PFPE-Based Polymeric 19F MRI Agents: A New Class of Contrast Agents with Outstanding Sensitivity

In vitro and in vivo evaluation of biohybrid tissue-engineered vascular grafts with transformative 1H/19F MRI traceable scaffolds

Biohybrid tissue-engineered vascular grafts (TEVGs) promise long-term durability due to their ability to adapt to hosts' needs. However, the latter calls for sensitive non-invasive imaging approaches to longitudinally monitor their functionality, integrity, and positioning. Here, we present an imaging approach comprising the labeling of non-degradable and degradable TEVGs' components for their in vitro and in vivo monitoring by hybrid 1H/19F MRI. TEVGs (inner diameter 1.5 mm) consisted of biodegradable poly(lactic-co-glycolic acid) (PLGA) fibers passively incorporating superparamagnetic iron oxide nanoparticles (SPIONs), non-degradable polyvinylidene fluoride scaffolds labeled with highly fluorinated thermoplastic polyurethane (19F-TPU) fibers, a smooth muscle cells containing fibrin blend, and endothelial cells. 1H/19F MRI of TEVGs in bioreactors, and after subcutaneous and infrarenal implantation in rats, revealed that PLGA degradation could be faithfully monitored by the decreasing SPIONs signal. The 19F signal of 19F-TPU remained constant over weeks. PLGA degradation was compensated by cells' collagen and α-smooth-muscle-actin deposition. Interestingly, only TEVGs implanted on the abdominal aorta contained elastin. XTT and histology proved that our imaging markers did not influence extracellular matrix deposition and host immune reaction. This concept of non-invasive longitudinal assessment of cardiovascular implants using 1H/19F MRI might be applicable to various biohybrid tissue-engineered implants, facilitating their clinical translation.

Polymeric Nanoparticles for Drug Delivery

The recent emergence of nanomedicine has revolutionized the therapeutic landscape and necessitated the creation of more sophisticated drug delivery systems. Polymeric nanoparticles sit at the forefront of numerous promising drug delivery designs, due to their unmatched control over physiochemical properties such as size, shape, architecture, charge, and surface functionality. Furthermore, polymeric nanoparticles have the ability to navigate various biological barriers to precisely target specific sites within the body, encapsulate a diverse range of therapeutic cargo and efficiently release this cargo in response to internal and external stimuli. However, despite these remarkable advantages, the presence of polymeric nanoparticles in wider clinical application is minimal. This review will provide a comprehensive understanding of polymeric nanoparticles as drug delivery vehicles. The biological barriers affecting drug delivery will be outlined first, followed by a comprehensive description of the various nanoparticle designs and preparation methods, beginning with the polymers on which they are based. The review will meticulously explore the current performance of polymeric nanoparticles against a myriad of diseases including cancer, viral and bacterial infections, before finally evaluating the advantages and crucial challenges that will determine their wider clinical potential in the decades to come.

Fluorinated Organic Polymers for Cancer Drug Delivery

In the realm of cancer therapy, the spotlight is on nanoscale pharmaceutical delivery systems, especially polymer-based nanoparticles, for their enhanced drug dissolution, extended presence in the bloodstream, and precision targeting achieved via surface engineering. Leveraging the amplified permeation and retention phenomenon, these systems concentrate therapeutic agents within tumor tissues. Nonetheless, the hurdles of systemic toxicity, biological barriers, and compatibility with living systems persist. Fluorinated polymers, distinguished by their chemical idiosyncrasies, are poised for extensive biomedical applications, notably in stabilizing drug metabolism, augmenting lipophilicity, and optimizing bioavailability. Material science heralds the advent of fluorinated polymers that, by integrating fluorine atoms, unveil a suite of drug delivery merits: the hydrophobic traits of fluorinated alkyl chains ward off lipid or protein disruption, the carbon-fluorine bond's stability extends the drug's lifecycle in the system, and a lower alkalinity coupled with a diminished ionic charge bolsters the drug's ability to traverse cellular membranes. This comprehensive review delves into the utilization of fluorinated polymers for oncological pharmacotherapy, elucidating their molecular architecture, synthetic pathways, and functional attributes, alongside an exploration of their empirical strengths and the quandaries they encounter in both experimental and clinical settings.

Tailored Fluorosurfactants through Controlled/Living Radical Polymerization for Highly Stable Microfluidic Droplet Generation

Droplet-based microfluidics represents a disruptive technology in the field of chemistry and biology through the generation and manipulation of sub-microlitre droplets. To avoid droplet coalescence, fluoropolymer-based surfactants are commonly used to reduce the interfacial tension between two immiscible phases to stabilize droplet interfaces. However, the conventional preparation of fluorosurfactants involves multiple steps of conjugation reactions between fluorinated and hydrophilic segments to form multiple-block copolymers. In addition, synthesis of customized surfactants with tailored properties is challenging due to the complex synthesis process. Here, we report a highly efficient synthetic method that utilizes living radical polymerization (LRP) to produce fluorosurfactants with tailored functionalities. Compared to the commercialized surfactant, our surfactants outperform in thermal cycling for polymerase chain reaction (PCR) testing, and exhibit exceptional biocompatibility for cell and yeast culturing in a double-emulsion system. This breakthrough synthetic approach has the potential to revolutionize the field of droplet-based microfluidics by enabling the development of novel designs that generate droplets with superior stability and functionality for a wide range of applications.

