Abstract
In this research, we sought to surmount the poor dissolvability and transdermal absorption rate of licorice flavonoids (LFs) by fabricating a LFs microemulsion. LFs content was determined using high performance liquid chromatography. Initial studies such as dissolution testing, emulsification testing, and pseudo ternary phase diagram generation were implemented for screening components and optimized adopting the central composite design. While the tested responses were solubility, droplet size and PDI, thirteen trials were performed using two different variables, oil percentage and optimized emulsifier and co-emulsifier ratio. Microemulsions were then characterized for droplet size, PDI, transmission electron microscopy, viscosity, electrical conductivity, pH, entrapment efficiency, drug content and stability. Additionally, skin release profile, percutaneous absorption and retention were investigated adopting Franz diffusion cell. The optimal formulation was found to compose of laureth-9 (emulsifier, 6.72 g), propylene glycol (co-emulsifier, 1.80 g), isopropyl myristate (IPM, oil, 1.48 g), LFs (1.50 g) and at least more than 85% deionized water. The optimized and storage for 3 months of microemulsion was found to clear, light yellow color without phase separation or precipitation indicated the stability of the preparation to long-term placement. The mean droplet size, PDI, entrapment efficiency and drug content were discovered as 12.68 ± 0.12 nm, 0.049 ± 0.005, 97.28 ± 0.13% and 122.67 ± 0.40 mg·g−1, respectively. Furthermore, the optimal formulation sustained release LFs, remarkably deliver more LFs through the skin layer (644.95 ± 6.73 μg cm−2) and significantly retained LFs in the skin layer (9.98 μg cm−2). The study concluded that optimized microemulsion has potential and enhanced the dissolvability and cumulative penetration amount of LFs.
Highlights
Skin pigmentation is a result of melanin produced by melanocytes in the epidermis (Zhang et al, 2020)
According to the measurement results, in order to increase the loading of licorice flavonoids (LFs) in the microemulsion, the experiment preliminarily determined that olive oil (5.63 ± 0.12 mg·g−1) and Isopropyl myristate (6.21 ± 0.20 mg·g−1) were used as the oil phase; laureth-9 (124.34 ± 1.18 mg·g−1) and tween 20 (119.42 ± 0.94 mg·g−1) were used as emulsifiers; propylene glycol and butylene glycol acts as coemulsifiers
O/W microemulsion system of LFs was formulated and evaluated by the water titration method. firstly, the pseudo ternary phase diagram was prepared for distinct ratios and different types of emulsifiers and co-emulsifier and the best ratio range of W % and Km was deemed to be appropriate for further study
Summary
Skin pigmentation is a result of melanin produced by melanocytes in the epidermis (Zhang et al, 2020). When the skin is over-exposed to factors such as ultraviolet rays and intense visible light, melanin will be overproduced and accumulated, leading to hyperpigmentation, freckles, melasma and other diseases (Lakhan and Lynch, 2021). Some disorders can be difficult and resistant to treatment (Rachmin et al, 2020). Many agents for treatment of skin hyperpigmentation have been developed. Arbutin derivatives are generally cytotoxic, limiting their application to some range (Rainforest et al, 2019). Other agents, such as kouji acid, hydroquinone and its derivatives, etc. The medical and cosmetic field is increasingly attracting attention to products of natural origin, especially those of herbs with pharmacological effects including flavonoids (Faccio, 2020)
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