The poly(diallyldimethylammonium chloride)(PDADMAC)/poly(styrene sulfonate) (PSS) microcapsules assembled by layer-by-layer on PSS-doped CaCO₃ particles were used to load photosensitizer methylene blue (MB) by combination of spontaneous deposition and heat-induced shrinkage. After annealing at 80 ^oCfor 30 min, the capsules shrink dramatically from 6.9±0.3 µm to 3.1±0.5 µm, accompanied with wall thickness increase. Incubation of MB in the capsule suspension following with annealing resulted in MB-loaded capsules with a concentration of 22 mg/mL, which was 1000 times higher than that of the feeding concentration. Although about 1/3 MB was released rapidly from the capsules in phosphate buffered saline, the remained MB were stably retained for long time, which were then protected by capsule wall against reductive enzyme and kept their photodynamic activity. The viability of HeLa cells incubated with MB-loaded capsules decreased sharply from ~75% (dark cytotoxicity) to ~20% after irradiation with a laser at 671 nm and 60 J/cm² for 75 s.

Yuanyuan Han, Jing Bu, Yuying Zhang, Weijun Tong*, Changyou Gao*.Encapsulation of Photosensitizer into Multilayer Microcapsules by Combination of Spontaneous Deposition and Heat-induced Shrinkage for Photodynamic Therapy, Macromolecular Bioscience, 2012, doi: 10.1002/mabi.201200191. Download Pdf