Effect of the hydrophobic segment of an amphiphilic block copolymer on micelle formation, zinc phthalocyanine loading, and photodynamic activity

A series of amphiphilic block copolymers, i.e., poly(N-substituted acrylamide)-block-poly(polyethylene glycol monomethyl ether acrylate) (P(R)-b-PPEGA) were prepared via RAFT polymerization and post-polymerization modification, and the formation of polymeric micelles as zinc(II) phthalocyanine (ZnPc) carriers for photodynamic therapy was investigated. The effect of hydrophobic R groups at the hydrophobic segment of the block copolymer on critical micelle concentration, hydrodynamic diameters ZnPc-loading ability, and in vitro photocytotoxicity of the polymer micelles was examined. The hydrodynamic diameters of the polymer micelles were insensitive to R groups and falls in a narrow range between 23 and 25 nm, whereas those of the ZnPc-loaded micelles vary from 167 to 230 nm depending on the R groups. The Q bands in UV-vis spectra of the ZnPc-loaded micelles indicate that the presence of aromatic R groups results in loose ZnPc aggregates, whereas those containing aliphatic R groups are well packed. The photodynamic effect examined in RGK-1 cell lines was also dependent on the R groups; ZnPc-loaded micelles having aromatic R groups exert higher photodynamic effect than those with aliphatic R groups. These findings indicate that aromatic R groups form larger polymeric micelles with loosely packed ZnPc aggregates, leading to enhanced release of ZnPc in cellular environment and therefore higher photodynamic effect.

Automated summary

The study investigated the impact of hydrophobic R groups on various properties of polymeric micelles loaded with ZnPc for photodynamic therapy. The presence of aromatic R groups led to larger micelles with loosely packed ZnPc aggregates, resulting in higher release and enhanced photodynamic effect compared to micelles with aliphatic R groups.