19 F magnetic resonance imaging (MRI) is a powerful noninvasive imaging technique with demonstrated potential for the detection of important diseases. The major challenge in the design of 19 F MRI agents is signal attenuation caused by the reduced solubility and segmental mobility of probes with high numbers of fluorine atoms. Careful choice of the fluorinated moiety is required to maintain image quality at the fluorine contents required for high imaging sensitivity. Here we report the synthesis of perfluoropolyether (PFPE) end-functionalized homopolymers of oligo(ethylene glycol) methyl ether acrylate (poly(OEGA) m -PFPE) as highly sensitive 19 F MRI contrast agents (CAs). The structural characteristics, conformation and aggregation behavior, 19 F NMR relaxation properties, and 19 F MR imaging were studied in detail. Dynamic light scattering and molecular dynamics (MD) simulations were conducted and demonstrated that poly(OEGA) m -PFPE with the longest poly(OEGA) m segments (m = 20) undergoes single-chain folding in water while poly(OEGA) 10 -PFPE and poly(OEGA) 4 -PFPE with shorter OEGA segments experience multiple-chain aggregation. Long 19 F T 2 relaxation times were measured for all poly(OEGA) m -PFPE polymers in PBS and in the presence of serum (>80 ms), and no obvious decrease in 19 F T 2 was observed with increasing fluorine content up to ∼30 wt %. Moreover, the signal-to-noise ratio increased linearly with increasing concentration of fluorine, indicating that the PFPE-based polymers can be applied as quantitative tracers. Furthermore, we investigated the in vivo behavior, in particular their biodistribution, of the polymers with different aggregation properties. Control over the balance of hydrophobicity and hydrophilicity allows manipulation of the aggregation state, and this leads to different circulation behavior in a murine model. This first report of the synthesis of polymeric PFPE-based 19 F MRI CAs demonstrates that these polymers are an exciting new class of 19 F MRI CAs with extremely high fluorine content and outstanding imaging sensitivity.

High-resolution NMR measurements and molecular dynamics (MD) simulations have been applied to the study of thermo-responsive copolymers of poly(ethylene glycol) methyl ether methacrylate (OEGMA) and 2,2,2-trifluoroethyl acrylate (TFEA) (poly(OEGMA-co-TFEA)) synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization.The detailed chemical microstructure of poly(OEGMA-co-TFEA) was investigated by means of various high-resolution NMR techniques. The polymer in aqueous solution possesses a lower critical solution temperature (LCST) at which significant changes in conformation are apparent.1 H 2D NOESY spectra were collected at temperatures below and above the LCST and demonstrated closer association of the exterior segments of the OEGMA side chains with the TFEA units above the LCST. MD simulations provided additional information on the changes in conformation and were consistent with the experimental findings. The combination of MD simulations with a detailed experimental study of poly(OEGMA-co-TFEA) in water leads to a clearer understanding of conformation occurring at the phase transition.

There is currently intense interest in new methods for understanding the fate of therapeutically-relevant cells, such as mesenchymal stem cells (MSCs). The absence of a confounding background signal and consequent unequivocal assignment makes 19F MRI one of the most attractive modalities for the tracking of injected cells in vivo. We describe here the synthesis of novel partly-fluorinated polymeric nanoparticles with small size and high fluorine content as MRI agents. The polymers, constructed from perfluoropolyether methacrylate (PFPEMA) and oligo(ethylene glycol) methacrylate (OEGMA) have favourable cell uptake profiles and excellent MRI performance. To facilitate cell studies the polymer was further conjugated with a fluorescent dye creating a dual-modal imaging agent. The efficacy of labelling of MSCs was assessed using 19F NMR, flow cytometry and confocal microscopy. The labelling efficiency of 2.6 ± 0.1 × 1012 19F atoms per cell, and viability of >90% demonstrates high uptake and good tolerance by the cells. This loading translates to a minimum 19F MRI detection sensitivity of ∼7.4 × 103 cells per voxel. Importantly, preliminary in vivo data demonstrate that labelled cells can be readily detected within a short acquisition scan period (12 minutes). Hence, these copolymers show outstanding potential for 19F MRI cellular tracking and for quantification of non-phagocytic and therapeutically-relevant cells in vivo.

