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The specific influence of polyethersulfone (PES) endfunctionalization with chlorine or hydroxyl end groups at same molar mass on PES-epoxy composites based on a high-performance tetra-epoxide with di-amine hardener resin (RTM6) is investigated in terms of morphology,thermal behavior, and toughness. A model study on PES filaments embedded in epoxy precursor is first performed to compare the interdiffusion and resulting morphology upon curing. PES-OH shows a larger interdiffusion distance compared to PES-Cl in the model systems and the laminates. This effect is more pronounced at high heating rate. Cross sections and fracture surfaces of composite panels are analyzed by scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDX) spectroscopy to establish the link between the microstructures and fracture mechanisms. The toughness of PES-OH-modified epoxy composites is doubled compared to unmodified reference panels, whereas the PES-Cl shows no improvement. The favorable influence of PES-OH is ascribed to enhanced miscibility, interfacial adhesion and morphology, resulting from the better affinity between hydroxyl-terminated PES and the epoxy-resin.

The spatial resolution and the contrast in mechanical property mapping by atomic force microscopy (AFM) modes based on dynamic force-curve acquisition, HarmoniX™(HMX) and Peak-Force-Tapping-QNM™(PFT-QNM) modes, are discussed in terms of contact radius, probe type and imaging parameters. The study is based on model polymer samples including elastomers, thermoplastics and thermoset resins and on contact mechanics considerations to provide a better understanding of the main parameters governing spatial resolution and property contrast in AFM-based nanomechanical mapping. The tip-sample interaction area and volume characterized by the contact radius are the key parameters governing the spatial resolution in adhesion force and elastic modulus images, respectively. The contrast in mechanical properties depends on the proper choice of the probe and on the control of the pixel size and the imaging force. The study also demonstrates that all these parameters are mutually interconnected and may have contradictory influences.

Absorption in excess of 90% is induced over a 22 GHz bandwidth by the combination of carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) dispersed in a polymer matrix. This performance is achieved by a stack of polymer films showing a concentration gradient of mixed CNTs and GNPs from layer to layer, having a total thickness of only $$0.76\,\lambda /4.$$ Excellent agreement is observed from 18 to 40 GHz between the predicted and measured reflectivity and the resulting high absorption.

Monoclonal antibodies targeting the programmed-death 1 (PD-1) immune checkpoint or its ligand PD-L1 have significantly improved the treatment of cancers but more efficient drugs and combinations are still needed to increase the therapeutic efficacy. As the oxidative state of the immune microenvironment plays a critical role in the antitumor immune response, it is important to evaluate the impact of molecules and drugs used for oxidative stress control on PD-L1 expression and functions. Here we have reviewed the functional relationship between reactive oxygen species (ROS) and PD-L1 expressed on cancer cells, and analyzed the effects of 15 pharmacological ROS modulators - both ROS inducers and attenuators - on PD-L1 expression. The interplay between tumor hypoxia, the HIF-1α/YAP1/NFκB signaling routes and PD-L1 expression has been analyzed and specific non-cytotoxic ROS-associated drugs known to modulate this system are discussed. A complex interplay between ROS effectors and PD-L1 expression is revealed, showing that depending on their targets and mechanisms, ROS effectors can engender an up or down-regulation of PD-L1 expression in cancer cells. An enhanced generation of ROS often promotes PD-L1 expression and, conversely, ROS scavenging generally represses PD-L1. But there are noticeable exceptions with drugs that augment ROS production while reducing PD-L1 expression and vice versa. The variable PD-L1 response to ROS modulation reflects the complexity of ROS biology in the tumor microenvironment. A deeper knowledge of the contribution of ROS to PD-(L)1 immune checkpoint control is warranted.

This review provides a comprehensive analysis of the anticancer potential of the natural product citral (CIT) found in many plants and essential oils, and extensively used in the food and cosmetic industry. CIT is composed of two stereoisomers, the trans-isomer geranial being a more potent anticancer compound than the cis-isomer neral. CIT inhibits cancer cell proliferation and induces cancer cell apoptosis. Its pluri-factorial mechanism of anticancer activity is essentially based on three pillars: (i) a drug-induced accumulation of reactive oxygen species in cancer cells leading to an oxidative burst and DNA damages, (ii) a colchicine-like inhibition of tubulin polymerization and promotion of microtubule depolymerization, associated with an inhibition of the microtubule affinity-regulating kinase MARK4, and (iii) a potent inhibition of the aldehyde dehydrogenase isoform ALDH1A3 which is associated with cancer stem cell proliferation and chemoresistance. This unique combination of targets and pathways confers a significant anticancer potential. However, the intrinsic potency of CIT is limited, mainly because the drug is not very stable and has a low bioavailability and it does not present a high selectivity for cancer cells versus non-tumor cells. Stable formulations of CIT, using cyclodextrins, biodegradable polymers, or various nano-structured particles have been designed to enhance the bioavailability, to increase the effective doses window and to promote the anticancer activity. The lack of tumor cell selectivity is more problematic and limits the use of the drug in cancer therapy. Nevertheless, CIT offers interesting perspectives to design more potent analogues and drug combinations with a reinforced antitumor potential.

This paper presents an approach for electromagnetic shielding by absorption based on polycarbonate films containing oriented carbon nanotubes. Films with and without in plane CNT orientation were obtained by squeezing nanocomposites in the melt. The results reveal that the thick non-oriented and thin oriented nanocomposites have comparable highest electromagnetic absorption around 50% over a broad microwave frequency range but achieved this performance at different CNT concentration, i.e. 1 and 3wt% for thin and thick samples respectively. Thanks to the reduced thickness, the oriented composites contain a comparable weight of CNT per unit area but they are significantly lighter and flexible.

