Synthesis, characterization and drug delivery behaviors of new PCP polymeric micelles

A new PCP tri-block copolymer consisting of poly (ε-caprolactone)-b-chitooligosaccharide-b-poly(ethylene glycol) (PCL-b-COS-b-PEG, PCP) was synthesized and characterized. The potential for delivering doxorubicin (DOX), a model drug, with or without genipin crosslinking was evaluated. The PCP copolymers were analyzed by Fourier-transform infrared spectrometry (FT-IR) to confirm the amine and ester groups of the COS and the PCL of the copolymer, respectively. ¹H nuclear magnetic resonance (¹H NMR) was performed to determine the structure of the PCP copolymer for demonstrating both PCL and PEG blocks grafted onto the COS block. Moreover, gel permeation chromatography (GPC) was applied to determine the number average molecular weight of the tri-block copolymer (M_n), which was 11,340 Da/mole. The PCP form polymeric micelles at the critical micelle concentration (CMC) of 0.0107 wt% (or 1.0 μM) with the mean diameter 90 nm, as determined by a dynamic light-scattering (DLS) analyzer. Since PCP micelles contain COS, the zeta potentials of the micelles are changed from a neutral (e.g., -3.2 ± 1.3 mV at pH 7.4) to a cationic state (13.9 ± 4.4 mV at pH 3.0) when pH values of the suspension medium are varied. This change is a unique property of the micelles. In addition, drug delivery behavior of the PCP micelles is influenced by genipin crosslinking COS. The DOX release period of crosslinked micelles is significantly longer than that of the non-crosslinked ones (e.g., 8 days vs. 4 days, respectively) while the burst release of DOX of crosslinked ones is significantly reduced compared with that of non-crosslinked ones. In conclusion, a new tri-block COS-containing PCP copolymer/polymeric micelle has been synthesized and characterized. Moreover, the unique properties of COS-containing PCP micelles are demonstrated by varying zeta potentials via changing pH of medium and by influencing DOX delivering behaviors after genipin crosslinking.