Self-assembly, drug encapsulation, and cellular uptake of block and gradient copolymers of 2-methyl-2-oxazine and 2-n-propyl/butyl-2-oxazoline

Self-assembled amphiphilic polymers have been extensively studied for various biomedical applications, as they show advantageous properties for diagnosis and therapy. In this work, we extensively compared amphiphilic copolymers of the hydrophilic monomer 2-methyl-2-oxazine (MeOzi) and the thermoresponsive or hydrophobic monomers 2-propyl-2-oxazoline (PrOx) or 2-butyl-2-oxazoline (BuOx) in both block and gradient monomer distributions. Such a head-to-head comparison between block and gradient copolymers, which has thus far been mostly missing in the available literature, should provide important insight into the differences and similarities between these two architectures. We investigated the properties of our polymers using a wide array of analytical methods, including dynamic light scattering (DLS), small-angle neutron (SANS) and X-ray scattering (SAXS), one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy, transmission electron microscopy (TEM), drug loading (DL), cellular uptake, and cytotoxicity studies. Most of the studied polymers formed self-assembled nanoparticles, but their properties varied with the monomer ratio, polymer length, and polymer architecture, and these factors could be used to fine-tune the properties of the polymer to meet the demands of the desired application. Both block and gradient copolymers showed similar critical association concentrations and DL properties for the antituberculosis drug rifampicin. Finally, we confirmed that the nanoparticles could be internalized by macrophages, which indicates great potential for the utilization of these nanoparticles in drug delivery

Thermoresponsive Triblock Copolymers as Widely Applicable 19F Magnetic Resonance Imaging Tracers

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

Fluorinated ferrocene moieties as a platform for redox-responsive polymer F-19 MRI theranostics

Fluorine-19 magnetic resonance imaging (F-19 MRI) stands out as a powerful tool for noninvasive diagnostics. In particular, polymer-based F-19 MRI tracers ofler tunable physicochemical properties, including solubility and thermoresponsive-ness, and enhanced F-19 MRI performance. However, these tracers do not detectably respond to redox changes or do so in only one redox state, thereby preventing potential applications to reactive oxygen species (ROS) bioimaging. Herein, we report the first amphiphilic redox-responsive, poly(2-oxazoline)-based polymers bearing fluorinated ferrocene moieties. Their hydrophobicity and redox responsiveness were tailored by changing the monomer ratio and substitution pattern of the fluorinated ferrocene units. Converting the diamagnetic fluorinated ferrocene moieties into paramagnetic ferrocenium markedly changed the chemical shift and relaxation times of the F-19 nuclei distinguishable by F-19 MRI. In turn, the statistical-diblock copolymers formed nanoparticles that disassemble upon oxidation, with no toxicity to cultured cells. Therefore, these polymers may be used to release lipophilic drugs in ROS-rich malignancies

Thermoresponsive properties of polyacrylamides in physiological solutions

Polymer solutions with a lower critical solution temperature (LCST) undergo reversible phase separation when heated above their cloud point temperature (T-CP or CPT). As such, they have been proposed for a wide range of biomedical applications, from injectable drug depots to switchable coatings for cell adhesion. However, in systematic studies, the T-CP of these thermoresponsive polymers has been mostly measured in non-physiological solutions, thereby hindering the development of their medicinal applications. Here, we analysed the thermoresponsive properties of four acrylamide-based polymers with LCST, namely poly[(N-2,2-difluoroethyl)acrylamide] (pDFEA), poly[(N-isopropyl)acrylamide] (pNIPAM), poly[(N,N-diethyl)acrylamide] (pDEA), and poly[(N-acryloyl)pyrrolidine] (pAP). As shown by turbidimetty, their T-CP in phosphate saline buffer (PBS) and foetal bovine serum (FBS) were consistently lower than those reported in the literature, typically assessed in pure water, even when using the same setup. in addition, these physiological solutions affected the variation of T-CP as a function of polymer concentration (1.25 to 10.0 mg mL(-)(1)) and molar mass (20 to 50 kg mol(-1)). As shown by isothermal calorimetry, interactions between proteins in FBS and polymer aggregates were predominantly exothermic, which indicates that protein polymer complexes are formed through enthalpically driven processes. in conclusion, the T-CP of thermoresponsive polymers strongly depends on solvent composition and therefore should be measured under physiological conditions for future medicinal applications

Cell-Interactive Gelatin-Based ¹⁹F MRI Tracers: An <i>In Vitro</i> Proof-of-Concept Study

Cross-linked gelatin-based hydrogels are highly promising cell-interactive, biocompatible, and biodegradable materials serving tissue engineering. Moreover, gelatins with covalently bound methacrylamide (gel-MA) and 2-aminoethyl methacrylate moieties (gel-AEMA) can be cross-linked through ultraviolet (UV) irradiation, which allows light-based three-dimensional (3D)-printing of such hydrogels. Furthermore, the physicochemical and biological properties of these hydrogels can be broadly tuned by incorporating various comonomers into the polymer chains, which makes these hydrogels a widely applicable platform in tissue engineering and reconstructive surgery. However, monitoring the degradation rate of hydrogel-based implants in vivo is challenging, thereby prohibiting their broad clinical transition and further research. Therefore, herein, we describe the synthesis of 3D-printable gelatin-based hydrogels with N-(2,2-difluoroethyl)­acrylamide (DFEA), detectable with the chemical shift of −123 ppm, which enables us to monitor these implants in vivo with 19F magnetic resonance imaging (MRI) and assess their degradation kinetics. Next, we describe the physicochemical and biological properties of these hydrogels. Adding DFEA monomers into the reaction mixture accelerates their cross-linking kinetics. Moreover, increasing the DFEA content within the hydrogels increases their swelling ratio and 19F MRI signal. All hydrogels were detectable at small quantities (<16 mg) using 19F MRI. Moreover, our hydrogels supported the cell proliferation of adipose tissue-derived stem cells (ASCs) and had tunable biodegradation rates. Finally, we present a strategy for increasing the DFEA content without affecting the mechanical properties. Our results may be implemented in the future development of hydrogel implants, whose fate and biodegradation rate can be monitored via 19F MRI

Pharmacokinetics of intramuscularly administered thermoresponsive polymers

Aqueous solutions of some polymers exhibit a lower critical solution temperature (LCST); that is, they form phase-separated aggregates when heated above a threshold temperature. Such polymers found many promising (bio)medical applications, including in situ thermogelling with controlled drug release, polymer-supported radiotherapy (brachytherapy), immunotherapy, and wound dressing, among others. Yet, despite the extensive research on medicinal applications of thermoresponsive polymers, their biodistribution and fate after administration remained unknown. Thus, herein, they studied the pharmacokinetics of four different thermoresponsive polyacrylamides after intramuscular administration in mice. In vivo, these thermoresponsive polymers formed depots that subsequently dissolved with a two-phase kinetics (depot maturation, slow redissolution) with half-lives 2 weeks to 5 months, as depot vitrification prolonged their half-lives. Additionally, the decrease of T-CP of a polymer solution increased the density of the intramuscular depot. Moreover, they detected secondary polymer depots in the kidneys and liver; these secondary depots also followed two-phase kinetics (depot maturation and slow dissolution), with half-lives 8 to 38 days (kidneys) and 15 to 22 days (liver). Overall, these findings may be used to tailor the properties of thermoresponsive polymers to meet the demands of their medicinal applications. Their methods may become a benchmark for future studies of polymer biodistribution