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143 results on '"Lichtenegger, Helga C."'

4. Energy‐dispersive Laue diffraction analysis of the influence of statherin and histatin on the crystallographic texture during human dental enamel demineralization.

Author

Sakr, Charbel, Al-Mosawi, Mohammed, Grünewald, Tilman A., Cook, Philip, Tack, Pieter, Vincze, Laszlo, Micha, Jean-Sebastien, Anderson, Paul, Al-Jawad, Maisoon, and Lichtenegger, Helga C.

Subjects
DENTAL enamel, CRYSTAL texture, SALIVARY proteins, TOOTH demineralization, PEPTIDES
Abstract

Energy‐dispersive Laue diffraction (EDLD) is a powerful method to obtain position‐resolved texture information in inhomogeneous biological samples without the need for sample rotation. This study employs EDLD texture scanning to investigate the impact of two salivary peptides, statherin (STN) and histatin‐1 (HTN) 21 N‐terminal peptides (STN21 and HTN21), on the crystallographic structure of dental enamel. These proteins are known to play crucial roles in dental caries progression. Three healthy incisors were randomly assigned to three groups: artificially demineralized, demineralized after HTN21 peptide pre‐treatment and demineralized after STN21 peptide pre‐treatment. To understand the micro‐scale structure of the enamel, each specimen was scanned from the enamel surface to a depth of 250 µm using microbeam EDLD. Via the use of a white beam and a pixelated detector, where each pixel functions as a spectrometer, pole figures were obtained in a single exposure at each measurement point. The results revealed distinct orientations of hydroxyapatite crystallites and notable texture variation in the peptide‐treated demineralized samples compared with the demineralized control. Specifically, the peptide‐treated demineralized samples exhibited up to three orientation populations, in contrast to the demineralized control which displayed only a single orientation population. The texture index of the demineralized control (2.00 ± 0.21) was found to be lower than that of either the STN21 (2.32 ± 0.20) or the HTN21 (2.90 ± 0.46) treated samples. Hence, texture scanning with EDLD gives new insights into dental enamel crystallite orientation and links the present understanding of enamel demineralization to the underlying crystalline texture. For the first time, the feasibility of EDLD texture measurements for quantitative texture evaluation in demineralized dental enamel samples is demonstrated. [ABSTRACT FROM AUTHOR]

Published
2024
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13. Polymers / Solvent-free Ultrasonic Dispersion of Nanofillers in Epoxy Matrix

Author

Zanghellini, Benjamin, Knaack, Patrick, Schörpf, Sebastian, Semlitsch, Karl-Heinz, Lichtenegger, Helga C., Praher, Bernhard, Omastova, Maria, and Rennhofer, Harald

Subjects
carbon nanotubes, functionalization, Rheologie, dispersion, rheology, Ultraschall, ultrasonication, Funktionalisierung
Abstract

Dispersion of carbon nanotubes and carbon nanofibers is a crucial processing step in the production of polymer-based nanocomposites and poses a great challenge due to the tendency of nanofillers to agglomerate. One of the most effective methods for dispersion is the use of a three-roll mill, which is a well-established method and results in agglomerates below 5 m. Nevertheless, this process is time-consuming and thus a limiting factor for industrial applications. Our aim was to establish an easy and efficient ultrasonic dispersion process, characterize the dispersion parameters, and compare both methods, ultrasonication and the three-roll mill. We applied rheological tests and analyzed the agglomerate sizes by an image fit of the microscopy images. All these analyses combined deliver a valuable set of information about the dispersions quality and, therefore, allows the improvement and further adaptation of the dispersion process. (VLID)5734995

Published
2021

15. Poly(ester amide)s from poly(alkylene succinate)s and rapid crystallizing amido diols

Author

Kluge, Marcel, Rennhofer, Harald, Lichtenegger, Helga C., Liebner, Falk W., Robert, Tobias, and Publica

Subjects
bio-based polymers, thermal properties, microstructure, poly(ester amide), succinic acid, amido diol
Abstract

Random poly(ester amide)s are synthesized from succinic acid, ethylene glycol or 1,4-butanediol and different aliphatic amido diols - symmetric a,o-diols containing two amide moieties. The formation of chain-terminating N-succinimide end groups, which limit the molecular weight attainable by common synthetic strategies, is effectively suppressed. Poly(ester amide)s crystallize in a suprastructure similar to that of even-even polyamides. The thermal properties of both types of poly(ester amide)s synthesized are considerably improved and transition temperatures are tunable by changing the ratio of aliphatic diol to rapidly crystallizing amido diol in the feed. Using ethylene glycol as diol component, Tg and Tm of the material could be enhanced from −12 to −2 °C and 97 to 157 °C, respectively, while an increase from −33 to −8 °C and 115-153 °C was observed for their 1,4-butanediol derived counterparts. Furthermore, the slow crystallization rate of poly(ethylene succinate) from molten state could be significantly accelerated by the introduction of amide moieties into the polymer backbone.

Published
2020

27. Exploring molecular and mechanical gradients in structural bioscaffolds

Author

Waite, Herbert J., Lichtenegger, Helga C., Stucky, Galen D., and Hansma, Paul

Subjects
Molecular biology -- Research, Tissues -- Research, Biological sciences, Chemistry
Abstract

Most organisms consist of a functionally adaptive assemblage of hard and soft tissues. Although little s known about how nature relieves these stresses, it is generally agreed that fundamental insights about molecular adaptation at hard/soft interfaces could profoundly influence how one thinks about biomaterials.

