INMdok (Leibniz Institute for New Materials)
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Bending as Key Mechanism in the Tactile Perception of Fibrillar Surfaces
Get PDFThe touching of fibrillar surfaces elicits a broad range of affective reactions, which range from the adverse stinginess of a stiff bristle brush to the pleasant feel of velvet. To study the tactile perception of model fibrillar surfaces, a unique set of samples carrying dense, regular arrays of cylindrical microfibrils with high aspect ratio made from different elastomer materials have been created. Fibril length and material compliance are varied independently such that their respective influence on tactile perception can be elucidated. This work finds that the tactile perception of similarity between samples is dominated by bending of the fibrils under sliding touch. The results demonstrate that variations of material stiffness and of surface structure are not necessarily perceived independently by touch. In the case of fibrillar elastomer surfaces, it is rather the ratio of fibril length and storage modulus which determines fibril bending and becomes the dominant tactile dimension. Visual access to the sample during tactile exploration improves the tactile perception of fibril bendability. Experiments with colored samples show a distraction by color in participants’ decisions regarding tactile similarity only for yellow samples of outstanding brightness
Transformations of the polycyclic Alumosiloxane Al2(OSiPh2OSiPh2O)3 into new Polycycles and Co(II) and In(III) derivatives of (Ph2SiO)8[Al(O)OH]4
Get PDFIn the presence of water and amines the etherate of bicyclic Al2(OSiPh2OSiPh2O)3 (II a) can be used to generate novel alumosiloxane polycycles like [O(Ph2SiOSiPh2)O−]2Al2O[O(Ph2SiOSiPh2)O] ⋅ 2 H2N+Et2 (1), [O(Ph2SiOSiPh2)O−]2Al2[O(Ph2Si)O]2 ⋅ 2 HN+Et3 (2), [O(Ph2SiOSiPh2)O−]2Al2[O(Ph2SiOSiPh2)O]2 ⋅ 2 HN+Et3 (3 a, 3 b), which crystallizes in two different phases, and [O(Ph2SiOSiPh2)O−]2Al2[O(Ph2SiOSiPh2)O]2 ⋅ 2 HN+(CH2CH2)3N (4). As a common structural feature of these compounds two aluminum atoms which are incorporated in six-membered Al[O(SiPh2OSiPh2)O−] rings are connected as spiro cyclic centers through oxygen and/or siloxane bridges [(OSiPh2)nO] (n=1, 2) to form an assembly of three fused rings at the aluminum corners. The central ring is either eight- (1, 2) or twelve-membered (3, 4). Alkyl ammonium cations balance the charges and form hydrogen bridges to oxygen atoms of the six membered rings. The pentacyclic (Ph2SiO)8[Al(O)OH]4 (I) can be used indirectly (addition of water) and directly as chelating ligand versus Co(II)Cl and In-CH3 fragments as shown with the isolated and structurally characterized compounds (HN+Et3)2{[(Ph2Si)2O3][Al4(OH)4O2](CoCl)2}2− (5 a, 5 b) and (Ph2SiO)8[AlO(OH)]2[AlO2]2(InCH3) ⋅ 2 O(CH2)4 (6)
Self-Adhesive Silicone Microstructures for the Treatment of Tympanic Membrane Perforations
Get PDFInspired by the gecko foot, polymeric microstructures have demonstrated reliable dry adhesion to both stiff objects and sensitive surfaces such as skin. Microstructured silicone patches are here proposed for the treatment of tympanic membrane perforations with the aim of serving as an alternative for current surgical procedures that require anesthesia and ear canal packing. Sylgard 184 PDMS micropillars of 20 µm in diameter and 60 µm in length are topped by a Soft Skin Adhesive (SSA) MG7-1010 terminal layer, of about 25 µm thickness. The adhesion is evaluated by specially designed tack tests against explanted murine eardrums and, for comparison, against a rigid substrate. Functional effects are evaluated using auditory brainstem responses (ABR) and distortion product otoacoustic emissions (DPOAE). The adhesion strength of the microstructure and unstructured controls to explanted murine tympanic membranes is comparable (typically 12 kPa), but the microstructured patches are easier to handle by the surgeon. For the first time, partial recovery of hearing performance is measured immediately after patch application. The novel patches adhere without the need for further fixation, removing the need for ear canal packing. The proposed material design holds great promise for improving clinical treatments of tympanic membrane perforation
Highly Tunable Nanostructures in a Doubly pH-Responsive Pentablock Terpolymer in Solution and in Thin Films