Protein-Engineered Fibers For Drug Encapsulation Traceable via 19F Magnetic Resonance

Theranostic materials research is experiencing rapid growth driven by the interest in integrating both therapeutic and diagnostic modalities. These materials offer the unique capability to not only provide treatment but also track the progression of a disease. However, to create an ideal theranostic biomaterial without compromising drug encapsulation, diagnostic imaging must be optimized for improved sensitivity and spatial localization. Herein, we create a protein-engineered fluorinated coiled-coil fiber, Q2TFL, capable of improved sensitivity to 19F magnetic resonance spectroscopy (MRS) detection. Leveraging residue-specific noncanonical amino acid incorporation of trifluoroleucine (TFL) into the coiled-coil, Q2, which self-assembles into nanofibers, we generate Q2TFL. We demonstrate that fluorination results in a greater increase in thermostability and 19F magnetic resonance detection compared to the nonfluorinated parent, Q2. Q2TFL also exhibits linear ratiometric 19F MRS thermoresponsiveness, allowing it to act as a temperature probe. Furthermore, we explore the ability of Q2TFL to encapsulate the anti-inflammatory small molecule, curcumin (CCM), and its impact on the coiled-coil structure. Q2TFL also provides hyposignal contrast in 1H MRI, echogenic signal with high-frequency ultrasound and sensitive detection by 19F MRS in vivo illustrating fluorination of coiled-coils for supramolecular assembly and their use with 1H MRI, 19F MRS and high frequency ultrasound as multimodal theranostic agents.

Fluoropolymer Nanoparticles Synthesized via Reversible-Deactivation Radical Polymerizations and Their Applications

Fluorinated polymeric nanoparticles (FPNPs) combine unique properties of fluorocarbon and polymeric nanoparticles, which has stimulated massive interest for decades. However, fluoropolymers are not readily available from nature, resulting in synthetic developments to obtain FPNPs via free radical polymerizations. Recently, while increasing cutting-edge directions demand tailored FPNPs, such materials have been difficult to access via conventional approaches. Reversible-deactivation radical polymerizations (RDRPs) are powerful methods to afford well-defined polymers. Researchers have applied RDRPs to the fabrication of FPNPs, enabling the construction of particles with improved complexity in terms of structure, composition, morphology, and functionality. Related examples can be classified into three categories. First, well-defined fluoropolymers synthesized via RDRPs have been utilized as precursors to form FPNPs through self-folding and solution self-assembly. Second, thermally and photoinitiated RDRPs have been explored to realize in situ preparations of FPNPs with varied morphologies via polymerization-induced self-assembly and cross-linking copolymerization. Third, grafting from inorganic nanoparticles has been investigated based on RDRPs. Importantly, those advancements have promoted studies toward promising applications, including magnetic resonance imaging, biomedical delivery, energy storage, adsorption of perfluorinated alkyl substances, photosensitizers, and so on. This Review should present useful knowledge to researchers in polymer science and nanomaterials and inspire innovative ideas for the synthesis and applications of FPNPs.

Perfluoro-tert-butyl Group-Derived Capmatinib: Synthesis, Biological Evaluation and Its Application in 19 F Magnetic Resonance Imaging

Capmatinib is an FDA-approved drug to treat metastatic non-small cell lung cancer with MET-exon 14 skipping. Herein, the perfluoro-tert-butyl group, which possesses nine chemically identical fluorine atoms, was introduced on Capmatinib to afford a targeted 19 F magnetic resonance imaging (MRI) probe, perfluoro-tert-butyl group-derived Capmatinib (9F-CAP). The 19 F MRI concentration limit was found to be 25 mM in FLASH sequence. Molecular docking simulation, surface plasmon resonance (SPR) (with a Kd of 40.7 μM), half-inhibitory concentration (with a IC50 of 168 nM), Annexin V, and cytotoxicity assays jointly demonstrated that the 9F-CAP targeted cMET protein specifically. Therefore, the targeted imaging capability of 9F-CAP is of great significance for the preoperative diagnosis of specific cancers.

How to 19F MRI: applications, technique, and getting started

Magnetic resonance imaging (MRI) plays a significant role in the routine imaging workflow, providing both anatomical and functional information. 19F MRI is an evolving imaging modality where instead of 1H, 19F nuclei are excited. As the signal from endogenous 19F in the body is negligible, exogenous 19F signals obtained by 19F radiofrequency coils are exceptionally specific. Highly fluorinated agents targeting particular biological processes (i.e., the presence of immune cells) have been visualised using 19F MRI, highlighting its potential for non-invasive and longitudinal molecular imaging. This article aims to provide both a broad overview of the various applications of 19F MRI, with cancer imaging as a focus, as well as a practical guide to 19F imaging. We will discuss the essential elements of a 19F system and address common pitfalls during acquisition. Last but not least, we will highlight future perspectives that will enhance the role of this modality. While not an exhaustive exploration of all 19F literature, we endeavour to encapsulate the broad themes of the field and introduce the world of 19F molecular imaging to newcomers. 19F MRI bridges several domains, imaging, physics, chemistry, and biology, necessitating multidisciplinary teams to be able to harness this technology effectively. As further technical developments allow for greater sensitivity, we envision that 19F MRI can help unlock insight into biological processes non-invasively and longitudinally.

Fluorinated hydrogel nanoparticles with regulable fluorine contents and T2 relaxation times as 19F MRI contrast agents

Medical imaging contrast agents that are able to provide detailed biological information have attracted increasing attention. Among the new emerging imaging contrast agents, ¹⁹F magnetic resonance imaging contrast agents (¹⁹F MRI CAs) are extremely promising for their weak background disturbing signal from the body. However, to prepare ¹⁹F MRI CAs with a long T₂ relaxation time and excellent biocompatibility in a simple and highly effective strategy is still a challenge. Herein, we report a new type of ¹⁹F MRI hydrogel nanocontrast agents (¹⁹F MRI HNCAs) synthesized by a surfactant-free emulsion polymerization with commercial fluorinated monomers. The T₂ relaxation time of ¹⁹F MRI HNCA-1 was found to be 25-40 ms, guaranteeing its good imaging ability in vitro. In addition, according to an investigation into the relationship between the fluorine content and ¹⁹F MRI signal intensity, the ¹⁹F MRI signal intensity was not only determined by the fluorine content in ¹⁹F MRI HNCAs but also by the hydration microenvironment around the fluorine atoms. Moreover, ¹⁹F MRI HNCAs demonstrated excellent biocompatibility and imaging capability inside cells. The primary exploration demonstrated that ¹⁹F MRI HNCAs as a new type of ¹⁹F MRI contrast agent hold potential for imaging lesion sites and tracking cells in vivo by ¹⁹F MRI technology.

