bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hybrid Hydrogels: Macromolecular Assemblies through Inorganic Cross‐Linkers
Authors: Hourdet Dominique , Petit Laurence 
Published: June 2010

AbstractThe adsorption process onto a silica surface of oligomers from three different monomers, N,N‐dimethylacrylamide (DMA), N‐isopropylacrylamide (NIPA) and ethylene oxide (EO), was studied. From the adsorption isotherms and calorimetric experiments, it was shown that N‐alkylacrylamide derivatives strongly interact with silica nanoparticles. At low coverage (Γ < 0.5 mg m−2), the polymers were adsorbed in a flat conformation with a high proportion of trains, while for higher coverages (Γ = 0.5 – 1 mg m−2), the adsorption of new chains proceeded by chain displacement, forming an increasing proportion of loops and tails. Similarly, PEO chains readily interacted with silica nanoparticles but showed a lower affinity with an adsorbed amount (Γ ≅ 0.6 mg m−2) that was approximately half of the value obtained for both PDMA and PNIPA. When these oligomers were grafted onto a non‐adsorbing poly(acrylamide‐co‐sodium acrylate) backbone (PAMH), the binding process of these adsorbing side‐chains with silica nanoparticles proceeded very similarly and gave rise to the formation of hybrid hydrogels above critical copolymer and silica concentrations. The viscoelastic properties of these networks were controlled by the concentration of inorganic cross‐links and the fraction of adsorbing grafts that participated in the formation of bridges between particles, the others being involved in inelastic loops or pendant chains. For all the hybrid mixtures investigated, an optimum weight ratio between silica and grafts was found for the viscoelastic properties, which was in agreement with the saturation of silica beads by the graft precursors. Due to the temperature‐dependence of the solubility of the PNIPA side‐chains in aqueous solutions, the PAMH‐g‐PNIPA copolymer was also able to self‐assemble with temperature, giving rise to a hybrid conetwork in the presence of added silica.
Theoretical Modelling of Hierarchically Associated Structures in Hydrophobically Modified PNIPAM Aqueous Solutions on the Basis of a Neutron Scattering Study
Authors: Koga Tsuyoshi , Tanaka Fumihiko , Motokawa Ryuhei , Koizumi Satoshi , Winnik Françoise M. 
Published: June 2010

AbstractWe developed a theoretical model for a self‐assembling telechelic poly(N‐isopropylacrylamide) (PNIPAM) carrying octadecyl end‐groups in aqueous solution, as a function of temperature and concentration, on the basis of small‐angle neutron scattering data. In solutions of concentration 10 g L−1 at temperatures between 10 and 20 °C, the telechelic PNIPAM of molecular weight of 22,200 g mol−1 associates in the form of flower micelles containing about 12 polymer chains. Micelles have a 3‐layered core‐shell morphology with an inner core consisting of the octadecyl units, a dense inner shell consisting of partly collapsed PNIPAM chains, and an outer shell of swollen hydrated PNIPAM chains. Drastic changes in the scattering profile of the solution heated above 31 °C are attributed to the formation of mesoglobules of diameter of 100 nm consisting of about 1000 polymer chains. In solutions of lower concentration (1 g L−1), association of flower micelles and mesoglobules is suppressed. The structure of the individual flower micelles and mesoglobules is not affected by changes in concentration. In solutions of 50 g L−1, a peak attributed to a correlation between flower micelles appears in the scattering profiles at low temperature (10 °C). Despite the difference in the population of intermicellar bridges, the overall temperature dependence of the scattering profile at 50 g L−1 remains similar to that at 10 g L−1.
Jamming in Filled Polymer Systems
Authors: Richter Sven , Saphiannikova Marina , Stöckelhuber Klaus Werner , Heinrich Gert 
Published: June 2010

AbstractAfter an introduction into the general characteristics of the jamming behavior, two filler flocculation experiments on a polycarbonate melt filled with multi‐walled carbon nanotubes and on a silica‐filled ethylene propylene diene monomer elastomer are presented. We propose that these experiments can be regarded as jamming phenomena. The experimental data are successfully modeled using the power saturation equation. Further insights into the physics of such jamming processes have been obtained with the help of X‐ray photon correlation spectroscopy experiments.
Physical Gels Based on Polyrotaxanes: Kinetics of the Gelation, and Relative Contributions of α‐Cyclodextrin and Poly(ethylene oxide) to the Gel Cohesion
Authors: Travelet Christophe , Schlatter Guy , Hébraud Pascal , Brochon Cyril , Anokhin Denis V. , Ivanov Dimitri A. , Hadziioannou Georges 
Published: June 2010

