A large, international research team have provided insight into guiding principles for controlling confined active matter systems and supporting the use of synthetic microswimmers to drive drops for targeted drug delivery applications.
Microswimmers
Many actively swimming biological microorganisms and cells exist within organisms. These microorganisms (e.g. gut bacteria) and cells (e.g. spermatozoa) must propel themselves within confined environments filled with viscous liquid. In recent years, the motion of these ‘microswimmers’ has be exploited and mimicked to design self-propelled micro- and nano-scale machines for several applications, including targeted drug delivery.
The dynamics of microswimmers moving inside a drop of viscous liquid is dependent on many factors. This includes the shape and size of the drop, the number of microswimmers and the Reynolds number of the liquid. Reynolds number is a measure of viscosity. Liquids with a low Reynolds number are more viscous and flow in a linear manner with little turbulence. Optimising the design of these machines is important and requires a detailed and mathematical understanding of microswimmers within these environments.
Mathematical models
In this study, published in The European Physical Journal E, a group led by Abdallah Daddi-Moussa-Ider of Heinrich-Heine-Universität Düsseldorf, Germany, generated mathematical models of microswimmers in clean and surfactant-covered drops. The team found that the surfactant significantly altered the swimmers’ behaviour. Specifically, it enhanced the swimmers’ reorientation compared to that of a clean drop.
The results from this paper constitute a step towards understanding the complex dynamics from interactions within confined and complex environments. The team noted that these models of swimmer dynamics may be useful in better designing various systems, including drug delivery systems.
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