Preparation of PFPE-Based Polymeric Nanoparticles via Polymerization-Induced Self-Assembly as Contrast Agents for 19F MRI

Fluorine-19 magnetic resonance imaging (¹⁹F MRI) probes have received considerable research interest as imaging contrast agents (CAs), but they remain neglected and underutilized due to the limited fluorine content or poor performance of fluorinated tracers. Here, we present polymeric nanoparticles (NPs) as ¹⁹F MRI CAs with a simple synthesis method and promising imaging performance. First, hydrophilic random copolymers were synthesized from oligo(ethylene glycol) methyl ether acrylate and perfluoropolyether methacrylate by reversible addition-fragmentation chain transfer (RAFT) polymerization. The optimal fluorine content, polymer concentration, and cytotoxicity as ¹⁹F MRI CAs were investigated in detail. Then, the optimal copolymer was selected as the macromolecular chain transfer agent, and the chain extension was performed with 2-(perfluorooctyl ethyl methacrylate). Subsequently, the NPs with different morphologies, such as ellipsoidal, spherical nanoparticles and vesicles, were prepared in situ by the RAFT-mediated polymerization-induced self-assembly method. In addition, the ¹⁹F MRI signal and cytotoxicity studies further confirmed that these polymeric NPs are nontoxic and have great potential as promising ¹⁹F MRI CAs for biological applications.

Synthesis of 5-Fluorouracil Polymer Conjugate and 19F NMR Analysis of Drug Release for MRI Monitoring

To monitor the release of fluorinated drugs from polymeric carriers, a novel 19F MRI enzyme-responsive contrast agent was developed and tested. This contrast agent was prepared by conjugation of 5-fluorouracil (5-FU) to hyperbranched poly(N,N-dimethylacrylamide) (HB-PDMA) via an enzyme-degradable peptide linker. Due to the different molecular sizes, the release of 5-FU from the 5-FU polymer conjugate resulted in a sufficiently substantial difference in spin-spin T2 19F NMR/MRI relaxation time that enabled differentiating between attached and released drug states. The 5-FU polymer conjugate exhibited a broad signal and short T2 relaxation time under 19F NMR analysis. Incubation with the enzyme induced the release of 5-FU, accompanied by an extension of T2 relaxation times and an enhancement in the 19F MRI signal. This approach is promising for application in the convenient monitoring of 5-FU drug release and can be used to monitor the release of other fluorinated drugs.

Ultra-stable all-solid-state sodium metal batteries enabled by perfluoropolyether-based electrolytes

Rechargeable batteries paired with sodium metal anodes are considered to be one of the most promising high-energy and low-cost energy-storage systems. However, the use of highly reactive sodium metal and the formation of sodium dendrites during battery operation have caused safety concerns, especially when highly flammable liquid electrolytes are used. Here we design and develop solvent-free solid polymer electrolytes (SPEs) based on a perfluoropolyether-terminated polyethylene oxide (PEO)-based block copolymer for safe and stable all-solid-state sodium metal batteries. Compared with traditional PEO SPEs, our results suggest that block copolymer design allows for the formation of self-assembled nanostructures leading to high storage modulus at elevated temperatures with the PEO domains providing transport channels even at high salt concentration (ethylene oxide/sodium = 8/2). Moreover, it is demonstrated that the incorporation of perfluoropolyether segments enhances the Na⁺ transference number of the electrolyte to 0.46 at 80 °C and enables a stable solid electrolyte interface. The new SPE exhibits highly stable symmetric cell-cycling performance at high current density (0.5 mA cm^-2 and 1.0 mAh cm^-2, up to 1,000 h). Finally, the assembled all-solid-state sodium metal batteries demonstrate outstanding capacity retention, long-term charge/discharge stability (Coulombic efficiency, 99.91%; >900 cycles with Na₃V₂(PO₄)₃ cathode) and good capability with high loading NaFePO₄ cathode (>1 mAh cm^-2).

Unique Random-Block Polymer Architecture for Site-Specific Mitochondrial Sequestration-Aided Effective Chemotherapeutic Delivery and Enhanced Fluorocarbon Segmental Mobility-Facilitated 19F Magnetic Resonance Imaging

The elevation of the chemotherapeutic efficacy and attenuation of its side effects on healthy cells and tissues become one of the prime targets for the treatment of cancer. Toward this direction, a sequential receptor and mitochondria dual-targeting strategy was implemented in the DX TP PG BN ¹⁹F theranostic polymer that was anchored with the chemotherapeutic agent doxorubicin, receptor-targeting biotin, and mitochondria-targeting triphenylphosphonium cations. The polymer was flourished with a unique ¹⁹F magnetic resonance imaging (MRI) tracer that exhibited high segmental mobility and eventually led to prolonged T₂ relaxation time. Furthermore, for the sake of amphiphilicity, the DX TP PG BN ¹⁹F polymer spontaneously aggregated into nano-sphere with positive zeta potential, where the MRI tracer and biotin embedded at the exterior and displayed site-specific targeting and remarkable ¹⁹F MRI capability simultaneously. The mitochondria-targeting competency of the DX TP PG BN ¹⁹F theranostic polymer was investigated by comparing the non-mitochondrial-targeting DX PG BN ¹⁹F polymer using fluorescence microscopic cell imaging in human cervical, HeLa, and breast MCF-7 carcinoma cell lines. Moreover, cytotoxicity experiments of the aforementioned theranostic polymers clarified the enhancement of the chemotherapeutic efficacy of DX TP PG BN ¹⁹F theranostic polymers through effective and precise mitochondrial doxorubicin delivery that forced to follow the apoptotic path.

