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

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