A multifunctional hybrid material class in the form of a sandwich panel has been developed towards the combined optimization of mechanical and electromagnetic absorption performance. The faces of the panel are made of glass fibre reinforced epoxy composites and the core is made of carbon nanotube reinforced polymer foam filling a metallic honeycomb. The different processing strategies and options tested to fabricate the core material are described as well as the associated scientific and technological issues. The most efficient processing route is by foaming the nanocomposite with a chemical foaming agent directly inside the honeycomb. This route offers a good surface finish and the operation can be achieved in one step. But, in order to produce large panels with a semi-continuous process, thermo-mechanical insertion of the foamed nanocomposite with supercritical CO2 can be more suitable. The characterization of the electromagnetic absorption of the panels produced by different routes shows that the performance is not much sensitive to processing defects making possible upscaling to mass production. Keywords: Nanocomposite, Foam filled honeycomb, Electromagnetic absorption, Multifunctional structure

The use of phenoxy nanocomposite films as carriers of nanofillers involving multiwalled carbon nanotubes and nanoclays is successfully demonstrated for application in epoxy carbon fibers reinforced composites (CFRC) processed by RTM. Model studies on individual nanocomposite filaments embedded in epoxy precursors show that the nanofillers are passively transported by the interdiffusion gradient during heating over distance around 800 lm. A morphology gradient is generated after reaction induced phase separation and the nanofillers end up in the epoxy, despite their initial dispersion in the phenoxy. The proof of concept is extended to CFRC panels where nanocomposite phenoxy films are prepositioned between every odd carbon layer of the preform. Carbon nanotubes are filtered by the carbon fabrics, which limits their full diffusion and that of phenoxy through the preform. This has negative consequences on fracture toughness (GIc). For nanoclay, GIc is rather slightly improved although the origin is not fully clear.

A screening program aimed at discovering novel anticancer agents based on natural products led to the selection of koningic acid (KA), known as a potent inhibitor of glycolysis. A method was set up to produce this fungal sesquiterpene lactone in large quantities by fermentation, thus allowing (i) an extensive analysis of its anticancer potential in vitro and in vivo and (ii) the semi-synthesis of analogues to delineate structure-activity relationships. KA was characterized as a potent, but non-selective cytotoxic agent, active under both normoxic and hypoxic conditions and inactive in the A549 lung cancer xenograft model. According to our SAR, the acidic group could be replaced to keep bioactivity but an intact epoxide is essential.

The local mechanical properties of partially cured epoxy resins based on tetraglycidyl methylene dianiline (TGMDA) are proved to be heterogeneous at the nanoscale with the degree of heterogeneity decreasing when the crosslinking density increases. The fully cured resin can be considered homogeneous on both the nano- and macroscale. These conclusions are supported by a comprehensive statistical analysis of AFM-based local mechanical properties measurements, which reveal changes in the modulus distributions from multimodal to monomodal. Furthermore, the histograms of adhesion force and energy dissipation exhibit decreasing fluctuations with increasing degree of curing. The surface topography of all samples is very flat at the nanoscale, which indicates that the observed features are not the result of surface irregularities. The existence of differently cured domains due to local fluctuations in the curing kinetics is proposed as the origin of the observed properties contrast.

The effect of poly(ethylene oxide) [PEO]−metal salt complexation on the dynamics and microstructure of PEO−nickel chloride [NiCl2] systems is investigated by rheology and X-ray scattering. Annealed PEO−nickel salt systems exhibit network properties above the melting temperature of PEO, characterized by a second elastic plateau, beyond the reptation time of PEO chains. The level of the second plateau strongly depends on the annealing conditions and the ion content. In PEO−NiCl2 networks, the linear viscoelastic region is experimentally out of reach, meaning that their viscoelastic properties strongly depend on strain and strain rate as well as any deformation history. The network can be broken down by large-amplitude shear and reversibly reformed under quiescent conditions. X-ray scattering reveals formation of distinct crystalline structures of PEO−NiCl2 complexes, which are different from those of both neat PEO and nickel salt. The combined rheology and X-ray scattering results indicate that the network results from a small fraction of trapped PEO chains, which are bridging the crystalline domains of PEO−NiCl2 complexes

We explore the influence of the interdiffusion of two thermoplastic tougheners and RTM6 epoxy resin precursors on the resulting morphologies after curing and the consequences on delamination toughness of the corresponding carbon fiber reinforced composites. Two thermoplastics with contrasting Tg and compatibility, i.e. poly(ether sulfone) (PES) and phenoxy are compared. The dramatic improvement of the interlaminar fracture toughness (GIC) found for the phenoxy-RTM6 system as compared to the pure thermoset reference can be ascribed to the broad morphology gradient only observed for that system. By contrast, the PES-RTM6 system is characterized by a steep morphology gradient and a corresponding decrease of as compared to the reference.

The scratch resistance of thin brittle coatings deposited on rigid substrates with a soft intermediate layer has been characterized by instrumented nanoscratch testing in order to identify the damage mechanisms. Several "hard thin film/polymer/rigid substrate" multilayers have been addressed with varying compositions and thicknesses. The relevance of the use of nanoscratch with respect to end-user performances has been confirmed by the analysis of the damage and cracking mechanisms triggered by more empirical tests. The scratch wear resistance behavior is interpreted in the light of fracture mechanics since the dominant damage mode is the cracking of the brittle film. This behavior is related to the mechanical properties of the individual layers, e.g. elastic modulus, hardness, fracture toughness, internal stress, and to soft interlayer thickness. The influence of the soft interlayer on the enhancement of the cracking energy release rate in the coating plays a major role, depending directly on the elastic mismatch and adhesion characteristics. The fracture toughness and adhesion of the hard coating jointly determine the morphology and the extension of the crack density and the amount of delamination, whereas the soft interlayer thickness controls the scratch depth. The constraint effect induced by the rigid substrate for thinner interlayer thicknesses favors the cracking of the hard coating despite lower scratch depths.