Fluorine in Medicinal Chemistry: In Perspective to COVID-19

Over two years into the outbreak of COVID-19, the quest for effective and economical drugs has become starkly clear to reduce the risk of progression of coronavirus disease. A number of drugs have been investigated, and they can be taken orally at home and be used after exposure to SARS-CoV-2 or at the first sign of COVID-19. Fluorinated oral anti-COVID-19 drugs-including Paxlovid, the first oral tablet for the treatment of COVID-19-constitute an important subgroup. Fluorine has been widely used in the pharmaceutical market and can lead to improved selectivity indices, increased lipophilicity, greater metabolic stability, and improved anti-COVID-19 efficacy. In this mini-review, we will give an update on fluorinated anti-COVID-19 drugs by providing the key information and current knowledge of these drugs, including their molecular design, metabolism and pharmacokinetics, and mechanism of action.

A Multifunctional Contrast Agent for 19F-Based Magnetic Resonance Imaging

Magnetic resonance imaging, MRI, relying on ¹⁹F nuclei has attracted much attention, because the isotopes exhibit a high gyromagnetic ratio (comparable to that of protons) and have 100% natural abundance. Furthermore, due to the very low traces of intrinsic fluorine in biological tissues, fluorine labeling allows easy visualization in vivo using ¹⁹F-based MRI. However, one of the drawbacks of the available fluorine tracers is their very limited solubility in water. Here, we detail the design and preparation of a set of water-compatible fluorine-rich polymers as contrast agents that can enhance the effectiveness of ¹⁹F-based MRI. The agents are synthesized using the nucleophilic addition reaction between poly(isobutylene-alt-maleic anhydride) copolymer and a mixture of amine-appended fluorine groups and polyethylene glycol (PEG) blocks. This allows control over the polymer architecture and stoichiometry, resulting in good affinity to water solutions. We further investigate the effects of introducing additional segmental mobility to the fluorine moieties in the polymer, by inserting a PEG linker between the moieties and the polymer backbone. We find that controlling the polymer stoichiometry and introducing additional segmental mobility enhance the NMR signals and narrow the peak profile. In particular, we assess the impact of the PEG linker on T₂* and T₁ relaxation times, using a series of gradient-recalled echo images with varying echo times, TE, or recovery time, TR, respectively. We find that for equivalent concentrations, the PEG linker greatly increases T₂*, while maintaining high T₁ values, as compared to polymers without this linker. Phantom images collected from these compounds show bright signals over a background with high intensities.

Click-Ready Perfluorocarbon Nanoemulsion for 19F MRI and Multimodal Cellular Detection

We describe an in vivo imaging probe platform that is readily modifiable to accommodate binding of different molecular targeting moieties and payloads for multimodal image generation. In this work, we demonstrate the utility of perfluorocarbon (PFC) nanoemulsions incorporating dibenzocyclooctyne (DBCO) by enabling postemulsification functionalization via a click reaction with azide-containing ligands. The addition of DBCO-lipid to the surfactant in PFC nanoemulsions did not affect nanoemulsion size or nanoemulsion stability. As proof-of-concept, fluorescent dye-azides were conjugated to PFC nanoemulsions, demonstrating the feasibility of functionalization the by click reaction. Uptake of the fluorescent PFC by macrophages was demonstrated both in vitro in cultured macrophages and in situ in an acute inflammation mouse model, where fluorescence imaging and ¹H/¹⁹F magnetic resonance imaging (MRI) were used for in vivo detection. Overall, these data demonstrate the potential of PFC nanoemulsions incorporating DBCO as a versatile platform for generating functionalized probes.

Nanotechnology as a Versatile Tool for 19F-MRI Agent’s Formulation: A Glimpse into the Use of Perfluorinated and Fluorinated Compounds in Nanoparticles

Simultaneously being a non-radiative and non-invasive technique makes magnetic resonance imaging (MRI) one of the highly sought imaging techniques for the early diagnosis and treatment of diseases. Despite more than four decades of research on finding a suitable imaging agent from fluorine for clinical applications, it still lingers as a challenge to get the regulatory approval compared to its hydrogen counterpart. The pertinent hurdle is the simultaneous intrinsic hydrophobicity and lipophobicity of fluorine and its derivatives that make them insoluble in any liquids, strongly limiting their application in areas such as targeted delivery. A blossoming technique to circumvent the unfavorable physicochemical characteristics of perfluorocarbon compounds (PFCs) and guarantee a high local concentration of fluorine in the desired body part is to encapsulate them in nanosystems. In this review, we will be emphasizing different types of nanocarrier systems studied to encapsulate various PFCs and fluorinated compounds, headway to be applied as a contrast agent (CA) in fluorine-19 MRI (¹⁹F MRI). We would also scrutinize, especially from studies over the last decade, the different types of PFCs and their specific applications and limitations concerning the nanoparticle (NP) system used to encapsulate them. A critical evaluation for future opportunities would be speculated.

Biological Utility of Fluorinated Compounds: from Materials Design to Molecular Imaging, Therapeutics and Environmental Remediation

The applications of fluorinated molecules in bioengineering and nanotechnology are expanding rapidly with the controlled introduction of fluorine being broadly studied due to the unique properties of C-F bonds. This review will focus on the design and utility of C-F containing materials in imaging, therapeutics, and environmental applications with a central theme being the importance of controlling fluorine-fluorine interactions and understanding how such interactions impact biological behavior. Low natural abundance of fluorine is shown to provide sensitivity and background advantages for imaging and detection of a variety of diseases with ¹⁹F magnetic resonance imaging, ¹⁸F positron emission tomography and ultrasound discussed as illustrative examples. The presence of C-F bonds can also be used to tailor membrane permeability and pharmacokinetic properties of drugs and delivery agents for enhanced cell uptake and therapeutics. A key message of this review is that while the promise of C-F containing materials is significant, a subset of highly fluorinated compounds such as per- and polyfluoroalkyl substances (PFAS), have been identified as posing a potential risk to human health. The unique properties of the C-F bond and the significant potential for fluorine-fluorine interactions in PFAS structures necessitate the development of new strategies for facile and efficient environmental removal and remediation. Recent progress in the development of fluorine-containing compounds as molecular imaging and therapeutic agents will be reviewed and their design features contrasted with environmental and health risks for PFAS systems. Finally, present challenges and future directions in the exploitation of the biological aspects of fluorinated systems will be described.

