Biology subjects

Kirkpatrick, T. R.

Publications and source records attributed to Kirkpatrick, T. R..

2 recordsLinked to original sources

bioRxiv2022

On the origin of viscosity saturation at high densities during zebrafish morphogenesis

A recent experiment on zebrafish blastoderm morphogenesis showed that the viscosity ({eta}) of a non-confluent embryonic tissue grows sharply until a critical cell packing fraction ({phi}S). The increase in{eta} up to{phi} S is similar to the behavior observed in several glass forming materials, which suggests that the cell dynamics is sluggish or glass-like. Surprisingly,{eta} is a constant above{phi} S. To determine the mechanism of this unusual dependence of{eta} on{phi} , we performed extensive simulations using an agent-based model of a dense non-confluent two-dimensional tissue. We show that polydispersity in the cell size, and the propensity of the cells to deform, results in the saturation of the available free area per cell beyond a critical packing fraction. Saturation in the free space not only explains the viscosity plateau above{phi} S but also provides a relationship between equilibrium geometrical packing to the dramatic increase in the relaxation dynamics.

biophysics↗

bioRxiv2022

Topological transitions, turbulent-like motion and long-time-tails driven by cell division in biological tissues

The complex spatiotemporal flow patterns in living tissues, driven by active forces, have many of the characteristics associated with inertial turbulence even though the Reynolds number is extremely low. Analyses of experimental data from two-dimensional epithelial monolayers in combination with agent-based simulations show that cell division and apoptosis lead to directed cell motion for hours, resulting in rapid topological transitions in neighboring cells. These transitions in turn generate both long ranged and long lived clockwise and anticlockwise vortices, which gives rise to turbulent-like flows. Both experiments and simulations show that at long wavelengths the wave vector (k) dependent energy spectrum E(k) {approx} k-5/3, coinciding with the Kolmogorov scaling in fully developed inertial turbulence. Using theoretical arguments and simulations, we show that long-lived vortices lead to long-time tails in the velocity auto-correlation function, Cv(t) [~] t-1/2, which has the same structure as in classical 2D fluids but with a different scaling exponent.

biophysics↗