*2.9.4 Aquasomes*

Aquasomes have recently emerged as solid nanoparticle drug carriers with a three-layered structure – core, coating, and drug (**Figure 15**) [90, 91]. It consists of a ceramic core coated with poly hydroxyl oligomer on which the protein or peptide of interest can be adsorbed. This polyhydroxy oligomer film protects proteins and peptides from changing shape and being damaged when they are surface-bound [92]. The layers that form aquasomes are assembled through the non-covalent bond, ionic bond, and van der Waals interactions [93].

Ceramics are mainly used as core material. These materials provide structural regularity and a high degree of order due to their crystallinity. This structure leads to efficient carbohydrate-binding on its surface resulting in the stable structure of aquasomes. Common materials used as the ceramic core in aquasomes are tin oxide, calcium phosphate, diamond nanoparticles, and hydroxyapatite. Among these, calcium phosphate and hydroxyapatite have excellent biocompatibility, biodegradability, and stability.

Carbohydrate coating provides a molecular layer capable of adsorbing therapeutic proteins or peptides without modification. Carbohydrates provide an environment that resembles water to the protein or peptide but keeps it in a dry solid-state, protecting the three-dimensional structure of the protein or peptide of interest [94, 95]. Carbohydrates commonly used for coating are trehalose,

**Figure 15.** *General structure of aquasomes.*

#### *Protein and Peptide Drug Delivery DOI: http://dx.doi.org/10.5772/intechopen.99608*

cellobiose, lactose and sucrose. The coating is achieved by the adsorption of the carbohydrate onto the core. The protein or peptide of interest interacts with the coating film by non-covalent or ionic interactions. Trehalose was previously reported to induce stress tolerance in bacteria, yeast, fungi, and some plants. Trehalose protects protein within the plant cell during the dehydration process and thus preserves cell structure [96]. It was observed that trehalose increased the transition temperature of proteins, resulting in increased stability [97]. Also, the hydroxyl group of carbohydrates interacts with the polar and charged group of proteins. Upon drying, the large number of hydroxyl groups of the carbohydrate replaces the water around polar groups in protein, thus maintaining their integrity [98].

A nanosized ceramic core-based drug delivery system has been developed for the oral administration of serratiopeptidase [99]. In this method, the calcium phosphate core was coated with chitosan, and the enzyme was adsorbed by the coating. The enzyme was further stabilized by encapsulating the enzyme-loaded core into alginate gel. The results indicated the ability of aquasomes to protect the structural integrity of the enzyme, resulting in a more potent therapeutic effect.
