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- 2019
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Álvarez-Asencio, Rubén, et al.
(författare)
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Nanomechanical properties of human skin and introduction of a novel hair indenter
- 2016
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Ingår i: Journal of The Mechanical Behavior of Biomedical Materials. - : Elsevier. - 1751-6161 .- 1878-0180. ; 54, s. 185-193
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical resistance of the stratum corneum, the outermost layer of skin, to deformation has been evaluated at different length scales using Atomic Force Microscopy. Nanomechanical surface mapping was first conducted using a sharp silicon tip and revealed that Young’s modulus of the stratum corneum varied over the surface with a mean value of about 0.4 GPa. Force indentation measurements showed permanent deformation of the skin surface only at high applied loads (above 4 μN). The latter effect was further demonstrated using nanomechanical imaging in which the obtained depth profiles clearly illustrate the effects of increased normal force on the elastic/plastic surface deformation. Force measurements utilizing the single hair fiber probe supported the nanoindentation results of the stratum corneum being highly elastic at the nanoscale, but revealed that the lateral scale of the deformation determines the effective elastic modulus.This result resolves the fact that the reported values in the literature vary greatly and will help to understand the biophysics of the interaction of razor cut hairs that curl back during growth and interact with the skin.
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| 3. |
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| 4. |
- Besharat, Zahra, et al.
(författare)
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Mixed monolayers of alkane thiols with polar terminal group on gold : Investigation of structure dependent surface properties
- 2016
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 484, s. 279-290
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Tidskriftsartikel (refereegranskat)abstract
- Adsorption of thiols with cationic or anionic terminal group on gold has been studied from mixed solutions of 11-Amino-1-undecanethiol (AUT) and 3-Mercaptopropionic acid (MPA) using Quartz Crystal Microbalance with Dissipation (QCM-D), X-ray Photoelectron Spectroscopy (XPS), atomic force microscopy (AFM) and contact angles. The goal is to probe the nature of such layers, and the additivity or otherwise of the pH responsiveness, with a view to evaluate their suitability as smart materials. For each of the two pure (unmixed) cases, ordered molecular monolayers are formed with sulfur binding to gold and the alkane chain pointing out from the surface as expected. Adsorption from the thiol mixtures, however, leads to a more complex behaviour. The surface concentration of thiols from the mixtures, as determined by QCM-D, is considerably lower than for the pure cases and it reaches a minimum at a 3:1 MPA/AUT relative concentration in the solution. The XPS results confirm a reduction in adsorbed amount in mixtures with the lowest overall intensity for the 3:1 ratio. Monolayers formed from mixtures display a wettability which is much lower and less pH sensitive. Collectively these results confirm that for adsorption from mixed systems, the configuration is completely different. Complex formation in the mixed solutions leads to the adsorption of molecules parallel to the surface in an axially in-plane configuration. This parallel layer of thiols is mechanically relatively robust to nano-shaving based on AFM measurements. These results will have a significant impact on the design of biomimetic surface coatings particularly when mixtures of oppositely charged molecules are present on the surface, as is commonly the case in biological, proteinaceous surfaces (e.g. hair and skin).
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| 5. |
- Liljeblad, Jonathan F.D., et al.
(författare)
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Self-assembly of long chain fatty acids : Effect of a methyl branch
- 2014
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 16:33, s. 17869-17882
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Tidskriftsartikel (refereegranskat)abstract
- The morphology and molecular conformation of Langmuir-Blodgett deposited and floating monolayers of a selection of straight chain (eicosanoic acid, EA), iso (19-methyl eicosanoic acid, 19-MEA), and anteiso (18-methyl eicosanoic acid, 18-MEA) fatty acids have been investigated by Vibrational Sum Frequency Spectroscopy (VSFS), AFM imaging, and the Langmuir trough. While the straight chain fatty acid forms smooth, featureless monolayers, all the branched chain fatty acids display 10-50 nm sized domains (larger for 19-MEA than the 18-MEA) with a homogeneous size distribution. A model is suggested to explain the domain formation and size in terms of the branched fatty acid packing properties and the formation of hemispherical caps at the liquid-air interface. No difference between the chiral (S) form and the racemic mixture of the 18-MEA is observed with any of the utilized techniques. The aliphatic chains of the straight chain fatty acids appear to be oriented perpendicular to the sample surface, based on an orientational analysis of VSFS data and the odd/even effect. In addition, the selection of the subphase (neat water or CdCl2 containing water buffered to pH 6.0) used for the LB-deposition has a profound influence on the monolayer morphology, packing density, compressibility, and conformational order. Finally, the orientation of the 19-MEA dimethyl moiety is estimated, and a strategy for performing an orientational analysis to determine the complete molecular orientation of the aliphatic chains of 19-MEA and 18-MEA is outlined and discussed.