Fluorine NMR study of proline-rich sequences using fluoroprolines

Proline homopolymer motifs are found in many proteins; their peculiar conformational and dynamic properties are often directly involved in those proteins' functions. However, the dynamics of proline homopolymers is hard to study by NMR due to a lack of amide protons and small chemical shift dispersion. Exploiting the spectroscopic properties of fluorinated prolines opens interesting perspectives to address these issues. Fluorinated prolines are already widely used in protein structure engineering - they introduce conformational and dynamical biases - but their use as 19 F NMR reporters of proline conformation has not yet been explored. In this work, we look at model peptides where Cγ -fluorinated prolines with opposite configurations of the chiral Cγ centre have been introduced at two positions in distinct polyproline segments. By looking at the effects of swapping these (4R )-fluoroproline and (4S )-fluoroproline within the polyproline segments, we were able to separate the intrinsic conformational properties of the polyproline sequence from the conformational alterations instilled by fluorination. We assess the fluoroproline 19 F relaxation properties, and we exploit the latter in elucidating binding kinetics to the SH3 (Src homology 3) domain.

Machine-Learning-Guided Discovery of 19F MRI Agents Enabled by Automated Copolymer Synthesis

Modern polymer science suffers from the curse of multidimensionality. The large chemical space imposed by including combinations of monomers into a statistical copolymer overwhelms polymer synthesis and characterization technology and limits the ability to systematically study structure-property relationships. To tackle this challenge in the context of 19F magnetic resonance imaging (MRI) agents, we pursued a computer-guided materials discovery approach that combines synergistic innovations in automated flow synthesis and machine learning (ML) method development. A software-controlled, continuous polymer synthesis platform was developed to enable iterative experimental-computational cycles that resulted in the synthesis of 397 unique copolymer compositions within a six-variable compositional space. The nonintuitive design criteria identified by ML, which were accomplished by exploring <0.9% of the overall compositional space, lead to the identification of >10 copolymer compositions that outperformed state-of-the-art materials.

Therapeutic oxygen delivery by perfluorocarbon-based colloids

After the protocol-related indecisive clinical trial of Oxygent, a perfluorooctylbromide/phospholipid nanoemulsion, in cardiac surgery, that often unduly assigned the observed untoward effects to the product, the development of perfluorocarbon (PFC)-based O₂ nanoemulsions ("blood substitutes") has come to a low. Yet, significant further demonstrations of PFC O₂-delivery efficacy have continuously been reported, such as relief of hypoxia after myocardial infarction or stroke; protection of vital organs during surgery; potentiation of O₂-dependent cancer therapies, including radio-, photodynamic-, chemo- and immunotherapies; regeneration of damaged nerve, bone or cartilage; preservation of organ grafts destined for transplantation; and control of gas supply in tissue engineering and biotechnological productions. PFC colloids capable of augmenting O₂ delivery include primarily injectable PFC nanoemulsions, microbubbles and phase-shift nanoemulsions. Careful selection of PFC and other colloid components is critical. The basics of O₂ delivery by PFC nanoemulsions will be briefly reminded. Improved knowledge of O₂ delivery mechanisms has been acquired. Advanced, size-adjustable O₂-delivering nanoemulsions have been designed that have extended room-temperature shelf-stability. Alternate O₂ delivery options are being investigated that rely on injectable PFC-stabilized microbubbles or phase-shift PFC nanoemulsions. The latter combine prolonged circulation in the vasculature, capacity for penetrating tumor tissues, and acute responsiveness to ultrasound and other external stimuli. Progress in microbubble and phase-shift emulsion engineering, control of phase-shift activation (vaporization), understanding and control of bubble/ultrasound/tissue interactions is discussed. Control of the phase-shift event and of microbubble size require utmost attention. Further PFC-based colloidal systems, including polymeric micelles, PFC-loaded organic or inorganic nanoparticles and scaffolds, have been devised that also carry substantial amounts of O₂. Local, on-demand O₂ delivery can be triggered by external stimuli, including focused ultrasound irradiation or tumor microenvironment. PFC colloid functionalization and targeting can help adjust their properties for specific indications, augment their efficacy, improve safety profiles, and expand the range of their indications. Many new medical and biotechnological applications involving fluorinated colloids are being assessed, including in the clinic. Further uses of PFC-based colloidal nanotherapeutics will be briefly mentioned that concern contrast diagnostic imaging, including molecular imaging and immune cell tracking; controlled delivery of therapeutic energy, as for noninvasive surgical ablation and sonothrombolysis; and delivery of drugs and genes, including across the blood-brain barrier. Even when the fluorinated colloids investigated are designed for other purposes than O₂ supply, they will inevitably also carry and deliver a certain amount of O₂, and may thus be considered for O₂ delivery or co-delivery applications. Conversely, O₂-carrying PFC nanoemulsions possess by nature a unique aptitude for ¹⁹F MR imaging, and hence, cell tracking, while PFC-stabilized microbubbles are ideal resonators for ultrasound contrast imaging and can undergo precise manipulation and on-demand destruction by ultrasound waves, thereby opening multiple theranostic opportunities.

