Physical mechanisms of cell rearrangements : from tissue liquidity to artificial organ structures

Embryonic development represents a sequence of spectacular morphogenetic transformations involving intense cellular rearrangements. Although developmental patterning is under genetic control, a living organism acquires its final form through physical shape transformations, a particular one being based on the apparent liquid-like properties of tissues composed of adhesive and motile cells (e.g. embryonic tissues). The Differential Adhesion Hypothesis (DAH) provides the molecular basis for these properties, which in turn provide the biophysical basis for a number of morphogenetic processes (e.g. sorting, epithelial folding, convergent extension, etc.). In the present study we exploit these self-organizing properties to build functional 3D tissue constructs of prescribed shape. We demonstrate that tissue liquidity manifests also on the cellular level; the force relaxation under constant strain proceeds similarly to the mechanisms encountered in true liquids. Employing tissue liquidity, spherical cell aggregates were embedded contiguously into biocompatible gels creating templates for geometric configurations encountered in living organisms. Depending on the properties of the gels and the initial