Get PDFMultiblock copolymers with charged blocks are complex systems that show great potential for enhancing the structural control of block copolymers. A pentablock terpolymer PMMA-b-PDMAEMA-b-P2VP-b-PDMAEMA-b-PMMA is investigated. It contains two types of midblocks, which are weak cationic polyelectrolytes, namely poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(2-vinylpyridine) (P2VP). Furthermore, these are end-capped with short hydrophobic poly(methyl methacrylate) (PMMA) blocks in dilute aqueous solution and thin films. The self-assembly behavior depends on the degrees of ionization α of the P2VP and PDMAEMA blocks, which are altered in a wide range by varying the pH value. High degrees of ionization of both blocks prevent structure formation, whereas microphase-separated nanostructures form for a partially charged and uncharged state. While in solutions, the nanostructure formation is governed by the dependence of the P2VP block solubility of the and the flexibility of the PDMAEMA blocks on α, in thin films, the dependence of the segregation strength on α is key. Furthermore, the solution state plays a crucial role in the film formation during spin-coating. Overall, both the mixing behavior of the 3 types of blocks and the block sequence, governing the bridging behavior, result in strong variations of the nanostructures and their repeat distances
Optically transparent vertical silicon nanowire arrays for live-cell imaging
Get PDFProgrammable nano-bio interfaces driven by tuneable vertically configured nanostructures have recently emerged as a powerful tool for cellular manipulations and interrogations. Such interfaces have strong potential for ground-breaking advances, particularly in cellular nanobiotechnology and mechanobiology. However, the opaque nature of many nanostructured surfaces makes non-destructive, live-cell characterization of cellular behavior on vertically aligned nanostructures challenging to observe. Here, a new nanofabrication route is proposed that enables harvesting of vertically aligned silicon (Si) nanowires and their subsequent transfer onto an optically transparent substrate, with high efficiency and without artefacts. We demonstrate the potential of this route for efficient live-cell phase contrast imaging and subsequent characterization of cells growing on vertically aligned Si nanowires. This approach provides the first opportunity to understand dynamic cellular responses to a cell-nanowire interface, and thus has the potential to inform the design of future nanoscale cellular manipulation technologies
A novel universal algorithm for filament network tracing and cytoskeleton analysis
Get PDFThe rapid development of advanced microscopy techniques over recent decades has significantly increased the quality of imaging and our understanding of subcellular structures, such as the organization of the filaments of the cytoskeleton using fluorescence and electron microscopy. However, these recent improvements in imaging techniques have not been matched by similar development of techniques for computational analysis of the images of filament networks that can now be obtained. Hence, for a wide range of applications, reliable computational analysis of such two-dimensional methods remains challenging. Here, we present a new algorithm for tracing of filament networks. This software can extract many important parameters from grayscale images of filament networks, including the mesh hole size, and filament length and connectivity (also known as Coordination Number). In addition, the method allows sub-networks to be distinguished in two-dimensional images using intensity thresholding. We show that the algorithm can be used to analyze images of cytoskeleton networks obtained using different advanced microscopy methods. We have thus developed a new improved method for computational analysis of two-dimensional images of filamentous networks that has wide applications for existing imaging techniques. The algorithm is available as open-source software
On the viscous dissipation caused by randomly rough indenters in smooth sliding motion
Get PDFThe viscous dissipation between rigid, randomly rough indenters and linearly elastic counter bodies sliding past them is investigated using Green’s function molecular dynamics. The study encompasses a variety of models differing in the height spectra properties of the rigid indenter, in the viscoelasticity of the elastomer, and in their interaction. All systems reveal the expected damping linear in sliding velocity v at small v and a pronounced maximum at intermediate v. Persson’s theory of rubber friction, which is adopted to the studied model systems, reflects all observed trends. However, close quantitative agreement is only found up to intermediate sliding velocities. Relative errors in the friction force become significant once the contact area is substantially reduced by sliding
Metal oxide / carbon hybrid anode materials for lithium-ion batteries
