The physical and chemical disruption of human hair after bleaching - studies by transmission electron microscopy and redox proteomics.

OBJECTIVE: To understand the structural and chemical effects of cosmetic peroxide bleaching on human hair. METHODS: Human hair was progressively bleached using alkaline peroxide-persulphate treatment. Proteins lost through leaching were examined using amino acid analysis and mass spectrometric sequencing. Fibre damage was assessed using transmission electron microscopy, amino acid analysis and redox proteomics. RESULTS: Protein loss through leaching increased with bleaching severity. Leached proteins were not limited to the cuticle, but also included cortical intermediate filaments and matrix keratin-associated proteins. The leached proteins were progressively oxidized as bleaching severity increased. Bleached fibres demonstrated substantial damage to the cuticle layers and to the cortex. Extensive melanin granule degradation was present after the mildest bleach treatment. Protein oxidation in bleached fibres was principally in cortical intermediate filaments - the most abundant hair proteins - and targeted the sulphur-containing amino acids, particularly the conversion of cystine disulphide bonds to cysteic acid. CONCLUSION: Peroxide chemical treatments quickly access the cortex, causing untargeted oxidative damage across the fibre in addition to the desired loss of melanin. Peroxide ingress is likely facilitated by the considerable structural degradation caused to the cuticle layers of hair fibres. The consequences of the peroxide action within the cuticle and cortex are oxidation of the proteins, and subsequent protein loss from the fibre that correlates to bleaching severity.

Advantages of a high-throughput measure of hair fiber torsional properties.

While the tensile response of fibers of human hair is the most extensively studied mode of mechanical deformation, the properties of hair in different deformation modes remain of interest and can provide valuable insight into the effects of chemical treatments. Previously reported methods for the measurement of fibers in torsional deformation have inherent systematic errors, are low-throughput, and are operator-intensive. This paper presents a new method for the measurement of fiber torsional properties developed to reduce these errors and to improve the efficiency of the technique. This method was designed to be fully automated, requiring no operator input during an experiment, and affording higher sample throughput while improving the ease of use in variable climatic conditions. The new method is compared to a conventional torsional pendulum method for measuring fiber shear modulus, and an evaluation of experimental reproducibility is made using hair and nylon fibers. It was found that the new method provides absolute values for shear modulus similar to those of the pendulum technique, with reduced run-to-run variability between fibers, while enabling larger sample numbers to be explored in shorter times.