Structural regulation and enhanced sunscreen performances of functional shellac nanoparticles

To reduce the cellular components damage and marine ecosystem pollution caused by common chemical sunscreens, natural or biologically derived sunscreen ingredients have become one of the major priorities, due to their effective protection against ultraviolet (UV) radiation while minimizing potential health risks. Herein, we develop a novel sunscreen agent, shellac, that is refined from biological sources with good biocompatibility and amphiphilicity. Shellac was first modified with natural source materials through amidation reaction, dextran (DEX), coumarin (CM) or cinnamic (CA), in which the former provided the hydrogen-bonding interaction, and the latter two provided UV absorption performance. The structures of these modified products were confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier Transform Infrared (FTIR) and Proton Nuclear Magnetic Resonance ( 1 HNMR). Then, a plant sunscreen, sinapic acid (SA) was encapsulated into modified shellac nanoparticles (MSNPs), which showed uniform spherical structure observed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Zeta potential and nanoparticle analyzer, and the resultant MSNPs were further blended with sunscreen cream matrix. The sunscreen cream showed good enhanced UV-absorption capacity, and the Sun Protection Factor (SPF) increased to above 50. In addition, FTIR and UV-Vis absorption spectra were carried out to explore the possible synergistic effect between functional shellac, SA and sunscreen cream matrix. The obtained MSNPs also have superior biosafety according the cytotoxicity test, which makes them an ideal skin sunscreen agent.