Hollow Polymeric Capsules from POSS-Based Block Copolymer for Photodynamic Therapy

A novel amphiphilic diblock copolymer, PHEMAPOSS-b-P(DMAEMA-co-CMA), was prepared via reversible addition fragmentation chain transfer (RAFT) polymerization, where PHEMAPOSS block was first synthesized using a methacrylate monomer based on polyhedral oligomeric silsesquioxane (HEMAPOSS), and PHEMAPOSS was further utilized to prepare the block copolymer via RAFT copolymerization of 2(dimethylamino)ethyl methacrylate (DMAEMA) and reduction cleavable coumarin methacrylate (CMA) monomer. PHEMAPOSS-b-P(DMAEMA-co-CMA) could self-assemble in water to form spherical micelles with POSS core and stimuli-responsive shell. The micelles were cross-linked by photodimerization of coumarin, and then hollow polymeric capsules could be finally obtained via etching the POSS core in the solution of hydrofluoric acid (HF). The morphologies of the micelles and hollow polymeric capsules were well characterized by TEM, SEM, and DLS. The hollow polymeric capsules are responsive to typical physiological stimuli such as pH, and redox potential, and could be further utilized in the encapsulation and release of tetraphenylporphyrin tetrasulfonic acid hydrate (TPPS) for photodynamic therapy (PDT). The in vitro release of TPPS-loaded polymeric capsules allowed a relatively low TPPS release at pH = 7.4. However, a burst release of TPPS was observed in the presence of 10 mM glutathione (GSH) at pH = 5.5. Confocal laser scanning microscopy (CLSM) confirmed that TPPS-loaded polymeric capsules could well improve the internalization rate in MCF-7 cells. According to the result of MTT assay, TPPS-loaded polymeric capsules demonstrated efficient PDT efficacy and low dark toxicity toward MCF-7 cells. Thus, TPPS-loaded polymeric capsules have presented potential application in PDT.