Cuticle - Designed by Nature for the Sake of the Hair

The kinetics of moisture sorption by hair

OBJECTIVE

The rate process of moisture sorption by human hair has been analysed in order to hints for helping deepen knowledge on the hair structure and to explain the behaviour of hair in response to moisture.

METHODS

The isotherms of moisture sorption by hair were recorded, via dynamic vapour sorption (DVS), for untreated (virgin) and treated (heat-shaped and bleached) hair, as well as for separated cuticle and cortex.

RESULTS

By considering that, during moisture uptake, the hair fibres also swell, it is possible to introduce a time-dependent rate constant for describing the kinetics of the moisture sorption. This model allows for clearly separating the moisture sorption processes occurring in Cuticle and in Cortex and for proposing a role of chain entanglement in the two main compartments of the fibre. It may also provide some hints on the structural changes occurring in the fibre after different cosmetic treatments. The influence of the weight of the sample on the kinetics of the sorption process has also been noted and quantified. The analysis pointed to a transition occurring at around 30% relative humidity, assigned to the opening of the hair inner structure, and accommodation of more water molecules. This allowed for an estimate of the value of the activation energy of the water molecules reacting with the active sites, which was found to be in good agreement with results published in the literature.

CONCLUSION

The analysis of the kinetics of moisture sorption by hair was shown not only to provide information on the chain entanglement inside the fibre and the effect of cosmetic treatments but also to demonstrate and quantify the influence of fibre density on the sorption process. It is thus suggested that, along with examination of the hysteresis, the analysis of sorption kinetics helps reveal a more complete picture of hair moisture management.

Chemical bonds and hair behaviour-A review

When undertaking any review of the structure of the hair and its mechanical properties it becomes apparent that the overall behaviour of keratin fibres is commonly attributed to the presence of hydrogen, disulfide and ionic bonds. The action of physico-chemical agents used during various cosmetic treatments is viewed as the result of an interaction with these bonds. Thus, the breaking of bonds by chemical agents, or via mechanical or thermal stresses, affects the relative balance of disulfide and hydrogen bonds and the contribution of hydrophobic interactions, which are all important factors that may alter hair behaviour. Generally, these chemical bonds are considered as responding homogeneously to the environmental and cosmetic factors. This unitary image is challenged, however, by evaluating the results of chemical, nanomechanical, tensile and thermal measurements, which suggest that disulfide bonds may be grouped into several types, according to their location within the fibre and the way they respond to various agents. A compensatory effect of newly formed hydrogen bonds for broken disulfide bonds may also be seen, and additionally involves different types of hydrogen bonds. As a result, the picture of chemical bonding in hair appears to be far from a homogeneous one. In addition, it is apparent that further investigation is required for clarifying the action of ionic bonds and hydrophobic interactions within the hair fibre. The present review aims, thus, at offering a deeper background for understanding how the hair behaves under various conditions.

Atomistic Characterization of Healthy and Damaged Hair Surfaces: A Molecular Dynamics Simulation Study of Fatty Acids on Protein Layer

Amid the bourgeoning demand for in-silico designed, environmentally sustainable, and highly effective hair care formulations, a growing interest is evident in the exploration of realistic computational model for the hair surface. In this work, we present an atomistic model for the outermost layer of the hair surface derived through molecular dynamics simulations, which comprises 18-Methyleicosanoic acid (18-MEA) fatty acid chains covalently bound onto the keratin-associated protein 10-4 (KAP10-4) at a spacing distance of ~1 nm. Remarkably, this hair surface model facilitates the inclusion of free fatty acids (free 18-MEA) into the gaps between chemically bound 18-MEA chains, up to a maximum number that results in a packing density of 0.22 nm2 per fatty acid molecule, consistent with the optimal spacing identified through free energy analysis. Atomistic insights are provided for the organization of fatty acid chains, structural features, and interaction energies on protein-inclusive hair surface models with varying amounts of free 18-MEA (FMEA) depletion, as well as varying degrees of anionic cysteic acid from damaged bound 18-MEA (BMEA), under both dry and wet conditions. In the presence of FMEA and water, the fatty acid chains in a pristine hair surface prefers to adopt a thermodynamically favored extended chain conformation, forming a thicker protective layer (~3 nm) on the protein surface. Our simulation results reveal that, while the depletion of FMEA can induce a pronounced impact on the thickness, tilt angle, and order parameters of fatty acid chains, the removal of BMEA has a marked effect on water penetration. There is a "sweet spot" spacing between the 18-MEA whereby damaged hair surface properties can be reinstated by replenishing FMEA. Through the incorporation of the protein layer and free fatty acids, the hair surface models presented in this study enables a realistic representation of the intricate details within the hair epicuticle, facilitating a molecular scale assessment of surface properties during the formulation design process.