AbstractPolyrotaxanes (PRs) based on α‐cyclodextrins (α‐CDs) threaded onto 22 kg mol−1 poly(ethylene oxide) (PEO) chains in concentrated solution in dimethyl sulfoxide (DMSO) showed the particularity to form physical gels when resting at 21 °C. The wide range of studied degrees of complexation N (from 7 up to 176), where N is the number of threaded α‐CDs per PEO chain, allowed to better understand the molecular origin of the physical gelation. The non‐monotonous evolution of the mechanical properties of the gels with the complexation degree can be attributed to the crystallization of naked PEO segments and the aggregation of α‐CDs. In fact, differential scanning calorimetry measurements carried out on these physical gels showed two distinct endothermic peaks. The first peak at 29.4 °C was attributed to the crystals of naked PEO segments (the parts of the PR molecule not covered by α‐CDs). The second peak at 32.0 °C was attributed to α‐CD aggregates. The dissolution enthalpy of the low temperature peak decreased monotonously with increasing N and the dissolution enthalpy of the high temperature peak increased monotonously with increasing N. These results were confirmed using X‐ray scattering and 1H NMR spectroscopy measurements showing these two contributions to gelation. These results showed that the cohesion of the physical gel was due to the crystallization of naked PEO segments, on the one hand, and, on the other hand, to the regular aggregation of α‐CDs driven by intra‐ and inter‐molecular hydrogen bonding interactions of their hydroxyl groups.
Kinetic Modeling of the Molecular Architecture of Cross‐Linked Copolymers Synthesized by Controlled Radical Polymerization Techniques
Authors: Gonçalves Miguel AD. , Trigo Ivone MR. , Dias Rolando CS. , Costa Mário Rui PFN. 
Published: June 2010

AbstractA recently developed general kinetic approach, based on population balances in terms of generating functions, is applied to the modeling of the molecular architecture of branched copolymers produced through controlled radical polymerization (CRP) techniques, namely nitroxide‐mediated radical polymerization (NMRP) and atom‐transfer radical polymerization (ATRP). Thanks to this method, it is possible to carry out dynamic predictions of distributions of molecular weights, sequence lengths and z‐average mean square radius of gyration of the products, both before and after gelation (whenever it occurs) with consideration of complex kinetic schemes. The model chemical systems styrene + divinylbenzene (S/DVB) and methyl methacrylate + ethylene glycol dimethacrylate (MMA/EGDMA) are experimentally investigated in order to assess the prediction capabilities of the aforementioned approach. Measurements of absolute molecular weights and z‐average radius of gyration of the copolymers are performed for different times of polymerization using a SEC system with a refractive index detector coupled with MALLS. It is shown that the proposed computational tool can enhance the possibility of better design of these complex materials but additional studies concerning the impact of intramolecular cyclizations on the structure of materials synthesized at diluted conditions are needed.
Forced Gelation in an Off‐Stoichiometric Copolymerization of A2 and B3 Monomers
Authors: Lechowicz Jaromir B. , Galina Henryk 
Published: June 2010

AbstractA step‐growth alternating copolymerization of monomers A2 and B3 was studied by an off‐lattice Monte‐Carlo simulation. In the random systems, i.e. with no substitution effect, the polymerization leads to gel formation provided the molar ratio of monomers is not very far from the stoichiometric one (A2: B3 ≈ 3: 2) and the reaction is carried out in one batch. A substantial deviation from the stoichiometric ratio may halt gelation altogether, even at conversions of the minority functional groups approaching unity. We demonstrate that in these non‐gelling off‐stoichiometric systems, one can force the system to gel, after all, without altering the kinetics or diffusion parameters of the reaction. The clue is to carry out the reaction in steps.
Bioapplications of Networks Based on Photo‐Cross‐Linked Hyperbranched Polymers
Authors: Pedrón Sara , Anseth Kristi , Benton Julie A. , Bosch Paula , Peinado Carmen 
Published: June 2010

