Fluidization of epithelial sheets by active cell rearrangements

Area of Science:

• Biophysics
• Developmental Biology
• Soft Matter Physics

Background:

• Epithelial tissues exhibit complex behaviors, including fluidization, crucial for development and wound healing.
• Cell-cell junction geometry and dynamics play a key role in tissue mechanics and morphogenesis.
• Understanding active processes driving tissue rearrangements is essential for predicting tissue-level responses.

Purpose of the Study:

• To theoretically investigate the fluidization of epithelial tissues driven by active T1 neighbor exchanges.
• To elucidate the relationship between cell junction geometry, active noise, and tissue mechanical properties.
• To establish a link between cell rearrangement dynamics and macroscopic tissue behavior, such as viscosity.

Main Methods:

• Utilizing an elastic theory of T1 transformations to analyze cell-cell junction geometry.
• Employing a 3D vertex model to simulate tissue dynamics under active noise and external forces.
• Developing a coarse-grained theory to model the tissue as an active fluid.

Main Results:

• Cell-cell junction geometry provides insights into the local energy landscape of T1 transformations.
• The timescale of stress relaxation in tissues is governed by the level of active noise driving cell rearrangements.
• Epithelial tissues exhibit a transition from solid-like to fluid-like behavior over time, with effective viscosity scaling with the rate of active T1 transformations.
• Results from the vertex model are corroborated by the coarse-grained active fluid theory.

Conclusions:

• Active T1 neighbor exchanges are a fundamental mechanism for epithelial tissue fluidization.
• Tissue mechanical properties, including viscosity, are dynamically regulated by the rate of active cell rearrangements.
• The study provides a theoretical framework linking microscopic cell behaviors to macroscopic tissue dynamics, with implications for understanding tissue morphogenesis and disease.