Viscocapillary instability in cellular spheroids

We describe a viscocapillary instability that can perturb the spherical symmetry of cellular aggregates in culture, also called multicellular spheroids. In condition where cells constituting spheroid get their necessary metabolites from immediate, outer microenvironment, permanent cell flow exists within its rim divide toward core they die. A perturbation induces viscous shear stresses tissue destabilise aggregate. The proposed is nature and does not rely on external heterogeneities, such as pre-existing pattern blood vessels or presence substrate which exert pulling forces. It arises for sufficiently large cell-cell adhesion strengths, cell-renewal rates, metabolite supplies, described by our model parameters. Since spheroids culture are good systems small, avascular tumours, mimicking concentration gradients found vivo, we speculate description applies to microtumour instabilities cancer progression.