Oil-free sunscreen templates enabled by aqueous two-phase system emulsion

Ultraviolet (UV) exposure is a major cause of skin damage and long-term health risks, driving the widespread use of sunscreen formulations as a primary protective strategy. Most commercial sunscreens are formulated using oil-based emulsion systems that incorporate lipophilic UV filters; however, increasing attention has been directed toward their potential environmental impact and biocompatibility concerns. These limitations have motivated the development of alternative sunscreen platforms that reduce dependence on oil-based components while maintaining effective UV protection. To overcome these limitations, we first report an oil-free sunscreen platform based on aqueous two-phase systems (ATPS)-derived emulsions. The formulation consists of polyvinyl alcohol (PVA), dextran, titanium dioxide nanoparticles (TiO₂), and phenylbenzimidazole sulfonic acid (Ensulizole), forming an ATPS emulsion structure that enables homogeneous particle distribution and uniform film formation upon application. The resulting emulsion exhibited enhanced UV-protection performance compared with conventional aqueous particle suspensions. In vitro SPF measurements reached approximately 40 at 15 w/v% TiO₂, exceeding the values obtained from a commercial sunscreen tested under identical conditions (SPF 20~50). Furthermore, while particle suspensions became increasingly heterogeneous with increasing TiO₂ concentration, the W/W emulsion maintained a highly uniform coating layer, indicating improved film-forming capability and spatial consistency of UV protection. These results demonstrate that ATPS emulsions can serve as a promising formulation platform for environmentally friendly sunscreen systems by combining effective UV protection with uniform surface coverage. The proposed approach expands the design space of sunscreen formulations and highlights the potential of all-aqueous emulsion systems for next-generation UV-protective materials.