Viscoelastic Properties of Living Embryonic Tissues: a Quantitative Study

Abstract

A number of properties of certain living embryonic tissues can be explained by considering them as liquids. Tissue fragments left in a shaker bath round up to form spherical aggregates, as do liquid drops. When cells comprising two distinct embryonic tissues are mixed, typically a nucleation-like process takes place, and one tissue sorts out from the other. The equilibrium configurations at the end of such sorting out phenomena have been interpreted in terms of tissue surface tensions arising from the adhesive interactions between individual cells. In the present study we go beyond these equilibrium properties and study the viscoelastic behavior of a number of living embryonic tissues. Using a specifically designed apparatus, spherical cell aggregates are mechanically compressed and their viscoelastic response is followed. A generalized Kelvin model of viscoelasticity accurately describes the measured relaxation curves for each of the four tissues studied. Quantitative results are obtained for the characteristic relaxation times and elastic and viscous parameters. Our analysis demonstrates that the cell aggregates studied here, when subjected to mechanical deformations, relax as elastic materials on short time scales and as viscous liquids on long time scales.

Self-Assembled Peptide Amphiphile Nanofibers and PEG Composite Hydrogels as Tunable ECM Mimetic Microenvironment

“…On the other hand, during bone development, cellular differentiation into bone forming osteoblasts occurs within a soft matrix in the range of 100−1000 Pa shear modulus. 64,65 Previous studies also showed that in vitro osteogenic differentiation can be supported on soft hydrogel matrices, which have similar stiffness to developing bone. 66,67 The gene expression results obtained from PA/PEG composite system also pointed to similar conclusions showing that the optimal design of a material for the desired cellular outcome requires the consideration of multiple factors since cells can sense complex niche cues, and these signals can direct cell fate in an interactive manner.…”

A Mathematical Model of Liver Cell Aggregation In Vitro

“…b measurements in (Forgacs et al, 1998) are for spherical aggregates of embryonic chick liver cells Thomas et al, 2005)). We estimate the packing density to be n * = 0.8 (see Powers et al (2002))…”

Computational modeling of morphogenesis regulated by mechanical feedback

“…Relatively few data are available for the mechanical properties of embryonic tissues (Forgacs et al, 1998;Davidson et al, 1999;Zamir et al, 2003;Zamir and Taber, 2004). Some measurements indicate that embryonic tissues are more linear than mature tissues, and some investigators have suggested that embryonic epithelia behave as a viscous fluid during the slow process of morphogenesis (Forgacs et al, 1998;Beysens et al, 2000).…”