SP-NLC dispersion was incorporated into 1% w/v Carbopol gel containing 0.2 g methyl paraben as preservative. The obtained gel was allowed to hydrate for 24 h. The resulting mixture was then stirred followed by neutralization with tri-ethanolamine (approximately 10 drops) to obtain an adequate semisolid carbopol gel matrix (for a full composition of each formulation refer to Table 1S in the Supplementary material).