Novel core-shell lipid-chitosan and lipid-poloxamer nanocapsules: stability by hydration forces

In the last few years, a great attention has been paid to core-shell structured lipid nanocapsules. The interest of these colloids lies in their very promising applications as delivery systems of hydrophobic drugs or as DNA carriers. The aim of this work was to provide fuller knowledge concerning the physicochemical properties of these new colloidal particles, paying special attention to the role played by the constituting components. Our lipid nanocapsules were comprised of a triglyceride-lecithin core surrounded by a chitosan and/or poloxamer (Pluronic (R) F68) shell. Four different systems were formulated by varying the chitosan and poloxamer contents. We have estimated their shell composition from electrokinetic mobility measurements and stability studies. They revealed a high incorporation of chitosan to the shell, while Pluronic (R) F68 only presented a secondary role during the nanocapsule formation, providing final systems with low poloxamer content. In addition, the stability studies, performed not only on ideal solutions but also on simulated physiological fluids, revealed that hydration forces were crucial to maintain the integrity of these nanocapsules under physicochemical conditions similar to those found in real physiological fluids. Theoretical treatment of stability data has allowed us to determine the role that ions play on hydration forces when they act as counterions.