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Mechanical characterisation of biological cells and biofunctional interfaces

Czajor, Julian Angel

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Biological cells sense the mechanical properties of their surrounding environment and adapt their shape and function. Moreover, the mechanical properties of cells and tissues tightly correlate with their functions. The main thrust of this thesis is to quantitatively determine the mechanical proper- ties of cells and cell-repellent coating materials by the combination of unique experimental techniques by covering different spatio-temporal domains. In chapter 7 the viscoelastic shape relaxation of malaria-infected human red blood cells with a di- ameter of about 10 μm was monitored by the combination of a custom-designed microfluidic device and a high-speed imaging platform under collaboration with Prof. Dr. M. Lanzer (Center for Inte- grative Infectious Diseases, Heidelberg University). Using the binarised cell rims extracted from the live-cell images, the shape recovery of red blood cells upon the ejection from the narrow constriction was monitored with a time resolution of 30 μs per frame. The mechanical responses of the malaria- infected red blood cells were monitored through the entire life cycle of parasites. The systematic comparison of the red blood cells with genetically mutated hemoglobin (hemoglobinopathie) with normal red blood cells indicated a less pronounced change in the relaxation time in hemoglobinopa- thetic red blood cells, which might correlate with delayed protein synthesis in hemoglobinopathetic red blood cells. In chapter 8 the film elastic properties and internal structures of the monolayers of oligoethylene glycol-based dendrons for the coating of iron-oxide nanoparticles were studied by the combination of high energy X-ray reflectivity and high-speed atomic force microscopy. To achieve higher film sta- bility in blood stream, the dendrons, synthesized by the group of Prof. Dr. Felder-Flesch (Institut de Physique et Chimie des Materiaux , Univ. Strasbourg) were coupled to the oxide surface via two phosphonate groups. The interfacial force measurements were performed on planar silicon dioxide surfaces instead of iron oxide nanoparticle surfaces due to the technical limitations. The internal structures of dendron monolayers in water were probed by high energy specular X-ray reflectivity. An analytical model considering the transition from a soft layer to a hard layer was introduced to cal- culate the Young’s modulus from nm-thick monolayers. To gain deeper insights into the interfacial force interactions, the coarse-scale surface force-distance curves were measured by a cell-sized particle attached to an atomic force cantilever cantilever, while the size and distribution of nanoscopic pin- ning centers were monitored by fast force mapping with a pixel rate of 200 Hz. The capability of the dendron coating to prevent the platelet aggregation was assessed by observing the non-specific adhesion of human platelets on dendron-coated substrates. The dynamic uptake and localisation of fluorescent dendron-coated iron oxide nanoparticles into hypoxic mouse breast cancer cells was tracked using fluorescence imaging and cryo-transmission electron microscopy. Together, these meth- ods revealed a continuous uptake of iron oxide nanoparticles into in intracellular compartments such as endosomes via endocytosis. The iron oxide particles were found either agglomerated or as single nanoparticles.

Document type: Dissertation
Supervisor: Tanaka, Prof. Dr. Motomu
Place of Publication: Heidelberg
Date of thesis defense: 7 June 2023
Date Deposited: 06 Jul 2023 09:08
Date: 2023
Faculties / Institutes: The Faculty of Physics and Astronomy > Institute of Physics
DDC-classification: 500 Natural sciences and mathematics
530 Physics
540 Chemistry and allied sciences
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