Removal of pigments from human hair to obtain purer keratin fractions for downstream biofabrication

Abstract

The incineration of large amounts of human hair waste from salons has led to concerns over toxic gas emissions and global warming. As such, studies on the conversion of human hair resources into high-value products have become common. Human hair is mostly made up of proteins consisting of keratin-associated proteins (KAPs) and keratins. These proteins make up the structure of the human hair. Melanosomes are also present in the hair cortex region, where most proteins are located. They contain melanin that contributes to the colour of human hair and has UV barrier properties. The utilisation efficiency of human hair as a resource would be further improved with the use of keratins and melanosomes as biomaterials.

However, extracted keratins contain melanosomes that cause high pigmentation in fabricated templates, making them unsuitable for applications where transparency is key. Hence, this project aims to obtain purer keratin fractions from human hair by studying and improving the process of keratin extraction. Two approaches were proposed to reduce the level of pigmentation in hair and keratin extracts: chemical bleaching of hair and enzymatic extraction of melanosomes from matrix-free hair. The extraction of melanosomes via enzymatic means is deemed a greener alternative. Extraction from matrix-free hair allows melanosomes to be extracted before the extraction of keratins from human hair shafts. A clean separation between keratins and melanosomes will enhance the resource recovery efficiency of human hair fibres.

Firstly, one cycle of chemical bleaching of hair of Asian ethnicity turned black hair into dark blonde hair. The surface morphology and structure of hair after each process were evaluated through scanning electron microscope (SEM) imaging and Fourier transform infrared (FTIR) spectroscopy, respectively. Surface cuticle damage observed on bleached hair did not affect the secondary structure of the hair fibre. Higher transmittance also indicated reduced pigmentation in hair. The yield and quality of keratins extracted from bleached hair were also assessed via various assay techniques, SDS-PAGE, FTIR spectroscopy, circular dichroism (CD) spectroscopy, and ultraviolet-visible (UV) spectroscopy. It was found that chemical bleaching of hair successfully reduced the level of pigmentation in keratin extracts while maintaining the yield and quality of the protein.

Secondly, the enzymatic extraction of melanosomes from matrix-free hair yielded structurally intact and functional melanosomes with good yield. The extracted melanosomes were characterised using SEM, FTIR, and UV-vis spectroscopy. The UV-filtering abilities of melanosomes extracted from KAP-free hair were retained. Further studies on the yield and quality of melanosome-extracted keratins yielded high amounts of low-molecular-weight keratins. Further studies on the reduction in pigmentation of keratin extracts via enzymatic extraction of melanosomes are recommended.

Overall, the chemical bleaching of hair and enzymatic extraction of melanosomes from matrix-free hair conducted in this project provides useful insights into the reduction of pigmentation in keratin extracts for better utilisation efficiency of human hair resources in the future.