Novel hybrid block copolymer nanocarrier systems to load lipophilic drugs prepared by microphase inversion method

Nanoparticles based on block copolymers of oligosaccharides [β-cyclodextrin (βCyD) and maltoheptaose (Mal7)] and poly(ε-caprolactone) (PCL) were prepared by microphase inversion method. Zeta-potential, particle size measurements and morphological analysis of drug-free and drug-loaded nanoparticles were performed by using, respectively, laser-doppler anemometry, dynamic and static light scattering and transmission electron microscopy. ρ-Ratio values were correlated with transmission electron microscopy observations. Both types of amphiphilic block copolymers, βCyD-b-PCL5k and Mal7-b-PCL5k, self-assembled in water to form spherical vesicles, presented a hydrodynamic diameter of 72 and 34 nm, respectively. The incorporation of drugs into nanoparticles did not affect significantly the particle size for βCyD-b-PCL5k-based nanoparticles with progesterone, unlike the other tested systems. On the other hand, all nanoparticles (with and without drug) were negatively charged. Both nanoparticulate systems showed high drug loading efficiency (higher than 95%), confirming their suitability as delivery system for lipophilic drugs.