The melt dynamics of poly(ethylene oxide) [PEO]–nickel chloride [NiCl2] systems are analyzed by proton NMR relaxometry and rheology. A consistent picture of the corresponding microstructure is proposed based on the combined results. Rheology reveals the presence of a weak gel due to PEO–metallic salt complexation, evidenced by a low second storage modulus plateau (

Sorption and diffusion of supercritical carbon dioxide (scCO2) into polycarbonate (PC) nanocomposites loaded with 0, 1 and 2 wt% of multi-walled carbon nanotubes (MWNTs) have been investigated. After determination of the saturation equilibrium, the samples have been saturated with scCO2 to ensure a partial foaming with a density gradient from the surface to the center of the samples and the morphology of the porous materials has been analysed by SEM. The gradient materials were very advantageous for EMI shielding since the foamed structure at the surface had low dielectric constant and limited the reflection of the EM signal while the presence of highly conductive solid in the middle ensured a high absorption of the electromagnetic radiation.

(−)-Cryptopleurine 1 is one of the most potent anti-proliferative member of the phenanthroquinolizidine class of alkaloids. We report here the synthesis of (−)-6-O-desmethylcryptopleurine (−)-2 and (−)-6-O-desmethyl-(15R)-hydroxycryptopleurine (−)-4 in their enantiomerically enriched form through a convergent synthetic route, where the chirality is introduced by the use of commercially available (R)-methyl piperidine-2-carboxylate hydrochloride 17. Anti-proliferative activities of these compounds were evaluated on a panel of four cancer cell lines, revealing that compounds (−)-2 and (−)-4 are potent cytotoxic compared to cryptopleurine.

Ethnopharmacological relevance Extracts of the fruit of Prunus mume (Rosaceae) have been used for a long time in Eastern Asia, in many culinary and medicinal preparations. The plant originates from the south of mainland China (named mei) and was introduced later in Japan (ume), Korea (maesil) and Vietnam (mai or mo). Extracts of the fruits (Chinese plum or Japanese apricot, ‘Nanko’ mume cultivar of Prunus mume Sieb. et Zucc.) are used in traditional Chinese and Japanese medicine, and various Korean medical preparations, for more than 2000 years. The medicinal use of the flesh of the fruits is cited in ancient Japanese monographies (such as Shokokukodenhiho published in 1817). Aim of the study To analyze the anticancer activities of P. mume extracts and their potential use to prevent or treat cancers. The use of P. mume extracts to alleviate the side effects of chemotherapy, notably drug-induced gastro-intestinal toxicities, is also reviewed. Methods Extensive database retrieval, such as SciFinder and PubMed, was performed by using keywords such as “Prunus mume”, “Chinese plum”, “Japanese apricot”, and “cancer”. In addition, relevant textbooks, patents, reviews, and digital documents (in English) were consulted to collate all available scientific literature and to provide a complete science-based survey of the topic. Results P. mume extracts display hepatoprotective, anti-inflammatory, antioxidative and antibacterial effects, as well as anticancer properties. A survey of the antitumor activities of MK615 and other P. mume extracts is provided here, with information about the natural products found in the extracts (such as ursolic acid and oleanic acid) and the mechanisms of action of these extracts. MK615 inhibits proliferation and induces apoptotic death of different types of cancer cells from both solid and hematological tumors. Conclusion The pool of in vitro data and signs of anticancer activities in mice models and in Human, although very limited, support the use of this extract to treat cancer, notably gastro-intestinal tumors. However, more robust evidence of anticancer activity in Human are awaited. Beyond cancer treatment, the use of P. mume extracts to prevent or to treat mucositis and other gastro-intestinal damages induced by anticancer drugs is underlined. The woody plant Prunus mume, a member of the Rosaceae family, has a long plantation history in China, and has widely been planted in Asia due to its high ornamental value (colorful corollas, pleasant fragrance, weeping trait) and the culinary, nutritional and medicinal potential of the fruits from the specie Prunus mume Sieb. et Zucc (Mei). Over the past 20 years the therapeutic potential of the extract of Japanese apricot “Ume” has been regularly reported. Anti-bacterial, anti-oxidative, anti-inflammatory and anti-cancer properties have been described. A complete analysis of the published scientific literature on Ume and cancer is presented here.

The traditional Chinese medicine, Xihuang pills (XHP), has long been used for the management of cancers, both to limit tumor cells proliferation and dissemination, and to protect nontumor cells from damages induced by conventional therapeutic agents. XHP is made from two plant extracts (from Boswellia carteri and Commiphora myrrha) and two animal-derived products (from Moschus moschiferus and Calculus bovis). Recent advances into the mechanism of action of XHP and its clinical efficacy are reviewed here to highlight its potential to treat breast and colon cancers in particular. The immunoregulatory effects of XHP are underlined. Similar traditional medicinal preparations containing Boswellia and Commiphora are discussed, as well as the activities of the major natural products found in XHP including abietic acid, acetyl-keto-boswellic acid, and muscone. Pharmacological and clinical studies of XHP and similar medicinal preparations, such as the Korean medicine HangAmDan-B, are encouraged.

We describe a novel multilayer arrangement of polymer nanocomposites, which is able to very effectively absorb microwave radiation over a broad frequency range or selectively reflect desired wavelengths. The structure is built from alternating films of dielectric polymer and conducting layers. The latter are stacked in a precise gradient of conductivity. The conducting layers consist of either polycarbonate nanocomposite films with carbon nanotubes (CNT) or a very thin CNT coating deposited on insulating polymer from a CNT waterborne ink. In order to ensure good wetting of polycarbonate by the ink and high resulting conductivity of the dry coating, a plasma treatment of the polymer is essential. The stacked multilayer structures are easy to make, modular, and open up new possibilities in the area of microwave management (broadband shielding by absorption or frequency-selective filtering, also called bandgap control). The analytical model developed to simulate the absorbers and filters is in good agreement with experimental characterisation and could be further extended to the design of systems operating in other frequency ranges.

