Cell-cell separation device: A new approach to measuring intercellular detachment forces.

Whether at the molecular or cellular scale in organisms, cell-cell adhesion adapts to external mechanical cues arising from the static environment of cells and from dynamic interactions between neighboring cells. Cell-cell adhesion needs to resist detachment forces to secure the integrity and internal organization of organisms. In the past, various techniques have been developed to characterize adhesion properties of molecules and cells in vitro and to understand how cells sense and probe their environment. Atomic force microscopy and dual-pipette aspiration, where cells are mainly present in suspension, are common methods for studying detachment forces of cell-cell adhesion. How cell-cell adhesion forces are developed for adherent and environment-adapted cells, however, is less clear. Here, we designed the Cell-Cell Separation Device (CC-SD), a microstructured substrate that provides a step toward measuring both the intercellular forces and external stresses of cells toward the substrate. The device is based on micropillar arrays, originally developed for cell traction-force measurements. We designed PDMS micropillar-blocks, to which cells could adhere and be able to connect to each other across the gap. Controlled stretching of the whole substrate changed the distance between blocks and increased the gap size. This allowed us to apply strains to cell-cell contacts, eventually leading to cell-cell adhesion detachment, which was measured by pillar deflections. The CC-SD provided an increase in the gap between the blocks of up to 2.4-fold, which was sufficient to separate substrate-attached cells with a fully developed F-actin network. Simultaneously measured pillar deflections allowed us to address cellular response to the intercellular strain applied. The CC-SD thus opens up possibilities for the analysis of intercellular detachment forces and sheds light on the robustness of cell-cell adhesion against rupture in dynamic processes during tissue development.