J. Cosmet. Sci., 71, 23–35 (January/February 2020) 23 Stability and Release Kinetics of Natural Oil Microemulsions Containing Nicotinamide NANG HNIN EI HLAING, NATTHIDA PAKPAYAT, and PRAPAPORN BOONME, Department of Pharmaceutical Technology, Faculty of Pharmaceutical Sciences, Prince of Songkla University, Songkhla 90112, Thailand (N.H.E.H., N.P., P.B.), Drug Delivery System Excellence Center, Prince of Songkla University, Songkhla 90112, Thailand (N.H.E.H., P.B.) Accepted for publication October 16, 2019. Synopsis This research aimed to evaluate stability and release characteristics of nicotinamide-loaded microemulsions (MEs). Four MEs were prepared with Tween 80 as surfactant, Span 80 as cosurfactant, either virgin coconut oil or olive oil as oil phase, water as aqueous phase, and nicotinamide as an active ingredient. They were composed of 3% w/w nicotinamide and designated as MEC1-N, MEC2-N, MEO1-N, and MEO2-N. All samples were kept in clear glass containers at 4°C, room temperature (RT, 28° ± 2°C), and 45°C for 3 months. Afterward, they were observed for physical changes and analyzed for remaining nicotinamide by a validated high-performance liquid chromatography technique. MEC1-N and MEO1-N were compared for nicotinamide released through dialysis membrane using modifi ed Franz diffusion cells. It was found that all samples were clear liquid and water-in-oil type. Phase separation was found in MEO2-N at all storage conditions. Discoloration was observed in all samples after being kept at 45°C for 3 months. MEC1-N, MEC2-N, and MEO1-N were both physically and chemically stable after being kept at 4°C and RT for 3 months. Release kinetics of MEC1-N and MEO1-N were the best fi tted with the Higuchi model. INTROD U CTION Nicoti namide, also known as vitamin B3, is an attractive active ingredient in skin-care products because of its many benefi ts. It is well known as a skin-lightening agent because it can inhibit melanosome transfer from melanocytes to keratinocytes (1). Moreover, it can provide other advantages for skin conditions such as anti-acne, anti-aging, and anti-infl ammatory (2,3). However, it is generally known that stratum corneum, the out- ermost layer of human skin, obstructs the penetration of all chemicals into deeper layers of the skin (4). Therefore, formulations are necessary for development of effective skin-care products. Microemulsions (MEs) are thermodynamically stable nanosystems composed of two normally immiscible phases, i.e., oil and water, which can simultaneously form as a Address all correspondence to Prapaporn Boonme at prapaporn.b@psu.ac.th.
JOURNAL OF COSMETIC SCIENCE 24 single-phase liquid with the help of interfacial fi lm of a surfactant (S) or a mixture of S and cosurfactant (CoS). MEs have been used in formulation development of many cos- metic products (5–7). MEs have been proposed to increase skin penetration of active ingredients by many possible mechanisms such as enhancer function of surfactant, hydration effect of aqueous phase, and carrier property of nano-sized droplets (5,8). Besides, the clear appearance and low viscous texture of MEs align with consumers’ expectations on sensory properties of skin-care products. It has been reported that topical water-in-oil (w/o) MEs are able to make their cosmetic active ingredients be highly accumulated in the skin membrane rather than permeated to the receptor fl uid, representative of blood circulation (9–11). Although w/o ME–containing nicotinamide was previously reported for its benefi ts (11), it contained synthetic oil and alcohol. Nowadays, consumers pay high concern to safety and global environment. Therefore, w/o MEs that were formulated from components with generally recognized as safe and natural status were focused in this study. Two nonionic surfactants, i.e., Tween 80 and Span 80, were used as an S and a CoS in the developed MEs, respectively. Both are generally recognized for low skin irritation potential and usually used as skin penetration enhancers (12). Natural oils, i.e., virgin coconut oil or olive oil, were studied as oil phase in the MEs. Virgin coconut oil is extracted from mature kernel of coconut (Cocos nucifera) and has long been used for skin application as a moisturizer (13). Olive oil is extracted from the fl esh of olive fruit (Olea europaea) and provides moisturizing, antioxidant, and photoprotective effects (14). Water was used as aqueous phase. This study aimed to examine stability and release kinetics of the developed nicotinamide-loaded MEs. EXPERI MENTAL METHODS MATERI ALS Nicoti namide, olive oil, Tween 80 (polyoxyethylene 20 sorbitan monooleate), and Span 80 (sorbitan monooleate) were purchased from P.C. Drug Center Co., Ltd. (Bangkok, Thailand). Virgin coconut oil extracted from coconut meat by the cold-pressed process was procured from Chemipan Corporation (Bangkok, Thailand). Buffer solutions were prepared in-house and composed of potassium dihydrogen orthophosphate, disodium hydrogen orthophosphate, and sodium chloride which were acquired from Univar (New South Wales, Australia) in appropriate concentrations. Triethylamine was obtained from Fluka Chemika (Busch, Switzerland). Acetonitrile was purchased from RCI LabScan (Bangkok, Thailand). All chemicals were of pharmaceutical or analytical grade and used without modifi cation. Deionized water was prepared in-house and used throughout the experiment. DETERM INATION OF FATTY ACIDS IN THE STUDIED OILS Fatty acid compositions of virgin coconut oil and olive oil were analyzed by gas chroma- tography with fl ame ionization detector (GC-FID, Agilent, Palo Alto, CA) as described in a prior report with some modifi cations (15). The fl ow rate of helium (carrier gas) was 1 mL/min and the split ratio was 50:1. Hydrogen gas and air were supplied to FID with fl ow rates of 30 and 300 mL/min, respectively. Separation was carried out on capillary column, Select Biodiesel for FAME, with a length of 30 m and diameter of 320 μm (Agi- lent). The injector and detector temperatures were set at 290° and 300°C, respectively.
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