Supercritical carbon dioxide readily induced foaming of various polymers. In that context, supercritical CO2 was applied to carbon nanotubes based polycarbonate nanocomposites to ensure their foaming. Surprisingly, efficient foaming only occurs when low pressure is applied while at high pressure, no expansion of the samples was observed. This is related to the ability of supercritical carbon dioxide to induce crystallization of amorphous polycarbonate. Moreover, this behaviour is amplified by the presence of carbon nanotubes that act as nucleating agents for crystals birth. The thermal behaviour of the composites was analysed by DSC and DMA and was related to the foaming observations. The uniformity of the cellular structure was analyzed by scanning electron microscopy (SEM). By saturating the polycarbonate nanocomposites reinforced with 1 wt% of MWNTs at 100 bar and 100°C during 16h, microcellular foams were generated, with a density of 0.62, a cell size ranging from 0.6 to 4 μm, and a cellular density of 4.1.1011 cells.cm-3. The high ability of these polymeric foams to absorb electromagnetic radiation was demonstrated at low MWNT content as the result of the high affinity of the polycarbonate matrix for MWNTs, and therefore to the good MWNTs dispersion.

In this paper, we exploit the stochastic slip-spring model to quantitatively predict the stress relaxation dynamics of star/linear blends with well-separated longest relaxation times and we analyze the results to assess the validity limits of the two main models describing the corresponding relaxation mechanisms within the framework of the tube picture (Doi’s tube dilation and Viovy’s constraint release by Rouse motions of the tube). Our main objective is to understand and model the stress relaxation function of the star component in the blend. To this end, we divide its relaxation function into three zones, each of them corresponding to a different dominating relaxation mechanism. After the initial fast Rouse motions, relaxation of the star is dominated at intermediate times by the “skinny” tube (made by all topological constraints) followed by exploration of the “fat” tube (made by long-lived obstacles only). At longer times, the tube dilation picture provides the right shape for the relaxation of the stars. However, the effect of short linear chains results in time-shift factors that have never been described before. On the basis of the analysis of the different friction coefficients involved in the relaxation of the star chains, we propose an equation predicting these time-shift factors. This allows us to develop an analytical equation combining all relaxation zones, which is verified by comparison with simulation results.

Twenty-five years ago, the cytotoxic drug irinotecan (IRT) was first approved in Japan for the treatment of cancer. For more than two decades, the IRT prodrug has largely contributed to the treatment of solid tumors worldwide. Nowadays, this camptothecin derivative targeting topoisomerase 1 remains largely used in combination regimen, like FOLFIRI and FOLFIRINOX, to treat metastatic or advanced solid tumors, such as colon, gastric and pancreatic cancers and others. This review highlights recent discoveries in the field of IRT and its derivatives, including analogues of the active metabolite SN38 (such as FL118), the recently approved liposomal form Nal-IRI and SN38-based immuno-conjugates currently in development (such as sacituzumab govitecan). New information about the IRT mechanism of action are presented, including the discovery of a new protein target, the single-stranded DNA-binding protein FUBP1. Significant progress has been made also to better understand and manage the main limiting toxicities of IRT, chiefly neutropenia and diarrhea. The role of drug-induced inflammation and dysbiosis is underlined and strategies to limit the intestinal toxicity of IRT are discussed (use of β-glucuronidase inhibitors, plant extracts, probiotics). The detailed knowledge of the metabolism of IRT has enabled the identification of potential biomarkers to guide patient selection and to limit drug-induced toxicities, but no robust IRT-specific therapeutic biomarker has been approved yet. IRT is a versatile chemotherapeutic agent which combines well with a variety of anticancer drugs. It offers a large range of drug combinations with cytotoxic agents, targeted products and immuno-active biotherapeutics, to treat a variety of advanced solid carcinoma, sarcoma and cancers with progressive central nervous system diseases. A quarter of century after its first launch, IRT remains an essential anticancer drug, largely prescribed, useful to many patients and scientifically inspiring.

The fracture toughness of 100 nm-thick chromium nitride films deposited on a soft interlayer is evaluated using two different test methods. Both methods take advantage of the enhanced crack driving force resulting fromthe large elastic stiffness mismatch between the film and the polymer interlayer. The first method is based on the presence of channel cracks developing during the deposition as a result of large internal stress. The second method relies on nanoindentation induced cracking. The presence of a soft interlayer is shown to be essential to promote cracking otherwise impossible on a hard substrate, hence to determine the fracture toughness of very thin films. The assumptions underlying the two methods are very different, which allows critical cross comparison and assessment. A fracture toughness value between 1.5 and 2MPa·m1/2 is obtained.

The respect of the manufacturing tolerances is a challenging issue due to the complex distortions caused by the curing process, being sometimes a major obstacle to an increasing use of composites in aeronautics. The cure-induced distortions are modeled and mitigated owing to the development of a computational mold compensation strategy. An in-house surrogate-based optimizer coupled to three-dimensional curing simulations, is used to iteratively alter the shape of the mold in order to minimize the discrepancy with respect to the nominal geometry. Two parametrization strategies are proposed and applied to a generic curved C-spar geometry. One strategy consists in the characterization of the major distortion modes caused by the curing process, and in the parametrization of the geometry to compensate for each mode. The other strategy is to select a number of control points which can move freely in space to find the optimal configuration. Each method performs well but in a different manner, and the optimal choice depends on the industrial specifications of the problem.

This work aims to evaluate the efficiency of halloysite as synergistic agent in an intumescent PP system based on a coated ammonium polyphosphate (IFR). The first part of the study analyses the thermal stability and fire performance of PP when using the intumescent formulation alone or in combination with the aluminosilicate nanotubes (HNTs). Cone calorimetry reveals that partial substitution of IFR by HNTs (3 wt.%) imparts substantial improvement in flame retardancy with reduced heat release rate and longer burning times. Additionally, a shift from V-1 to V-0 classification is achieved at the UL-94 test with only 1.5 wt.% HNTs. The second part provides a better understanding of the physical and chemical mechanisms of action of HNTs in the intumescent systems. The chemical evolution of the condensed phase during combustion is described by solid state NMR, and in particular using 2D NMR. Results indicate that halloysite speeds up the development of the intumescent shield, but also enhances its mechanical properties by physical reinforcement (i.e. aluminosilicate “skeleton-frame” for the phosphocarbonaceous structure) and/or by chemical interactions with IFR yielding to aluminophosphates. These new chemical species allow thermal stabilization of the char at high temperatures and provide good macro- and micro-structural properties. Both effects increase the mechanical strength of the protective layer during burning ensuring excellent heat and mass transfer limitations between gas and condensed phases.

In this study, polyamide 12 (PA12)/untreated halloysite nanotubes (HNTs) nanocomposites are prepared in a semiindustrial scale extruder using a non-traditional “one step” water-assisted extrusion process. A morphological study is carried out using a combination of scanning electron microscopy and transmission electron microscopy analyses to evaluate the influence of water injection and filler content on the quality of clay dispersion. The use of water injection slightly improves the nanoscale dispersion at low HNTs content (

This paper presents a study of polyethersulfone (PES)/halloysite nanotube (HNTs) nanocomposites prepared by melt compounding either through a simple extrusion process or via a water-assisted extrusion procedure. Scanning and transmission electron microscopy techniques are combined with rheological measurements to assess the influence of polymer end groups (eCl or eOH) and water injection on the HNTs dispersion state. A morphological transition form microcomposite to nanocomposite is achieved when replacing eCl chain ends of PES by eOH groups, especially when water is injected during processing. By a combination of Soxhlet extraction and thermogravimetric analysis, we show that some PES(OH) chains are covalently bonded onto the aluminosilicate surface during extrusion. A mechanism describing the physico-chemical action of water is presented. The best system in terms of clay dispersion has been retained to characterize PES-HNTs nanocomposites with respect to their thermo-mechanical, thermal and fire (mass loss calorimetry and UL-94) properties. Dynamic mechanical analysis shows a significant enhancement in the storage modulus of halloysite-based nanocomposites when compared to the unfilled matrix. The improved thermal and thermo-oxidative stability of PES in presence of HNTs is mainly attributed to the labyrinth effect provided by individually dispersed nanotubes, which is reinforced during the decomposition process by the formation of a protective charred ceramic surface layer. The mechanism of action of HNTs for fire retardancy of PES presumably arises from a synergistic effect between physical (i.e. ceramic-like structure formation and mechanical reinforcement of the intumescent char) and chemical (i.e. charring promotion) processes taking place in the condensed phase. According to this study, the straightforward and cost-effective melt compounding route could pave the way for future development of high-performance nanoscale polymeric materials combining enhanced thermal properties and excellent flame retardant behaviour.

We hypothesized that vascular endothelial growth factor (VEGF)-containing hydrogels that gelify in situ after injection into a traumatized spinal cord, could stimulate spinal cord regeneration. Injectable hydrogels composed of 0.5% Pronova UPMVG MVG alginate, supplemented or not with fibrinogen, were used. The addition of fibrinogen to alginate had no effect on cell proliferation in vitro but supported neurite growth ex vivo. When injected into a rat spinal cord in a hemisection model, alginate supplemented with fibrinogen was well tolerated. The release of VEGF that was incorporated into the hydrogel was influenced by the VEGF formulation [encapsulated in microspheres or in nanoparticles or in solution (free)]. A combination of free VEGF and VEGF-loaded nanoparticles was mixed with alginate:fibrinogen and injected into the lesion of the spinal cord. Four weeks post injection, angiogenesis and neurite growth were increased compared to hydrogel alone. The local delivery of VEGF by injectable alginate:fibrinogen-based hydrogel induced some plasticity in the injured spinal cord involving fiber growth into the lesion site.

The extensive development of electronic systems and telecommunications has lead to major concerns regarding electromagnetic pollution. Motivated by environmental questions and by a wide variety of applications, the quest for materials with high efficiency to mitigate electromagnetic interferences (EMI) pollution has become a mainstream field of research. This paper reviews the state-of-the-art research in the design and characterization of polymer/carbon based composites as EMI shielding materials. After a brief introduction, in Section 1, the electromagnetic theory will be briefly discussed in Section 2 setting the foundations of the strategies to be employed to design efficient EMI shielding materials. These materials will be classified in the next section by the type of carbon fillers, involving carbon black, carbon fiber, carbon nanotubes and graphene. The importance of the dispersion method into the polymer matrix (melt-blending, solution processing, etc.) on the final material properties will be discussed. The combination of carbon fillers with other constituents such as metallic nanoparticles or conductive polymers will be the topic of Section 4. The final section will address advanced complex architectures that are currently studied to improve the performances of EMI materials and, in some cases, to impart additional properties such as thermal management and mechanical resistance. In all these studies, we will discuss the efficiency of the composites/devices to absorb and/or reflect the EMI radiation.

The therapeutic arsenal for the treatment of cancers has been considerably revised over the past 15 years, with the continuous launch of molecularly-targeted drugs, essentially kinases inhibitors and monoclonal antibodies. In the mean time, different conventional cytotoxic agents derived from natural products have also been developed successfully, providing novel advances for certain forms of advanced cancers. But most drug development are now oriented toward the design of cancer-cell targeted molecules, in particular products incorporating a tumor cell-delivery vector or a penetrating moiety. This emerging class of anti-cancer agents is discussed here with two specific drug candidates currently in clinical development. The first example is the tubulin-binding Vinca-alkaloid vintafolide, targeted to cancer cell over-expressing the folate receptor and currently in phase 3 for the treatment of patients with platinum-resistant ovarian cancer. The second example is that of the hybrid compound F14512 composed of an epipodophyllotoxin core coupled to a spermine side in order to promote the uptake of the drug by cells over-expressing the polyamine transport system. The topoisomerase II poison F14512 is currently in phase 1 for the treatment of acute myeloid leukemia. These two promising drugs, both derived from plant natural products and developed with a specific biomarker, are the leaders in the class of cell-targeted cytotoxic agents that should offer not only gains in efficacy, but also in safety and tolerability in the treatment of patients with cancer. Different strategies are proposed to guide the delivery of cytotoxic agents to cancer cells.

