Unlocking the Potential of Organ-on-Chip Models through Pumpless and Tubeless Microfluidics.

Microfluidic organs-on-chips are rapidly being developed toward eliminating the shortcomings of static in vitro models and better addressing basic and translational research questions. A critical aspect is the dynamic culture environment they provide. However, the associated inherent requirement for controlled fluid shear stress (FSS) and therefore the need for precise pumps limits their implementation. To address this issue, here a novel approach to manufacture pumpless and tubeless organs-on-chips is reported. It relies on the use of a hydrophilic thread to provide a driving force for the perfusion of the cell culture medium through constant evaporation in the controlled conditions of a cell incubator. Well-defined and tuneable flow rates can be applied by adjusting the length and/or diameter of the thread. This approach for the preparation of an intestine-on-chip model based on the Caco-2 cell line is validated. Five days culture under 0.02 dyn·cm-2 shear conditions yield monolayers similar to those prepared using a high-precision peristaltic pump. A pumpless device can also be used to delineate the effect of FSS on the phenotype of adenocarcinomic human alveolar basal epithelial A549 cells. It is anticipated that the pumpless approach will facilitate and herefore increase the use of organs-on-chips models in the future.

A systematic investigation of the effect of the fluid shear stress on Caco-2 cells towards the optimization of epithelial organ-on-chip models.

Epithelial cells experience constant mechanical forces, including fluid shear stress (FSS) on their apical surface. These forces alter both structure and function. While precise recapitulation of the complex mechanobiology of organs remains challenging, better understanding of the effect of mechanical stimuli is necessary towards the development of biorelevant in vitro models. This is especially relevant to organs-on-chip models which allow for fine control of the culture environment. In this study, the effects of the FSS on Caco-2 cell monolayers were systematically determined using a microfluidic device based on Hele-Shaw geometry. This approach allowed for a physiologically relevant range of FSS (from ∼0 to 0.03 dyn/cm2) to be applied to the cells within a single device. Exposure to microfluidic FSS induced significant phenotypical and functional changes in Caco-2 cell monolayers as compared to cells grown in static conditions. The application of FSS significantly altered the production of mucus, expression of tight junctions, vacuolization, organization of cytoskeleton, formation of microvilli, mitochondrial activity and expression of cytochrome P450. In the context of the intestinal epithelium, this detailed understanding of the effects of the FSS will enable the realization of in vitro organs-on-chip models with well-defined and tailored characteristics to a specific purpose, including for drug and nanoparticle absorption studies. The Hele-Shaw approach used in this study could be readily applied to other cell types and adapted for a wide range of physiologically relevant FSS.