Microphysiological systems, also known as organ-on-a-chip systems, possess significant potential as organotypic models of human tissues, including vascular tissue interfaces that are ubiquitous throughout the human body. As microfluidic systems, organs-on-chips also possess significant untapped analytical potential. Cellular analysis in organs-on-chips, however, currently relies on standard methods designed for traditional in vitro cell culture vessels like microtiter plates. These methods disturb the cell culture environment, rely on multiple manual steps and are not designed to operate in small microfluidic volumes.

The aim of this thesis was to design and develop online cellular analysis methods that are suitable for integration into the organotypic microenvironment of microvessel-on-a-chip models. Cellular analysis methods for cell secretion and barrier function monitoring were specifically considered. For integrated cell secretion monitoring, a numerical study correlated physiological shear flow to biosensor reaction kinetics in a microfluidic vascular model with online biosensing. Three critical parameters (critical shear stress, Peclet and Biot numbers) in conjunction with the numerical analysis enabled the minimization of biosensor response times while preserving physiological shear flows. For integrated barrier function monitoring, endothelial permeability was measured online in a Transwell-based microfluidic vascular model using a novel electrochemical permeability assay. Unlike the standard fluorescence-based permeability assay, this enabled endothelial permeability to be measured directly on-chip inside an incubator without the need for manual sampling, or bulky and costly optical instrumentation. Finally, the electrochemical permeability assay was implemented in a hydrogel-based microfluidic vascular model with gel-embedded electrodes. Online endothelial permeability measurements were performed in a 3D culture environment, demonstrating the ability of the assay to operate in the low volume organotypic microenvironments characteristic of microphysiological systems. The miniaturized electrochemical format is furthermore suitable for parallelization and higher throughput analysis.

In summary, the integration of cellular analysis methods is critical to fulfilling the tremendous promise of microphysiological systems. The capability to perform multiparametric online analysis at the cellular level has the potential to set these systems apart from current models of the human organism.