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- ItemDevulcanization of Waste Rubber and Generation of Active Sites for Silica Reinforcement(Washington, DC : ACS Publications, 2019) Ghorai, Soumyajit; Mondal, Dipankar; Hait, Sakrit; Ghosh, Anik Kumar; Wiessner, Sven; Das, Amit; De, DebapriyaEach year, hundreds of millions of tires are produced and ultimately disposed into nature. To address this serious environmental issue, devulcanization could be one of the sustainable solutions that still remains as one of the biggest challenges across the globe. In this work, sulfur-vulcanized natural rubber (NR) is mechanochemically devulcanized utilizing a silane-based tetrasulfide as a devulcanizing agent, and subsequently, silica (SiO2)-based rubber composites are prepared. This method not only breaks the sulfur–sulfur cross-links but also produces reactive poly(isoprene) chains to interact with silica. The silica natural rubber composites are prepared by replacing 30% fresh NR by devulcanized NR with varying contents of silica. The composites exhibit excellent mechanical properties, tear strength, abrasion resistance, and dynamic mechanical properties as compared with the fresh natural rubber silica composites. The tensile strength of devulcanized rubber-based silica composites is ∼20 MPa, and the maximum elongation strain is ∼921%. The devulcanized composites are studied in detail by chemical, mechanical, and morphological analyses. Thus, the value added by the devulcanized rubber could attract the attention of recycling community for its sustainable applications.
- ItemFlexible Materials for High-Resolution 3D Printing of Microfluidic Devices with Integrated Droplet Size Regulation(Washington, DC : ACS Publications, 2021) Weigel, Niclas; Männel, Max J.; Thiele, JulianWe develop resins for high-resolution additive manufacturing of flexible micromaterials via projection microstereolithography (PμSL) screening formulations made from monomer 2-phenoxyethyl acrylate, the cross-linkers Ebecryl 8413, tri(propyleneglycol) diacrylate or 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, the photoabsorber Sudan 1, and the photoinitiator diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide. PμSL-printed polymer micromaterials made from this resin library are characterized regarding achievable layer thickness depending on UV exposure energy, and for mechanical as well as optical properties. The best-candidate resin from this screening approach allows for 3D-printing transparent microchannels with a minimum cross section of approximately 35 × 46 μm2, which exhibit proper solvent resistance against water, isopropanol, ethanol, n-hexane, and HFE-7500. The mechanical properties are predestined for 3D-printing microfluidic devices with integrated functional units that require high material flexibility. Exemplarily, we design flexible microchannels for on-demand regulation of microdroplet sizes in microemulsion formation. Our two outlines of integrated droplet regulators operate by injecting defined volumes of air, which deform the droplet-forming microchannel cross-junction, and change the droplet size therein. With this study, we expand the library of functional resins for PμSL printing toward flexible materials with micrometer resolution and provide the basis for further exploration of these materials, e.g., as microstructured cell-culturing substrates with defined mechanics. © 2021 American Chemical Society. All rights reserved.
- ItemStealth Effect of Short Polyoxazolines in Graft Copolymers: Minor Changes of Backbone End Group Determine Liver Cell-Type Specificity(Washington, DC : ACS Publications, 2021) Muljajew, Irina; Huschke, Sophie; Ramoji, Anuradha; Cseresnyés, Zoltán; Hoeppener, Stephanie; Nischang, Ivo; Foo, Wanling; Popp, Jürgen; Figge, Marc Thilo; Weber, Christine; Bauer, Michael; Schubert, Ulrich S.; Press, Adrian T.Dye-loaded micelles of 10 nm diameter formed from amphiphilic graft copolymers composed of a hydrophobic poly(methyl methacrylate) backbone and hydrophilic poly(2-ethyl-2-oxazoline) side chains with a degree of polymerization of 15 were investigated concerning their cellular interaction and uptake in vitro as well as their interaction with local and circulating cells of the reticuloendothelial system in the liver by intravital microscopy. Despite the high molar mass of the individual macromolecules (Mn ≈ 20 kg mol-1), backbone end group modification by attachment of a hydrophilic anionic fluorescent probe strongly affected the in vivo performance. To understand these effects, the end group was additionally modified by the attachment of four methacrylic acid repeating units. Although various micelles appeared similar in dynamic light scattering and cryo-transmission electron microscopy, changes in the micelles were evident from principal component analysis of the Raman spectra. Whereas an efficient stealth effect was found for micelles formed from polymers with anionically charged or thiol end groups, a hydrophobic end group altered the micelles' structure sufficiently to adapt cell-type specificity and stealth properties in the liver. © 2021 The Authors. Published by American Chemical Society.
