## 4 Bionanosystems
### Bionanosystems for RA
#### 4.1.2. Bionanosystems Based on Inorganic Carriers  
Most examples of carriers for RA encapsulation or immobilization have involved polymer-based or lipid-based systems, while inorganic carriers are less investigated (Table 2). However, considering the possible application of RA as a natural antioxidant or antimicrobial additive for industries such as food packaging, cosmetics and pharmaceutical, bionanosystems made of inorganic nanoparticles and RA might have several advantages. It has been found that the high surface area and layered structure of nanoclays, as well as the hollow tubular structure of halloysite are ideal for promoting the absorption of essential oils (EOs) [128; 129; 130]. Furthermore, combining nanofillers with functional additives afford to host-guest systems that can be processed with a polymer matrix improving polymer performance due to the synergistic combination of physicochemical and biological properties of both phases. The intercalation of bioactive compounds into inorganic layered materials, such as cationic and anionic clays, allows for host-guest systems that can be used as biocompatible carriers for drugs and other active chemicals. The 2D geometry of layered nanofillers is advantageous for self-assembly into organized layered structures of functional organic molecules, which are released in a controlled manner. Notably, nanoclays have been widely used as carriers of essential oils (EOs) and polyphenols for various applications such as food packaging and agricultural applications [131; 132; 133]. These hybrid systems act as a carrier to disperse hydrophobic molecules into hydrophilic matrices [134; 135] and represent an option to prepare aroma-controlled release systems for pest control [136]. Montmorillonite (MMT) is the most widely studied cationic clay. MMT has a layered structure where each layer consists of an octahedral sheet of alumina sandwiched between two tetrahedral sheets of silica. The layers are spaced from each other by a regular interlamellar space in which cations are located to compensate for the negative charge of the lamellae due to isomorphic substitution, and dur to these characteristics it is possible to insert organic molecules into the interlamellar space, generally by cation exchange, but also by adsorption. Some studies show that polyphenols can be intercalated into the interlayer spaces of MMT or adsorbed onto the external planar surfaces [130; 137; 138]. To the best of our knowledge, only two examples are described concerning the immobilization of RA on MMT. [PERSON] et al. [131] investigated the immobilization of EOs from thymme, oregano, and basil into Na-MMT and organo-MMT. Primary components of these EOs are monoterrepends and monoterrepens, but additional active compounds such as polyphenols, and among them eugenol, thymmol, carvacrol, and RA, are also present. The immobilization of EOs on MMT was successful, and results demonstrated that in the case of Na-MMT the phenolic components of EO were immobilized on the external surface of clay layers via hydrogen bond with the OH groups, whereas in the case of organo-MMT they were intercalated as demonstrated by the increment of the interlayer space. Another interesting example of immobilization of RA into a layered silicate is that reported by [PERSON] et al. [139], which describes the intercalation by cation exchange of aqueous-based basil extract containing RA into Na-MMT for preparing a green inhibitive nanocarir (G-MMT). Tannins, alkaloids, flavonoids, saponins, steroids, sterols, and phenols are indeed efficient corrosion inhibitors for protection of metals [140; 141] owing to heterocyclic rings, heteroatoms, and double/triple bonds. Therefore, G-MMT was here used in combination with a sol-gel silane coating to protect steel coupons against 3.5 wt.% NaCl electrolyte. It was demonstrated a time-dependent release of the green inhibitor from the carrier and an efficient protective effect against steel corrosion which was five times higher than that of the additive-free hybrid silane coating.