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| 6. |
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| 7. |
- Mizuno, Hiroyasu, et al.
(författare)
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Interactions between Crossed Hair Fibers at the Nanoscale
- 2010
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:24, s. 18909-18915
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Tidskriftsartikel (refereegranskat)abstract
- The atomic force microscope fiber probe is used to directly measure the forces and friction between two human hairs under various conditions. It is shown that the forces between the hair fibers in solution can be well explained by a DLVO interaction and that cationic surfactant modifies the interactions in a manner entirely consistent with current views of adsorption behavior. A Coulombic attraction occurs between the crossed hair fibers in air due to the heterogeneity of the surface, and at shorter separations a clear dispersion interaction is observed. Exposure of the hair to a bleaching solution leads to the removal of the adhesion and solely a double-layer interaction. Two crossed hair fibers obey Amontons' classic law of friction, with a linear relation between applied load and frictional force, allowing the determination of a friction coefficient; positively charged surfactant adsorption is shown to reduce the friction coefficient between the fibers in a manner consistent with boundary lubrication by a palisade layer.
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| 8. |
- Mizuno, Hiroyasu, et al.
(författare)
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New insight on the friction of natural fibers. Effect of sliding angle and anisotropic surface topography
- 2013
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 29:19, s. 5857-5862
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Tidskriftsartikel (refereegranskat)abstract
- The friction anisotropy of human hair has been investigated as a function of angle using AFM fiber probe measurements to evaluate the role of cuticle alignment. It is found that friction hysteresis, the difference in friction coefficients between sliding with or against the cuticle direction, is essentially nonexistent for native human hair. For damaged human hair, however, a clear friction hysteresis is observed, which appears to be a periodic function of the angle between the fibers. The implication is that antiparallel sliding is not in itself sufficient for friction isotropy but that lifting of the cuticle edges is required. A methodology to perform friction analysis independently for trace and retrace was therefore developed, which is applicable to any type of AFM lateral force measurement. It explicitly accounts for roll, noncircular cross section, and off-axis alignment as well as baseline drift, which allows real anisotropy in the friction coefficient to be deconvoluted from these artifacts.
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| 9. |
- Sjövall, Peter, et al.
(författare)
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Imaging the distribution of skin lipids and topically applied compounds in human skin using mass spectrometry
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- The barrier functions of skin against water loss, microbial invasion and penetration of xenobiotics rely, in part, on the spatial distribution of the biomolecular constituents in the skin structure, particularly its horny layer (stratum corneum). However, all skin layers are important to describe normal and dysfunctional skin conditions, and to develop adapted therapies or skin care products. In this work, time-of-flight secondary ion mass spectrometry (ToF-SIMS) combined with scanning electron microscopy (SEM) was used to image the spatial distribution of a variety of molecular species, from stratum corneum down to dermis, in cross-section samples of human abdominal skin. The results demonstrate the expected localization of ceramide and saturated long-chain fatty acids in stratum corneum (SC) and cholesterol sulfate in the upper part of the viable epidermis. The localization of exogenous compounds is demonstrated by the detection and imaging of carvacrol (a constituent of oregano or thyme essential oil) and ceramide, after topical application onto ex vivo human skin. Carvacrol showed pronounced accumulation to triglyceride-containing structures in the deeper parts of dermis. In contrast, the exogenous ceramide was found to be localized in SC. Furthermore, the complementary character of this approach with classical ex vivo skin absorption analysis methods is demonstrated.
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| 10. |
- Skedung, Lisa, et al.
(författare)
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Mechanisms of tactile sensory deterioration amongst the elderly
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- It is known that roughness-smoothness, hardness-softness, stickiness-slipperiness and warm-cold are predominant perceptual dimensions in macro-, micro- and nano- texture perception. However, it is not clear to what extent active tactile texture discrimination remains intact with age. The general decrease in tactile ability induces physical and emotional dysfunction in elderly, and has increasing significance for an aging population. We report a method to quantify tactile acuity based on blinded active exploration of systematically varying micro-textured surfaces and a same-different paradigm. It reveals that elderly participants show significantly reduced fine texture discrimination ability. The elderly group also displays statistically lower finger friction coefficient, moisture and elasticity, suggesting a link. However, a subpopulation of the elderly retains discrimination ability irrespective of cutaneous condition and this can be related to a higher density of somatosensory receptors on the finger pads. Skin tribology is thus not the primary reason for decline of tactile discrimination with age. The remediation of cutaneous properties through rehydration, however leads to a significantly improved tactile acuity. This indicates unambiguously that neurological tactile loss can be temporarily compensated by restoring the cutaneous contact mechanics. Such mechanical restoration of tactile ability has the potential to increase the quality of life in elderly.
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