**2.9 Nanoparticle-based delivery systems**

Nanoparticles can be used as a delivery system to administer protein or peptide therapeutics via different routes such as oral, intravenous, subcutaneous, and transdermal. Delivery of proteins or peptides via nanoparticles can be achieved by employing different approaches such as encapsulation of the drug molecule by the nanoparticle, adsorption of the drug molecule on the surface of the nanoparticle, etc. [61]. Nanoparticle-based delivery system protects the protein or peptide of interest from enzymatic degradation in the GIT [62]. Nanoparticles can also deliver the protein or peptide to the desired location, such as tumor cell, inflammation site, etc. This site-specificity results in reduced side effects of the therapeutic agent [63, 64].

The uptake of nanoparticles by the cells usually occurs via endocytosis. This process involves phagocytosis, receptor-mediated phagocytosis, and pinocytosis.

**Figure 11.** *General structure of microspheres.*

Endocytosis starts with the association of the nanoparticle with the cell membrane to form an endosome, followed by the internalization of the endosome. Subsequent degradation of the nanoparticle by the lysosome leads to the release of the protein or peptide inside the cell [65]. Other ways of the release of drug molecules from the nanoparticle depend on factors such as the solubility of the therapeutic agent at a specific pH, polymer swelling, composition of the nanoparticle, etc. [41].
