Viewpoint Cellular aggregates under pressure

It is widely accepted by now that the mechanical characteristics of cells and tissues play an important role in numerous biological processes, such as early morphogenesis [1, 2], signal transduction [3], cell adhesion [4], and even stem cell differentiation [5, 6]. In particular, it was suggested and experimentally demonstrated that a number of phenomena in embryonic tissues can be interpreted through their viscoelastic properties [7]. Tissue mechanical properties have often been quantified by measurements using spherical aggregates of cells (as models of tissues) and parallel-plate tensiometry [8]. In this technique the aggregates are exposed to a fixed strain by compression between the plates and the viscoelastic parameters such as surface tension (γ), elastic constant (E), and viscosity (η) are determined from the relaxation of the compressive force (i.e., stress) to equilibrium. In a work published in Physical Review Letters[9], Karine Guevorkian and collaborators from CNRS-Institut Curie and Ecole Polytechnique, both in France, and McMaster University, Canada, use, for the first time, micropipette aspiration—a method normally applied to individual cells—to test the mechanical behavior of multicellular spheroids and to determine γ, E, and η.