Get PDFThe global warming fact has been calling for a change in our current energy infrastructure, which is based on fossil fuels. Lithium-ion batteries (LIBs) are one of our main tools that can serve our society for the desired transition from non-renewable energy sources to renewable ones, for instance, by opening the door of e-mobility with their high energy efficiency. However, the current state-of-art revealed that the electrode architecture has a crucial role in the obtained electrochemical performance of LIBs. In the traditional composite electrodes based on a physical admixture of components, particle-to-particle contact loss occurs between the electrochemically active metal oxide and conductive carbon additive, eventuate in poor electrochemical performance. On the other hand, hybrid electrode architecture provides nanoscopic chemical blending between the metal oxide and carbon, resulting in advanced electrochemical performance due to a continuous conductive network. However, the synthesis techniques for hybrid materials are limited to wet chemical synthesis. Therefore, the aim of this doctoral work is to explore novel synthesis approaches for the metal oxide/carbon hybrid materials and investigate their performances for LIBs with the comparison of their composite counterparts. For that purpose, this dissertation investigates the promising anode candidates for LIBs, namely, V2O3, Nb2O5, and Ti2Nb10O29, which were synthesized from their relatively cheap carbide sources via a new synthesis approach, chloroxidation or simple CO2 oxidation. The successfully-synthesized carbide-derived metal oxide/carbon hybrids displayed advanced rate handling abilities and cyclic stabilities compared to their counterparts.Die Tatsache der globalen Erwärmung hat eine Änderung unserer gegenwärtigen Energieinfrastruktur, die auf fossilen Brennstoffen basiert, erforderlich gemacht. Lithium- Ionen-Batterien (LIBs) sind eines unserer Hauptinstrumente, die unserer Gesellschaft für den gewünschten Übergang von nicht erneuerbaren Energiequellen zu erneuerbaren Energiequellen dienen können, indem sie zum Beispiel mit ihrer hohen Energiedichte und Effizienz die Tür zur E-Mobilität öffnen. Der derzeitige Stand der Technik hat jedoch gezeigt, dass die Elektrodenarchitektur eine entscheidende Rolle bei der erzielten elektrochemischen Leistung von LIBs spielt. Bei den traditionellen Verbundelektroden, die auf einer physikalischen Beimischung von Komponenten basieren, tritt ein Kontaktverlust von Partikel zu Partikel zwischen dem elektrochemisch aktiven Metalloxid und dem leitfähigen Kohlenstoffzusatz auf, was zu einer schlechten elektrochemischen Leistung führt. Andererseits bietet die hybride Elektrodenarchitektur eine nanoskopische chemische Mischung zwischen dem Metalloxid und dem Kohlenstoff, was zu einer verbesserten elektrochemischen Leistung aufgrund eines kontinuierlichen leitfähigen Netzwerks führt. Die Syntheseverfahren für Hybridmaterialien sind jedoch auf die nasschemische Synthese beschränkt. Ziel dieser Doktorarbeit ist es daher, neue Syntheseansätze für die Metalloxid/Kohlenstoff-Hybridmaterialien zu erforschen und ihre Leistungen für LIBs im Vergleich zu ihren Verbundwerkstoff-Pendants zu untersuchen. Zu diesem Zweck wurden vielversprechende Anodenmaterialien für LIBs, nämlich V2O3, Nb2O5 und Ti2Nb10O29, mit Hilfe eines neuen Syntheseansatzes aus relativ billigen Karbidquellenmittels Chloroxidation oder einfachen CO2-Oxidation synthetisiert. Die aus dem Karbid hergestellten Metalloxid/Kohlenstoff-Hybride wiesen im Vergleich zu ihren Pendants fortgeschrittene Ratenhandhabungsfähigkeiten und zyklische Stabilitäten auf
Light responsive cell-cell like biointerface using cadherin peptidomimetics
Get PDFInteraction between the cells plays a vital role in tissue formation and transmembrane signalling. The family of Cadherin proteins is among the important classes of adhesion molecules engaged in cell-cell interactions. Whose members mediate homophilic Ca2+ dependent cell-cell adhesion, and they are dynamic and spatiotemporally tightly regulated in a wide variety of tissues. Dynamic control of cadherin mediated interactions is a key to understand and modulate various cellular events for biomedical applications. This thesis presents a new strategy to spatiotemporally control cadherin mediated cell-cell interactions at biomimetic interfaces. For this purpose photoactivatable peptidomimetics of E-cadherin and N-cadherin were developed by introducing a light responsive non-natural amino acid, His[Ru(bpy)2PPh3] at the His residue of the HAV cadherin binding motif. These peptides were immobilized on poly(acrylamide) hydrogels and cadherin-mediated cell adhesion and derived cellular responses as a function of the activity of the peptide were studied. Flat and micropatterned hydrogels were used to reconstruct polarized cellular