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

Expression levels of biomarkers are generally unknown at initial diagnosis. The development of theranostic probes that do not rely on biomarker availability would expand therapy options for cancer patients, improve patient selection for nanomedicine and facilitate treatment of inoperable patients or patients with acquired therapy resistance. Herein, we report the development of star polymers, also known as nanostars, that allow for molecular imaging and/or endoradiotherapy based on passive targeting via the enhanced permeability and retention (EPR) effect.Methods: We synthesised a star copolymer, consisting of 7-8 centre-cross-linked arms that were modified with Gd3+ for magnetic resonance imaging (MRI), and functionalised either with 89Zr for in vivo quantification and positron emission tomography (PET) imaging, or with 177Lu for endoradiotherapy. 1H longitudinal relaxivities were determined over a continuum of magnetic field strengths ranging from 0.24 mT - 0.94 T at 37 °C (nuclear magnetic relaxation dispersion (NMRD) profile) and T1-weighted MRI contrast enhancement was visualized at 3 T and 7 T. PET imaging and ex vivo biodistribution studies were performed in mice bearing tumours with high EPR (CT26) or low EPR (BxPC3) characteristics. Therapy studies were performed in mice with high EPR tumours and mean absorbed organ doses were estimated for a standard human model.Results: The star copolymer with Gd3+ displayed a significantly superior contrast enhancement ability (T1 = 0.60 s) compared to the standard clinical contrast agent Gadovist (T1 = 1.0 s). Quantification of tumour accumulation using the radiolabelled nanostars in tumour-bearing mice demonstrated an exceptionally high uptake in tumours with high EPR characteristics (14.8 - 21.7 %ID/g). Uptake of the star polymers in tumours with low EPR characteristics was significantly lower (P<0.001), suggesting passive tumour accumulation of the nanostars via the EPR effect. Survival of mice treated with high dose 177Lu-labelled star polymers was significantly higher than survival of mice treated with lower therapy doses or control mice (P=0.001), demonstrating the utility of the 177Lu-labelled star polymers as platforms for endoradiotherapy.Conclusion: Our work highlights the potential of star polymers as probes for the molecular imaging of cancer tissue or for the passive delivery of radionuclides for endoradiotherapy. Their high functionalisability and high tumour accumulation emphasises their versatility as powerful tools for nanomedicine.

Highly branched polymers are a promising platform for the design of next-generation contrast agents for (19)F magnetic resonance imaging (MRI). A series of segmented highly branched polymers (SHBPs) consisting of fluoro- and PEG-based monomers were synthesized by self-condensing vinyl copolymerization (SCVP) using the reversible addition-fragmentation chain transfer (RAFT) technique. SHBPs having different compositions and degrees of branching were obtained by varying the monomer type and feed ratio of monomer to chain transfer agent (CTA). The chemical structures and physical properties of the branched polymers were thoroughly characterized in detail by NMR, SEC and DSC. The systematic variation in structural parameters allowed the relationships between molecular structure, sequence distribution, and imaging performance to be examined. The (19)F NMR properties were strongly affected by the sequence distribution of the fluorinated monomers, the type of polymer backbone and the degree of branching. As a result, SHBPs consisting of statistical copolymeric segments of acrylate units were identified as excellent candidates for imaging due to a single (19)F signal, long T2 relaxation times, and high fluorine contents. The SHBPs could be all imaged or selectively imaged by taking advantage of the differences in relaxation times, demonstrating tunable and selective imaging performance through tailoring the structure and composition of the SHBPs.

Thermoresponsive dendronized polymers, displaying remarkable phase behavior, are currently being studied for their potential exploitation as polymeric sensors and biomaterials.Understanding the conformational transitions occurring at the LCST is essential for improved design and translation of these polymers. The combination of NMR and molecular dynamics simulations opens a unique window onto the thermal behavior, showing that the peripheries of the dendrons, while driving the thermal properties, largely retain mobility above the critical temperature. The cores of the dendrons and the polymeric main chain are highly rigid below the thermal transition and increasingly so above the LCST. Both the experimental and computational studies reveal stretching of the interior segments of the dendrons with associated changes in spatial arrangements of the structural units. Furthermore, diffusion-ordered NMR and DLS below and above the LCST show a further hierarchy of dynamics within different size aggregates. The combination of the detailed experimental study and molecular dynamics simulations provides a detailed understanding of thermoresponsive behavior of these dendronized polymers.