Microswimmers modeling for drug delivery



Many types of motile cells, such as the bacteria in our gut and spermatozoa in the female reproductive organs, have to move through confined spaces filled with viscous fluid. In recent years, the movement of these ‘microswimmers’ has been mimicked in the design of self-propelled micro and nanoscale machines for applications such as targeted drug delivery. Optimizing the design of these machines requires a detailed, mathematical understanding of microswimmers in these environments. A large, international group of physicists led by Abdallah Daddi-Moussa-Ider of Heinrich-Heine-Universität Düsseldorf, Germany has now generated mathematical models of microswimmers in clean and surfactant-coated viscous droplets, demonstrating that the surfactant’s behavior the swimmers changes significantly. . They have published their work in EPJ E.

The dynamics of microswimmers moving in a drop of viscous liquid depends on many things, including the shape and size of the drop, the number of microswimmers and the Reynolds number of the liquid. This is a measure of viscosity; liquids with a low Reynolds number are more viscous and flow linearly with little turbulence. The flow of such a fluid can be modeled by solving a series of partial differential equations known as the Navier-Stokes equations. In this case, the microswimmer itself was considered a force dipole trapped in the drop and at some point. The presence of a surfactant layer around the microswimmer droplet was modeled using boundary conditions.

By solving these equations under different conditions – droplets with or without surfactant layers, stationary and free-moving, and with different Reynolds numbers and radii – Daddi-Moussa-Ider and his colleagues gave a series of subtly different flow fields, from which the dynamics of the microswimmer could be defined. They note that these models of swimmer dynamics can be useful in the design of micro-machines for material assembly, biosensors and microsurgery, as well as for drug delivery.

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Reference

AR Sprenger, VA Shaik, AM Ardekani, M. Lisicki, AJTM Mathijssen, F. Guzmán-Lastra, H. Löwen, AM Menzel, and A. Daddi-Moussa-Ider (2020), Towards an analytical description of active microswimmers in clean and surfactant-coated droplets, EUR. Phys. J. E 43:58. https: //doi.org /10.1140 /flexibility /i2020-11980-9

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