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Fluorine-19 magnetic resonance imaging (19F MRI) has emerged as a promising noninvasive diagnostic tool, broad-ening the diagnostic possibilities of commonly used proton MRI. Despite the potential of 19F MRI, an ideal tracer paving the way toward the entry of this method into common medical practice is yet to be developed. In this study, we report on a series of polymeric systems based on thermoresponsive poly[N-(2,2-difluoroethyl)acrylamide] (PDFEA), a polymer considered to be an ideal tracer for 19F MRI. The described systems are designed as BAB triblock copolymers, where B corresponds to thermores-ponsive PDFEA blocks and A is a hydrophilic poly(ethylene glycol) block. These BAB triblock copolymers are able to form nanoparticles in dilute aqueous solutions, which undergo a transition into physically cross-linked hydrogels upon increasing the polymer concentration. Since thermoresponsive particle-and hydrogel-based systems are applicable in a wide range of biomedical applications, we created a diagnostic system with potential therapeutic properties (theranostic) as a widely tunable platform through straightforward synthesis while serving a multitude of applications. We analyzed the effect of the BAB block ratio on the self-assembly, thermoresponsiveness, and mechanical properties of the studied hydrogels, together with their suitability for 19F MRI. Finally, their biocompatibility was assessed on a relevant cell line.

Brachytherapy represents effective local therapy of unresectable solid tumors with very few side effects. Radiolabeled thermoresponsive polymers offer almost noninvasive approach to brachytherapy applications. A radioiodinated, water-soluble, thermosensitive poly(N-vinylcaprolactam) (PVCL) polymer was prepared using two approaches. The direct copolymerization with N-methacryloyl- l -tyrosinamide, as well as end-capping of carboxy-terminated PVCL homopolymer with tyramine, were used. In both cases the product was successfully radiolabeled with 125I. The obtained polymers demonstrate cloud-point temperature (TC) values in the range of 33–35 °C in all the studied solvent systems (water, PBS (pH 7.4) and physiological saline solution). Above the cloud point temperature, the molecularly dissolved polymer is macroprecipitated from the solution. The TC values close to the human body temperature of this biocompatible poly(N-vinylcaprolactam) polymer makes it a promising material intended for local therapy of solid tumors.