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- ItemProbing carbonyl-water hydrogen-bond interactions in thin polyoxazoline brushes(Melville, NY : AIP Publishing, 2016) Kroning, Annika; Furchner, Andreas; Adam, Stefan; Uhlmann, Petra; Hinrichs, KarstenTemperature-responsive oxazoline-based polymer brushes have gained increased attention as biocompatible surfaces. In aqueous environment, they can be tuned between hydrophilic and hydrophobic behavior triggered by a temperature stimulus. This transition is connected with changes in molecule–solvent interactions and results in a switching of the brushes between swollen and collapsed states. This work studies the temperature-dependent interactions between poly(2-oxazoline) brushes and water. In detail, thermoresponsive poly(2-cyclopropyl-2-oxazoline), nonresponsive hydrophilic poly(2-methyl-2-oxazoline), as well as a copolymer of the two were investigated with in situ infrared ellipsometry. Focus was put on interactions of the brushes' carbonyl groups with water molecules. Different polymer–water interactions could be observed and assigned to hydrogen bonding between C=O groups and water molecules. The switching behavior of the brushes in the range of 20–45 °C was identified by frequency shifts and intensity changes of the amide I band.
- ItemAmphiphilic block copolymer micelles in selective solvents: The effect of solvent selectivity on micelle formation(Basel : MDPI, 2019) Kumar, Labeesh; Horechyy, Andriy; Bittrich, Eva; Nandan, Bhanu; Uhlmann, Petra; Fery, AndreasWe investigated the micellar behavior of a series of asymmetric polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymers in different P4VP-selective alcoholic solvents. The micellar behavior was further correlated with the spectroscopic ellipsometry results obtained on swelling of PS and P4VP polymer films in the corresponding solvent vapors. The time-resolved (in situ) dynamic light scattering (DLS) measurements, in combination with (ex situ) electron microscopy imaging, revealed information about the aggregation state of PS-b-P4VP BCP in different alcohols and the effect of heat treatment. The ellipsometry measurements allowed us to estimate the difference in solvent selectivity toward PS/P4VP pair. Both DLS and ellipsometric studies suggested that less polar alcohols (i.e., 1-propanol, 1-butanol, and 1-pentanol) are likely to be close to each other in terms of their selectivity toward PS/P4VP pair, whereas more polar ethanol and methanol show the highest and the lowest affinity toward P4VP, respectively.
- ItemIn-situ-investigation of enzyme immobilization on polymer brushes(Lausanne : Frontiers Media, 2019) Koenig, Meike; König, Ulla; Eichhorn, Klaus-Jochen; Müller, Martin; Stamm, Manfred; Uhlmann, PetraHerein, we report on the use of a combined setup of quartz-crystal microbalance, with dissipation monitoring and spectroscopic ellipsometry, to comprehensively investigate the covalent immobilization of an enzyme to a polymer layer. All steps of the covalent reaction of the model enzyme glucose oxidase with the poly(acrylic acid) brush by carbodiimide chemistry, were monitored in-situ. Data were analyzed using optical and viscoelastic modeling. A nearly complete collapse of the polymer chains was found upon activation of the carboxylic acid groups with N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide and N-Hydroxysuccinimide. The reaction with the amine groups of the enzyme occurs simultaneously with re-hydration of the polymer layer. Significantly more enzyme was immobilized on the surface compared to physical adsorption at similar conditions, at the same pH. It was found that the pH responsive swelling behavior was almost not affected by the presence of the enzyme. © 2019 Koenig, König, Eichhorn, Müller, Stamm and Uhlmann.
