Topical gel of Metformin solid lipid nanoparticles: A hopeful promise as a dermal delivery system

[Display omitted] •Metformin solid lipid nanoparticles were prepared by the ultra-sonication method.•Solid state analysis ruled out any interaction between metformin and excipients.•Ratio of Tween:Span had a significant influence on performance of Met-SLN.•Gels containing Met-SLN showed better performance on the skin delivery of metformin. The aim of the present study was to enhance the skin delivery of metformin by making solid lipid nanoparticles containing metformin using the ultra-sonication method. To achieve the optimum skin delivery for metformin, the effects of the ratio of two surfactants (Tween:Span) on nanoparticles properties and their performance were investigated. Photon correlation spectroscopy, scanning electron microscopy (SEM), Powder X-ray Diffractometer (PXRD), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) were used to characterize the solid state of metformin in solid lipid nanoparticles. Generally, the particle size of nanoparticles decreased by the addition of co-emulsifier (Span®60). Results showed that all formulations made by binary mixtures of surfactants had low particle size, low Polydispersity index and high zeta potential. It was interesting to note that the smallest nanoparticles (203.8 ± 15.356) was obtained when the HLB of the binary surfactants (HLB of 11.67) was closer to the HLB of beeswax (HLB of 12) used in the preparation of SLN. It was also found that by decreasing the HLB of the system from 14.9 to 10.06 the zeta potential of SLNs increased from −0.651 ± 0.315 to −6.18 ± 0.438 mV. But, a further reduction in the HLB from 10.06 to 8.45 caused a reduction in the zeta potential from −6.18 to −3.596 ± 0.255. Results showed that the highest entrapment efficiency of 45.98 ± 9.20% was obtained for formulation with larger particle size and with the highest HLB value (HLB 14.9). DSC study showed that metformin in SLN is in an amorphous form. FT-IR spectra of Met-SLN showed that the prominent functional groups existed in the formulations which could be an indication of good entrapment of metformin in a lipid matrix. FT-IR results also ruled out any chemical interaction between the drug and the excipients. The amounts of metformin detected in the skin layers and the receptor chamber at all sampling times were higher for nanogel compared to metformin gel. This is an indication of a better performance of Metformin nanogel ex-vivo and could be developed further for clinical studies.