19.1

Introduction

Nanoemulsions are classified as nanoscale emulsions which are specifically regarded

as kinetically stable systems. The nanoemulsions are optically isotropic mixtures and

can be translucent or transparent. However, microemulsions are also nanoscale

emulsion but are both thermodynamically and kinetically stable as compared to

nanoemulsions with a droplet size of less than 100 nm. These emulsions are liquid-

liquid colloidal dispersion with amphiphilic surface-active agents (Barkat et al.

2020; McClements 2012). Due to its nano-size, these novel drug delivery systems

offer enhanced solubility and permeability of poorly aqueous soluble compounds

(Ghai and Sinha 2012), optical clarity (de Oca-Ávalos et al. 2017), better bioavail-

ability (Li et al. 2017), and increased shelf life (de Oca-Ávalos et al. 2017; Sharma

and Sinha 2018; Parveen et al. 2015). Nanoemulsion mainly comprises three

components, i.e., oleaginous phase, surface-active agents, and aqueous phase. The

oleaginous phase involves the lipophilic components such as free fatty acids, mono-,

di-, or triacylglycerols, essential oils, etc. The role of surface-active agents is to

stabilize the nanoemulsion by preventing Ostwald ripening, coalescence, and floc-

culation. These surface-active molecules also prevent collision of small droplets and

provide kinetic stability to nanoemulsions. Surface-active agents form a layer around

the dispersed phase or droplet which can be monolayer or multilayer and reduce the

interfacial tension between two immiscible liquids. Selection of surface-active

agents with an appropriate hydrophilic-lipophilic balance (HLB) value is necessary

as this is an important parameter which determines the type of emulsion (oil in water

or water in oil). Moreover, the surface-active agents are important components of

nanoemulsion which determine as well as maintain the droplet size throughout the

shelf life. These surface-active molecules may be used as stabilizers, emulsifiers,

wetting agents, and viscosifiers. Finally, the third component is aqueous phase

which influences polarity, ionic strength, and phase behavior of nanoemulsion.

Sometimes apart from the aforesaid components, cosolvents are also utilized in

nanoemulsion formulation so as to increase the emulsification attribute and provide

stability to the nanoemulsion. Short-chain alcohols, proteins, and carbohydrates are

some of the examples that are utilized as cosolvents in nanoemulsion (Saxena et al.

2017). Amid the advancement in novel drug delivery systems for herbal bioactives,

nanoemulsion technology is highly popular throughout the globe. Herbal-derived

molecules or extracts have several therapeutic benefits and are scientifically proven

also. But challenges like higher molecular size, low aqueous solubility, lipid perme-

ability, and elevated degradation profile in vitro and in vivo lead to ineffective

pharmacodynamic and pharmacokinetic profile. Nanoemulsion technology is the

nanocarrier system which has the ability to overcome all aforesaid challenges and

potentiate the biological efficacy of herbal bioactives. Also, scientific studies have

meticulously provided the evidences which demonstrate dose minimization (Kazemi

et al. 2020), facilitate targeting (Shobo et al. 2018; Ahmad et al. 2018), improving

bioavailability (Zhao et al. 2013), release behavior (Macedo et al. 2014), and

reducing side effects (Maghbool et al. 2020). In this chapter, we highlight the

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