Design of solid lipid nanoparticles for caffeine topical administration

Context: Solid lipid nanoparticles (SLN) are drug carriers possessing numerous features useful for topical application. A copious scientific literature outlined their ability as potential delivery systems for lipophilic drugs, while the entrapment of a hydrophilic drug inside the hydrophobic matrix of SLN is often difficult to obtain. Objective: To develop SLN intended for loading caffeine (SLN-CAF) and to evaluate the permeation profile of this substance through the skin once released from the lipid nanocarriers. Caffeine is an interesting compound showing anticancer and protective effects upon topical administration, although its penetration through the skin is compromised by its hydrophilicity. Materials and methods: SLN-CAF were formulated by using a modification of the quasi-emulsion solvent diffusion technique (QESD) and characterized by PCS and DSC analyses. In vitro percutaneous absorption studies were effected using excised human skin membranes (i.e. Stratum Corneum Epidermis or SCE). Results: SLN-CAF were in a nanometric range (182.6 ± 8.4 nm) and showed an interesting payload value (75% ± 1.1). DSC studies suggest the presence of a well-defined system and the successful drug incorporation. Furthermore, SLN-CAF generated a significantly faster permeation than a control formulation over 24 h of monitoring. Discussion and conclusions: SLN-CAF were characterized by valid dimensions and a good encapsulation efficiency, although the active to incorporate showed a hydrophilic character. This result confirms the suitability of the formulation strategy employed in the present work. Furthermore, the in vitro evidence outline the key role of lipid nanoparticles in enhancing caffeine permeation through the skin.