Microfluidics preparation of poly(lactic acid) microcapsules encapsulated with octyl methoxycinnamate for sunscreen application

OBJECTIVE: The systemic absorption of active ingredients in commercial sunscreens has raised safety concerns. This has created a need for advanced delivery systems that can enhance efficacy while minimising skin penetration. A promising solution is the encapsulation of sunscreen agents within microcapsules. The objective of this study is to demonstrate a simple and controllable method based on microfluidics for the preparation of sunscreen microcapsules with high ultraviolet absorption, good thermal stability, enhanced monodispersity and improved UV absorption performance. METHODS: A microfluidics-assisted method was employed to encapsulate a typical chemical UV filter, octyl methoxycinnamate (OMC), within biodegradable poly(lactic acid) (PLA) microcapsules using a commercial Corning Advanced-Flow microreactor. The effects of residence time on the morphology, size, encapsulation efficiency (EE) and loading capacity (LC) of the microcapsules were examined through comprehensive characterisation. Sun protection factor (SPF), UV stability and skin penetration of the microcapsules were also assessed, with release kinetics investigated by different models. RESULTS: The microfluidics-prepared microcapsules exhibited a uniform spherical morphology with adjustable sizes (10-38 μm), high encapsulation efficiency (>95%) and loading capacity (>22%). Compared to microcapsules prepared by the homogenisation method, the microfluidics-prepared ones displayed improved monodispersity and UV absorption performance. These improvements arise from microfluidics' precise control over droplet formation and narrow residence time distribution. Moreover, formulations containing OMC-loaded microcapsules achieved a 113% increase in SPF and significantly enhanced UV stability, along with a 50% reduction in skin permeation of OMC. CONCLUSIONS: This study highlights the significant potential of microfluidics encapsulation for producing uniform sunscreen microcapsules with enhanced efficacy, stability and safety. By minimising systemic absorption while improving UV protection, this approach meets growing regulatory and consumer demands for safer, high-performance sunscreen formulations. These findings offer valuable insights for advancing next-generation cosmetic products.