Preparation and characterization of hydrolyzed keratin-loaded casein microspheres for nail care

Nail decoration causes damage of nails though the use of polish remover containing harmful compounds. Therefore, development of a method for repairing the damaged nails is important because they have no ability to heal themselves. Hydrolyzed keratin has attracted much attention as a repairing agent of damaged nails. However, application of raw hydrolyzed keratin to damaged nails is impractical because the material is sticky and niffy. The purpose of this study was to develop hydrolyzed keratin-loaded microspheres for overcoming the issues. We used casein, a protein, as a microsphere material. Hydrolyzed keratin-loaded microspheres were prepared through water-in-oil (w/o) emulsion. Cross-linking of casein and hydrolyzed keratin dissolved in the aqueous solution were achieved by glutaraldehyde. After preparation of the microspheres, they were frozen at -20 °C or -196 °C, and vacuum-dried. Inner structures of the microspheres were observed using a scanning electron microscope (SEM). Freezing temperature of the microspheres influenced the inner structure. We confirmed that low freezing temperature resulted in decreased mechanical strength of the microspheres and the breaking load was lower than minimum adult pinch strength. Subsequently, we examined the effect of the volume ratio of aqueous phase to oil phase (Φw/o) on recovery ratio of the microspheres. Much difference among the recovery ratio at each Φw/o was not observed. This result shows that the emulsion system in this study is a promising for a large-scale production of the microspheres for nail care.