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Karlsruhe, Germany

Burck J.,Institute of Biological Interfaces IBG2 | Heissler S.,Institute of Functional Interfaces IFG | Geckle U.,Institute of Applied Materials | Ardakani M.F.,Karlsruhe Institute of Technology | And 4 more authors.
Langmuir | Year: 2013

Electrospinning is a promising method to mimic the native structure of the extracellular matrix. Collagen is the material of choice, since it is a natural fibrous structural protein. It is an open question how much the spinning process preserves or alters the native structure of collagen. There are conflicting results in the literature, mainly due to the different solvent systems in use and due to the fact that gelatin is employed as a reference state for the completely unfolded state of collagen in calculations. Here we used circular dichroism (CD) and Fourier-transform infrared spectroscopy (FTIR) to investigate the structure of regenerated collagen samples and scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to illuminate the electrospun nanofibers. Collagen is mostly composed of folded and unfolded structures with different ratios, depending on the applied temperature. Therefore, CD spectra were acquired as a temperature series during thermal denaturation of native calf skin collagen type I and used as a reference basis to extract the degree of collagen folding in the regenerated electrospun samples. We discussed three different approaches to determine the folded fraction of collagen, based on CD spectra of collagen from 185 to 260 nm, since it would not be sufficient to obtain simply the fraction of folded structure θ from the ellipticity at a single wavelength of 221.5 nm. We demonstrated that collagen almost completely unfolded in fluorinated solvents and partially preserved its folded structure θ in HAc/EtOH. However, during the spinning process it refolded and the PP-II fraction increased. Nevertheless, it did not exceed 42% as deduced from the different secondary structure evaluation methods, discussed here. PP-II fractions in electrospun collagen nanofibers were almost same, being independent from the initial solvent systems which were used to solubilize the collagen for electrospinning process. © 2012 American Chemical Society. Source

Guerdane M.,Institute of Applied Materials
Particle-Based Methods III: Fundamentals and Applications - Proceedings of the 3rd International Conference on Particle-based MethodsFundamentals and Applications, Particles 2013 | Year: 2013

We address the question of whether and how atomistic molecular dynamics (MD) simulations can be used to calibrate macroscopic phase-field (PF) models, as hierarchical multiscale approaches usually proceed. We carry out a systematic consistency analysis by confronting results from MD with predictions of PF modeling in the case of the propagation of a planar [NicZr1-c]liquid-Zrcrystal interface during solidification and melting under chemical nonequilibrium conditions. Our study illustrates clearly that the PF approach is able to describe the same aspects of physics than MD, when the key physical parameters are transferred from the latter method to the former one. We use then this consistent MD/PF multiscale model to estimate quantitatively the influence of the in-plane solid-liquid interface ordering on the growth kinetics. Source

Chen R.,Institute of Nanotechnology | Chen R.,Institute of Applied Materials | Chen R.,Helmholtz Institute Ulm | Knapp M.,Institute of Applied Materials | And 15 more authors.
Physical Chemistry Chemical Physics | Year: 2015

Intercalation pseudocapacitive Li+ storage has been recognized recently in metal oxide materials, wherein Li+ intercalation into the lattice is not solid-state diffusion-limited. This may bridge the performance gap between electrochemical capacitors and battery materials. To date, only a few materials with desired crystal structure and with well-defined nanoarchitectures have been found to exhibit such attractive behaviour. Herein, we report for the first time that nanoscale spinel LiFeTiO4 as a cathode material for Li-ion batteries exhibits intercalation pseudocapacitive Li+ storage behaviour. Nanoscale LiFeTiO4 nanoparticles with native carbon coating were synthesized by a sol-gel route. A fast and large-amount of Li+ storage (up to 1.6 Li+ per formula unit over cycling) in the nanoscale LiFeTiO4 host has been achieved without compromising kinetics. ©the Owner Societies 2015. Source

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