PHARMACEUTICALLY OPTIMIZED TOPICAL NANOGEL FORMULATION 59 results of in vitro dissolution studies, it is observed that F1 formulation releases more slowly than the others. F19 is the fastest release formulation among the studied formula- tions. The F27 formulation selected as the optimum formulation achieved 100% release at 5 h. This release profi le was found to be suitable for developed formulations. Graphs of in vitro release of active substances from nanogels are given in Figure 4. ANTIOXID ANT ACTIVITY OF NANOGELS The anti oxidant activity of nanogels was tested by in vitro DPPH assay. The results of antioxidant activity of empty nanogels (EF1, EF9, EF19, EF27, and EF31) and vitamin C–loaded nanogels (F1, F9, F19, F27, and F31) are presented in Table VI and Figure 5. Antioxidant activity of F19 nanogel was higher than vitamin C (10 μg/mL). No signifi - cant difference was observed among vitamin C (10 μg/mL), F1, F9, and F31 groups in Figure 4. In vitro drug release profi les of formulations. Table VI Antioxidant Activity of Nanogels According to In Vitro DPPH Assay Samples % Inhibition Samples % Inhibition Vit. C (1 mg/mL) 96.90 ± 1.39 Vitamin C (10 μg/ml) 63.94 ± 1.25 Empty nanogels Vitamin C–loaded nanogels EF1 13.61 ± 1.71 F1 62.52 ± 1.63 EF9 3.38 ± 1.78 F9 61.49 ± 1.84 EF19 8.08 ± 1.12 F19 80.14 ± 4.06 EF27 10.37 ± 1.12 F27 51.18 ± 2.35 EF31 8.13 ± 1.05 F31 62.36 ± 2.33

JOURNAL OF COSMETIC SCIENCE 60 terms of antioxidant activity. The antioxidant activity of F27 nanogel was found to be low compared with both vitamin C (10 μg/mL) and other vitamin C–loaded nanogels. STABILITY S TUDIES OF FORMULATIONS The formula tions selected optimally for stability studies were placed in two different conditions in the stability chamber containing 60% relative humidity at room tempera- ture at 25°C and 75% relative humidity at 40°C at certain time intervals (15 d, 1, 2, 3, and 6 mo). Selected formulations were stable, and there was no serious change in physical properties during 6 mo (data not shown). CONCLUSION Be cause nanog el-based materials have high drug loading capacity, biocompatibility, stabil- ity, and biodegradability, which are the key points to design a topical drug delivery system, in our study, nanogels were used to develop a formulation, which overcame the stability and absorption problems of vitamin C. And nanogels were successfully prepared by physical self-formation with the polymers, BSA, and CS by a simple green self-assembly technique. The results of in vitro characterization and the antioxidant activity studies were proved that vitamin C–loaded nanogels including CS:BSA with a 1:4 ratio (F19 formulation) presented optimum properties in terms of entrapping vitamin C, formulation homogeneity, pH, viscosity, rheological properties, zeta potential, PI, particle size, in vitro dissolution, and cell culture studies. In light of this study, a stable and an applicable topical nanogel of vitamin C was prepared, and it is promising for clinical studies for antiaging purposes. Figure 5. In vitro antioxidant activity of nanogels. ap 0.05 versus 1 mg vitamin C, F1, F9, F19, F27, and F31, bp 0.05 versus other groups, cp 0.05 versus 10 μg vitamin C, 1 mg vitamin C, F1, F9 F27, and F31, dp 0.05 versus 10 μg vitamin C, 1 mg vitamin C, F1, F9, F19, and F31.