Effect of Surface Treatments on the Nanomechanical Properties of Human Hair.

The structural properties of hair are largely determined by the state of the surface. Advanced imaging modes of atomic force microscopy, where the surface mechanics can be correlated with surface topography, have been used to spatially map variations in hair surfaces following chemical and mechanical treatments. Through analysis of multilayered data obtained in this way, we show that the processes of bleaching and combing of hair not only alter the surface roughness, but also alter the mechanical stiffness, adhesion properties, and surface potential of hair, in terms of the mean values and their distributions. These treatments are shown to have a significant effect on the nanoscale surface properties, consistent with what has previously been observed at the macroscopic fiber-level scale.Unileve

Human hair and the impact of cosmetic procedures: a review on cleansing and shape-modulating cosmetics

Hair can be strategically divided into two distinct parts: the hair follicle, deeply buried in the skin, and the visible hair fiber. The study of the hair follicle is mainly addressed by biological sciences while the hair fiber is mainly studied from a physicochemical perspective by cosmetic sciences. This paper reviews the key topics in hair follicle biology and hair fiber biochemistry, in particular the ones associated with the genetically determined cosmetic attributes: hair texture and shape. The traditional and widespread hair care procedures that transiently or permanently affect these hair fiber features are then described in detail. When hair is often exposed to some particularly aggressive cosmetic treatments, hair fibers become damaged. The future of hair cosmetics, which are continuously evolving based on ongoing research, will be the development of more efficient and safer procedures according to consumers needs and concerns.Portuguese Foundation for Science and Technology (FCT) for providing Célia F. Cruz the grant for PhD studies (scholarship SFRH/BD/100927/2014) and Teresa Matamá the grant for post-doctoral research (SFRH/BPD/102153/2014). This work was also supported by FCT under the scope of the strategic funding of UID/BIO/04469/2013 and UID/BIA/04050/2013 units, COMPETE 2020 (POCI-01-0145-FEDER-006684andPOCI-01-0145-FEDER-007569) and under the Project RECI/BBB-EBI/0179/2012 (FCOMP-01-0124-FEDER-027462).info:eu-repo/semantics/publishedVersio

Nanomechanics of single keratin fibres: A Raman study of the alpha helix -> beta sheet transition and water effect

The use of micro-Raman spectroscopy, through chemical bond nano-scale probes, allows the changes in conformations (alpha helix -> beta sheet), chain orientation, disconnection of disulfide bonds (-20%) and the increase of intra and inter-chain distances during the strain to be distinguished. The combination of micro-Raman spectroscopy and a allows a quantitative measure of the extension of chemical bonds in the peptidic chain during loading. The nano-structural transformations of keratin during the strain of human hair in a dry environment (40-60 % relative humidity) and saturated with water have been studied. The water permits the sliding of the chains and decreases the bond energy hair. Spectral analyses and 2D correlation are two coherent and independent methods to follow change the Raman probes which are sensitive to structural . The between nano-mechanical (Raman) and micro-mechanical (strain/stress) analyses confirms the validity of the experimental results, tools and principles used, as well as the agreement with the structural model of keratin fibres described by Chapman & Hearle

Polydispersity and ordered phases in solutions of rodlike macromolecules

We apply density functional theory to study the influence of polydispersity on the stability of columnar, smectic and solid ordering in the solutions of rodlike macromolecules. For sufficiently large length polydispersity (standard deviation $\sigma>0.25$) a direct first-order nematic-columnar transition is found, while for smaller $\sigma$ there is a continuous nematic-smectic and first-order smectic-columnar transition. For increasing polydispersity the columnar structure is stabilized with respect to solid perturbations. The length distribution of macromolecules changes neither at the nematic-smectic nor at the nematic-columnar transition, but it does change at the smectic-columnar phase transition. We also study the phase behaviour of binary mixtures, in which the nematic-smectic transition is again found to be continuous. Demixing according to rod length in the smectic phase is always preempted by transitions to solid or columnar ordering.Comment: 13 pages (TeX), 2 Postscript figures uuencode