microenvironments, as they occur in epithelial or musculoskeletal tissues. Cellular morphology on the novel cadherin mimetic hydrogels was explored. Light-regulated myogenic differentiation of C2C12 cells by temporal control of N-cadherin peptide presentation was demonstrated using the photoactivatable N-cadherin mimetic peptide.Die Interaktion zwischen den Zellen spielt eine entscheidende Rolle bei der Gewebebildung und der Transmembransignalisierung. Die Familie der Cadherin-Proteine gehört zu den wichtigen Klassen von Adhäsionsmolekülen, die an Zell-Zell-Interaktionen beteiligt sind. Deren Mitglieder vermitteln die homophile Ca2+ abhängige Zell-Zell-Adhäsion, und sie sind in einer Vielzahl von Geweben dynamisch und räumlich-zeitlich streng reguliert. Die dynamische Kontrolle der durch Cadherin vermittelten Interaktionen ist ein Schlüssel zum Verständnis und zur Modulation verschiedener zellulärer Ereignisse für biomedizinische Anwendungen. In dieser Dissertation wird eine neue Strategie zur raum-zeitlichen Kontrolle von Cadherin-vermittelten Zell-Zell-Interaktionen an biomimetischen Grenzflächen vorgestellt. Zu diesem Zweck wurden photoaktivierbare Peptidomimetika von E-Cadherin und N-Cadherin entwickelt, indem eine lichtempfindliche nicht-natürliche Aminosäure, His[Ru(bpy)2PPh3] am His-Rest des HAV-Cadherin-Bindungsmotivs eingeführt wurde. Diese Peptide wurden auf Poly(acrylamid)-Hydrogelen und durch Cadherin vermittelte Zelladhäsion immobilisiert, und es wurden abgeleitete zelluläre Antworten als Funktion der Aktivität des Peptids untersucht. Zur Rekonstruktion polarisierter zellulärer Mikroumgebungen, wie sie in epithelialen oder muskuloskelettalen Geweben vorkommen, wurden flache und mikroparenchymierte Hydrogele verwendet. Die zelluläre Morphologie der neuartigen Cadherin-mimetischen Hydrogele wurde untersucht. Die lichtgesteuerte myogene Differenzierung von C2C12-Zellen durch zeitliche Kontrolle der N-Cadherin-Peptid-Präsentation wurde mit dem photoaktivierbaren N-Cadherin-Mimetikum-Peptid nachgewiesen
The stability and assembly of sterically stabilized non-polar nanoparticles
Get PDFSterically stabilized, non-polar nanoparticles find already first applications beyond research. Predictions how such particles behave in different medias are difficult. To get a better understanding of the physical and chemical connections between core, ligand, and solvent, two fields were investigated in this dissertation: The stability of non-polar nanoparticles at different temperatures and the controlled assembly during confinement. It was shown, that the stability of sterically stabilized nanoparticles depends on core-diameter, ligand, and solvent. The temperature induced assembly of the nanoparticles showed two different areas: Ligand-dominated and core-dominated. The non-linear transition is thereby a function of the core-diameter and the ligand length. With the help of emulsion, it was possible to produced binary supraparticles from binary nanoparticle dispersions. By varying the pressure during the production process binary supraparticles with three different structures were produced: Crystalline, Janus, and core-shell. The pressure was either applied by the surfactant (Laplace-pressure) or externally. In-situ measurements with small angle X-ray scattering shown, that the pressure influences the dispersity of the nanoparticles.Sterisch stabilisierte, unpolare Nanopartikel finden bereits erste Anwendungen außerhalb der Forschung. Vorhersagen, wie sich solche Partikel in verschiedenen Medien verhalten, fällt dabei schwer. Um die physikalischen und chemischen Zusammenhänge zwischen den Kernen, Liganden und Lösemittel besser zu verstehen, wurden in dieser Dissertation zwei Gebiete untersucht: Die Stabilität von unpolaren Nanopartikeln bei verschiedenen Temperaturen und die kontrollierte Anordnung bei räumlicher Restriktion. Es konnte gezeigt werden, dass die Stabilität von sterisch stabilisierten Nanopartikeln abhängig vom Kerndurchmesser, Ligand und Lösemittel ist. Die temperaturinduzierte Anordnung von den Nanopartikeln hat zwei Bereiche aufgezeigt: Liganden-dominiert und Kern-dominiert. Der nichtlineare Übergang hängt dabei vom Durchmesser des Kerns und von der Länge des Liganden ab. Mit der Hilfe von Emulsionen konnten binäre Suprapartikel aus binären Nanopartikel Dispersionen herstellt werden. Durch die Variation vom Druck während des Herstellungsprozesses konnten binäre Suprapartikel mit drei verschiedenen Strukturen hergestellt werden: Kristallin, Janus und Kern-Hülle. Der Druck konnte dabei entweder durch das Tensid (Laplace-Druck) oder extern angewendet werden. In-situ Messungen mittels Kleinwinkel-Röntgenstreuung haben gezeigt, dass der Druck die Dispersität der Nanopartikel beeinflusst