlining remaining challenges and identifying areas of underinvestment and untapped opportunities. Meanwhile, recent discoveries provide proofs of principle for breakthroughs in a family of research areas surrounding biopreservation. These developments indicate that a new paradigm, integrating multiple existing preservation approaches and new technologies that have flourished in the past 10 years, could transform preservation research. Capitalizing on these opportunities will require engagement across many research areas and stakeholder groups. A coordinated effort is needed to expedite preservation advances that can transform several areas of medicine and medical science.

A strategy for generating kidney organoids: Recapitulating the development in human pluripotent stem cells.

Directed differentiation of human pluripotent stem cells (hPSCs) can provide us any required tissue/cell types by recapitulating the development in vitro. The kidney is one of the most challenging organs to generate from hPSCs as the kidney progenitors are composed of at least 4 different cell types, including nephron, collecting duct, endothelial and interstitium progenitors, that are developmentally distinguished populations. Although the actual developmental process of the kidney during human embryogenesis has not been clarified yet, studies using model animals accumulated knowledge about the origins of kidney progenitors. The implications of these findings for the directed differentiation of hPSCs into the kidney include the mechanism of the intermediate mesoderm specification and its patterning along with anteroposterior axis. Using this knowledge, we previously reported successful generation of hPSCs-derived kidney organoids that contained all renal components and modelled human kidney development in vitro. In this review, we explain the developmental basis of the strategy behind this differentiation protocol and compare strategies of studies that also recently reported the induction of kidney cells from hPSCs. We also discuss the characterization of such kidney organoids and limitations and future applications of this technology.

Dishing out mini-brains: Current progress and future prospects in brain organoid research.

The ability to model human brain development in vitro represents an important step in our study of developmental processes and neurological disorders. Protocols that utilize human embryonic and induced pluripotent stem cells can now generate organoids which faithfully recapitulate, on a cell-biological and gene expression level, the early period of human embryonic and fetal brain development. In combination with novel gene editing tools, such as CRISPR, these methods represent an unprecedented model system in the field of mammalian neural development. In this review, we focus on the similarities of current organoid methods to in vivo brain development, discuss their limitations and potential improvements, and explore the future venues of brain organoid research.

Towards artificial tissue models: past, present, and future of 3D bioprinting.

Regenerative medicine and tissue engineering have seen unprecedented growth in the past decade, driving the field of artificial tissue models towards a revolution in future medicine. Major progress has been achieved through the development of innovative biomanufacturing strategies to pattern and assemble cells and extracellular matrix (ECM) in three-dimensions (3D) to create functional tissue constructs. Bioprinting has emerged as a promising 3D biomanufacturing technology, enabling precise control over spatial and temporal distribution of cells and ECM. Bioprinting technology can be used to engineer artificial tissues and organs by producing scaffolds with controlled spatial heterogeneity of physical properties, cellular composition, and ECM organization. This innovative approach is increasingly utilized in biomedicine, and has potential to create artificial functional constructs for drug screening and toxicology research, as well as tissue and organ transplantation. Herein, we review the recent advances in bioprinting technologies and discuss current markets, approaches, and biomedical applications. We also present current challenges and provide future directions for bioprinting research.

From Single Cells to Engineered and Explanted Tissues: New Perspectives in Bacterial Infection Biology.

Cell culture techniques are essential for studying host-pathogen interactions. In addition to the broad range of single cell type-based two-dimensional cell culture models, an enormous amount of coculture systems, combining two or more different cell types, has been developed. These systems enable microscopic visualization and molecular analyses of bacterial adherence and internalization mechanisms and also provide a suitable setup for various biochemical, immunological, and pharmacological applications. The implementation of natural or synthetical scaffolds elevated the model complexity to the level of three-dimensional cell culture. Additionally, several transwell-based cell culture techniques are applied to study bacterial interaction with physiological tissue barriers. For keeping highly differentiated phenotype of eukaryotic cells in ex vivo culture conditions, different kinds of microgravity-simulating rotary-wall vessel systems are employed. Furthermore, the implementation of microfluidic pumps enables constant nutrient and gas exchange during cell cultivation and allows the investigation of long-term infection processes. The highest level of cell culture complexity is reached by engineered and explanted tissues which currently pave the way for a more comprehensive view on microbial pathogenicity mechanisms.

Human hair follicle organ culture: theory, application and perspectives.

For almost a quarter of a century, ex vivo studies of human scalp hair follicles (HFs) have permitted major advances in hair research, spanning diverse fields such as chronobiology, endocrinology, immunology, metabolism, mitochondrial biology, neurobiology, pharmacology, pigmentation and stem cell biology. Despite this, a comprehensive methodological guide to serum-free human HF organ culture (HFOC) that facilitates the selection and analysis of standard HF biological parameters and points out both research opportunities and pitfalls to newcomers to the field is still lacking. The current methods review aims to close an important gap in the literature and attempts to promote standardisation of human HFOC. We provide basic information outlining the establishment of HFOC through to detailed descriptions of the analysis of standard read-out parameters alongside practical examples. The guide closes by pointing out how serum-free HFOC can be utilised optimally to obtain previously inaccessible insights into human HF biology and pathology that are of interest to experimental dermatologists, geneticists, developmental biologists and (neuro-) endocrinologists alike and by highlighting novel applications of the model, including gene silencing and gene expression profiling of defined, laser capture-microdissected HF compartments.

