Robust Grafting of Polyionenes: New Potent and Versatile Antimicrobial Surfaces.

Polyionenes (PI) with stable positive charges and tunable hydrophobic spacers in the polymer backbone, are shown to be particularly efficient regarding antimicrobial properties. This effect can be modulated since it increases with the length of hydrophobic spacers, i.e., the number of methylene groups between quaternary ammoniums. Now, to further explore these properties and provide efficient antimicrobial surfaces, polyionenes should be grafted onto materials. Here a robust grafting strategy to covalently attach polyionenes is described. The method consisted in a sequential surface chemistry procedure combining polydopamine coating, diazonium-induced polymerization, and polyaddition. To the best of knowledge, grafting of PI onto surfaces is not reported earlier. All chemical steps are characterized in detail via various surface analysis techniques (FTIR, X-ray photoelectron spectroscopy, contact angle, and surface energy measurements). The antibacterial properties of polyionene-grafted surfaces are then studied through bacterial adhesion experiments consisting in enumeration of adherent bacteria (total and viable cultivable cells). PI-grafted surfaces are showed to display effective and versatile bacteriostatic/bactericidal properties associated with a proadhesive effect.

How Do Surface Properties of Nanoparticles Influence Their Diffusion in the Extracellular Matrix? A Model Study in Matrigel Using Polymer-Grafted Nanoparticles.

Diffusion of nanomedicines inside the extracellular matrix (ECM) has been identified as a key factor to achieve homogeneous distribution and therefore therapeutic efficacy. Here, we sought to determine the impact of nanoparticles' (NPs) surface properties on their ability to diffuse in the ECM. As model nano-objects, we used a library of gold nanoparticles grafted with a versatile polymethacrylate corona, which enabled the surface properties to be modified. To accurately recreate the features of the native ECM, diffusion studies were carried out in a tumor-derived gel (Matrigel). We developed two methods to evaluate the diffusion ability of NPs inside this model gel: an easy-to-implement one based on optical monitoring and another one using small-angle X-ray scattering (SAXS) measurements. Both enabled the determination of the diffusion coefficients of NPs and comparison of the influence of their various surface properties, while the SAXS technique also allowed to monitor the NPs' structure as they diffused inside the gel. Positive charges and hydrophobicity were found to particularly hinder diffusion, and the different results suggested on the whole the presence of NPs-matrix interactions, therefore underlying the importance of the ECM model. The accuracy of the tumor-derived gels used in this study was evidenced by in vivo experiments involving intratumoral injections of NPs on mice, which showed that diffusion patterns in the peripheral tumor tissues were quite similar to the ones obtained within the chosen ECM model.

Combining surface chemistry modification and in situ small-angle scattering characterization to understand and optimize the biological behavior of nanomedicines.

Nanomedicines are considered as promising therapeutics for cancer treatment. However, clinical translation is still scarce, partly because their biological behavior is not well understood. Extracting general guidelines from the great variety of nanoparticles and conditions studied is indeed difficult, and relevant techniques are lacking to obtain in situ information. Here, both issues are solved by combining versatile model nanoparticles with in situ tools based on small-angle scattering techniques (SAS). The strategy was to develop a library of nanoparticles and perform systematic study of their interactions with biological systems. Considering the promising properties of gold nanoparticles as cancer therapeutics, polymethacrylate-grafted gold nanoparticles were chosen as models. Modulation of polymer chemistry was shown to change the surface properties while keeping the same structure for all nanoparticles. This unity allowed reliable comparison to extract general principles, while the synthesis versatility enabled to fine-tune the nanoparticles surface properties, especially through copolymerization, and thus to optimize their biological behavior. Two specific aspects were particularly examined: colloidal stability and cell uptake. Positive charges and hydrophobicity were identified as key parameters influencing toxicity and internalization. In situ SAS gave valuable information about nanoparticles evolution in biologically relevant environments. Good colloidal stability was thereby shown in cell culture media, while intracellular transformation and quantity of nanoparticles were monitored, highlighting the potential of these techniques for nanomedicines studies.

Improving 131I Radioiodine Therapy By Hybrid Polymer-Grafted Gold Nanoparticles.

