Mobility of Active Particle on Adhesive Surfaces at Nano- and Micro-Scales

Self-propelled active particles capable of transducing energy to drive self-motion have enormous potentials in many applications such as cancer treatment and drug delivery. To understand the mobility of active particles at nano- and micro-scales, we performed molecular dynamics simulations of an active particle in contact with a rigid substrate. The active particle consists of a soft gel-like shell filled with a mixture of active and inactive beads. The transduction of the energy from active beads to the elastic shell could lead to stationary, steady rolling, and accelerating state depending on the strength of shell-substrate adhesion and the magnitude of external forces acting on active beads. In the stationary state, the limiting friction is larger than the external force generated by active beads and the active particle sticks to the substrate. In the steady rolling state, the rolling friction balances the driving force and active particle maintains a constant rolling speed. In this regime the elastic shell has a constant contact area with the substrate. In the accelerating state, the external driving force exceeds the friction force and the contact area of the elastic shell with the substrate decreases with increasing particle acceleration.