Fatigue failure testing of human hair: Weibull-analysis for constant strain experiments.

Fatigue failure testing of materials is an important aspect of assessing their strength and resilience under long-term, oscillatory stresses and/or strains. This also applies to human hair. For this investigation, we decided to complement existing experience on cyclic tests at various levels of constant stress with those at various constant strains (4-30%).

pH-equilibration of human hair: Kinetics and pH-dependence of the partition ratios for H - and OH -ions based on a Freundlich isotherm.

Hair is an insoluble, fibrous, α-keratinous, protein composite material, providing outer coverage, e.g., for mammals.

Comparing hair tensile testing in the wet and the dry state: Possibilities and limitations for detecting changes of hair properties due to chemical and physical treatments.

Objectives: This investigation focuses, first, on the question to which extent wet and dry tensile tests on human hair may be considered as leading to independent results. Second, we try to assess the sensitivities of wet and dry-testing to detect changes of mechanical properties. Specifically, we were interested in separating changes, which were induced by a combination of a chemical (oxidation/bleach) and a physical treatment (heat).

The information content of tensile tests of human hair (wet) is limited: Variables mainly cluster in just two principal components.

Tensile testing of keratin fibres, such as wool and hair, in the wet state is a well established tool in the academic as well as applied portfolio of mechanical analyses. For the tensile curve of a hair fibre, fourteen material-specific stress-, strain, and work-related variables were identified. Analysing twelve samples of cosmetically untreated hair, we show that the variables show good precision and a satisfactory degree of homogeneity across samples.

Perm-waved human hair: a thermorheologically complex shape memory composite.

A "permanent" bent shape can be imposed on a straight human hair by a two-stage reduction/oxidation (perm-waving) process. The process relies on the molecular level on sulfhydryl/disulfide interchange as bond exchange reaction (BER). We expected a well-documented transition temperature around 60°C to be the trigger for the shape memory (SM) process of perm-waved hair.

Why is hair curly?-Deductions from the structure and the biomechanics of the mature hair shaft.

The final shape of a head hair is predetermined through a variety of factors during its formation in the follicle. These are genetic pathways, specific growth factors, cell differentiation and segregation, etc, with spatial as well as chronological dynamics. The cortex of hair consists of two major cell groups.

Model-based analysis of the torsional loss modulus in human hair and of the effects of cosmetic processing.

Torsional analysis of single human hairs is especially suited to determine the properties of the cuticle and its changes through cosmetic processing. The two primary parameters, which are obtained by free torsional oscillation using the torsional pendulum method, are storage (') and loss modulus (″). Based on previous work on ', the current investigation focuses on ″.

Debunking the Myth of Wool Allergy: Reviewing the Evidence for Immune and Non-immune Cutaneous Reactions.

Although wool is commonly believed to cause irritant (non-immune) and hypersensitivity (immune) cutaneous reactions, the evidence basis for this belief and its validity for modern garments have not been critically examined. Publications from the last 100 years, using MEDLINE and Google Scholar, were analysed for evidence that wool causes cutaneous reactions, both immune-mediated (atopic dermatitis exacerbation, contact urticaria, allergic contact dermatitis) and non-immune-mediated (irritant contact dermatitis, itch). Secondary aims of this paper were to examine evidence that lanolin and textile-processing additives (formaldehyde, chromium) cause cutaneous reactions in the context of modern wool-processing techniques.

Analysis of the torsional storage modulus of human hair and its relation to hair morphology and cosmetic processing.

Through measurements of three different hair samples (virgin and treated) by the torsional pendulum method (22°C, 22% RH) a systematic decrease of the torsional storage modulus G' with increasing fiber diameter, i.e., polar moment of inertia, is observed.

Thermal denaturation and structural changes of α-helical proteins in keratins.

To gain insight into the thermal stability of intermediate filaments and matrix in the biological composite structure of α-keratins, the thermal denaturation performance of human hair fibers was investigated by Modulated Differential Scanning Calorimetry (MDSC) in the dry and the wet state. Denaturation enthalpy ΔH(D) in water was found to be independent of heating rate (11.5J/g) and to be approximately double as high as in the dry state (5.

Spatial probing of the properties of the human hair surface using Wilhelmy force profiles.

The natural surface of human hair (epicuticle) consists of a bilayer of heavily cross-linked proteins toward the individual cuticle cell inside combined with a monomolecular, hydrophobic layer of mixed fatty acids to the outside (F-layer), which is generally assumed to be homogeneous. Wetting force profiles along segments of hair from female test persons with lengths equivalent to about 1 month of growth (approximately 10 mm) are presented. In a multistep analysis, applying curve smoothing as well as Fourier and principal components analysis, for hair lengths comprising daily and weekly growth (2 mm) pronounced systematic changes are observed in the profiles, which show that the wettability curves are nonstochastic in nature and that hair exhibits a strongly nonhomogeneous surface.