ORCID Profile
0000-0003-1538-1371
Current Organisation
University of Stuttgart
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Publisher: Elsevier BV
Date: 08-2019
DOI: 10.1016/J.JMBBM.2019.04.032
Abstract: This work discusses the first set of rheometric measurements carried out on commercially accessible juvenile and aged skin models under large litude oscillatory shear deformations. The results were compared with those of native male whole human and dermis-only foreskin specimens, catering to a few ages from 0.5 to 68 years, including specimens from a 23-year-old male abdomen. At large strains, strain thinning was more pronounced for the dermis of the young skins and for their whole skin counterparts. An inverse qualitative tendency was observed for the adult skins and the skin models. This can be explained by the high dermal collagen compactness associated with an incomplete epidermal proliferation. The qualitative Lissajous plots as well as the quantitative dimensionless indices analyzed using the MITlaos software indicated predominant nonlinear intracycle elastic strain stiffening and viscous shear thinning for all the native specimens at the maximum deformation. For the full thickness models, we have evidence of structure collapse and yielding under similar conditions. The whole skin specimen from the 68-year-old male showed smaller age-dependent nonlinear elastic contributions than the dermis, which we relate to the epidermal degeneration taking place during aging. Regardless of the age group, the models manifested more pronounced intercycle and intracycle elastic nonlinearities, and their magnitudes were significantly larger. The nonlinear elastic trends will serve as advanced standards for understanding and delineating the mechanical limits of destructive and non-destructive deformations of such unique biomaterials.
Publisher: Elsevier BV
Date: 03-2201
Publisher: American Chemical Society (ACS)
Date: 02-2021
Publisher: Society of Rheology
Date: 03-2021
DOI: 10.1122/8.0000136
Publisher: Society of Rheology
Date: 22-08-2017
DOI: 10.1122/1.4998931
Abstract: The response of semidilute entangled and salt-free solutions of aqueous polyacrylamide under large litude oscillatory shear deformations was studied in this work. We systemically probed the effects of four polymer concentrations from 5 to 15 wt. % and two molecular weights (5–6 and 18 M) at De & 1. The mitlaos software package was utilized to analyze the nonlinear moduli, among other nonlinear parameters. We found that the polymer concentration is the dominant parameter controlling the progression into the nonlinear regime. The trends of elastic decomposition indicate an intensive strain-rate softening behavior under high strain litudes. At high strain rates and at higher concentrations, however, a gradual transition from shear thickening to shear thinning could be noticed for the viscous dissipation. In addition, the effect of the measuring geometry was also considered, since the rheometer was coupled with a particle image velocimetry (PIV) system in the second part of this study. The PIV results suggest that the flow field is significantly altered during the oscillatory cycle. Banded profiles were observed for both molecular weights studied.
Publisher: Elsevier BV
Date: 10-2021
Publisher: Elsevier BV
Date: 02-2019
DOI: 10.1016/J.JMBBM.2018.11.013
Abstract: The study reports first ever account of measurements of linear viscoelastic moduli under small litude oscillatory shear deformations, for commercially available juvenile and aged in vitro 3D reconstructed skin models. The results were compared with those of native male whole human and dermis-only foreskin s les, catering to a wide age group from 0.5 to 68 years, including s les from a 23-year-old male abdomen. In the strain sweep tests, the dermis of the juvenile/young age group assumed a higher intrinsic elastic modulus than the whole skin. A reverse qualitative trend was noted for the adult/aged age group. Confirmed by the histological examination of the stained cross-sections, this is attributed to the nascent epidermal differentiation and the high fiber density of dermal collagen. The oscillation frequency sweeps exposed a greater dependence of the elasticity on the frequency for the native male dermis foreskin s les as compared to the whole skins, irrespective of age. This is anticipated since the extremely structured epidermis confers higher resistance to the whole skins towards intracycle deformations compared to the dermis, thereby storing smaller elastic energy. The 3D skin models examined in this work exhibited a broader linear viscoelastic region, a larger viscoelasticity, and much higher dynamic moduli, compared to the native skin. The rheological trends are a significant addition to the literature and may be used as a reference for the design of next generation of scaffolds.
Publisher: Springer Science and Business Media LLC
Date: 16-05-2020
DOI: 10.1007/S00707-020-02691-X
Abstract: This work documents the first account of advanced mechanical properties of six commercial lipsticks, some of which serve as market leads. We systematically studied their nonlinear viscoelastic properties under large litude oscillatory shear deformations. At large strains, all lipsticks showed intercycle strain softening, the extent of which initially depended on the prototype in the nonlinear regime. This behavior, markedly, was absent after the crossover of the dynamic moduli. Parameters obtained from the strain litude sweeps, i.e., the intrinsic elastic modulus and the stress maximum, demonstrated distinct prototype dependence. The Lissajous plots and the dimensionless nonlinear indices were determined using the MITlaos software. They showed intracycle elastic strain stiffening and viscous shear thinning. The angular oscillation frequency directly influenced the linear viscoelastic measures of all the benchmark lipsticks, and the nonlinear properties of only a few benchmark ones. The current study generates standard nonlinear rheology data that can be associated with the lipstick sensory attributes and typical tribological parameters. This may serve as an effective way to examine the transition from the initial spreading to the post-application sensation.
Publisher: Elsevier BV
Date: 09-2019
No related grants have been discovered for Natalie Germann.