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Andreas Fery: „Complex particles- micromechanics and motility”
Physikalische Chemie II, Universität Bayreuth

Modern colloid chemistry allows producing colloidal objects of increasing complexity, that start showing features reminiscent of biological objects like cells. We give an overview of recent developments with a focus on responsive microcapsules and motile particles:

Using the layer-by-layer electrostatic self-assembly of polyelectrolytes, hollow microcapsules with diameters on the micron- and wall thicknesses on the sub-micron scale can be produced in a well defined fashion. We introduce novel experiments that allow investigating the mechanical properties of individual microcapsules. We observe that the deformation properties of the microcapsules can be tailored and show pronounced response towards parameters like pH, salt concentration and temperature. We discuss consequences of these findings for potential applications as well as fundamental understanding of the forces stabilizing the walls.

In the second part, we present recent results on motile microparticles. We use an in vitro system derived from listeria monocytes, which is a robust example of biomimetic motility. Listeria are parasitic bacteria that make use of the infected cells’ actin-machinery. They are propelled by a polymerizing / depolymerzing actin gel that is nucleated on their surface. As the proteins involved in this process are well-known and can be isolated, the principle of motion can be studied in vitro using coated particles. We discuss findings on the trajectories which show "circle swimming" - potentially a generic feature of active motility - as well as measurements of the forces generated in the process under confinement.