The combined tensile and torsional behavior of irregular fibers

Most fibers are irregular, and they are often subjected to combined loading conditions during processing and end-use. In this paper, polyester and wool fibers under the combined tensile and torsional loads have been studied for the first time, using the finite element method (FEM). The dimensional irregularities of these fibers are simulated with sine waves of different magnitude and frequency. The breaking load and breaking extension of the fibers at different twist or torsion levels are then calculated from the finite element model. The results indicate that twist and level of fiber irregularity have a major impact on the mechanical properties of the fiber and the effect of the frequency of irregularity is relatively small.<br /

Defects in Chiral Columnar Phases: Tilt Grain Boundaries and Iterated Moire Maps

Biomolecules are often very long with a definite chirality. DNA, xanthan and poly-gamma-benzyl-glutamate (PBLG) can all form columnar crystalline phases. The chirality, however, competes with the tendency for crystalline order. For chiral polymers, there are two sorts of chirality: the first describes the usual cholesteric-like twist of the local director around a pitch axis, while the second favors the rotation of the local bond-orientational order and leads to a braiding of the polymers along an average direction. In the former case chirality can be manifested in a tilt grain boundary phase (TGB) analogous to the Renn-Lubensky phase of smectic-A liquid crystals. In the latter case we are led to a new "moire" state with twisted bond order. In the moire state polymers are simultaneously entangled, crystalline, and aligned, on average, in a common direction. In the moire state polymers are simultaneously entangled, crystalline, and aligned, on average, in a common direction. In this case the polymer trajectories in the plane perpendicular to their average direction are described by iterated moire maps of remarkable complexity, reminiscent of dynamical systems.Comment: plain TeX, (33 pages), 17 figures, some uufiled and included, the remaining available at ftp://ftp.sns.ias.edu/pub/kamien/ or by request to [email protected]

Protein disulphide isomerase-mediated grafting of cysteine-containing peptides onto over-bleached hair

The ability of Protein disulphide isomerase (PDI) to promote the grafting of two cysteine-containing peptides onto hair was investigated in order to develop an alternative treatment for over-bleached hair. The studied peptides were designed based on human keratin and human lung surfactant proteins and were linked to a fluorescent dye to facilitate visualisation of the grafting process and to assess hair penetration. The ability of the peptides to restore mechanical and thermal properties lost by repeated bleaching treatments was also studied. After eight bleaching treatments, hair samples displayed 42% less mechanical resistance, coupled with a decrease in α-helix denaturation enthalpies and temperatures. Hair surface damage following bleaching was visualized by scanning electron microscopy. Addition of PDI to the treatment formulations promoted peptide attachment to the hair via disulphide bonds, facilitating their penetration into the hair cortex, as observed by fluorescence microscopy. The proposed peptide treatment resulted in an increase in α-helix denaturation enthalpy in over-bleached hair, as well as an increase in both Young's modulus and tensile strength. Thus, mechanical and thermal properties were improved after the peptide treatment in the presence of PDI; suggesting that the formulations presented in this work are promising candidates for hair-care applications

Mechanical analysis of infant carrying in hominoids

In all higher nonhuman primates, species survival depends upon safe carrying of infants clinging to body hair of adults. In this work, measurements of mechanical properties of ape hair (gibbon, orangutan, and gorilla) are presented, focusing on constraints for safe infant carrying. Results of hair tensile properties are shown to be species-dependent. Analysis of the mechanics of the mounting position, typical of heavier infant carrying among African apes, shows that both clinging and friction are necessary to carry heavy infants. As a consequence, a required relationship between infant weight, hair–hair friction coefficient, and body angle exists. The hair–hair friction coefficient is measured using natural ape skin samples, and dependence on load and humidity is analyzed. Numerical evaluation of the equilibrium constraint is in agreement with the knuckle-walking quadruped position of African apes. Bipedality is clearly incompatible with the usual clinging and mounting pattern of infant carrying, requiring a revision of models of hominization in relation to the divergence between apes and hominins. These results suggest that safe carrying of heavy infants justify the emergence of biped form of locomotion. Ways to test this possibility are foreseen here