Synthesis and self-assembly of a dual thermal and pH-responsive ternary graft copolymer for sustained release drug delivery

Abstract

The ternary graft copolymer PGMA-g-(PS-r-PDMAEMA-r-POEGMA) (TGC) was prepared by a one-pot method involving the quantitative grafting of alkyne-end polystyrene (PS–CCH), poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA-CCH) and poly(oligo(ethylene glycol)methacrylate) POEGMA-CCH onto P(GMA-N₃) via click chemistry. TGCs self-assembled and produced stable water soluble PS-centered nano-micelles, and exhibited intriguing collapse upon suitable adjustment of the solution pH and temperature. Hydrophilic rhodamine B (RB) and hydrophobic doxorubicin (DOX) were used to investigate the encapsulation and release properties of the TGC as a drug carrier. The results showed that the TGC exhibited excellent loading capacities for both DOX and RB. For the hydrophilic RB, the TGC displayed two release stages; upon increasing the micelle solution pH from 7.0 to 9.0, the PDMAEMA block aggregated and caused the original stabilizing layer to aggregate and release RB initially; while on further increasing the temperature from 20 °C to 40 °C, the POEGMA block aggregated and caused the second release of RB. The rate and extent of RB release could be changed by matching the numbers of PDMAEMA and POEGMA blocks per graft copolymer. In addition, DOX was encapsulated in the hydrophobic core, upon increasing the temperature and pH, the TGC formed compact layers and inhibited DOX release.