Polymersomes with high loading capacity prepared by solvent annealing method and their controlled release behaviors
Date Issued
2014
Date
2014
Author(s)
Lin, Fang-Yu
Abstract
It is well known that amphiphilic block copolymers in selective solvents can form self-assembled structures, where solvophilic blocks tend to contact with solvents while solvophobic blocks are shielded from the solvents. Different from the conventional preparation of vesicles in liquid systems, we found that block copolymers, including poly(styrene-b-acrylic acid) (PS-b-PAA), poly(styrene-b-ethylene oxide) (PS-b-PEO), and poly(caprolactone-b-ethylene oxide) (PCL-b-PEO), can directly self-assemble into vesicles in aspirin, a drug molecule, by solvent annealing. When mixing the block copolymers in a great amount of aspirin, aspirin works as “selective solvent” that associates with one of the blocks and swells the block, thus changing the volume fraction of the blocks, which firstly leads to the formation of bilayer structures. During following solvent annealing, the penetrated solvent molecules impart mobility to block copolymers and aspirin. The bilayers are then wrapped into vesicles with aspirin filled in both interior and exterior. The advantage of solvent annealing method is that it prevents unnecessary chemical reactions of drug molecules that may be caused by conventional thermal annealing method at high temperature. The vesicular structures after extracting by appropriate solvents were probed by transmission electron microscopy (TEM). The extracted vesicles are filled with aspirin in the core and the drug loading content can reach as high as 59±5％, which is much higher than that of conventional vesicles formed in liquid systems (~30-40%). We have tested the release behaviors of the aspirin-loaded vesicles. Aspirin can be released in a controlled manner from PS-b-PAA vesicles in aqueous solutions with different concentrations of n-dioxane, a good solvent to both PS and PAA blocks. We also examined the effect of pH values on the release behaviors of the aspirin-loaded vesicles in aqueous solutions. The cumulative release of aspirin was found to be strongly pH-dependent.
Subjects
雙親性團聯式共聚物
自組裝
液胞
阿斯匹靈
Type
thesis
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