Copper(II) Pyridyl Aminophenolates: Hypoxia-Selective, Nucleus-Targeting Cytotoxins, and Magnetic Resonance Probes

Targeting the low-oxygen (hypoxic) environments found in many tumours by using redox-active metal complexes is a strategy that can enhance efficacy and reduce the side effects of chemotherapies. We have developed a series of Cu^II complexes with tridentate pyridine aminophenolate-based ligands for preferential activation in the reduction window provided by hypoxic tissues. Furthermore, ligand functionalization with a pendant CF₃ group provides a ¹⁹ F spectroscopic handle for magnetic-resonance studies of redox processes at the metal centre and behaviour in cellular environments. The phenol group in the ligand backbone was substituted at the para position with H, Cl, and NO₂ to modulate the reduction potential of the Cu^II centre, giving a range of values below the window expected for hypoxic tissues. The NO₂ -substituted complex, which has the highest reduction potential, showed enhanced cytotoxic selectivity towards HeLa cells grown under hypoxic conditions. Cell death occurs by apoptosis, as determined by analysis of the cell morphology. A combination of ¹⁹ F NMR and ICP-OES indicates localization of the NO₂ complex in HeLa cell nuclei and increased cellular accumulation under hypoxia. This correlates with DNA nuclease activity being the likely origin of cytotoxic activity, as demonstrated by cleavage of DNA plasmids in the presence of the Cu^II nitro complex and a reducing agent. Selective detection of the paramagnetic Cu^II complexes and their diamagnetic ligands by ¹⁹ F MRI suggests hypoxia-targeting theranostic applications by redox activation.

Photoresponsive host-guest chemistry and relaxation time of fluorinated cyclodextrin and arylazopyrazole-functionalized DOTA metal complexes

Light-responsive modulation of the longitudinal (T1) and transversal relaxation times of a fluorinated cyclodextrin has been achieved by host-guest complexation with arylazopyrazole-modified metal complexes in aqueous solution. This supramolecular concept can potentially be applied to the development of contrast agents for 19F magnetic resonance imaging (MRI).

Tuning the thermoresponsive properties of PEG-based fluorinated polymers and stimuli responsive drug release for switchable 19F magnetic resonance imaging

Switching on of the 19F MRI signal via stimuli-responsive release of hydrophobic drug from PEG-based partly-fluorinated polymers due to change in thermoresponsive properties.

Fluoropolymers in biomedical applications: state-of-the-art and future perspectives

Biomedical applications of fluoropolymers in gene delivery, protein delivery, drug delivery, ¹⁹F MRI, PDT, anti-fouling, anti-bacterial, cell culture, and tissue engineering.

Efficient temperature-feedback liposome for 19F MRI signal enhancement

A new non-encapsulated fluorinated liposome (TSL) was developed, which showed instantaneous temperature-induced 19F MR signal enhancement and excellent stability under reversible signal transition at different conditions.

Fluorinated PLGA Nanoparticles for Enhanced Drug Encapsulation and 19 F NMR Detection

In the continuous search for multimodal systems with combined diagnostic and therapeutic functions, several efforts have been made to develop multifunctional drug delivery systems. In this work, through a covalent approach, a new class of fluorinated poly(lactic-co-glycolic acid) co-polymers (F-PLGA) were designed that contain an increasing number of magnetically equivalent fluorine atoms. In particular, two novel compounds, F₃ -PLGA and F₉ -PLGA, were synthesized and their chemical structure and thermal stability were analyzed by solution NMR, DSC, and TGA. The obtained F-PLGA compounds were proven to form in aqueous solution colloidal stable nanoparticles (NPs) displaying a strong ¹⁹ F NMR signal. The fluorinated NPs also showed an enhanced ability to load hydrophobic drugs containing fluorine atoms compared to analogous pristine PLGA NPs. Preliminary in vitro studies showed high cell viability and the NP ability to intracellularly deliver and release a functioning drug.

Implant-forming polymeric 19F MRI-tracer with tunable dissolution

Magnetic resonance imaging (MRI) using ¹⁹F-based tracers has emerged as a promising multi-purpose noninvasive diagnostic tool and its application requires the use of various ¹⁹F-based tracers for the intended diagnostic purpose. In this study, we report a series of double-stimuli-responsive polymers for use as injectable implants, which were designed to form implants under physiological conditions, and to subsequently dissolve with different dissolution rates (t_1/2 ranges from 30 to more than 250 days). Our polymers contain a high concentration of fluorine atoms, providing remarkable signal detectability, and both a hydrophilic monomer and a pH-responsive monomer that alter the biodistribution properties of the implant. The implant location and dissolution were observed using ¹⁹F MRI, which allows the anatomic extent of the implant to be monitored. The dissolution kinetics and biocompatibility of these materials were thoroughly analyzed. No sign of toxicity in vitro or in vivo or pathology in vivo was observed, even in chronic administration. The clinical applicability of our polymers was further confirmed via imaging of a rat model by employing an instrument currently used in human medicine.

Tuning of the Aggregation Behavior of Fluorinated Polymeric Nanoparticles for Improved Therapeutic Efficacy

Incorporation of fluorinated moieties in polymeric nanoparticles has been shown in many instances to increase their uptake by living cells and, hence, has proven to be a useful approach to enhancing delivery to cells. However, it remains unclear how incorporation of fluorine affects critical transport processes, such as interactions with membranes, intracellular transport, and tumor penetration. In this study, we investigate the influence of fluorine on transport properties using a series of rationally designed poly(oligo(ethylene glycol) methyl ether acrylate)-block-perfluoropolyether (poly(OEGA)_m-PFPE) copolymers. Copolymers with different fluorine contents were prepared and exhibit aggregate in solution in a manner dependent on the fluorine content. Doxorubicin-conjugated poly(OEGA)₂₀-PFPE nanoparticles with lower fluorine content exist in solution as unimers, leading to greater exposure of hydrophobic PFPE segments to the cell surface. This, in turn, results in greater cellular uptake, deeper tumor penetration, as well as enhanced therapeutic efficacy compared to that with the micelle-state nanoaggregates (poly(OEGA)₁₀-PFPE and poly(OEGA)₅-PFPE) with higher fluorine content but with less PFPE exposed to the cell membranes. Our results demonstrate that the aggregation behavior of these fluorinated polymers plays a critical role in internalization and transport in living cells and 3D spheroids, providing important design criteria for the preparation of highly effective delivery agents.

