Smart Chitosan-Based Stimuli-Responsive Nanocarriers for the Controlled Delivery of Hydrophobic Pharmaceuticals

We report here a green chemistry method to conjugate hydrophobic payloads (Lilial as a prototype) highly efficiently (35.8 wt %) with (1 -> 4)-2-amino-2-deoxy-beta-D-glucan (i.e., chitosan) via Schiff base bond formation in an ionic liquid, which renders chitosan easily dissolvable in common organic solvents and amenable to further functional modifications. As an example, thermoresponsive poly(N-isopropylacrylamide) was grafted to the chitosan-Lilial conjugate. The graft copolymer self-assembled in water at neutral pH into core-shell nanocarriers with a favorable size distribution (d similar to 142 +/- 60 nm) for intravenous administration. Under conditions of enhanced temperature and acidity (T = 37 degrees C, pH = 4.5) mimicking endosomal or lysosomal uptake, the nanocarriers fell apart and formed reversed micelles with greatly reduced sizes (d similar to 8 +/- 3 nm) favoring clearance by renal filtration, and 70% Lilial molecules were liberated within 30 h through hydrolytic cleavage of the exposed Schiff base conjugation. This smart stimuli-responsive drug release profile reveals a viable approach in the development of chitosan-based nanocarriers for intravenous administration of hydrophobic pharmaceuticals.