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- ItemMesoporous Coatings with Simultaneous Light‐Triggered Transition of Water Imbibition and Droplet Coalescence(Weinheim : Wiley-VCH, 2021) Khalil, Adnan; Rostami, Peyman; Auernhammer, Günter K.; Andrieu‐Brunsen, AnnetteA systematic study of gating water infiltration and condensation into ceramic nanopores by carefully adjusting the wetting properties of mesoporous films using photoactive spiropyran is presented. Contact angle measurements from the side reveal significant changes in wettability after irradiation due to spiropyran/merocyanine-isomerization, which induce a wetting transition from dry to wet pores. The change in wettability allows the control of water imbibition in the nanopores and is reflected by the formation of an imbibition ring around a droplet. Furthermore, the photoresponsive wettability is able to overcome pinning effects and cause a movement of a droplet contact line, facilitating droplet coalescence, as recorded by high-speed imaging. The absorbed light not only effectuates droplet merging but also causes flows inside the drop due to heat absorption by the spiropyran, which results in gradients in the surface tension. IR imaging and particle tracking is used to investigate the heat absorption and temperature-induced flows, respectively. These flows can be used to manipulate, for example, molecular movement inside water and deposition inside solid mesoporous materials and are therefore of great importance for nanofluidic devices as well as for future water management concepts, which include filtering by imbibition and collection by droplet coalescence. © 2021 The Authors. Advanced Materials Interfaces published by Wiley-VCH GmbH
- ItemSperm-Driven Micromotors Moving in Oviduct Fluid and Viscoelastic Media(Weinheim : Wiley-VCH, 2020) Striggow, Friedrich; Medina-Sánchez, Mariana; Auernhammer, Günter K.; Magdanz, Veronika; Friedrich, Benjamin M.; Schmidt, Oliver G.Biohybrid micromotors propelled by motile cells are fascinating entities for autonomous biomedical operations on the microscale. Their operation under physiological conditions, including highly viscous environments, is an essential prerequisite to be translated to in vivo settings. In this work, a sperm-driven microswimmer, referred to as a spermbot, is demonstrated to operate in oviduct fluid in vitro. The viscoelastic properties of bovine oviduct fluid (BOF), one of the fluids that sperm cells encounter on their way to the oocyte, are first characterized using passive microrheology. This allows to design an artificial oviduct fluid to match the rheological properties of oviduct fluid for further experiments. Sperm motion is analyzed and it is confirmed that kinetic parameters match in real and artificial oviduct fluids, respectively. It is demonstrated that sperm cells can efficiently couple to magnetic microtubes and propel them forward in media of different viscosities and in BOF. The flagellar beat pattern of coupled as well as of free sperm cells is investigated, revealing an alteration on the regular flagellar beat, presenting an on–off behavior caused by the additional load of the microtube. Finally, a new microcap design is proposed to improve the overall performance of the spermbot in complex biofluids. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim