Emulsifiers, also known as surfactants, can reduce the surface tension of the liquid, thereby increasing the diffusion and wetting properties. An emulsifier consists of a polar (or hydrophilic) head and a hydrophobic tail which can be dissolved in both polar and non-polar solvents. These emulsifiers have physicochemical properties of self-aggregation, solubilization or emulsification. Typically, emulsifiers help particles remain suspended in liquid, prevent settling and clumping of elements in the form of vaccine liquids, by lowering the surface tension of the liquid. The most commonly used emulsifiers in vaccines can be natural or synthetic origin, anionic, cationic or non-ionic with a formula weight between 600 and 4000 g/mol. Gall  compared the systemic humoral immune response in guinea pigs injected subcutaneously with protein Ag with that elicited by emulsifiers. The study demonstrated adjuvanticity in lipoidal amines with tail groups of 16 carbon atoms or more. Woodard  also assessed the adjuvanticity of cationic amines and nonionic emulsifiers in mice immunized subcutaneously with protein Ag. All these results show that emulsifiers can be used as auxiliary raw materials for vaccines and play an important role in the vaccine field.
Hydrophobic groups in vaccine emulsifiers
The hydrophobic groups in vaccine emulsifiers are mainly expressed as aliphatic hydrocarbon chains. These chains are usually not a unique structure, but are described as a mixture of different chain lengths. The length of the fatty chain is important in vaccine applications. As the fat chains increase, the emulsification effect gradually increases, while the irritation of the fat chains themselves gradually decreases. It has been shown that C18-centered fatty chains have sufficient chain length and are less irritating to provide an optimal balance of efficacy and safety for vaccine applications.
Main roles of emulsifiers in vaccines
The main roles of emulsifiers in vaccines are as follows.
The adjuvant effect of the amphiphilic components (water and oil loving materials) is significant and works through different pathways. Oil emulsion adjuvants made with Span-85 or Tween-80 emulsifiers are among the most commonly used adjuvants in veterinary biologics today.
The addition of emulsifiers to low solubility aggregates or fatty lipophilic molecules helps to obtain a stable and homogeneous liquid phase. In such cases, micelles of emulsifiers of small size (few nanometers) can contain other amphiphilic molecules (proteins or lipids) presented in a different way than in a simple aqueous solution.
Emulsifier, in this case, is used to stabilize the dispersion of one phase into another. These two non-miscible phases (generally, the oil and water phases) reduce the interfacial energy of the system after emulsification to form a wide specific surface.
What we offer
Alfa Chemistry supplies emulsifiers to companies researching vaccines. If you cannot find the emulsifier you need, please contact us. We also offer product customization according to customer's detailed requirements.
- Gall, D., et al. The adjuvant activity of aliphatic nitrogenous bases. Immunology. 1966, 11: 369-386.
- Woodard. L. F.; et al. Adjuvant activity of water-insoluble surfactants. Lab. Anim. Sci. 1989, 39: 222-225.
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