Rapid Generation of Block Copolymer Libraries Using Automated Chromatographic Separation

A versatile and scalable strategy is reported for the rapid generation of block copolymer libraries spanning a wide range of compositions starting from a single parent copolymer. This strategy employs automated and operationally simple chromatographic separation that is demonstrated to be applicable to a variety of block copolymer chemistries on multigram scales with excellent mass recovery. The corresponding phase diagrams exhibit increased compositional resolution compared to those traditionally constructed via multiple, individual block copolymer syntheses. Increased uniformity and lower dispersity of the chromatographic libraries lead to differences in the location of order-order transitions and observable morphologies, highlighting the influence of dispersity on the self-assembly of block copolymers. Significantly, this separation technique greatly simplifies the exploration of block copolymer phase space across a range of compositions, monomer pairs, and molecular weights (up to 50000 amu), producing materials with increased control and homogeneity when compared to conventional strategies.

A Fluorinated Ionic Liquid-Based Activatable 19F MRI Platform Detects Biological Targets

¹⁹F magnetic resonance imaging (¹⁹F MRI) is a promising technique for in vivo molecular imaging and clinical diagnosis, benefiting from its negligible background and unlimited tissue penetration depth. However, the development of ¹⁹F probes with good water solubility and versatile functions for bioresponsive and practical applications remains a challenge. Here, we report fluorinated ion liquids (ILs) as a new type of fluorine agents and build a fluorinated ionic liquid-based activatable ¹⁹F MRI platform (FILAMP), which relies on the phase transition of ILs. Upon exposure to environmental stimulation, coating polymer dissolves or degrades to release the fluorinated ILs payload, which rapidly enhances ¹⁹F signal. This "turn-on" response is verified by the successful detection of biological targets (for example, dysregulated pH and MMP overexpression) at the cellular level and in mice, demonstrating the potential of FILAMP as a robust activatable ¹⁹F probe for diagnosis and monitoring of biological and pathological processes.

Integrating Fluorinated Polymer and Manganese-Layered Double Hydroxide Nanoparticles as pH-activated 19 F MRI Agents for Specific and Sensitive Detection of Breast Cancer

¹⁹ F magnetic resonance imaging (¹⁹ F MRI) agents capable of being activated upon interactions with cancer triggers are attracting increasing attention, although challenges still remain for precise and specific detection of cancer tissues. In this study, a novel hybrid ¹⁹ F MRI agent for pH-sensitive detection of breast cancer tissues is reported, a composite system designed by conjugating a perfluoropolyether onto the surface of manganese-incorporated layered double hydroxide (Mn-LDH@PFPE) nanoparticles. The ¹⁹ F NMR/MRI signals from aqueous solutions of Mn-LDH@PFPE nanoparticles are quenched at pH 7.4, but "turned on" following a reduction in pH to below 6.5. This is due to partial dissolution of Mn²⁺ from the Mn-LDH nanoparticles and subsequent reduction in the effect of paramagnetic relaxation. Significantly, in vivo experiments reveal that an intense ¹⁹ F MR signal can be detected only in the breast tumor tissue after intravenous injection of Mn-LDH@PFPE nanoparticles due to such a specific activation. Thus pH-activated Mn-LDH@PFPE nanoparticles are a potential "smart" ¹⁹ F MRI agent for precise and specific detection of cancer diseases.

The Transition from Metal-Based to Metal-Free Contrast Agents for T1 Magnetic Resonance Imaging Enhancement

Magnetic resonance imaging (MRI) has received significant attention as the noninvasive diagnostic technique for complex diseases. Image-guided therapeutic strategy for diseases such as cancer has also been at the front line of biomedical research, thanks to the innovative MRI, enhanced by the prior delivery of contrast agents (CAs) into patients' bodies through injection. These CAs have contributed a great deal to the clinical utility of MRI but have been based on metal-containing compounds such as gadolinium, manganese, and iron oxide. Some of these CAs have led to cytotoxicities such as the incurable Nephrogenic Systemic Fibrosis (NSF), resulting in their removal from the market. On the other hand, CAs based on organic nitroxide radicals, by virtue of their structural composition, are metal free and without the aforementioned drawbacks. They also have improved biocompatibility, ease of functionalization, and long blood circulation times, and have been proven to offer tissue contrast enhancement with longitudinal relaxivities comparable with those for the metal-containing CAs. Thus, this Review highlights the recent progress in metal-based CAs and their shortcomings. In addition, the remarkable goals achieved by the organic nitroxide radical CAs in the enhancement of MR images have also been discussed extensively. The focal point of this Review is to emphasize or demonstrate the crucial need for transition into the use of organic nitroxide radicals-metal-free CAs-as against the metal-containing CAs, with the aim of achieving safer application of MRI for early disease diagnosis and image-guided therapy.