BACKGROUND: Human trials combining external radiotherapy (RT) and metallic nanoparticles are currently underway in cancer patients. For internal RT, in which a radioisotope such as radioiodine is systemically administered into patients, there is also a need for enhancing treatment efficacy, decreasing radiation-induced side effects and overcoming radio-resistance. However, if strategies vectorising radioiodine through nanocarriers have been documented, sensitizing the neoplasm through the use of nanotherapeutics easily translatable to the clinic in combination with the standard systemic radioiodine treatment has not been assessed yet. METHOD AND MATERIALS: The present study explored the potential of hybrid poly(methacrylic acid)-grafted gold nanoparticles to improve the performances of systemic 131I-mediated RT on cancer cells and in tumor-bearing mice. Such nanoparticles were chosen based on their ability previously described by our group to safely withstand irradiation doses while exhibiting good biocompatibility and enhanced cellular uptake. RESULTS: In vitro clonogenic assays performed on melanoma and colorectal cancer cells showed that poly(methacrylic acid)-grafted gold nanoparticles (PMAA-AuNPs) could efficiently lead to a marked tumor cell mortality when combined to a low activity of radioiodine, which alone appeared to be essentially ineffective on tumor cells. In vivo, tumor enrichment with PMAA-AuNPs significantly enhanced the killing potential of a systemic radioiodine treatment. CONCLUSION: This is the first report of a simple and reliable nanomedicine-based approach to reduce the dose of radioiodine required to reach curability. In addition, these results open up novel perspectives for using high-Z metallic NPs in additional molecular radiation therapy demonstrating heterogeneous dose distributions.

Irradiation Effects on Polymer-Grafted Gold Nanoparticles for Cancer Therapy.

In the context of cancer treatment, gold nanoparticles (AuNPs) are considered as very promising radiosensitizers. Here, well-defined polymer-grafted AuNPs were synthesized and studied under gamma irradiation to better understand the involved radiosensitizing mechanisms. First, various water-soluble and well-defined thiol-functionalized homopolymers and copolymers were obtained through atom transfer radical polymerization. They were then used as ligands in the one-step synthesis of AuNPs, which resulted in stable hybrid metal-polymer nanoparticles. Second, these nano-objects were irradiated in solution by γ rays at different doses. Structures were fully characterized through size exclusion chromatography, small-angle X-ray scattering, and small-angle neutron scattering measurements, prior to and after irradiation. We were thus able to quantify and to localize radiation impacts onto the grafted polymers, revealing the production sites of reactive species around AuNPs. Both external and near-surface scissions were observed. Interestingly, the ratio between these two effects was found to vary according to the nature of polymer ligands. Medium-range and long-distance dose enhancements could not be identified from the calculated scission yields, but several mechanisms were considered to explain high yields found for near-surface scissions. Then cytotoxicity was shown to be equivalent for both nonirradiated and irradiated polymer-grafted NPs, which suggested that released polymer fragments were nontoxic. Finally, the potential to add bioactive molecules such as anticancer drugs has been explored by grafting doxorubicin onto the polymer corona. This may lead to nano-objects combining both radiosensitization and chemotherapy effects. This work is the first one to study in details the impact of radiation on radiosensitizing nano-objects combining physical, chemical, and biological analyses.

Electrocatalytic (Bio)Nanostructures Based on Polymer-Grafted Platinum Nanoparticles for Analytical Purpose.

Functionalized platinum nanoparticles (PtNPs) possess electrocatalytic properties toward H2O2 oxidation, which are of great interest for the construction of electrochemical oxidoreductase-based sensors. In this context, we have shown that polymer-grafted PtNPs could efficiently be used as building bricks for electroactive structures. In the present work, we prepared different 2D-nanostructures based on these elementary bricks, followed by the subsequent grafting of enzymes. The aim was to provide well-defined architectures to establish a correlation between their electrocatalytic properties and the arrangement of building bricks. Two different nanostructures have been elaborated via the smart combination of surface initiated-atom transfer radical polymerization (SI-ATRP), functionalized PtNPs (Br-PtNPs) and Langmuir-Blodgett (LB) technique. The first nanostructure (A) has been elaborated from LB films of poly(methacrylic acid)-grafted PtNPs (PMAA-PtNPs). The second nanostructure (B) consisted in the elaboration of polymer brushes (PMAA brushes) from Br-PtNPs LB films. In both systems, grafting of the glucose oxidase (GOx) has been performed directly to nanostructures, via peptide bonding. Structural features of nanostructures have been carefully characterized (compression isotherms, neutron reflectivity, and profilometry) and correlated to their electrocatalytic properties toward H2O2 oxidation or glucose sensing.

Conformation of the Poly(ethylene Glycol) Chains in DiPEGylated Hemoglobin Specifically Probed by SANS: Correlation with PEG Length and in Vivo Efficiency.

