Rolling Dynamics of Nanoscale Elastic Shells Driven by Active Particles

Self-propelled elastic shells capable of transducing energy to rolling motion could have potential applications as drug delivery vehicles. To understand the dynamics of the nanoscale elastic shells, we performed molecular dynamics simulations of elastic shells filled with a mixture of active and passive beads in contact with an elastic substrate. The energy transduction from active beads to elastic shell results in stationary, steady rolling, and accelerating states. In stationary state, the torque produced by friction force in the contact area balances that due to the external force generated by the active beads and the shell sticks to the substrate. In steady rolling state, rolling friction force balances the driving force, and the shell maintains a constant rolling velocity. Theoretical analysis shows a universal scaling relationship between the magnitude of driving force and shell velocity. This is a manifestation of viscoelastic nature of shell skin deformation dynamics during rolling motion. In accelerating state, energy supplied to the system by active beads exceeds the energy dissipation due to viscoelastic shell deformation in the contact area. Furthermore, the contact area of the shell with substrate decreases with increasing shell instantaneous velocity.