Department of Pharmaceutical Technology, Faculty of Pharmacy, University of Ljubljana, Ljubljana, Slovenia.
Drug Dev Ind Pharm. 2010 Jul;36(7):852-60. doi: 10.3109/03639040903541187.
Colloidal silica is the thickener of interest for topical formulations and can therefore be used to optimize the viscosity of both hydrophilic and lipophilic microemulsions (MEs). To the best of our knowledge, no information is available about the effect of topically applied colloidal silica on skin penetration of drugs. So, our aim was to determine its influence on the effectiveness of ME in the simultaneous delivery of vitamins C and E to the skin.
Two different aspects of silica possible function were investigated. Its effects on formulation characteristics were studied by determination of partition coefficient of the vitamins, their solubility and release profile. The direct impact of silica on the skin was further evaluated by transepidermal water loss measurements, scanning electron microscopy (SEM), and cell toxicity determination (MTT assay).
The addition of colloidal silica to ME was shown to increase significantly the vitamins' solubility and their partition to the phase in which they were less soluble. Its presence also increased the amount of both vitamins in epidermis, which was confirmed by release studies. Furthermore, we demonstrated that colloidal silica interacts with excised skin. It decreased transepidermal water loss, probably by retaining water in the stratum corneum because of its massive accumulation in the upper layers, as revealed by SEM.
The results confirmed that addition of colloidal silica in ME simultaneously loaded with vitamins C and E enhanced vitamins' skin bioavailability by its dual influence on delivery characteristics of ME as well as on skin properties.
胶体二氧化硅是一种增稠剂，适用于局部制剂，因此可用于优化亲水和亲脂性微乳液（ME）的粘度。据我们所知，尚无关于局部应用胶体二氧化硅对药物经皮渗透的影响的信息。因此，我们的目的是确定其对 ME 同时向皮肤递送维生素 C 和 E 的有效性的影响。
研究了二氧化硅的两个可能作用的不同方面。通过测定维生素的分配系数、溶解度和释放曲线来研究其对制剂特性的影响。通过测量经皮水分流失、扫描电子显微镜（SEM）和细胞毒性测定（MTT 测定）进一步评估二氧化硅对皮肤的直接影响。
向 ME 中添加胶体二氧化硅可显著增加维生素的溶解度及其向溶解度较低的相中的分配。其存在还增加了表皮中两种维生素的含量，这通过释放研究得到了证实。此外，我们证明胶体二氧化硅与离体皮肤相互作用。它降低了经皮水分流失，可能是因为其在角质层中大量积累，从而保留了水分，SEM 显示其在上层大量积累。
结果证实，在同时负载维生素 C 和 E 的 ME 中添加胶体二氧化硅通过其对 ME 的输送特性以及对皮肤特性的双重影响增强了维生素的皮肤生物利用度。