Controlling the Hydration Structure with a Small Amount of Fluorine To Produce Blood Compatible Fluorinated Poly(2-methoxyethyl acrylate)

Poly(2-methoxyethyl acrylate) (PMEA) shows excellent blood compatibility because of the existence of intermediate water. Various modifications of PMEA by changing its main or side chain's chemical structure allowed tuning of the water content and the blood compatibility of numerous novel polymers. Here, we exploit a possibility of manipulating the surface hydration structure of PMEA by incorporation of small amounts of hydrophobic fluorine groups in MEA polymers using atom-transfer radical polymerization and the (macro) initiator concept. Two kinds of fluorinated MEA polymers with similar molecular weights and the same 5.5 mol % of fluorine content were synthesized using the bromoester of 2,2,3,3,4,4,5,5,6,6,7,7,8,8-pentadecafluoro-1-octanol (F15) and poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) as (macro) initiators, appearing liquid and solid at room temperature, respectively. The fibrinogen adsorption of the two varieties of fluorinated MEA polymers was different, which could not be explained only by the bulk hydration structure. Both polymers show a nanostructured morphology in the hydrated state with different sizes of the features. The measured elastic modulus of the domains appearing in atomic force microscopy and the intermediate water content shed light on the distinct mechanism of blood compatibility. Contact angle measurements reveal the surface hydration dynamics-while in the hydrated state, F15- b-PMEA reorients easily to the surface exposing its PMEA part to the water, the small solid PTFEMA block with high glass-transition temperature suppresses the movement of PTFEMA- b-PMEA and its reconstruction on the surface. These findings illustrate that in order to make a better blood compatible polymer, the chains containing sufficient intermediate water need to be mobile and efficiently oriented to the water surface.

Fluorine polymer probes for magnetic resonance imaging: quo vadis?

Over the last few years, the development and relevance of 19F magnetic resonance imaging (MRI) for use in clinical practice has emerged. MRI using fluorinated probes enables the achievement of a specific signal with high contrast in MRI images. However, to ensure sufficient sensitivity of 19F MRI, fluorine probes with a high content of chemically equivalent fluorine atoms are required. The majority of 19F MRI agents are perfluorocarbon emulsions, which have a broad range of applications in molecular imaging, although the content of fluorine atoms in these molecules is limited. In this review, we focus mainly on polymer probes that allow higher fluorine content and represent versatile platforms with properties tailorable to a plethora of biomedical in vivo applications. We discuss the chemical development, up to the first imaging applications, of these promising fluorine probes, including injectable polymers that form depots that are intended for possible use in cancer therapy.

A Hyperfluorinated Hydrophilic Molecule for Aqueous 19F MRI Contrast Media

Fluorine-19 (¹⁹F) magnetic resonance imaging (MRI) has the potential for a wide range of in vivo applications but is limited by lack of flexibility in exogenous probe formulation. Most ¹⁹F MRI probes are composed of perfluorocarbons (PFCs) or perfluoropolyethers (PFPEs) with intrinsic properties which limit formulation options. Hydrophilic organofluorine molecules can provide more flexibility in formulation options. We report herein a hyperfluorinated hydrophilic organoflourine, ET1084, with ∼24 wt. % ¹⁹F content. It dissolves in water and aqueous buffers to give solutions with ≥8 M ¹⁹F. ¹⁹F MRI phantom studies at 9.4T employing a 10-minute multislice multiecho (MSME) scan sequence show a linear increase in signal-to-noise ratio (SNR) with increasing concentrations of the molecule and a detection limit of 5 mM. Preliminary cytotoxicity and genotoxicity assessments suggest it is safe at concentrations of up to 20 mM.

High F-Content Perfluoropolyether-Based Nanoparticles for Targeted Detection of Breast Cancer by 19F Magnetic Resonance and Optical Imaging

Two important challenges in the field of ¹⁹F magnetic resonance imaging (MRI) are the maintenance of high fluorine content without compromising imaging performance, and effective targeting of small particles to diseased tissue. To address these challenges, we have developed a series of perfluoropolyether (PFPE)-based hyperbranched (HBPFPE) nanoparticles with attached peptide aptamer as targeting ligands for specific in vivo detection of breast cancer with high ¹⁹F MRI sensitivity. A detailed comparison of the HBPFPE nanoparticles (NPs) with the previously reported trifluoroethyl acrylate (TFEA)-based polymers demonstrates that the mobility of fluorinated segments of the HBPFPE nanoparticles is significantly enhanced (¹⁹F T₂ > 80 ms vs 31 ms), resulting in superior MR imaging sensitivity. Selective targeting was confirmed by auto- and pair correlation analysis of fluorescence microscopy data, in vitro immunofluorescence, in vivo ¹⁹F MRI, ex vivo fluorescence and ¹⁹F NMR. The results highlight the high efficiency of aptamers for targeting and the excellent sensitivity of the PFPE moieties for ¹⁹F MRI. Of relevance to in vivo applications, the PFPE-based polymers exhibit much faster clearance from the body than the previously introduced perfluorocarbon emulsions ( t_1/2 ∼ 20 h vs up to months). Moreover, the aptamer-conjugated NPs show significantly higher tumor-penetration, demonstrating the potential of these imaging agents for therapeutic applications. This report of the synthesis of polymeric aptamer-conjugated PFPE-based ¹⁹F MRI CAs with high fluorine content (∼10 wt %) demonstrates that these NPs are exciting candidates for detecting diseases with high imaging sensitivity.

Elucidating the Impact of Molecular Structure on the 19F NMR Dynamics and MRI Performance of Fluorinated Oligomers

To understand molecular factors that impact the performance of polymeric ¹⁹F magnetic resonance imaging (MRI) agents, a series of discrete fluorinated oligoacrylates with precisely defined structure were prepared through the combination of controlled polymerization and chromatographic separation techniques. These discrete oligomers enabled thorough elucidation of the dependence of ¹⁹F NMR and MRI properties on molecular structure, for example, the chain length. Importantly, the oligomer size and dispersity strongly influence NMR dynamics (T₁ and T₂ relaxation times) and MR imaging properties with higher signal-to-noise ratio (SNR) observed for oligomers with longer chain length and shorter T₁. Our approach enables an effective pathway and thus opportunities to rationally design effective polymeric ¹⁹F MR imaging agents with optimized molecular structure and NMR relaxivity.

A unique 19F MRI agent for the tracking of non phagocytic cells in vivo

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.