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Preparation and characterization of chitosan nanoparticles/PLLA-PEG-PLLA composite microparticles by supercritical fluid technology

The carriers with core-shell structure have been widely used in the field of co-loading gene and drug. In this study, chitosan(CS) nanoparticles(CS NPs)/poly(L-lactide)-poly(ethylene glycol)-poly(L-lactide) triblock copolymer(PLLA-PEG-PLLA) composite microparticles(MPs) with core-shell structure were prepared by the combination of ion gelation and suspension-enhanced dispersion by supercritical fluids(Sp EDS). The conditions for preparation of CS NPs and MPs were investigated and optimized, and the physicochemical properties and cytotoxicity of MPs were studied. The optimized condition for CS NPs were chitosan solution concentration of 2 mg·ml-1, chitosan solution p H of 5.0, and tripolyphosphate(TPP) solution concentration of 1 mg·ml-1. The ratio of solvent/non-solvent was the significant factor affecting sizes of MPs, and the optimized conditions for MPs were oil concentration of 5 mg·ml-1, W/O ratio of 0.75:10.00, solution flow rate of 2 ml·min-1 and solvent/non-solvent of 0.5:1.0. The MPs from optimized conditions had a size of 323.7 nm and the CS NPs were encapsulated in MPs, as observed by TEM. The results of experiments about physicochemical properties revealed that a reaction happened between CS and TPP. Little change occurred in the functional groups of materials used in the two processes, while the crystal forms of PLLA-PEG-PLLA in MPs were more uniform. The relative growth rates of Bcap-37 cells co-cultured with MPs with different concentrations of 0.25, 0.50 and 1.00 -g·ml-1 for 3 d were 105.3%, 101.9% and 100.9%, respectively. The above results demonstrated that the MPs with good biocompatibility could be used in the field of co-delivery for gene and antitumor drug to evaluate the antitumor effect and would achieve a good synergistic effect in the treatment of cancer.