Biodegradable core crosslinked star polymer nanoparticles as 19F MRI contrast agents for selective imaging

With the aim of developing stimuli-responsive imaging agents, we report here the synthesis of core crosslinked star (CCS) polymers and their evaluation as pH-sensitive F-19 magnetic resonance imaging (F-19 MRI) contrast agents. Block copolymers consisting of poly(ethylene glycol)methyl ether methacrylate (PPEGMA) as the first block and a copolymer of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and 2,2,2-trifluoroethyl methacrylate (TFEMA) as the second block were synthesised using RAFT polymerisation. The polymerisation kinetics were studied in detail. The block copolymers were then used as arm precursors for the arm-first synthesis of CCS polymers through RAFT dispersion polymerisation. The synthetic conditions were investigated and optimised. CCS polymers with a degradable core were also synthesised and evaluated as F-19 MRI contrast agents. The degradation of the core was confirmed by treatment with various reducing agents. The particle size, F-19 NMR signal and relaxation times as well as F-19 MRI imaging performance of the CCS polymers were studied at a range of value of solution pH. Significant enhancement of the image intensity was observed when the pH was decreased from 8 to 5, indicating that the CCS nanoparticles could be used as F-19 MRI contrast agents for the detection of the acidic environment within tumour tissue.