Abstract
Solid lipid nanoparticles (SLN) were recently proposed as carriers for various pharmaceutical and cosmetic actives. These lipid nanoparticles can act as moisturizers and physical sunscreens on their own. Therefore, the full potential of these carriers has yet to be determined. The present study was aimed to determine and compare moisturizing and UV-protecting effects of different solid lipid nanoparticles (SLN) prepared by different solid lipids including Glyceryl monostearate (GMS), Precirol® (P) and cetyl palmitate (CP) as carrier systems of moisturizers and sunscreens. The influence of the size and matrix crystallinity of the solid lipids on the occlusive factor, skin hydration and UV-protection were evaluated by in vitro and in vivo methods. The SLN were prepared by high-shear homogenization and ultrasound methods. Size, zeta potential and morphological characteristics of the samples were assessed by transmission electron microscopy (TEM) and thermotropic properties with differential scanning calorimetry (DSC) technique. Results of the assessments showed that SLN-CP significantly increases skin hydration and UV-protection, compared to SLN-GMS and SLN-P. It was demonstrated that the size of SLN, crystallinity index of solid lipid in SLN and probably other mechanisms besides the occlusive factor can influence skin hydration and UV-protection indices. Furthermore, findings of the assessments demonstrated significant difference between in vitro and in vivo assessments regarding occlusive factor and moisturizing effects. Findings of the present study indicate that the SLN-CP could be a promising carrier for sunscreens and moisturizers.
Highlights
Sunlight exposure can be both beneficial and harmful for the human body
The results showed that the Solid lipid nanoparticles (SLN)-cetyl palmitate (CP) has more ability to hydrate skin and protect skin against UV irradiation compared to SLN-Glyceryl monostearate (GMS) and SLN-P
The results demonstrated that the crystallinity and occlusive factor of solid lipid besides some other factors can influence on skin hydration
Summary
Sunlight exposure can be both beneficial and harmful for the human body. It has been known for decades that sunscreens are capable of protecting human body of solar radiation-induced harmful effects (Kullavanijaya et al, 2005; Potard et al, 2000). Solid lipid nanoparticles (SLN) have been introduced as a novel drug-delivery systems for pharmaceutical drugs and cosmetic active ingredients due to their advantages over conventional formulations (Muller et al, 2000; Wissing et al, 2003a). It was found that among Dynasan 112, Compritol 888 ATO and Softisan 154 as solid lipids in SLN; the highest occlusion will be achieved from low melting lipids with highly crystalline particles (Wissing et al, 2003b) These studies do not fully mimic the natural moisture loss conditions and there was no comparison between in vitro and in vivo skin hydration. UV protection properties of different lipids in SLN formulations were investigated by Transpore tape 3M in vitro method
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