Investigation of pH-responsive block glycopolymers with different structures for the delivery of doxorubicin.

To understand the influence of the construction of pH-responsive glycopolymer carriers on loading and release behaviors of the drug, three types of block glycopolymers with similar compositions but different constructions, PEG- b -P(DEA- co -GAMA), PEG- b -PDEA- b -PGAMA and PEG- b -PGAMA- b -PDEA, were successfully synthesized via atom transfer radical polymerization (ATRP) method. The compositions and structures of the three glycopolymers were characterized using 1 H NMR (nuclear magnetic resonance) and GPC (gel permeation chromatography), while the morphology and size of aggregates from pH-sensitive block glycopolymers were measured using TEM (transmission electron microscopy) and DLS (dynamic light scattering). The results indicated that the micelles prepared from PEG- b -PGAMA- b -PDEA had a more compact shell structure. The drug-loaded micelles were prepared using the diafiltration method at pH 10, and the loading content and loading efficiency were analyzed using a UV-visible spectrophotometer. DOX-loaded micelles formed by PEG- b -PGAMA- b -PDEA with the more compact shell construction showed the highest loading content and loading efficiency (12.0 wt% and 58.0%) compared with the other two micelles. Moreover, the DOX release tests of these micelles were carried out under two PBS conditions (pH 7.4 and pH 5.5), and the DOX release amount in a certain time was analyzed using a UV-visible spectrophotometer. The results showed that the more compact shell construction of the three layered micelle obstructed the diffusion of a proton into the PDEA core at pH 5.5 and delayed the drug from releasing under both conditions. Moreover the two-layered micelle with a PDEA and PGAMA mixed core showed a relatively high release amount owing to the porous core permitting unimpeded releasing at pH 7.4 and promoted the protonation of PDEA at pH 5.5. Insights gained from this study show that the structure of block copolymers, leading to different constructions of micelles, could adjust the drug loading and release behavior to certain extent, thus it may contribute to improving the design of desirable drug delivery systems.