- ItemFree polyethylenimine enhances substrate-mediated gene delivery on titanium substrates modified with RGD-functionalized poly(acrylic acid) brushes(Lausanne : Frontiers Media, 2019) Mantz, Amy; Rosenthal, Alice; Farris, Eric; Kozisek, Tyler; Bittrich, Eva; Nazari, Saghar; Schubert, Eva; Schubert, Mathias; Stamm, Manfred; Uhlmann, Petra; Pannier, Angela K.Substrate mediated gene delivery (SMD) is a method of immobilizing DNA complexes to a substrate via covalent attachment or nonspecific adsorption, which allows for increased transgene expression with less DNA compared to traditional bolus delivery. It may also increase cells receptivity to transfection via cell-material interactions. Substrate modifications with poly(acrylic) acid (PAA) brushes may improve SMD by enhancing substrate interactions with DNA complexes via tailored surface chemistry and increasing cellular adhesion via moieties covalently bound to the brushes. Previously, we described a simple method to graft PAA brushes to Ti and further demonstrated conjugation of cell adhesion peptides (i.e., RGD) to the PAA brushes to improve biocompatibility. The objective of this work was to investigate the ability of Ti substrates modified with PAA-RGD brushes (PAA-RGD) to immobilize complexes composed of branched polyethyleneimine and DNA plasmids (bPEI-DNA) and support SMD in NIH/3T3 fibroblasts. Transfection in NIH/3T3 cells cultured on bPEI-DNA complexes immobilized onto PAA-RGD substrates was measured and compared to transfection in cells cultured on control surfaces with immobilized complexes including Flat Ti, PAA brushes modified with a control peptide (RGE), and unmodified PAA. Transfection was two-fold higher in cells cultured on PAA-RGD compared to those cultured on all control substrates. While DNA immobilization measured with radiolabeled DNA indicated that all substrates (PAA-RGD, unmodified PAA, Flat Ti) contained nearly equivalent amounts of loaded DNA, ellipsometric measurements showed that more total mass (i.e., DNA and bPEI, both complexed and free) was immobilized to PAA and PAA-RGD compared to Flat Ti. The increase in adsorbed mass may be attributed to free bPEI, which has been shown to improve transfection. Further transfection investigations showed that removing free bPEI from the immobilized complexes decreased SMD transfection and negated any differences in transfection success between cells cultured on PAA-RGD and on control substrates, suggesting that free bPEI may be beneficial for SMD in cells cultured on bPEI-DNA complexes immobilized on PAA-RGD grafted to Ti. This work demonstrates that substrate modification with PAA-RGD is a feasible method to enhance SMD outcomes on Ti and may be used for future applications such as tissue engineering, gene therapy, and diagnostics. © 2019 Mantz, Rosenthal, Farris, Kozisek, Bittrich, Nazari, Schubert, Schubert, Stamm, Uhlmann and Pannier.
- ItemNeue funktionale und biomimetische Oberflächen zur Verhinderung/Verminderung von Eiswachstum : Schlussbericht - Verbundprojekt = New functional and biomimetical surfaces to reduce ice formation(Hannover : Technische Informationsbibliothek (TIB), 2011) Uhlmann, Petra; Höhne, Susanne; Frenzel, Ralf; Hanzelmann, Christian; Winkler, René; Schneider, Ulrike; Büchtner, Edwin; Hellmann, Rüdiger; Schiffels, Peter; Illgen, André; Noack, Ralf; Kizlauskas, Ceslovas; Ney, Alfons; Wagner, Georg; Schubert, Volker; Köhler, Thomas; Meyer, Albrecht[no abstract available]
- ItemGlassy dynamics of poly(2-vinyl-pyridine) brushes with varying grafting density(London : Royal Soc. of Chemistry, 2015) Neubauer, Nils; Winkler, René; Tress, Martin; Uhlmann, Petra; Reiche, Martin; Kipnusu, Wycliffe Kiprop; Kremer, FriedrichThe molecular dynamics of poly(2-vinyl-pyridine) (P2VP) brushes is measured by Broadband Dielectric Spectroscopy (BDS) in a wide temperature (250 K to 440 K) and broad spectral (0.1 Hz to 1 MHz) range. This is realized using nanostructured, highly conductive silicon electrodes being separated by silica spacers as small as 35 nm. A “grafting-to”-method is applied to prepare the P2VP-brushes with five different grafting densities (0.030 nm−2 to 0.117 nm−2), covering the “true-brush” regime with highly stretched coils and the “mushroom-to-brush” transition regime. The film thickness ranges between 1.8 to 7.1 (±0.2) nm. Two relaxations are observed, an Arrhenius-like process being attributed to fluctuations in the poly(glycidyl-methacrylate) (PGMA) linker used for the grafting reaction and the segmental dynamics (dynamic glass transition) of the P2VP brushes. The latter is characterized by a Vogel–Fulcher–Tammann dependence similar to bulk P2VP. The results can be comprehended considering the length scale on which the dynamic glass transition (≤1 nm) takes place.
- ItemVerbundprojekt: Entwicklung und produktionstechnische Umsetzung innovativer nanopartikelbasierter Schichtstrukturen aus schaltbaren multifunktionalen Polymeroberflächen, Akronym: Ultrasurf : Teilvorhaben Materialwissenschaftliche Grundlagen : Schlussbericht(Hannover : Technische Informationsbibliothek (TIB), 2011) Uhlmann, Petra; Rollberg, Anja; Kunder, Mandy; Messerschmidt, Martin; Ptacek, Saija[no abstract available]
- ItemFluidischer Partikel-Transport an Grenzflächen durch aktorisch bewegte Mikrohaare mit schaltbarer Nanostrukturierung - PaTra, Teilvorhaben: Funktionale Nanostrukturen : Abschlussbericht ; Berichtszeitraum: 01.04.2011 - 31.03.2014(Hannover : Technische Informationsbibliothek (TIB), 2014) Uhlmann, Petra; Kunder, Mandy; Rollberg, Anja; Bittrich, Eva; Rauch, Sebastian; König, Ulla[no abstract available]