ADVANCEMENTS IN HERBAL NANOEMULSIONS AND NANOSTRUCTURED LIPID CARRIERS: FORMULATION STRATEGIES, OPTIMISATION, AND THERAPEUTIC APPLICATIONS

Plant-derived bioactive compounds offer broad therapeutic promise, yet their clinical translation is constrained by poor aqueous solubility, chemical and metabolic instability, limited membrane permeability, efflux by P-glycoprotein, and extensive firstpass metabolism, which together depress oral bioavailability. Lipid-based nanocarriers have emerged as a rational strategy to overcome these biopharmaceutical barriers. This review critically synthesises advances in two complementary lipidic platforms for phytopharmaceutical delivery: herbal nanoemulsions and nanostructured lipid carriers (NLCs). We examine their composition and structural classes, the high-energy and low-energy fabrication strategies used to produce them, and the systematic optimisation paradigms (particularly Quality by Design and response-surface methods such as the Box-Behnken design) that have replaced empirical, trial-and-error development. The principal physicochemical critical quality attributes (droplet or particle size, polydispersity index, zeta potential, entrapment efficiency, and release behaviour) are discussed alongside the analytical methods used to characterise them. We then map the therapeutic landscape, drawing on representative studies of curcumin, essential oils, flavonoids, and repurposed lipophilic drugs across oral bioavailability enhancement, oncology, dermatology, central nervous system targeting, metabolic disease, ocular and antimicrobial therapy, and nutraceutical applications. Across this evidence base, nanoemulsions and NLCs consistently improved solubilisation, stability, permeation, and pharmacological activity relative to conventional formulations, with reported bioavailability gains ranging from severalfold to greater than four-fold. We conclude by appraising the outstanding challenges of physical stability, biological safety, regulatory standardisation, and industrial scale-up, and we identify priorities for translating herbal lipid nanocarriers from bench to clinic. The evidence assembled here is drawn from peer-reviewed literature indexed in PubMed