Preparation and characterization of biodegradable nanoparticles based on poly(γ-glutamic acid) with l-phenylalanine as a protein carrier

The objective of the present study was to prepare nanoparticles composed of poly(γ-glutamic acid) (γ-PGA) and l-phenylalanine ethylester (l-PAE) in order to evaluate the possibility of using these nanoparticles as protein carriers. Novel amphiphilic graft copolymers composed of γ-PGA as the hydrophilic backbone and l-PAE as the hydrophobic segment were successfully synthesized by grafting l-PAE to γ-PGA using water-soluble carbodiimide (WSC). Due to their amphiphilic properties, the γ-PGA-graft-l-PAE copolymers were able to form nanoparticles. The size of the γ-PGA nanoparticles was measured by photon correlation spectroscopy (PCS) and showed a monodispersed size distribution with a mean diameter ranging from 150 to 200 nm. The solvents selected to prepare the γ-PGA nanoparticles by a precipitation and dialysis method affected the particle size distribution. To evaluate the feasibility of vehicles for these proteins, we prepared protein-loaded γ-PGA nanoparticles by surface immobilization and encapsulation methods. Ovalbumin (OVA) was used as a model protein and was immobilized onto the γ-PGA nanoparticles or encapsulated into the inner core of these nanoparticles. Moreover, these OVA-encapsulated γ-PGA nanoparticles could be preserved by freeze-drying process. The results of cytotoxicity tests showed that the γ-PGA and γ-PGA nanoparticles did not cause any relevant cell damage. It is expected that biodegradable γ-PGA nanoparticles can immobilize proteins, peptides, plasmid DNA and drugs onto their surfaces and/or into the nanoparticles. These nanoparticles are potentially useful in pharmaceutical and biomedical applications.