Modelling of 3D spatially controlled compartmentalized tissues in microfluidics

Organs-on-chip have been widely addressed as potential tools for recreating tissue structure and functions within microdevices. In perspective, the possibility of engineering cellular threedimensional constructs with behaviour similar to physiological tissues or organs is a paramount aim for improving basic research studies and drug screening processes [1]. Biological functional structures are typically characterized by a compartmental architecture where multiple cellular units made up of different cell types and/or extracellular matrix are spatially organized to interact and contribute to biological homeostasis and function. Nevertheless, it is currently challenging to neatly interface multi-compartmental 3D biological constructs within microfluidic systems and there is a need for techniques that allow fine spatial control of 3D cell-laden matrices [2]. We here present a novel microfluidic technique for engineering complex micro-tissue structures made of controlled multi-compartmental three-dimensional cellular constructs. By employing molding PDMS layers, we show how to form pure composites of two stacked or flanking tissue constructs (made of human bone marrow-derived mesenchymal stem cells, Panel A and B) within existing microfluidic systems commonly used for controlled presentation of soluble factors (differentiation factors, drug compounds, etc.) or application of medium perfusion. We then applied this technique to form endothelialized constructs with vessel-like structures within microtissues. We demonstrate cell viability, continuity of composite constructs and endothelial barrier formation. As no confining structures (pillars or phaseguides) are present at the generated interfaces, this technique holds promise for advanced modelling of complex multi-compartmental tissues/organs and ongoing work is aimed at generating micro-tissues of relevant physiological structures (blood-brain barrier and osteochondral interface).