Dynamics of an Ellipsoidal Active Particle Wrapping by a Giant Unilamellar Vesicle

Engulfment of self-propelled particles by biological membranes is ubiquitous in cellular life. The particles can be very small organisms such as rod-shaped pathogenic bacteria that have the capacity to cause diseases in humans or artificially made active particles such as Janus colloids. In this article, we investigate the wrapping dynamics of an ellipsoidal self-propelled particle by a giant unilamellar vesicle (GUV). Within the Canham-Helfrich theory of membranes, the free energy of wrapping is derived. We found that the system exhibits a first-order transition from partially to completely wrapped states due to the active force generated by the particle. In addition, increasing the particle size and the adhesive energy, or decreasing the membranes's spontaneous curvature, can reduce the energy barrier. The kinetics of wrapping is studied in the framework of Onsager's variational principle. For small particles, the wrapping time is found to be minimum for the membranes with negative spontaneous curvature. Also, our phase diagrams suggest that the wrapping time can be reduced by increasing the active force for small particles, but this effect is hardly seen for large particles.