Abstract

Controlled locomotion on micro- or nanometer scales is of great interest for both, cell biology and microrobotics. In the former case, one aims to understand the swimming motion of microorganisms and cell motility. In the latter case, the goals are control and design of microrobots optimized for a variety of biomedical app- lications. We focus here on the propulsion of a liquid droplet which is driven by an encapsulated active device. Two driving mechanisms are discussed in detail: a collection of point forces representing an autonomous swimmer and a squirmer. In addition to self-propulsion, we also consider additional application of external forces or torques, which are necessary for a controlled locomotion of droplet and encapsulated device. The big advantage of self-propulsion is that energy can be supplied by the surroundings; the main disadvantage is lack of control. There- fore a combination of both, self-propulsion and actuation by external fields, is a promising candidate to achieve optimal control of an otherwise self-propelled composite device.