Natural polymer towards lustrous multicolored silk: Hermetical encapsulation and understanding of colorants via controlled de/recrystallization process

Abstract We develop an innovative approach to utilize silk, a natural polymer with discrete hydrophobic blocks interspersed with hydrophilic domains for hermetically encapsulating hydrophilic colorants to create a palette of lustrous multicolored silk while retaining its unique properties and rendering new functionalities. The success is largely dependent on the structures of colorants, the recrystallization of silk and the affinity between them. It is important to examine phase transfer capabilities and phase distribution coefficients of colorants in the presence/absence of silk, which are considered as influential factors in evaluation and selection of suitable colorants and matrices for effective encapsulation of colorants to produce safe and healthy cosmetics. As a result, this formulated silk increases color-encapsulating efficiency, prolongs color-retaining capability, enhances color physiochemical stability, reduces cytotoxicity and provides spreadability for potential use in cosmetic application. Meanwhile, it also presents flexibility to incorporate both organic and inorganic colorants together with a variety of more materials including fragrances, hydrating agents, antioxidants, UV fillers, etc.