J. Cosmet. Sci., 72, 47–62 (January/February 2021) 47 Design and Evaluation of Topical Antioxidant Nanogel Formulations GÖKÇE TETIK, SEDA RENÇBER, EZGI T. ÖZOĞLU, EVREN A. YAPAR, SINEM Y. KARAVANA, and ÖZGEN ÖZER, Department o f Pharmaceutical Technology, Faculty of Pharmacy, Ege University, Izmir 35100, Turkey (G.K., S.Y.K , Ö.Ö.), Department of Pharmaceutical Technology, Faculty of Pharmacy, Izmir Katip Celebi University, Izmir 35620, Turkey (S.R.), Departm ent of Biochemistry, Faculty of Pharmacy, Izmir Katip Celebi University, Izmir 35620, Turkey (E.T.Ö), Departm ent of Analysis and Control Laboratories, Turkish Medicines and Medical Devices Agency, MoH Turkey, Ankara 06430, Turkey (E.A.Y) Accepted for publication September 29, 2020. Synopsis Transde rm al deliv ery of an active substance is promising, but a challenging option is available for local and systemic effects. The prolonged residence of formulation in the skin is important for topical delivery. In this study, it was aimed to develop a formulation that can overcome the stability and absorption problems of the vitamin C active substance by preparing nanogels. Nanogel-based materials have high drug loading capacity, biocompatibility, stability, and biodegradability, which are the key points to design a topical drug delivery system. Bovine serum albumin (BSA) and chitosan (CS) were used to prepare nanogels by a simple green self-assembly technique. Prepared nanogels were successfully used to entrap vitamin C, with an entrapment ratio between 86.08% ± 1.29% and 107.93% ± 1.04%. The studies started with vitamin C analysis and continued with characterization studies such as homogeneity, pH, viscosity, rheological properties, zeta potential, polydispersity index, particle size, and in vitro dissolution studies of nanogels. The antioxidant activities of the formulations were also tested by cell culture studies. The antioxidant activities of the nanogels were also tested by in vitro 2,2-diphenyl-1-picrylhydrazyl assay. Although topical vitamin C is effective in many ways, it has a risk of serious stability and absorption problems. The present work was aimed at developing pharmaceutically optimized topical nanogel formulations of vitamin C for antioxidant effect. An optimum nanogel formulation was composed of a 1:4 ratio of CS:BSA with (F19 formulation) in terms of entrapping vitamin C, formulation homogeneity, pH, viscosity, rheological properties, zeta potential, PI, particle size, in vitro dissolution and cell culture studies. The optimized formulation showed higher antioxidant effi cacy in vitro than vitamin C. In conclusion, prepared topical nanogel of vitamin C was stable and could be used with promising potential for topical application. INTRODUCTION Vitam in C, also known as ascorbic acid, has been widely used in pharmaceutical and cosmetic preparations for the formulation protection against oxidation and to exert Address all correspondence to Sinem Y. Karavana at sinemyaprak@hotmail.com.

JOURNAL OF COSMETIC SCIENCE 48 physiological/biological activities. Its major biologic activity is related to the maintenance of the organism oxidation–reduction potential (1–3). In addition, vitamin C helps to regen- erate the oxidized forms of α-tocopherol. These properties of vitamin C are the basis for the antiaging claims made by the skincare industry (4–7). However, conventional vitamin C formulations have diffi culty in penetration to the skin in stabilization and topical applica- tion. It can be easily degraded in the presence of oxygen, humidity, and high temperature during processing and storage. Therefore, to overcome the instability of vitamin C, different approaches have been explored. Among them, one can cite encapsulation of vitamin C by liquid crystals, microemulsions, nanocapsulation, and liposomes (8–11). Nanoparticle delivery s ystems have been shown to be very effective in stabilizing drugs to overcome biological barriers and to control the release rate and duration of drugs. Moreover, the nanoscale particles are collected under high–vascular permeability sites, and nanoparticles can be made cell-specifi c by targeting to the surface of the ligands (12). Nanogels are nanoscale particles capable of swelling by physically, chemically cross-linking hydrophilic, or amphiphilic polymer chains, which may be ionic or nonionic. Nanogels act as carriers for drug delivery by absorbing the biologically active molecule through salt bonds, hydrogen bonds, or hydrophobic interactions. Nanogels are very promising as drug delivery carriers because of their high stability, high drug loading capacity, and hypersensi- tive reactions to factors such as ionic strength, pH, and temperature for commonly used nanocarriers (13). In this study, chitosan (CS) [low–, medium–, and high–molecular weight deacetylated chitin, poly(D-glucosamine)] was chosen as polymer for preparation of nanogel formulations because of its cationic, nontoxic, biocompatible, and biodegradable properties (14). Bovine serum albumin (BSA) was used as protein because of its medical importance, abundance, low cost, ease of purifi cation, unusual ligand-binding properties, and wide ac- ceptance in the pharmaceutical industry (15). Nanogels based on CS and BSA were fabri- cated by the self-assembly technique, which is a simple, green, and low-cost process (15). The aim of this study w as to prepare a more effective formulation by eliminating the stability and absorption problems of topical application of conventional preparations of vitamin C. For this purpose, it was aimed to prepare a high-stability dosage form with the potential to eliminate the absorption problem of the active ingredient vitamin C, which supports the production of the anti-infl ammatory agents, antioxidants, and colla- gen, to carry out quality control studies and to test the antioxidant effectiveness of this dosage form in vitro. Nanogel formulations were prepared using different ratios of CS and BSA. To determine the physicochemical properties of the formulations, characterization studies such as particle size, polydispersity index (PI), zeta potential, viscosity, pH, rheo- logical analyzes, and imaging studies were performed, and formulations were evaluated according to the results obtained. In addition, stability studies were carried out to exam- ine the physical stability of nanogel formulations, and the cell culture studies and anti- oxidant activities of these vitamin C–loaded nanogel formulations were also examined. MATERIALS AND METHODS M ATERIALS Vitamin C, 2, 2-difenil- 1-pikrilhidrazil, acetic acid, BSA, CS (high, medium, and low molecular weight), and methanol were purchased from Sigma-Aldrich, Germany. N-octanol