Cell-free hemoglobin (Hb)-based oxygen carriers have long been proposed as blood substitutes but their clinical use remains tricky due to problems of inefficiency and/or toxicity. Conjugation of Hb with the biocompatible polymer poly(ethylene glycol) (PEG) greatly improved their performance. However, physiological data suggested a polymer molecular weight (Mw) threshold of about 10 kDa, beyond which the grafting of two PEG chains no longer improves efficiency and nontoxicity of diPEG/Hb conjugates. We used small-angle neutron scattering and contrast variation, which are the only techniques able to probe separately the conformation of PEG chains and Hb protein within the complex, to investigate the role of PEG chain conformation in diPEGylated Hb conjugates as a function of the polymer Mw. We found out that the structure of Hb tetramer is not modified by the polymer grafting. Similarly, with a constant grafting of two chains per protein, there is no significant change of the Gaussian conformation between free and grafted PEG below ∼10 kDa, the complex being well described by the "dumbbell" model. However, beyond that threshold, the radius of gyration of grafted PEG is significantly smaller than that of the free polymer, showing a compaction of the PEG chains, either in the "dumbbell" model or in the "shroud" one. In the latter model, the polymer may be wrapped on the surface of the protein spreading a protective "shielding" effect over a larger fraction of the protein. Both proposed models are in good agreement with the physiological data reported in the literature.

Aqueous solutions of ionenes: interactions and counterion specific effects as seen by neutron scattering.

Aqueous solutions of ionenes with bromide and fluoride counterions have been investigated using small angle neutron scattering for the first time. Ionenes are a class of cationic polyelectrolytes based on quaternary ammonium atoms and, considering the very low solubility of their uncharged part (hydrocarbon chain), would be formally classified as hydrophobic. Ionenes present important structural differences over previously studied polyelectrolytes: (a) charge is located on the polyelectrolyte backbone, (b) the distance between charges is regular and tunable by synthesis, (c) hydrophobicity comes from methylene groups of the backbone and not from bulky side groups. Results for Br ionenes feature a disappearance of the well-known polyelectrolyte peak beyond a given monomer concentration. Below this concentration, the position of the peak depends on the chain charge density, f(chem), and scales as f(chem)(0.30±0.04). This is an indication of a hydrophilic character of the ionene backbone. In addition, osmotic coefficients of ionene solutions resemble again other hydrophilic polyelectrolytes, featuring no unusual increase in the water activity (or a significant counterion condensation). We conclude that despite the hydrophobicity of the hydrocarbon chain separating charged centers on ionenes, these chains behave as hydrophilic. In contrast to Br ionenes, the polyelectrolyte peak remains at all concentrations studied for the single F ionene investigated. This strong counterion effect is rationalized in terms of the different hydrating properties and ion pairing in the case of bromide and fluoride ions.

Enhanced drug loading in polymerized micellar cargo.

A new drug carrier system based on self-assembly and polymerization of polydiacetylenic amphiphiles is described. Although classical amphiphiles can help in solubilizing hydrophobic molecules upon self-arrangement into a variety of nanometric structures, a greater effect on drug loading was observed for our polymerized micelles as compared to the non-polymerized analogues. This permitted higher aqueous solubilization of lipophilic drugs with low micelle concentration. (14)C labeling of a model drug on one side and of the amphiphile on the other side permitted assessment, after intravenous injection, of biodistribution and excretion profiles of the drug cargo.

Polymer-grafted-platinum nanoparticles: from three-dimensional small-angle neutron scattering study to tunable two-dimensional array formation.

Nanohybrid objects based on polymer and platinum nanoparticles are of great interest for applications in fuel cells or as biosensors. The polymer part can help first to stabilize and to organize the particles, second to increase the amount of chemical functions available in the organic corona, and, finally, to improve or to mask the properties of the particles. The method to introduce the polymer consists of using both the "grafting from" technique and controlled radical polymerization (atom transfer radical polymerization). Small-angle neutron scattering (SANS) is a well-suited technique for the study of these objects, particularly due to the possibility to use contrast matching to see either the particle or the polymer corona. Polymerization kinetics was followed by SANS and the polymer corona spectra showed a plateau at small q which attested that the objects are individual and well-dispersed. These systems were exempt of free polymers, so the characterization via SANS could lead to quantitative data such as the radius of gyration of the object, the amount of grafted chains and the molecular weight of the chains, using a star model to fit the data. Langmuir films have then been obtained directly from the polymer-grafted-nanoparticles solutions, and compression isotherms have been recorded followed by transmission electron microscopy (TEM) characterization of the films at different pressures. A good correlation has therefore been observed from the distances between objects calculated using the compression isotherms or observed via TEM and the objects' dimensions determined from SANS study.

Oligomeric PEG-phospholipids for solubilization and stabilization of fluorescent nanocrystals in water.

Water soluble fluorescent nanocrystals were obtained by encapsulation of hydrophobic quantum dots (QDs) with amphiphilic phospholipids derived from the ring opening metathesis of norbornene-based monomers. The robustness of the newly coated quantum dots was assessed by comparative studies under various ionic conditions which indicated an overall enhancement of their fluorescence stability.

Boron-mediated polymerization of ylides derived from allylic arsonium salts: influence of the double bond substitution on the outcome.

New oligomers or polymers are prepared by polymerization of arsonium ylides in the presence of boron compounds.