An Overview of Micro- and Nanoemulsions as Vehicles for Essential Oils: Formulation, Preparation and Stability

Abstract

The interest around essential oils is constantly increasing thanks to their biological properties exploitable in several fields, from pharmaceuticals to food and agriculture. However, their widespread use and marketing are still restricted due to their poor physico-chemical properties; i.e., high volatility, thermal decomposition, low water solubility, and stability issues. At the moment, the most suitable approach to overcome such limitations is based on the development of proper formulation strategies. One of the approaches suggested to achieve this goal is the so-called encapsulation process through the preparation of aqueous nano-dispersions. Among them, micro- and nanoemulsions are the most studied thanks to the ease of formulation, handling and to their manufacturing costs. In this direction, this review intends to offer an overview of the formulation, preparation and stability parameters of micro- and nanoemulsions. Specifically, recent literature has been examined in order to define the most common practices adopted (materials and fabrication methods), highlighting their suitability and effectiveness. Finally, relevant points related to formulations, such as optimization, characterization, stability and safety, not deeply studied or clarified yet, were discussed.

Development and Optimization of Naringenin-Loaded Chitosan-Coated Nanoemulsion for Topical Therapy in Wound Healing

“…This increased fluidity at the interface of the two immiscible phases helps in reduction of the interfacial tension. Additionally, the co-surfactants also perform similar role in reduction in the hindrance of such penetration of hydrophobic tails of the surfactants within the oil droplets [ 38 ].…”

Developing a Highly Stable Carlina acaulis Essential Oil Nanoemulsion for Managing Lobesia botrana

“…NEs are colloidal systems offering a great advantage to encapsulate a higher amount of oil phase respective to similar nanosystems, i.e., microemulsions [ 79 ]. In fact, such a system has allowed to vehiculate 6% ( w / w ) of EO, respective to at least 1.5% ( w / w ) encapsulated into microemulsions, as reported in previous studies [ 80 , 81 ].…”

“…Further studies should be conducted on the larvicidal and adulticidal activity of EOs and EO-based NEs on L. botrana to find a valid substance to test in the open field. Moreover, as highlighted by Pavoni et al [ 79 ], it is crucial to consider that a lot of EO-based NEs contain several, non eco-friendly ingredients (i.e., polysorbates). Thus, further research is needed to evaluate the effects of nano-encapsulation on EO toxicological profiles.…”

“…We are aware that further studies on the effects of C. acaulis EO on non-target organisms will be needed to confirm environmental safety for this EO. Although solvents are usually added to EO-based formulations [ 79 ], NEs used in this study contain no solvents and are based on a surfactant with no effects in terms of eco-toxicity given its high level of biodegradability.…”

Synthesis and Technology of Nanoemulsion-Based Pesticide Formulation

“…In contrast, non-essential oils refer to a carrier oil that does not evaporate. The broad use of nanoemulsions as carriers of EOs has been widely reported as they reduce the volatilization [34], boost the bioactivity of EOs and reduce degradation processes such as oxidation, isomerization and polymerization [35]. Table 2 compiles a list of dispersant compositions that have been reported for the production of pesticide nanoemulsion.…”