Influence of the Ratio of Tween 80 to Span 80 on the Quality Parameters of Microemulsions with Sea Buckthorn Oil

Abstract

Background: Microemulsion (ME) is thermodynamically stable dispersion of oil and water, stabilized by an interfacial film of surfactants along with co-surfactants [1]. The dosage and type of surfactants used in ME directly influence the ME formation size and stability [2]. Microemulsions used as topical preparations possess beneficial characteristics such as enhanced rate and depth of moisturizing agents [3]. Sea buckthorn oil (SBO) is known to be effective in treating mucous-membrane-related disorders and has moisturizing and regenerative effects on nasal mucosa [4, 5]. Aim(s): Preparation of stable microemulsions with sea buckthorn oil using different ratios of tween 80 to span 80 as a mixture of surfactants and evaluation of their influence on physical properties of microemulsions. Methods: MEs containing fixed amount of SBO (2 %) were prepared by magnetic stirring and homogenization: first ME was prepared with only tween 80, second, third and fourth MEs were prepared with tween 80 and span 80 in ratio 9:1, 8:2 and 7:3, accordingly. Microemulsions were characterized by particle size and polydispersity index measurement using dynamic light scattering method, pH and viscosity measurements, kinetic stability by centrifugation test and thermodynamic stability study by freeze-thaw and heating-cooling cycles. Results: Only first three MEs were kinetically and thermodynamically stable with particle size of 11.74±0.12 nm (PDI = 0.123±0.012 ), 12.68±0.11 nm (PDI = 0.036±0.015 ) and 101.2±1.72 nm (PDI = 0.254±0.019) respectively. The pH ranged from 4.654±0.01 to 4.825±0.03. The viscosity increased from 566.4±3.2 to 687.2±2.9 mPa*s. Conclusion: Addition and higher proportion of span 80 increased microemulsion particle size, pH and viscosity, while surfactant ratio of 7:3 did not result in formation of stable microemulsion at all. Tween 80 and span 80 in ratio 9:1 impacted only a small increase in particle size and a significant decrease in PDI compared to the microemulsion containing only tween 80.