- ItemManual Versus Microfluidic-Assisted Nanoparticle Manufacture: Impact of Silk Fibroin Stock on Nanoparticle Characteristics(Washington, DC : ACS Publications, 2020) Solomun, Jana I.; Totten, John D.; Wongpinyochit, Thidarat; Florence, Alastair J.; Seib, F. PhilippSilk has a long track record of clinical use in the human body, and new formulations, including silk nanoparticles, continue to reveal the promise of this natural biopolymer for healthcare applications. Native silk fibroin can be isolated directly from the silk gland, but generating sufficient material for routine studies is difficult. Consequently, silk fibroin, typically extracted from cocoons, serves as the source for nanoparticle formation. This silk requires extensive processing (e.g., degumming, dissolution, etc.) to yield a hypoallergenic aqueous silk stock, but the impact of processing on nanoparticle production and characteristics is largely unknown. Here, manual and microfluidic-assisted silk nanoparticle manufacturing from 60-and 90-min degummed silk yielded consistent particle sizes (100.9-114.1 nm) with low polydispersity. However, the zeta potential was significantly lower (P < 0.05) for microfluidic-manufactured nanoparticles (-28 to-29 mV) than for manually produced nanoparticles (-39 to-43 mV). Molecular weight analysis showed a nanoparticle composition similar to that of the silk fibroin starting stock. Reducing the molecular weight of silk fibroin reduced the particle size for degumming times ≤30 min, whereas increasing the molecular weight polydispersity improved the nanoparticle homogeneity. Prolonged degumming (>30 min) had no significant effect on particle attributes. Overall, the results showed that silk fibroin processing directly impacts nanoparticle characteristics. Copyright © 2020 American Chemical Society.
- ItemBiochemical Characterization of Mouse Retina of an Alzheimer's Disease Model by Raman Spectroscopy(Washington, DC : ACS Publications, 2020) Stiebing, Clara; Jahn, Izabella J.; Schmitt, Michael; Keijzer, Nanda; Kleemann, Robert; Kiliaan, Amanda J.; Drexler, Wolfgang; Leitgeb, Rainer A.; Popp, JürgenThe presence of biomarkers characteristic for Alzheimer's disease in the retina is a controversial topic. Raman spectroscopy offers information on the biochemical composition of tissues. Thus, it could give valuable insight into the diagnostic value of retinal analysis. Within the present study, retinas of a double transgenic mouse model, that expresses a chimeric mouse/human amyloid precursor protein and a mutant form of human presenilin 1, and corresponding control group were subjected to ex vivo Raman imaging. The Raman data recorded on cross sections of whole eyes highlight the layered structure of the retina in a label-free manner. Based on the Raman information obtained from en face mounted retina samples, a discrimination between healthy and Alzheimer's disease retinal tissue can be done with an accuracy of 85.9%. For this a partial least squares-linear discriminant analysis was applied. Therefore, although no macromolecular changes in form of, i.e., amyloid beta plaques, can be noticed based on Raman spectroscopy, subtle biochemical changes happening in the retina could lead to Alzheimer's disease identification. ©
- ItemDNAzymes as Catalysts for l-Tyrosine and Amyloid β Oxidation(Washington, DC : ACS Publications, 2020) Köhler, Tony; Patsis, Panagiotis A.; Hahn, Dominik; Ruland, André; Naas, Carolin; Müller, Martin; Thiele, JulianSingle-stranded deoxyribonucleic acids have an enormous potential for catalysis by applying tailored sequences of nucleotides for individual reaction conditions and substrates. If such a sequence is guanine-rich, it may arrange into a three-dimensional structure called G-quadruplex and give rise to a catalytically active DNA molecule, a DNAzyme, upon addition of hemin. Here, we