Modular microfluidic systems cast from 3D-printed molds for imaging leukocyte adherence to differentially treated endothelial cultures

Microfluidic systems are very useful for in vitro studies of interactions between blood cells and vascular endothelial cells under flow, and several commercial solutions exist. However, the availability of customizable, user-designed devices is largely restricted to researchers with expertise in photolithography and access to clean room facilities. Here we describe a strategy for producing tailor-made modular microfluidic systems, cast in PDMS from 3D-printed molds, to facilitate studies of leukocyte adherence to endothelial cells. A dual-chamber barrier module was optimized for culturing two endothelial cell populations, separated by a 250 μm wide dividing wall, on a glass slide. In proof-of-principle experiments one endothelial population was activated by TNFα, while the other served as an internal control. The barrier module was thereafter replaced with a microfluidic flow module, enclosing both endothelial populations in a common channel. A suspension of fluorescently-labeled leukocytes was then perfused through the flow module and leukocyte interactions with control and TNFα-treated endothelial populations were monitored in the same field of view. Time-lapse microscopy analysis confirmed the preferential attachment of leukocytes to the TNFα-activated endothelial cells. We conclude that the functionality of these modular microfluidic systems makes it possible to seed and differentially activate adherent cell types, and conduct controlled side-by-side analysis of their capacity to interact with cells in suspension under flow. Furthermore, we outline a number of practical considerations and solutions associated with connecting and switching between the microfluidic modules, and the advantages of simultaneously and symmetrically analyzing control and experimental conditions in such a microfluidic system.