Integer Topological Defects Reveal Antisymmetric Forces in Active Nematics.

Area of Science:

• Physics, Biophysics
• Cell Biology
• Materials Science

Background:

• Active nematics are typically classified as contractile or extensile.
• Neural progenitor cells with topological defects challenge this binary classification.
• Understanding cell behavior in active nematics is crucial for developmental biology and tissue engineering.

Purpose of the Study:

• To investigate the behavior of cells within active nematics, particularly around topological defects.
• To reconcile experimental observations of cell accumulation at +1 defects with existing theories.
• To propose a unified framework for understanding active nematic behavior.

Main Methods:

• Particle-level modeling of cellular active nematics.
• Development and analysis of a derived continuum theory.
• Qualitative comparison of model predictions with experimental data on neural progenitor cells.

Main Results:

• Both particle-level models and continuum theory reproduce cell accumulation at +1 topological defects.
• Cellular accumulation is attributed to two previously overlooked antisymmetric active forces.
• The findings apply to all types of +1 defects, irrespective of nematic classification.

Conclusions:

• Antisymmetric active forces are key drivers of cell behavior in active nematics.
• This work provides a unified explanation for cell accumulation at topological defects.
• The findings have implications for understanding cellular active nematics in various biological and engineered systems.