present a DNAzyme-mediated reaction, which is the oxidation of l-tyrosine toward dityrosine by hydrogen peroxide. With an optimal stoichiometry between DNA and hemin of 1:10, we report an activity of 101.2 ± 3.5 μUnits (μU) of the artificial DNAzyme Dz-00 compared to 33.0 ± 1.8 μU of free hemin. Exemplarily, DNAzymes may take part in neurodegeneration caused by amyloid beta (Aβ) aggregation due to l-tyrosine oxidation. We show that the natural, human genome-derived DNAzyme In1-sp is able to oxidize Aβ peptides with a 4.6% higher yield and a 33.3% higher velocity of the reaction compared to free hemin. As the artificial DNAzyme Dz-00 is even able to catalyze Aβ peptide oxidation with a 64.2% higher yield and 337.1% higher velocity, an in-depth screening of human genome-derived DNAzymes may identify further candidates with similarly high catalytic activity in Aβ peptide oxidation.
- ItemDefect-free Naphthalene Diimide Bithiophene Copolymers with Controlled Molar Mass and High Performance via Direct Arylation Polycondensation(Washington, DC : ACS Publications, 2015) Matsidik, Rukiya; Komber, Hartmut; Luzio, Alessandro; Caironi, Mario; Sommer, MichaelA highly efficient, simple, and environmentally friendly protocol for the synthesis of an alternating naphthalene diimide bithiophene copolymer (PNDIT2) via direct arylation polycondensation (DAP) is presented. High molecular weight (MW) PNDIT2 can be obtained in quantitative yield using aromatic solvents. Most critical is the suppression of two major termination reactions of NDIBr end groups: nucleophilic substitution and solvent end-capping by aromatic solvents via C–H activation. In situ solvent end-capping can be used to control MW by varying monomer concentration, whereby end-capping is efficient and MW is low for low concentration and vice versa. Reducing C–H reactivity of the solvent at optimized conditions further increases MW. Chain perfection of PNDIT2 is demonstrated in detail by NMR spectroscopy, which reveals PNDIT2 chains to be fully linear and alternating. This is further confirmed by investigating the optical and thermal properties as a function of MW, which saturate at Mn ≈ 20 kDa, in agreement with controls made by Stille coupling. Field-effect transistor (FET) electron mobilities μsat up to 3 cm2/(V·s) are measured using off-center spin-coating, with FET devices made from DAP PNDIT2 exhibiting better reproducibility compared to Stille controls.
- ItemColor Tuning of Electrochromic TiO2Nanofibrous Layers Loaded with Metal and Metal Oxide Nanoparticles for Smart Colored Windows(Washington, DC : ACS Publications, 2021) Eyovge, Cavit; Deenen, Cristian S.; Ruiz-Zepeda, Francisco; Bartling, Stephan; Smirnov, Yury; Morales-Masis, Monica; Susarrey-Arce, Arturo; Gardeniers, HanCo-axial electrospinning was applied for the structuring of non-woven webs of TiO2 nanofibers loaded with Ag, Au, and CuO nanoparticles. The composite layers were tested in an electrochromic half-cell assembly. A clear correlation between the nanoparticle composition and electrochromic effect in the nanofibrous composite is observed: TiO2 loaded with Ag reveals a black-brown color, Au shows a dark-blue color, and CuO shows a dark-green color. For electrochromic applications, the Au/TiO2 layer is the most promising choice, with a color modulation time of 6 s, transmittance modulation of 40%, coloration efficiency of 20 cm2/C, areal capacitance of 300 F/cm2, and cyclic stability of over 1000 cycles in an 18 h period. In this study, an unexplored path for the rational design of TiO2-based electrochromic device is offered with unique color-switching and optical efficiency gained by the fibrous layer. It is also foreseen that co-axial electrospinning can be an alternative nanofabrication technique for smart colored windows. © 2021 The Authors. Published by American Chemical Society.
