Effects of Freezing and Freeze-drying on Protein Conjugated Nanoparticles

Abstract

Biodegradable poly(D,L-lactide-co-glycolide) PLGA nanoparticles (NPs) have been extensively investigated for drug delivery. Protein conjugated NPs provide the advantage of active targeting. To overcome the instability associated with storage of aqueous dispersions, NPs are usually lyophilized. However, the freezing and freeze-drying stress can lead to nanoparticle aggregation and protein denaturation. As such, sucrose is widely used as a cryoprotectant and minimal ‘cryoprotectant to particle ratio’ is required. In this study, we used trypsin as a model protein to conjugate on the PEGlyated NPs. The effects of the freezing and freeze-drying process on trypsin conjugated NPs was studied by comparing the size of the NPs, the morphology of the NPs under fluorescent images and the trypsin activity after of the fresh made, freeze-thawed and lyophilized NPs. A minimum sucrose to NPs ratio was founded to provide the complete protection of the trypsin conjugated NPs.