Self-Assembly 4-Butylresorcinol Deep Eutectic Solvent Nanoparticles for Efficient Transdermal Delivery and Whitening.

Background: Skin whitening agents often face challenges such as poor stability and low permeability. To overcome these issues, a novel 4-butylresorcinol (4-BR)/D-a- Tocopherol Polyethylene Glycol Succinate (TPGS) deep eutectic solvent (DES) system was developed, which can self-assemble into carrier-free nanoparticles (NPs). Methods: The 4-BR/TPGS DES was synthesized and characterized by theoretical calculations, DSC, FTIR, 1H-NMR, and 2D NMR to confirm its successful formation. Results: The self-assembled 4-BR/TPGS DES NPs showed a 3.46-fold increase in skin permeability, a 1.53-fold improvement in 4-BR stability, a 1.55-fold increase in melanin inhibition in B16 cells, and a 2.16-fold higher melanin suppression in zebrafish compared with traditional 4-BR oil-based formulations. These results indicated the excellent whitening efficacy and transdermal delivery potential of this formulation. Conclusions: The combination of TPGS-based DES and self-assembly technology represents a revolutionary approach for advanced transdermal delivery and the development of skin care products.