Design and characterization of postbiotics-loaded emulgels as stable skin-compatible topical delivery systems

The incorporation of postbiotics into structurally optimized emulgels represents a promising strategy for the stabilization and topical delivery of microbial-derived bioactive compounds. In this study, a series of emulgels containing postbiotics from Lacticaseibacillus rhamnosus, Lactiplantibacillus plantarum, Lactobacillus acidophilus, and Lacticaseibacillus paracasei were formulated. Microscopic analysis and comprehensive physicochemical evaluations, including organoleptic assessment, enabled a detailed characterization of the semi-solid systems. The pH values were within the range commonly reported for topical formulations (below 5.5). Furthermore, stability tests demonstrated that the emulgels resist phase separation even under cyclically varying temperatures. Dynamic Light Scattering (DLS) measurements showed nano- to submicron particles (80-280 nm) with moderate polydispersity (0.20-0.42), confirming relatively homogeneous yet complex dispersions. Importantly, the postbiotics modified the internal organization without compromising colloidal stability. The application of postbiotic formulations on human skin ex vivo did not significantly alter transepidermal water loss (TEWL), with values remaining comparable before and after application, validating that the developed emulgels do not impair skin barrier integrity. The findings demonstrate the feasibility of incorporating microbial-derived postbiotic materials into emulgels and support their further investigation as components of delivery systems intended for cosmetic and skincare applications.