Bioengineering for Organ Transplantation: Progress and Challenges.

Organ transplantation can offer a curative option for patients with end stage organ failure. Unfortunately the treatment is severely limited by the availability of donor organs. Organ bioengineering could provide a solution to the worldwide critical organ shortage. The majority of protocols to date have employed the use of decellularization-recellularization technology of naturally occurring tissues and organs with promising results in heart, lung, liver, pancreas, intestine and kidney engineering. Successful decellularization has provided researchers with suitable scaffolds to attempt cell reseeding. Future work will need to focus on the optimization of organ specific recellularization techniques before organ bioengineering can become clinically translatable. This review will examine the current progress in organ bioengineering and highlight future challenges in the field.

Bioreactor technologies to support liver function in vitro.

Liver is a central nexus integrating metabolic and immunologic homeostasis in the human body, and the direct or indirect target of most molecular therapeutics. A wide spectrum of therapeutic and technological needs drives efforts to capture liver physiology and pathophysiology in vitro, ranging from prediction of metabolism and toxicity of small molecule drugs, to understanding off-target effects of proteins, nucleic acid therapies, and targeted therapeutics, to serving as disease models for drug development. Here we provide perspective on the evolving landscape of bioreactor-based models to meet old and new challenges in drug discovery and development, emphasizing design challenges in maintaining long-term liver-specific function and how emerging technologies in biomaterials and microdevices are providing new experimental models.

The use of skin models in drug development.

Three dimensional (3D) tissue models of the human skin are probably the most developed and understood in vitro engineered constructs. The motivation to accomplish organotypic structures was driven by the clinics to enable transplantation of in vitro grown tissue substitutes and by the cosmetics industry as alternative test substrates in order to replace animal models. Today a huge variety of 3D human skin models exist, covering a multitude of scientific and/or technical demands. This review summarizes and discusses different approaches of skin model development and sets them into the context of drug development. Although human skin models have become indispensable for the cosmetics industry, they have not yet started their triumphal procession in pharmaceutical research and development. For drug development these tissue models may be of particular interest for a) systemically acting drugs applied on the skin, and b) drugs acting at the site of application in the case of skin diseases or disorders. Although quite a broad spectrum of models covering different aspects of the skin as a biologically acting surface exists, these are most often single stand-alone approaches. In order to enable the comprehensive application into drug development processes, the approaches have to be synchronized to allow a cross-over comparison. Besides the development of biological relevant models, other issues are not less important in the context of drug development: standardized production procedures, process automation, establishment of significant analytical methods, and data correlation. For the successful routine use of engineered human skin models in drug development, major requirements were defined. If these requirements can be accomplished in the next few years, human organotypic skin models will become indispensable for drug development, too.

Engineering kidneys from simple cell suspensions: an exercise in self-organization.

Increasing numbers of people approaching and living with end-stage renal disease and failure of the supply of transplantable kidneys to keep pace has created an urgent need for alternative sources of new organs. One possibility is tissue engineering of new organs from stem cells. Adult kidneys are arguably too large and anatomically complex for direct construction, but engineering immature kidneys, transplanting them, and allowing them to mature within the host may be more feasible. In this review, we describe a technique that begins with a suspension of renogenic stem cells and promotes these cells' self-organization into organ rudiments very similar to foetal kidneys, with a collecting duct tree, nephrons, corticomedullary zonation and extended loops of Henle. The engineered rudiments vascularize when transplanted to appropriate vessel-rich sites in bird eggs or adult animals, and show preliminary evidence for physiological function. We hope that this approach might one day be the basis of a clinically useful technique for renal replacement therapy.

An improved method of renal tissue engineering, by combining renal dissociation and reaggregation with a low-volume culture technique, results in development of engineered kidneys complete with loops of Henle.

BACKGROUND: Tissue engineering of functional kidney tissue is an important goal for clinical restoration of renal function in patients damaged by infectious, toxicological, or genetic disease. One promising approach is the use of the self-organizing abilities of embryonic kidney cells to arrange themselves, from a simply reaggregated cell suspension, into engineered organs similar to fetal kidneys. The previous state-of-the-art method for this results in the formation of a branched collecting duct tree, immature nephrons (S-shaped bodies) beside and connected to it, and supportive stroma. It does not, though, result in the significant formation of morphologically detectable loops of Henle - anatomical features of the nephron that are critical to physiological function. METHODS: We have combined the best existing technique for renal tissue engineering from cell suspensions with a low-volume culture technique that allows intact kidney rudiments to make loops of Henle to test whether engineered kidneys can produce these loops. RESULTS: The result is the formation of loops of Henle in engineered cultured 'fetal kidneys', very similar in both morphology and in number to those formed by intact organ rudiments. CONCLUSION: This brings the engineering technique one important step closer to production of a fully realistic organ.