Hydrogels of different composition based on the copolymerization of N-isopropyl acrylamide and surfmers of different chemical structure were tested in elongation using Hencky/real definitions for stress, strain, and strain rate, offering a more scientific insight into the effect of deformation on the properties. In a range between $\dot {\varepsilon }=10$ and 0.01 s $^{-1}$ , the material properties are independent of strain rate and show a very clear strain hardening with a “brittle” sudden fracture. The addition of surfmer increases the strain at break $\varepsilon _{\mathrm {H}}^{\max }$ and at the same time leads to a failure of hyperelastic models. The samples can be stretched up to Hencky strains $\varepsilon _{\mathrm {H}}^{\max }$ between 0.6 and 2.5, depending on the molecular structure, yielding linear Young’s moduli E $_{0}$ between 2,700 and 39,000 Pa. The strain-rate independence indicates an ideal rubberlike behavior and fracture in a brittle-like fashion. The resulting stress at break $\sigma _{\textrm max}$ can be correlated with $\varepsilon _{\mathrm {H}}^{\max } $ and $E_{0}$ as well as with the solid molar mass between the cross-linking points $M_{\mathrm {c}}^{\textrm {solids}} $ , derived from $E_{0}$ .

The hybrid concept of utilizing frequency selective surface (FSS) and polymer nanocomposite (PNC) for absorption modulation is presented in 8–18 GHz frequency band. The extruded PNCs are fabricated by incorporating different weight% fraction of conductive fillers, namely carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs), in high, low and mixed nano-filler concentration in a polycarbonate matrix. The FSS metallic resonator is patterned over a dielectric substrate which lies on grounded PNCs. It was found that absorption depends on wt% fraction of conductive inclusions in polycarbonate matrix, i.e., variation in conductivity of grounded PNCs due to varying concentration of conductive fillers results in modulation of absorption. Peaks of nearly 100% magnitude of absorption and modulated absorption band are observed at 8.2 GHz, and between 12 and 18 GHz frequency bands, respectively, by varying conductivity of polymer composite. We demonstrate here that the bandwidth and magnitude of absorption can be fixed by the combination of SSRs (for limits of the band) and concentrations in nanofillers (for intensity of absorption).

We present an ultrathin and flexible microwave broadband polarization transformer concept based on oriented carbon nanotubes dispersed in a polycarbonate matrix. Stacking anisotropic composite films with a controlled angle mismatch between successive layers produces a twist polarizer able to change the orientation of the electric field over broad frequency range in the microwave domain. The smart organization confers to the multilayer a high efficiency measured as a degree of twist, which reaches 75.1% at GHz frequencies for a 420 lm thick seven-layer stack.

The infl uence on interfacial energy of multiwall unfunctionalized carbon nanotubes (CNTs) trapped at the interface of an immiscible blend of polyamide 12 (PA12) and acrylate-ethylene (EA) copolymer is investigated with the help of the Palierne model combined with transmission electron microscopy (TEM) observations. It is found that the interfacial energy is unaffected by the interfacially trapped CNTs. The reduced droplet size observed in the presence of CNTs can neither be ascribed to a classical compatibilizer effect due to lower interfacial energy leading to enhanced breakup during processing, nor to the minute changes of the continuous phase viscosity induced by the CNTs. Another explanation based on steric hindrance is proposed. A network CNT layer that acts as a rigid shell is formed, which prevents coalescence of colliding droplets.

A sandwich structure involving a honeycomb core filled with a carbon nanotube-reinforced polymer foam and glass fiber-reinforced composite face sheets has been developed in order to combine high electromagnetic absorption and high mechanical performance. The large electromagnetic absorption is attained by simultaneously minimizing the reflection and transmission, which, in terms of effective material properties, requires a low dielectric constant and a conductivity around 1 S m1. The sandwich offers also high stiffness versus density performance.

We show how styrene-ethylene-propylene-styrene (SEPS) triblock copolymer uniquely reduces the electrical percolation threshold after matrix crystallization of conductive nanocomposites based on high viscosity HDPE with low amounts of pristine multiwall carbon nanotubes (CNT). Rheo-dielectric and Flash DSC techniques are used to demonstrate that SEPS interferes with the nucleation ability of CNT on HDPE crystallization in a way that favors contacts between the nanotubes after crystallization as well as it improves CNT dispersion.

In this work, halloysite nanotubes (HNTs) are used to prepare a polypropylene (PP)/HNTs nanocomposite via a melt blending process. The thermal stability of PP/clay nanocomposite compared to virgin PP is investigated in both inert nitrogen and air atmospheres using thermogravimetric analysis. The modelfree isoconversional method according to Friedman is used to estimate activation energies as a function of the conversion degree. The thermal behavior of PP and PP/HNTs 8 wt% nanocomposite is then modeled and simulated. A very good agreement, especially under nitrogen, is obtained between simulated curves and experimental ones, both in dynamic and isothermal conditions. Activation energies of the PP/HNTs nanocomposite increase compared to pure PP, whatever the degradation conditions. These results correlate well with the higher thermal stability of PP observed in presence of halloysite nanotubes, as well as the reduced flammability of PP/HNTs nanocomposites reported in a previous study.

Objectives The purpose of this study was to compare the mechanical and rheological properties of resin-based pit and fissure sealants to flowable resin composites in order to define clinical indications based on these properties. Methods: Eight flowable resin composites (Admira Flow, Filtek Supreme XT Flow, FlowLine, Grandio Flow, Point-4 Flowable, Premise Flowable, Revolution Formula 2, X-Flow) and four resin-based pit and fissure sealants (Clinpro, Delton FS+, Estiseal F, Guardian Seal) were used in this study. Their filler weight content was measured by thermogravimetric analysis. Mechanical properties were measured: dynamic and static moduli of elasticity, flexural strength and Vickers microhardness. Rheological measurements were performed using a dynamic oscillation rheometer. Results: Flowable resin composites have by far better mechanical properties than pit and fissure sealants, except for Delton FS+. All the materials tested are non-Newtonian, shear thinning fluids. They all showed elasticity even at the lowest frequencies but elasticity differs pretty much from one material to another. Significance: Resin-based pit and fissure sealants seem appropriate for preventive pit and fissure sealing. For enlarged fissures, it can be assumed that flowable resin composites with low elasticity at low frequency are more appropriate.

