Halloysite/keratin nanocomposite for human hair photoprotection coating.

We propose a novel keratin treatment of human hair by its aqueous mixtures with natural halloysite clay nanotubes. The loaded clay nanotubes together with free keratin produce micrometer thick protective coating on hair. First, colloidal and structural properties of halloysite/keratin dispersions and the nanotube loaded with this protein were investigated. Above the keratin isoelectric point (pH = 4), the protein adsorption into the positive halloysite lumen is favored due to the electrostatic attractions. The zeta-potential magnitude of these core-shell particles increased from -35 (in pristine form) to -43 mV allowing for an enhanced colloidal stability (15 hours at pH = 6). This keratin-clay tubule nanocomposite was used for the immersion treatment of hair. 3D measuring laser scanning microscopy demonstrated that 50-60 % of the hair surface coverage can be achieved with 1 wt. % suspension application. Hair samples have been exposed to UV irradiation for times up to 72 hours to explore the protection capacity of this coating by monitoring the cysteine oxidation products. The nanocomposites of halloysite and keratin prevent the deterioration of the human hair as evident by significant inhibition of cysteic acid. The successful hair structure protection was also visually confirmed by AFM and dark-field hyperspectral microscopy. The proposed formulation represents a promising strategy for a sustainable medical coating on the hair, which remediate UV irradiation stress.