Microengineered physiological biomimicry: Organs-on-Chips{ Dongeun Huh, ab Yu-suke Torisawa, a Geraldine A. Hamilton, a Hyun Jung Kim a and Donald E. Ingber* abc Received 23rd January 2012, Accepted 5th April 2012 DOI: 10.1039/c2lc40089h Microscale engineering technologies provide unprecedented opportunities to create cell culture microenvironments that go beyond current three-dimensional in vitro models by recapitulating the critical tissue–tissue interfaces, spatiotemporal chemical gradients, and dynamic mechanical microenvironments of living organs. Here we review recent advances in this field made over the past two years that are focused on the development of ‘Organs-on-Chips’ in which living cells are cultured within microfluidic devices that have been microengineered to reconstitute tissue arrangements observed in living organs in order to study physiology in an organ-specific context and to develop specialized in vitro disease models. We discuss the potential of organs-on-chips as alternatives to conventional cell culture models and animal testing for pharmaceutical and toxicology applications. We also explore challenges that lie ahead if this field is to fulfil its promise to transform the future of drug development and chemical safety testing. Introduction Understanding human pathophysiology requires investigation of how living cells and tissues function in the context of whole living organs. Organs are composed of different tissue types (e.g., blood vessels, immune system, nerves, lymphatics) organized in distinct three-dimensional (3D) arrangements. Tissues, in turn, are composed of groups of cells linked together by extracellular matrix (ECM) scaffolds and cell–cell junctions. In our bodies, cells also experience organ-specific dynamic variations in spatiotemporal chemical gradients and mechanical forces (e.g., cyclic strain, compression, fluid shear stresses) in their local tissue microenvironment that are crucial governors of their survival, growth, and function. Despite considerable technolo- gical advances, existing 2D and 3D culture models still fail to fully recapitulate these subtle organ-specific variations in the in vivo microenvironment. As a result, analysis of normal physiology and diseases processes commonly requires use of animal models, which are costly, slow, and questionable ethically; of even greater concern, is that they often fail to predict responses in humans. The limitations of existing cell culture and animal studies have provided an impetus for the development of alternative cell- based in vitro models that better mimic the complex structures and functions of living organs. Considerable advances have been made in this area as a result of the application of microsystems engineering for studies with cultured cells. Microfabrication techniques first developed to manufacture computer microchips have been adapted to enable precise control of cell shape, position, function, and tissue organization in highly structured 2D and 3D cell culture scaffolds. 1 Integration of microfabricated substrates with microfluidics technologies that enable precise control of dynamic fluid flows and pressures on the micrometer scale also has made it possible to create cell culture microenvir- onments that present cells (established human cell lines, primary cells or stem cells) with appropriate organ-relevant spatiotem- poral chemical gradients and dynamical mechanical cues, which can induce cells to express a more differentiated, normal phenotype. 2,3 These new capabilities that emerged from the convergence of microengineering with microfluidics and cell biology have led to development of ‘Organs-on-Chips’ that reconstitute the structural tissue arrangements and functional complexity of living organs using cells cultured in microfluidic devices with relevant microarchitecture and microenvironmental signals. These microfluidic organs-on-chips permit study of diverse biological processes in ways that are not possible using conventional 2D or 3D cell culture systems, or even animal models. 4–6 In this article, we provide an overview of progress made in this field over the past two years with a focus on the development and application of microengineered organomimetic microsystems for study of whole organ function and disease in vitro. We review engineering design principles and fabrication approaches that have enabled the creation of these biomimetic microsystems, which recreate minimal functional units of living organs that replicate their key structures and integrated functionalities. We also discuss the potential use of these ‘Organs-on-Chips’ for a Wyss Institute for Biologically Inspired Engineering at Harvard University, Boston, MA 02115, USA. E-mail: don.ingber@wyss.harvard.edu b Vascular Biology Program, Departments of Pathology & Surgery, Children’s Hospital Boston and Harvard Medical School, Boston, MA 02115, USA c School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA { Published as part of a LOC themed issue dedicated to research from the USA: Guest Editors Don Ingber and George Whitesides. Lab on a Chip Dynamic Article Links Cite this: Lab Chip, 2012, 12, 2156–2164 www.rsc.org/loc FRONTIER 2156 | Lab Chip, 2012, 12, 2156–2164 This journal is ß The Royal Society of Chemistry 2012 Downloaded on 02 September 2012 Published on 03 May 2012 on http://pubs.rsc.org | doi:10.1039/C2LC40089H View Online / Journal Homepage / Table of Contents for this issue