On the Assembly of Actin Polymerization-Powered Motors

Nano- and micromotors are a class of active colloids that can self-propel outperforming Brownian motion. Polymer synthesis or degradation are alternative ways to enzyme-based or externally-driven strategies to induce self-propulsion in particles, but they are often limited due to the reaction conditions. Nature leverages biopolymerization reactions to sustain locomotion either of whole microorganisms or of organelles inside cells. With the aim of integrating natural locomotion strategies into engineered motors, we have begun to explore the propulsion mechanism of the food-borne pathogen Listeria monocytogenes, which expresses the actin-recruiting protein ActA on its surface to harness host cell actin polymerization for rapid intracellular movement. Here, we compare the locomotion of silica particles depending on the ActA immobilization strategy on the motor surface, using either homogeneous coatings, Janus-type coatings, or ActA immobilization within polymer brushes. An up to 5-fold increase in the propulsion of the motors compared to their Brownian motion is observed when Janus motors are considered. The motors orbit around or dock onto larger tracer particles depending on the environmental pH and on whether they are individuals or in clusters. Altogether, these motors illustrate how integration of concepts of the natural and synthetic world can yield unique engineered units.