Permeability studies across epithelial barriers are of primary importance in drug delivery as well as in toxicology. However, traditional in vitro models do not adequately mimic the dynamic environment of physiological barriers. Here, we describe a novel two-chamber modular bioreactor for dynamic in vitro studies of epithelial cells. The fluid dynamic environment of the bioreactor was characterized using computational fluid dynamic models and measurements of pressure gradients for different combinations of flow rates in the apical and basal chambers. Cell culture experiments were then performed with fully differentiated Caco-2 cells as a model of the intestinal epithelium, comparing the effect of media flow applied in the bioreactor with traditional static transwells. The flow increases barrier integrity and tight junction expression of Caco-2 cells with respect to the static controls. Fluorescein permeability increased threefold in the dynamic system, indicating that the stimulus induced by flow increases transport across the barrier, closely mimicking the in vivo situation. The results are of interest for studying the influence of mechanical stimuli on cells, and underline the importance of developing more physiologically relevant in vitro tissue models. The bioreactor can be used to study drug delivery, chemical, or nanomaterial toxicity and to engineer barrier tissues.

Cell culture is the workhorse of biologists, toxicologists, tissue engineers and a whole host of research fields in both academia and industry. Having explored individual molecular mechanisms inside cells for decades using traditional cell culture techniques, researchers have only just begun to appreciate that the intricate interconnectivity between cells and cellular networks as well as with the external environment is far more important to cellular orchestration than are single molecular events inside the cell. For example many questions regarding cell, tissue, organ and system response to drugs, environmental toxins, stress and nutrients cannot possibly be answered by concentrating on the minutiae of what goes on in the deepest recesses of single cells. New models are required to investigate cellular cross-talk between different cell types and to construct complex in-vitro models to properly study tissue, organ and system interaction without resorting to animal experiments. This chapter describes how tissue and organ models can be developed using the Quasi-Vivo system and discusses how they may be used in drug toxicity studies.

Intelligent in vitro models able to recapitulate the physiological interactions between tissues in the body have enormous potential as they enable detailed studies on specific two-way or higher order tissue communication. These models are the first step toward building an integrated picture of systemic metabolism and signaling in physiological or pathological conditions. However, the rational design of in vitro models of cell–cell or cell–tissue interaction is difficult as quite often cell culture experiments are driven by the device used, rather than by design considerations. Indeed, very little research has been carried out on in vitro models of metabolism connecting different cell or tissue types in a physiologically and metabolically relevant manner. Here, we analyze the physiological relationship between cells, cell metabolism, and exchange in the human body using allometric rules, downscaling them to an organ-on-a-plate device. In particular, in order to establish appropriate cell ratios in the system in a rational manner, two different allometric scaling models (cell number scaling model and metabolic and surface scaling model) are proposed and applied to a two compartment model of hepatic-vascular metabolic cross-talk. The theoretical scaling studies illustrate that the design and hence relevance of multi-organ models is principally determined by experimental constraints. Two experimentally feasible model configurations are then implemented in a multi-compartment organ-on-a-plate device. An analysis of the metabolic response of the two configurations demonstrates that their glucose and lipid balance is quite different, with only one of the two models recapitulating physiological-like homeostasis. In conclusion, not only do cross-talk and physical stimuli play an important role in in vitro models, but the numeric relationship between cells is also crucial to recreate in vitro interactions, which can be extrapolated to the in vivo reality.