Shape and Displacement Fluctuations in Soft Vesicles Filled by Active Particles.

Area of Science:

• Soft matter physics
• Biophysics
• Computational modeling

Background:

• Vesicles are fundamental biological structures.
• Active particles introduce self-propulsion and complex dynamics.
• Understanding active vesicle behavior is key to cell mechanics.

Purpose of the Study:

• To numerically investigate the dynamics of shape and displacement fluctuations in 2D flexible vesicles filled with active particles.
• To explore how active particle concentration affects vesicle morphology and movement.
• To analyze the relationship between vesicle shape, particle distribution, and emergent motility.

Main Methods:

• Numerical simulations of 2D flexible vesicles.
• Modeling of active particles with self-propulsion.
• Analysis of particle concentration effects on vesicle shape, curvature, and pressure.
• Tracking vesicle center-of-mass motion and diffusivity.

Main Results:

• At low concentrations, active particles accumulate at the boundary, forming high-density, high-curvature pinched spots.
• At high concentrations, particles distribute uniformly, leading to near-circular shapes with homogeneous pressure and curvature.
• Vesicle shape transitions (polarized to spherical) are controlled by the number of active particles.
• Vesicle center-of-mass exhibits persistent random walk, with enhanced diffusivity for elongated active particles due to orientational correlations.
• Shape-shifting induces directional sensing, leading to spontaneous migration along the polarization direction.

Conclusions:

• Active particle concentration is a critical factor governing active vesicle shape and dynamics.
• The interplay between particle distribution, vesicle shape, and active forces drives emergent motility.
• Active vesicles can exhibit self-propelled motion and directional sensing, mimicking cellular behavior.