Viscoelastic dynamics of spherical composite vesicles.

Area of Science:

• * Biophysics
• * Materials Science
• * Mechanical Engineering

Background:

• * Composite vesicles (CVs) exhibit complex mechanical properties.
• * Understanding their low-frequency dynamics is crucial for various biological and material applications.
• * Existing models often simplify vesicle geometry, neglecting crucial solid-like viscoelastic effects.

Purpose of the Study:

• * To develop a micromechanical model for the low-frequency dynamics of spherical composite vesicles (CVs).
• * To investigate the influence of solid-like viscoelastic properties on vesicle motion.
• * To compare the dynamics of spherical CVs with flat membranes.

Main Methods:

• * Derivation of equations of motion for a CV in a viscous liquid.
• * Analysis of discrete solutions representing coupled stretching, bending, and shear modes.
• * Calculation of power spectra for experimental comparison.

Main Results:

• * Identified discrete solutions for linearly coupled stretching and bending relaxation modes, plus an independent shear mode.
• * Demonstrated qualitative differences in bending modes between spherical vesicles and flat membranes.
• * Showcased the significant contribution of shear elasticity to bending relaxation at low wave numbers.
• * Revealed that bending modes in spherical vesicles involve both radial and tangent displacements, unlike flat membranes.

Conclusions:

• * The proposed model accurately describes the low-frequency dynamics of spherical composite vesicles.
• * Shear elasticity plays a critical role in the bending relaxation of CVs.
• * Spherical CVs exhibit distinct in-plane and out-of-plane responses compared to flat membranes.
• * Theoretical predictions are validated against experimental data through power spectra analysis.