Vertex model with internal dissipation enables sustained flows

Area of Science:

• Biophysics
• Developmental Biology
• Cellular Mechanics

Background:

• Epithelial tissue flows are driven by complex intra- and inter-cellular mechanical forces.
• Cell shape anisotropy, or nematic order, is increasingly recognized for its role in tissue dynamics.
• Many early-stage embryos exhibit epithelia not supported by substrates, where internal viscous dissipation is dominant.

Purpose of the Study:

• To extend active nematic vertex models by incorporating internal viscous dissipation.
• To investigate the emergence of long-range velocity correlations and spatiotemporal organization in epithelial tissues.
• To link cell-level vertex models to continuum active nematics for understanding tissue flow.

Main Methods:

• Developed an active nematic vertex model.
• Replaced substrate friction with internal viscous dissipation.
• Simulated epithelial sheets confined to a channel.

Main Results:

• Internal viscous dissipation, coupled with cell shape anisotropy, enables long-range velocity correlations.
• Demonstrated sustained tissue flow in confined epithelial sheets.
• Showed spontaneous emergence of highly organized spatiotemporal flows.

Conclusions:

• Internal viscous dissipation is a key factor in generating organized tissue flows in substrate-free epithelia.
• The model provides a mechanistic link between cell-level dynamics and continuum active nematics.
• This mechanism may explain large-scale collective cell migration observed during morphogenesis.