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Micropatterned dry adhesives are promising candidates for the development of innovative adhesive platforms. Their reversible adhesion to various materials and surfaces has been reported over more than a decade. Switching between a strong and a weak adhesive state can be introduced by elastic buckling instabilities of the microstructure. In this work, we report on novel adhesive pads that exhibit micropatterned pillars on both sides. In double-sided PDMS micropatterns, the dimensions of the pillar structures were tuned by modulating the critical force for buckling during compressive loading. In this way, selective detachment of glass substrates was induced from one side of the pad. Our results indicate a significant switching efficiency of up to 83% between the strong and weak adhesive state. The new structures have high potential for emerging applications where temporary, double-sided fixations in combination with a predetermined detachment location are required.
Ultrafast high energy electron diffraction in reflection geometry is employed to study the structural dynamics of self-organized Germanium hut-, dome-, and relaxed clusters on Si(001) upon femtosecond laser excitation. Utilizing the difference in size and strain state the response of hut- and dome clusters can be distinguished by a transient spot profile analysis. Surface diffraction from {105}-type facets provide exclusive information on hut clusters. A pixel-by-pixel analysis of the dynamics of the entire diffraction pattern gives time constants of 40, 160, and 390 ps, which are assigned to the cooling time constants for hut-, dome-, and relaxed clusters.
Linear Chains of HER2 Receptors Found in the Plasma Membrane Using Liquid-Phase Electron Microscopy
(2018)
The spatial distribution of the human epidermal growth factor 2 (HER2) receptor in the plasma membrane of SKBR3 and HCC1954 breast cancer cells was studied. The receptor was labeled with quantum dot nanoparticles, and fixed whole cells were imaged in their native liquid state with environmental scanning electron microscopy using scanning transmission electron microscopy detection. The locations of individual HER2 positions were determined in a total plasma membrane area of 991 μm2 for several SKBR3 cells and 1062 μm2 for HCC1954 cells. Some of the HER2 receptors were arranged in a linear chain with interlabel distances of 40 ± 7 and 32 ± 10 nm in SKBR3 and HCC1954 cells, respectively. The finding was tested against randomly occurring linear chains of six or more positions, from which it was concluded that the experimental finding is significant and did not arise from random label distributions. Because the measured interlabel distance in the HER2 chains is similar to the 36-nm helix-repetition distance of actin filaments, it is proposed that a linking mechanism between HER2 and actin filaments leads to linearly aligned oligomers.
In dieser Arbeit wurden die Hafteigenschaften bio-inspirierter Mikrostrukturen untersucht. Es wurde ein Aufbau entwickelt, der eine Kombination aus Kraftmessungen und optischer in situ Beobachtung der realen Kontaktfläche mit Hilfe der frustrierten Totalreflexion ermöglicht. Die vorliegende Arbeit zeigt, dass Defekte an der Grenzfläche, Systemparameter (z. B. Maschinensteifigkeit, Fehlausrichtung) und äußere Einflüsse (z. B. Luftdruck) die Ablösemechanismen der Haftstrukturen verändern. Durch den maßgeblichen Einfluss von Defekten in der Kontaktfläche ergab sich eine breite Verteilung in der Haftfestigkeit der einzelnen Fibrillen im Array. Es konnte beobachtet werden, dass bereits bis zu 30 % der Fibrillen den Kontakt zum Substrat verloren, bevor die maximale Haftkraft erreicht wurde. Die Ergebnisse dieser Arbeit verdeutlichen, dass zur Optimierung der Adhäsionseigenschaften das Gesamtsystem betrachtet werden muss und nicht von Einzelfibrillen auf ein gesamtes Array geschlossen werden kann. Anhand von Weibullfunktionen lässt sich die Verteilung der Haftfestigkeiten und daraus die Qualität von Arrays beschreiben. Diese Verteilung konnte mit Hilfe des korrelativen Ansatzes zum ersten Mal nachgewiesen und bestimmt werden. Die neu entwickelte Methode liefert somit einen geeigneten Zugang Haftstrukturarrays hinsichtlich ihrer Qualität zu quantifizieren und anwendungsrelevanter Einflussfaktoren zu testen.
Fibrillar adhesion pads of insects and geckoes have inspired the design of high-performance adhesives enabling a new generation of handling devices. Despite much progress over the last decade, the current understanding of these adhesives is limited to single contact pillars and the behavior of whole arrays is largely unexplored. In the study reported here, a novel approach is taken to gain insight into the detachment mechanisms of whole micropatterned arrays. Individual contacts are imaged by frustrated total internal reflection, allowing in situ observation of contact formation and separation during adhesion tests. The detachment of arrays is found to be governed by the distributed adhesion strength of individual pillars, but no collaborative effect mediated by elastic interactions can be detected. At the maximal force, about 30% of the mushroom structures are already detached. The adhesive forces decrease with reduced air pressure by 20% for the smooth and by 6% for the rough specimen. These contributions are attributed to a suction effect, whose strength depends critically on interfacial defects controlling the sealing quality of the contact. This dominates the detachment process and the resulting adhesion strength.