Published
2004

28. Strain Hardening and Pore Size Harmonization by Uniaxial Densification: A Facile Approach toward Superinsulating Aerogels from Nematic Nanofibrillated 2,3-Dicarboxyl Cellulose

Author

Plappert, Sven F., Nedelec, Jean-Marie, Rennhofer, Harald, Lichtenegger, Helga C., and Liebner, Falk W.

Abstract

Dissolving pulp has been subjected to consecutive periodate/chlorite treatments to afford 2,3-dicarboxyl cellulose (DCC, 1.02 mmol g–1COOH). Subsequent nanofibrillation afforded stable nematic nf-DCC dispersions (average particle size 2.1 nm × 525 nm) at significantly lower energy input compared to TEMPO-oxidation. Acid-induced gelation triggered by extensive hydrogen bonding sets the ordered state and affords free-standing hydrogels that can be converted to highly transparent birefringent aerogels by scCO2drying. Uniaxial compression of the obtained ultra-lightweight ductile nf-DCC aerogels down to 5% of their original volume intriguingly preserves nematic orientation and transparence. Simultaneously, strain hardening translates into exceptionally good mechanical properties, such as toughness at nearly zero Poisson’s ratio. Uniaxial compression has been furthermore demonstrated to be a facile and efficient means for converting nf-DCC aerogels of broad, multiscale pore size distribution into entirely micro/mesoporous scaffolds of narrow size distribution at far-reaching preservation of porosity. Following this approach, thermally superinsulating nf-DCC aerogels (λ = 0.018 W m–1K–1) have been prepared, whose intriguing mechanical properties, transparence, and nematic ordering bear great potential for other applications as well.

Published
2024
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36. Core–Shell Structure of Monodisperse Poly(ethylene glycol)-Grafted Iron Oxide Nanoparticles Studied by Small-Angle X-ray Scattering

Author

Grünewald, Tilman A., primary, Lassenberger, Andrea, additional, van Oostrum, Peter D. J., additional, Rennhofer, Harald, additional, Zirbs, Ronald, additional, Capone, Barbara, additional, Vonderhaid, Iris, additional, Amenitsch, Heinz, additional, Lichtenegger, Helga C., additional, and Reimhult, Erik, additional

Published
2015
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37. Electrochemical synthesis of nanostructured ZnO films utilizing self-assembly of surfactant molecules at solid-liquid interfaces

Author

Choi, Kyoung-Shin, Lichtenegger, Helga C., and Stucky, Galen D.

Subjects
Dielectric films -- Electric properties, Dielectric films -- Research, Thin films -- Electric properties, Thin films -- Research, Surface active agents -- Electric properties, Zinc oxide -- Electric properties, Chemistry
Abstract

Nanostructured ZnO films utilizing cooperative surface assembly of surfactants and inorganic species are electrodeposited under the influence of an electrostatic potential. This approach effectively manipulates surfactant - inorganic aggregates at low concentration in solution to generate high-quality nanostructured films.

Published
2002

39. μXRF Elemental Mapping of Bioresorbable Magnesium-Based Implants in Bone.

Author

Turyanskaya, Anna, Rauwolf, Mirjam, Grünewald, Tilman A., Meischel, Martin, Stanzl-Tschegg, Stefanie, Löffler, Jörg F., Wobrauschek, Peter, Weinberg, Annelie M., Lichtenegger, Helga C., and Streli, Christina

Subjects
YTTRIUM, MAGNESIUM, ALLOYS, BIOABSORBABLE implants, X-ray spectroscopy
Abstract

This study investigated the distribution of the elemental constituents of Mg-based implants at various stages of the degradation process in surrounding bone tissue, with a focus on magnesium (Mg), as the main component of the alloy, and yttrium (Y), due to its potential adverse health effects. The measurements were performed on the implant-bearing thin sections of rat bone in a time series of implant degradation between one and 18 months. Micro X-ray fluorescence analysis (μXRF) with a special spectrometer meeting the requirements for the measurements of low-Z elements was used. It was found that the migration and accumulation behaviour of implant degradation products is element-specific. A sharp decrease in Mg was observed in the immediate vicinity of the interface and no specific accumulation or aggregation of Mg in the adjacent bone tissue was detected. By contrast, Y was found to migrate further into the bone over time and to remain in the tissue even after the complete degradation of the implant. Although the nature of Y accumulations must still be clarified, its potential health impact should be considered. [ABSTRACT FROM AUTHOR]

Published
2016
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40. Carbon Microparticles from Organosolv Lignin as Filler for Conducting Poly(Lactic Acid).

Author

Köhnke, Janea, Fürst, Christian, Unterweger, Christoph, Rennhofer, Harald, Lichtenegger, Helga C., Keckes, Jozef, Emsenhuber, Gerhard, Mahendran, Arunjunai raj, Liebner, Falk, and Gindl-Altmutter, Wolfgang

Subjects
POLYLACTIC acid, CARBON analysis, PARTICLE analysis, LIGNINS, ELECTRIC conductivity, TENSILE strength, TENSILE tests
Abstract

Carbon microparticles were produced from organosolv lignin at 2000 °C under argon atmosphere following oxidative thermostabilisation at 250 °C. Scanning electron microscopy, X-ray diffraction, small-angle X-ray scattering, and electro-conductivity measurements revealed that the obtained particles were electrically conductive and were composed of large graphitic domains. Poly(lactic acid) filled with various amounts of lignin-derived microparticles showed higher tensile stiffness increasing with particle load, whereas strength and extensibility decreased. Electric conductivity was measured at filler loads equal to and greater than 25% w/w. [ABSTRACT FROM AUTHOR]

Published
2016
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