Coherent Timescales and Mechanical Structure of Multicellular Aggregates

Area of Science:

• Biophysics
• Developmental Biology
• Cellular Mechanics

Background:

• Multicellular aggregates serve as models for studying tissue biomechanics in embryonic development and cancer.
• While long-timescale behaviors (hours) involve cell rearrangements and liquid-like properties, short-timescale mechanics (seconds to minutes) remain less understood.

Purpose of the Study:

• To investigate the structural characteristics of multicellular aggregates at short timescales using shape relaxation.
• To identify and characterize the inherent timescales governing the mechanical response of these aggregates.
• To correlate these timescales with specific mechanical properties and relate them to cellular-level regulation.

Main Methods:

• Utilizing shape relaxation experiments on multicellular aggregates.
• Analyzing the mechanical response over short timescales (seconds to tens of seconds).
• Applying mathematical theory to link observed timescales with tissue-level mechanical properties (surface tension, elastic modulus, viscosity).

Main Results:

• Discovery of two universal, conserved timescales (seconds and tens of seconds) in aggregate mechanical response.
• Identification of a unique structural characteristic: a strong envelope with a soft interior (low bulk elastic modulus).
• Demonstration of proportional relationships between tissue surface tension, elastic modulus, and viscosity.

Conclusions:

• The identified timescales and structural properties are conserved across species, suggesting fundamental biomechanical principles.
• The strong envelope/soft interior structure provides both integrity and flexibility for tissue remodeling.
• Proportionalities in tissue properties imply precise coregulation of cellular-level tensions at interfaces.