- ItemIn Situ Monitoring of Linear RGD-Peptide Bioconjugation with Nanoscale Polymer Brushes(Washington, DC : ACS Publications, 2017) Psarra, Evmorfia; König, Ulla; Müller, Martin; Bittrich, Eva; Eichhorn, Klaus-Jochen; Welzel, Petra B.; Stamm, Manfred; Uhlmann, PetraBioinspired materials mimicking the native extracellular matrix environment are promising for biotechnological applications. Particularly, modular biosurface engineering based on the functionalization of stimuli-responsive polymer brushes with peptide sequences can be used for the development of smart surfaces with biomimetic cues. The key aspect of this study is the in situ monitoring and analytical verification of the biofunctionalization process on the basis of three complementary analytical techniques. In situ spectroscopic ellipsometry was used to quantify the amount of chemisorbed GRGDS at both the homopolymer poly(acrylic acid) (PAA) brush and the binary poly(N-isopropylacrylamide) (PNIPAAm)-PAA brushes, which was finally confirmed by an acidic hydrolysis combined with a subsequent reverse-phase high-performance liquid chromatography analysis. In situ attenuated total reflection-Fourier transform infrared spectroscopy provided a step-by-step detection of the biofunctionalization process so that an optimized protocol for the bioconjugation of GRGDS could be identified. The optimized protocol was used to create a temperature-responsive binary brush with a high amount of chemisorbed GRGDS, which is a promising candidate for the temperature-sensitive control of GRGDS presentation in further cell-instructive studies.
- ItemSilk Hydrogel Substrate Stress Relaxation Primes Mesenchymal Stem Cell Behavior in 2D(Washington, DC : ACS Publications, 2021) Phuagkhaopong, Suttinee; Mendes, Luís; Müller, Katrin; Wobus, Manja; Bornhäuser, Martin; Carswell, Hilary V.O.; Duarte, Iola F.; Seib, F. PhilippTissue-mimetic silk hydrogels are being explored for diverse healthcare applications, including stem cell delivery. However, the impact of stress relaxation of silk hydrogels on human mesenchymal stem cell (MSC) biology is poorly defined. The aim of this study was to fabricate silk hydrogels with tuned mechanical properties that allowed the regulation of MSC biology in two dimensions. The silk content and stiffness of both elastic and viscoelastic silk hydrogels were kept constant to permit direct comparisons. Gene expression of IL-1β, IL-6, LIF, BMP-6, BMP-7, and protein tyrosine phosphatase receptor type C were substantially higher in MSCs cultured on elastic hydrogels than those on viscoelastic hydrogels, whereas this pattern was reversed for insulin, HNF-1A, and SOX-2. Protein expression was also mechanosensitive and the elastic cultures showed strong activation of IL-1β signaling in response to hydrogel mechanics. An elastic substrate also induced higher consumption of glucose and aspartate, coupled with a higher secretion of lactate, than was observed in MSCs grown on viscoelastic substrate. However, both silk hydrogels changed the magnitude of consumption of glucose, pyruvate, glutamine, and aspartate, and also metabolite secretion, resulting in an overall lower metabolic activity than that found in control cells. Together, these findings describe how stress relaxation impacts the overall biology of MSCs cultured on silk hydrogels. ©