Enhanced photoprotection with rheum ribes-loaded solid lipid nanoparticles: a novel sunscreen gel formulation

The limitations of current sunscreens in protecting against skin cancer and aging have been acknowledged. The use of Rheum ribes extract, rich in phenolic compounds and with strong antioxidant activity, for sunscreen applications has not been extensively studied. This study aims to develop a sunscreen gel containing Rheum ribes (Rhubarb) root extract-loaded solid lipid nanoparticles (SLNs) and evaluate its sun protection factor (SPF) through in vitro testing.

Rheum ribes extract-loaded SLNs were manufactured by an emulsification-solvent evaporation method. The impact of glyceryl monostearate (GMS) concentration on SLN size, polydispersity index (PDI), entrapment efficiency (EE), and in vitro drug release was investigated. The optimized formulation was incorporated into a gel base, and its SPF was determined using spectrophotometric techniques. Skin permeation and retention studies, as well as skin irritation and cytotoxicity assessments, were conducted.

The optimized extract-loaded SLN formulation exhibited a nano-sized diameter (298.07 ± 14.54 nm), uniform distribution (PDI = 0.308 ± 0.001), high entrapment efficiency (69.18 ± 2.60%), and significant skin permeation (32.03 ± 1.44% after 24 h) and retention (6.42 ± 0.39 mg/cm² after 24 h). This formulation demonstrated a substantially higher SPF (17.435) than the simple extract gel (SPF = 1.913). All gel preparations were found to be nonirritating and non-cytotoxic.

This study demonstrates the potential of Rheum ribes extract-loaded SLNs for developing effective and safe sunscreen gels. The optimized nanogel formulation achieved significant SPF enhancement while maintaining skin compatibility, highlighting its promising application in cosmetic sun protection.