Oral Administration of Lactilactobacillus curvatus LB-P9 Promotes Hair Regeneration in Mice

This study was designed to examine the effect of Lactilactobacillus curvatus LB-P9 on hair regeneration. The treatment of LB-P9 conditioned medium increased the proliferation of both hair follicle dermal papilla cells and hair germinal matrix cells (hGMCs). Moreover, the expression levels of hair growth factors such as vascular endothelial growth factor (VEGF) and fibroblast growth factor 7 were significantly elevated in hGMCs co-cultured with LB-P9. After time-synchronized depilation, mice were orally administered with either 4×107 colony forming unit (CFU) of LB-P9 (low dose) or 4×108 CFU of LB-P9 (high dose), once daily for 4 weeks. Compared with the vehicle (phosphate-buffered saline)-administrated group, the LB-P9-treated groups exhibited accelerated hair regrowth rate and enhanced hair thickness in a dose-dependent manner. Supporting this observation, both hair follicle numbers and the dermal thickness in skin tissues of the LB-P9-treated groups were increased, compared to those of the vehicle-treated group. These results might be explained by the increased level of β-catenin and number of hair follicle stem cells (CD34+CD49f+ cells) in the skin tissues of mice administered with LB-P9, compared to the vehicle-treated mice. Also, increased serum levels of hair growth factors such as VEGF and insulin-like growth factor-1, and superoxide dismutase were found in the LB-P9-treated groups, compared to those of the vehicle-treated group. Taken together, these results might demonstrate that the oral administration of LB-P9 promotes hair regeneration by the enhancement of dermal papilla proliferation through the stimulation of hair growth factor production.

Recent Progress in Hair Science and Trichology

Hair is important to our appearance as well as to protect our heads. Human hair mainly consists of proteins (80-85%), melanin pigments (0-5%), water (10-13%), and lipids (1-6%). The physicochemical properties of hair have been studied for over 100 years. However, they are not yet thoroughly understood. In this review, recent progress and the latest findings are summarized from the following three perspectives: structural characteristics, delivery and distribution of active ingredients, and hair as a template. The structural characteristics of hair have been mainly investigated by microscopic and/or spectroscopic techniques such as atomic force microscopy integrated with infrared spectroscopy (AFM-IR) and rheological measurements. The distribution of active ingredients has been generally evaluated through techniques such as nanoscale secondary ion mass spectrometry (NanoSIMS). And finally, attempts to explore the potential of hair to be used as a substrate for flexible device fabrication will be introduced.

Learning from hair moisture sorption and hysteresis

OBJECTIVE

The process of moisture sorption and desorption by human hair was analysed for extracting hints on the hair structure.

METHODS

The isotherms of moisture sorption and desorption by hair were recorded for untreated and chemically treated (permed and bleached) hair. Data of swelling were also considered.

RESULTS

By examining the swelling and moisture sorption of keratin fibres, it is possible to conclude that hysteresis is quite improbably caused by capillary condensation. The mobility of the protein chains and the strength of the bonds binding water molecules to the active sites inside the matrix are proposed as causes instead. The concept of "breaking symmetry", derived from moisture sorption-desorption data, and the method of evaluating this parameter, is proposed as a way of characterizing the chemical treatment of hair. The results show that bleaching produces a larger breaking of symmetry than perming, and this is suggested to be due to new hydrogen bonds, created as a result of the chemical treatment, replacing the original disulfide bonds, which are of different strength compared to the bonds of untreated hair. The quantitative sorption data matched well to the model of grains of matrix enveloped in layers of water molecules at increasing relative humidity, up to 100 %. The analysis suggested that, aside from the glass transition event occurring at around 60-70 % relative humidity, there is another, less examined, transition occurring at around 30 % relative humidity, assigned to the opening of the hair inner structure, and accommodation of more water molecules. Both transitions are reflected by corresponding changes in the fibre mechanical behaviour.

CONCLUSION

The moisture sorption-desorption by hair was shown not only to allow a quantitative differentiation among various cosmetic treatments of the hair, but also to provide valuable information on the structure of the fibre.