Toughening of epoxy thermosets with thermoplastics is an important avenue towards improved properties of high-performance systems. The main focus of the work reported was to study the complex issue of interdiffusion between thermoplastics and epoxy resin precursors, using a combination of experimental and numerical simulation methods, in order to understand the key parameters driving the process. Diameter changes of thermoplastic filaments in contact with epoxide and diamine precursors have been followed and an original approach using carbon nanotubes as tracers of the filament swelling front has been developed. This method shows that the improved mobility of low-molecular-weight resin monomers as well as the greater mobility of phenoxy of lower glass transition temperature as compared to poly(ether sulfone) control dissolution by favouring the penetration of precursors into the thermoplastic and lead to both swelling of the outer part of the filaments and reduction of the inner unaffected core. Simulation by molecular dynamics supports the idea that diffusion of polymer macromolecules remains limited compared to the dominant effect of precursor diffusion. Indeed, low diffusion coefficients have been predicted for thermoplastic oligomers compared to resin monomers. For the latter, the calculated values correlate well with the experimental data measured during interdiffusion

Carbon nanotube reinforced polymer foams filling a metallic honeycomb were processed and characterized for the production of hybrid materials with high electromagnetic absorption potential. Electromagnetic modeling and experimental characterization of the hybrids proved that the honeycomb, acting as a hexagonal waveguide, improves the absorption properties in the gigahertz range above the cutoff frequency. The electromagnetic absorption can be tuned by changing the hybrid material properties. The required levels of electrical conductivity are attained owing to the dispersion of low amounts (1-2 wt%) of carbon nanotubes inside the polymer matrix. The combination of the foam and honeycomb architecture contributes to decrease the real part of the relative effective permittivity Re{er,eff }. Varying the cell shape of the honeycomb changes the frequency range for high absorption. An analytical model for the absorption has been developed, showing good agreement with the experimental results.

Naturally occurring halloysite nanotubes (HNTs) are used to prepare Polypropylene (PP)/HNTs nanocomposites using a novel "one step" water-assisted extrusion process with and without the use of a PP-graft-maleic anhydride (PP-g-MA) as compatibilizer. In order to analyze the influence of PP-g-MA and/or water injection on the HNTs dispersion and therefore on nanocomposite properties, structural analysis (SEM and TEM) is combined with rheological and thermo-mechanical experiments. The best clay dispersion is obtained when compatibilizer and water injection are combined together (synergistic effect). As a consequence, the linear viscoelastic properties and the dynamic storage modulus are dramatically enhanced for this system. A mechanism explaining the interaction between HNTs and PP-g-MA in presence of water is proposed. The thermal stability and flame retardant property are also investigated. Thermal analyses reveal two opposite effects of HNTs on the thermal behaviour of PP. A surface catalytic action of the halloysite speeds up thermal degradation of PP. However, this effect is reduced with improved HNTs dispersion, presumably via an entrapment mechanism of the decomposition products inside the lumens. Finally, cone calorimeter results show that low flammability of nanocomposites is only achieved when combining water injection and PP-g-MA. In view of these results, PP/HNTs nanocomposites prepared using this novel processing route are promising candidates for flame retardant applications.

In this article, calcium carbonate filled low density polyethylene (LDPE) was prepared and the influence of filler content, particle size, and surface treatment with stearic acid on the strain hardening and viscoelastic properties of the composites were investigated. Both elongational and shear rheological measurements were conducted on the different formulations and completed by microscopical observations and by differential scanning thermal analysis. The obtained results indicate that the effect of filler content and particle size are negligible on strain hardening behavior. Also the filler surface treatment has a less important effect on the nonlinear elongational tests in comparison with low frequency range measurements. However in shear rheology, we noted the absence of yield stress and network structure at different filler contents, and the presence of shear thinning behavior. Scanning electron microscopy (SEM) observations showed the enhancement of dispersion for surface treated samples, while differential scanning calorimetry (DSC) experiments have shown that the content of crystallinity of LDPE matrix is slightly affected by the presence of filler. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

F14512 exploiting the polyamine transport system (PTS) for tumour cell delivery has been described as a potent antitumour agent. The optimal use of this compound will require a probe to identify tumour cells expressing a highly active PTS that might be more sensitive to the treatment. The aim of this study was to design and characterize a scintigraphic probe to evaluate its uptake in cancer cells expressing the PTS.Three polyamines coupled to a hydrazinonicotinamide (HYNIC) moiety were synthesized and labelled with 99mTc. Their radiochemical purity was determined by HPLC. The plasma stability of the 99mTc-HYNIC-spermine probe and its capacity to accumulate into PTS-active cells were also evaluated. In vitro internalization was tested using murine melanoma B16/F10 cells and human lung carcinoma A549 cells. Biodistribution was determined in healthy mice and tumour uptake was studied in B16/F10 tumour-bearing mice. A HL-60-Luc human leukaemia model was used to confront single photon emission computed tomography (SPECT) images obtained with the 99mTc-labelled probe with those obtained by bioluminescence.The 99mTc-HYNIC-spermine probe was selected for its capacity to accumulate into PTS-active cells and its stability in plasma. In vitro studies demonstrated that the probe was internalized in the cells via the PTS. In vivo measurements indicated a tumour to muscle scintigraphic ratio of 7.9±2.8. The combined bioluminescence and scintigraphic analyses with the leukaemia model demonstrated that the spermine conjugate accumulates into the tumour cells.The 99mTc-HYNIC-spermine scintigraphic probe is potentially useful to characterize the PTS activity of tumours. Additional work is needed to determine if this novel conjugate may be useful to analyse the PTS status of patients with solid tumours.

