Integer topological defects of cell monolayers: Mechanics and flows.

Area of Science:

• Biophysics
• Soft Matter Physics
• Developmental Biology

Background:

• Anisotropic cell monolayers display long-range orientational order and topological defects.
• Cellular orientational order is crucial for morphogenesis during organism development.
• The mechanical properties of cell monolayers and their relation to topological defects are not well understood, especially at developmental timescales.

Purpose of the Study:

• To explore the linkage between cell monolayer mechanics and topological defects.
• To determine material parameters of cell monolayers using a physics-based approach.
• To investigate steady-state mechanical patterns at topological defects in active polar fluids.

Main Methods:

• Utilized a hydrodynamical description of an active polar fluid, drawing from liquid crystal physics.
• Incorporated three activity sources: cell-substrate traction forces, and anisotropic/isotropic active nematic stresses.
• Applied the model to C2C12 cell monolayers in circular confinements, forming aster or spiral defects.

Main Results:

• Analyzed velocity and orientational order fields in spiral defects.
• Examined force and cell number density fields in aster defects.
• Successfully determined mechanical parameters of C2C12 cell monolayers.

Conclusions:

• Topological defects in cell monolayers serve as powerful tools for mechanical characterization.
• This work provides a framework for understanding the mechanics of biological active matter.
• The findings offer insights into tissue morphogenesis by linking mechanics and topological organization.