Application of Nanoemulsions in the Vaccination Process

1. Introduction

Vaccines are possibly the most paramount interventions developed in the history of mankind to date that have led to a significant reduction in the death rates of the populations since the testing of the world’s first vaccine of smallpox by Edward Jenner in 1798 (Riedel, 2005). The aim behind the development of vaccines is to prevent the infections that lead to morbidity, disability, and mortality of individuals. The process of vaccination has improved the quality of life as well as the life expectancy of people all over the world. Although vaccination has been a very successful process, improvement in the development and delivery procedures of vaccines would be of great benefit in this new world in which the unjustifiable anthropogenic actions are leading to the frequent development of new serious infectious diseases. The development of vaccines has seen a technological revolution from the concept of three Is (isolate, inactivate, and inject) to the formulations of rationally designed vaccines having a minimalist composition (Bragazzi et al., 2018; De Gregorio and Rappuoli, 2014). In the past few years, more focus has been given to the development of vaccines that are safe, stable, effective, eassy to administer, and are also cost-effective. An overview of the timeline of vaccine development from 1798 to the present has been depicted in Figure-1 (Gonzalez-Aramundiz et al., 2012).

Figure 1.

Timeline of vaccine development

Nowadays, nanocarriers-based vaccines are widely under investigation for needle-free administration. The most common nanocarriers being investigated to be used in the vaccination process are polymeric nanoparticles (NPs), liposomes, virus-like particles, carbon nanotubes, and nanoemulsions (NEs) (Karandikar et al., 2017).

NEs are submicron-sized emulsions that are under broad examination as medicate carriers for moving forward the conveyance of therapeutics such as drugs, vaccines, etc. NEs are thermodynamically steady straightforward (translucent) scatterings of oil and water stabilized by an interfacial film of surfactant and co-surfactant atoms having an average droplet diameter size ranging between 100 nm to 500 nm (Aboofazeli, 2010). They are colloidal scatterings composed of an oil phase, water phase, surfactant, and co-surfactant at suitable proportions. NEs possess varied benefits over other lipid-based carriers. For example, NEs have a way higher extent and free energy than macro emulsions that consign them a good transport system. They do not show the issues of inherent creaming action, coalescence, and deposit that are normally associated in the case of macroemulsions (McClements, 2012). Moreover, they can be developed in a variety of formulations like foams, creams, liquids, and sprays.

Specifically, nanoemulsions (NEs) in the nanometric scale are transparent, translucent, and non-stable dispersion colloidal phase droplets, that is about 100nm, but in some of the bibliography they refer to the limit which is up to 300nm (Comfort et al., 2015, Bahamondez-Canas and Cui 2018). The droplets of 300nm might also be called submicron emulsions, mini emulsions, ultrafine emulsions, and translucent emulsions (Cinar, 2017). In contrast to microemulsions, NEs cannot be manufactured impulsively, thus, in the preparation of NEs high energy methods are required, generally by ultrasound generators, high-pressure homogenizers, and high-shear stirring. During this process, the thermolabile compounds and other proteins, like some nucleic acids and enzymes, may go through deterioration because of the high temperatures and pressure (Çinar, 2017). Although, they are some other alternatives for the preparations of nanoemulsions, that consist of low-energy methods such as emulsion inversion and phase inversion temperature (Bonferoni et al., 2019)