We investigate the linear and non-linear rheological behavior in shear of a concentrated solution of “dumbbell” polystyrene with long linear backbone and dense short brushes at both ends and compare it with corresponding linear polymers. This type of dumbbells has never been rheologically characterized before. In linear viscoelasticity, the dumbbell polymers show significant differences with conventional linear polymers. In particular, the reptation relaxation of the dumbbell is strongly slowed down. Furthermore, the addition of the side chains increases the friction so that the dumbbell lies above the η 0 vs. number of entanglements relation of linear samples. Transient shear rheology experiments on weakly entangled solutions show a retardation of the chain stretch relaxation of the dumbbell by a factor 2.5 vs. a linear polymer with the same Rouse time. Additionally, a second peak in the transient viscosity is observed at high shear rates.

Electromagnetic (EM) interferences are ubiquitous in modern technologies and impact on the reliability of electronic devices and on living cells. Shielding by EM absorption, which is preferable over reflection in certain instances, requires combining a low dielectric constant with high electrical conductivity, which are antagonist properties in the world of materials. A novel class of hybrid materials for EM absorption in the gigahertz range has been developed based on a hierarchical architecture involving a metallic honeycomb filled with a carbon nanotube-reinforced polymer foam. The waveguide characteristics of the honeycomb combined with the performance of the foam lead to unexpectedly large EM power absorption over a wide frequency range, superior to any known material. The peak absorption frequency can be tuned by varying the shape of the honeycomb unit cell. A closed form model of the EM reflection and absorption provides a tool for the optimization of the hybrid. This designed material sets the stage for a new class of sandwich panels combining high EM absorption with mass efficiency, stiffness and thermal management.

Copolymer hydrogels were prepared from an aqueous micellar solution of the nonionic surfactant monomer (surfmer) ω-methoxy poly(ethylene oxide)(40)undecyl-α-methacrylate (PEO-R-MA-40) and acrylic acid (AA) in a one-step reaction using γ-irradiation. The hydrogels were transparent if the polymerization was carried out at pH ≥ 4, whereas turbid gels were obtained if the polymerization was carried out at lower pH. Exposure of the turbid gels to an aqueous solution of pH 11 led to swelling and clearing, whereas subsequent exposure to pH 1 had the reverse effect. Clear gels prepared at pH 4 became turbid, if exposed to an aqueous solution of lower pH and became clear again if reswollen at higher pH. The pH at which clouding set in increased with the amount of surfmer copolymerized in the gel. Pure poly(acrylic acid) (P-AA) hydrogels did not show any changes in transparency if the pH was varied. The presence of surfmer led to more pronounced shrinking and swelling, especially if the gels were prepared at pH 4. The mechanical stability of P-AA and copolymer hydrogels was studied using elongational flow measurements. The presence of surfmer led to increased mechanical stability of the hydrogels. The increase originates from copolymerized micellar aggregates acting as additional, stable cross-linking units in the gel. The true stress at break of copolymer hydrogels prepared at pH 2.4 (or 4) was 5.5 (or 3.4) times larger than for surfmer-free P-AA gels. Possible origins for the higher stability such as complex formation between P-AA and oxyethylene segments of copolymerized PEO-R-MA-40 are discussed.

Polyamide 12 (PA12) nanocomposites based on halloysite nanotubes (HNTs) were obtained using a batch internal mixer or a twin-screw mini-compounder. In order to analyze the influence of HNTs dispersion on nanocomposite properties, morphological analysis (SEM and TEM) was combined with rheological and thermo- mechanical experiments. The linear viscoelastic properties and the dynamic storage modulus were expectedly found to increase with increasing HNT loading. Higher enhancements were observed for PA12/HNTs nanocomposites obtained by twin-screw mini-compounding. This finding was related to the better degree of dispersion and alignment of the silicate nanotubes throughout the matrix. Thermal stability was also improved by the halloysite nanotubes presumably by an entrapment mechanism of the volatile products inside the hollow tubular structure. DSC measurements further highlighted a nucleation effect of HNTs on the nanocomposites. In view of these results, halloysite nanotubes are promising candidates in the field of PA nanocomposites for structural applications. (C) 2010 Elsevier Ltd. All rights reserved.

We extend van Ruymbeke et al.'s time marching algorithm (TMA) ( Macromolecules 2006, 39, 6248) in order to predict the linear viscoelastic properties of comb polymer melts. While former tube models have shown limitations for predicting the relaxation of comb polymer with short side branches, we observe here a good agreement between predictions and the experimental data for both combs with long and short side branches. In order to determine the origin of this improvement, we study the influence of the different elements present in the TMA model. In particular, we show the importance of taking into account the monomeric friction coming from the backbone itself in the total drag of the molecule, considering the modification of early time fluctuations and introducing the tube dilation process as a continuous function evolving through time. Then, based on a wide range of experimental data on different comb structures, we explore the limits of the relaxation behavior that comb polymers can show. If the friction from the relaxed side branches is significant, the backbone segments seem to fluctuate with respect to the closest branching point, just like a Cayley-tree molecule. On the other hand if the extra friction is negligible in comparison to the potential barrier of retraction along the backbone, the segments fluctuate with respect to the middle of the molecule, just like a linear chain.

The present study demonstrates the effect of unfunctionalized MultiWalled Carbon Nanotubes (MWNTs) interfacial confinement on coalescence suppression in an immiscible polymer blend exhibiting a sea-island morphology. The effect of carbon nanotubes on morphological stabilization in polyamide (PA)/ethylene-methyl acrylate random copolymer (EA) blends is studied using electronic microscopy techniques. Owing to their interfacial localization, MWNTs are shown to enhance both phase dispersion and stability of the dispersed phase for long mixing time (at least 60 min) and very low filler content (0.5 wt.-% MWNTs) compared to what was previously observed in literature. MWNTs also produce a more uniform distribution of droplets size. The main stabilization mechanism proposed is the formation of a deformable barrier network providing a mechanical barrier against coalescence. Blends stabilized by solid anisotropic nanoparticles, like MWNTs, could therefore offer an interesting alternative to blends compatibilized by block-copolymers. (C) 2010 Elsevier Ltd. All rights reserved.