Eumelanin encapsulated polymeric particles using poly(D-lactide-CO-caprolactone) block copolymers and their stereocomplex

Eumelanin as a natural pigment present several key functional properties that can protect human skin from ultraviolet (UV) light. Photoprotection ability that can absorb most of the UV light as a result of aromatic compounds in its structures has drawn vast interest to harness its excellent properties for various applications. Major drawbacks shown by organic molecules as UV absorber that limits their application includes their short lifespan. Encapsulation of the compound by various shell materials has been extensively studied to further optimize and extend its shielding efficiency fromUV radiation. Polylactide (PLA)-based copolymers are widely used in encapsulation of various active compounds, due to their biocompatibility and biodegradability, promoting the sustained release of the active compounds. In this study, stereocomplexPLA (sc-PLA) formed by blending of poly(D-lactide-caprolactone-D-lactide), P(DLAb-CL-b-DLA), triblock copolymer with linear poly(L-lactide), PLLA, was employed in the encapsulation of eumelanin. An oil in water emulsion (O/W) approach followed bysolvent evaporation was performed in encapsulation process. Effect of eumelanin distribution in PLA’s enantiomers and ultrasonication on physicochemical properties, encapsulation efficiency, and release behavior of nano/microparticles was evaluated. The potential application of the resulting particles for sunscreen was also examined by measuring the UV absorbance and in vitro sun protection factor (SPF) of sunscreen containing particles in the UVA-UVB region. FTIR spectra of the particles show characteristic peaks of sc-PLA with the changes in the intensity of significant peaks that correspond to eumelanin, denoting the success of the encapsulation process.Morphological image analysis reveals that the resulting particles have spherical shaped with the particle size that can be controlled by applying ultrasonication. Distribution of eumelanin in copolymer and ultrasonication process promote the growth of sc-PLAwith highly ordered arrangement and more efficient entrapment of eumelanin. The resulting particles present relatively higher initial burst release and faster release rate than its counterparts. The small particle size provided by ultrasonication also affects thecytotoxic activity of the resulting particles, where the cytotoxic activity increased at relatively high concentration of particles. High content of eumelanin inside the particles and large surface area improves the UV absorbance and sunscreen performance of theparticles. The results of this study suggest that eumelanin-loaded particles can be potentially used as UV shielding material in diverse applications, especially in the cosmetic and pharmaceutical fields.