Magnetic Flattening of Stem-Cell Spheroids Indicates a Size-Dependent Elastocapillary Transition

Institut Lumiere Matiere, UMR 5306, Universite Lyon 1-CNRS, Universite de Lyon, 69622 Villeurbanne cedex, France(Received 24 July 2014; revised manuscript received 5 December 2014; published 4 March 2015)Cellular aggregates (spheroids) are widely used in biophysics and tissue engineering as modelsystemsforbiologicaltissues.InthisLetterweproposenovelmethodsformoldingstem-cellspheroids,deforming them, and measuring their interfacial and elastic properties with a single method based oncell tagging with magnetic nanoparticles and application of a magnetic field gradient. Magneticmolding yields spheroids of unprecedented sizes (up to a few mm in diameter) and preserves tissueintegrity. On subjecting these spheroids to magnetic flattening (over150g), we observed a size-dependent elastocapillary transition with two modes of deformation: liquid-drop-like behavior forsmall spheroids, and elastic-sphere-like behavior for larger spheroids, followed by relaxation to aliquidlike drop.