AbstractThis article deals with some of the most recent developments in the use of hyperbranched polymers in biomedical applications. Some examples have been selected to show their potential in drug delivery, tissue engineering, imaging technologies and molecular imprinting. Moreover, the preparation of methacrylic networks using chemically‐modified hyperbranched polymers as multifunctional macromonomers by photopolymerization is described. The capability to support valve interstitial cell culture was demonstrated and the adhesion and functionality of the cells was related to the mechanical properties of these materials.
Cell Adhesion to Polymethacrylate Networks Prepared by Photopolymerization and Functionalized with GRGDS Peptide or Fibrinogen
Authors: Johnson C. , Perlin L. , Wyman P. , Zhao B. , Fullwood N. J. , MacNeil S. , Rimmer S. 
Published: June 2010

AbstractPolymethacrylate hydrogels are useful scaffolds for tissue engineering and cell‐based therapies provided they can be modified to give good cell adhesion characteristics. They have advantages over non‐swollen materials, such as good diffusion properties, tunable moduli and porosities. However, conventional non‐charged hydrogels are essentially non‐adhesive for cells and they are poor substrates for cell culture. In a previous volume in this series of symposia from the Polymer Networks Group, we described how both amphiphilic conetworks and alkyl‐aminated hydrogels were excellent substrates for cell culture.1 In this article we report our most recent work on understanding how to modify hydrogels for cell attachment. We report how the choice of photoinitiator affects the viability of human dermal fibroblasts (HDFs). Next, we provide further results involving the use of an enzyme deprotection strategy that can be carried out after copolymerization of a GRGDS methacrylate monomer. We show that the peptide enhanced the culture of HDFs in serum when the peptide was attached to poly(1,2‐propane diol methacrylate‐co‐ethane diol dimethacrylate). On the other hand, poly(n‐butyl methacrylate‐co‐ethane diol dimethacrylate) networks adsorb larger amounts of protein non‐specifically, and they are reasonable substrates for adhesion of HDFs without peptide modification. Attachment of GRGDS to an example of these networks did not increase the attachment and proliferation of HDFs in serum containing media. We also describe the attachment of fibrinogen/fibrin coatings by the transglutaminase mediated reaction of alkyl amines attached to a poly(1,2‐propane diol methacrylate‐co‐ethane diol dimethacrylate‐co‐dodecyl methacrylate) network. This work illustrates the reactivity of alkyl‐aminated hydrogels in transglutaminase catalyzed reactions, although the addition of the fibrin coating did not improve the performance of the material for cell culture which was already good on these hydrogels.
Alginate Oligoguluronates as a Tool for Tailoring Properties of Ca‐Alginate Gels
Authors: Sletmoen Marit , Draget Kurt I. , Stokke Bjørn T. 
Published: June 2010

AbstractAlginates represent a family of structural polysaccharides derived from either seaweeds or bacteria. They readily form ionotropically‐induced physcial gels in aqueous solution in the presence of multivalent ions. In this study, the homogeneous release of Ca2+ from Ca‐ethylene glycol tetraacetic acid (Ca‐EGTA) within an alginate solution is utilized to prepare homogeneous gelation conditions. The pH‐dependence of the multiple equilibria involved, i.e. between Ca2+, the various states of EGTA, the alginate and its protonation and ion binding, is modeled and used as a basis for designing the glucono‐δ‐lactone concentration to reduce the pH. This method is used for the perturbation of the Ca‐induced gelation of alginates in the presence of oligoguluronate oligomers. These oligoguluronate oligomers are able to be involved in the binding of Ca2+, but sufficiently short not to mediate connectivity through their chains. The results indicate that the oligoguluronate oligomers perturb the gelation of alginate differently in the Ca2+‐limited and non‐Ca2+‐limited regimes. In the calcium limited regime, the oligoguluronate oligomers appear to sequester calcium either by binding to oligoguluronate sequences of the network, or between the free oligoguluronates, yielding an overall net effect of reduced gel strength. In the non‐Ca2+ limited regime, the experimental data shows increased gel strength in the presence of oligoguluronate blocks. These results show that oligoguluronates can be used as modulators of gelation kinetics as well as local network structure formation and equilibrium properties in alginate gels.
Effect of interface properties on the effective properties of biopolymer composite materials
Authors: Rjafiallah S. , Benseddiq N. , Guessasma S. 
Published: June 2010

AbstractWeak adhesion between constituents in starch‐zein composites has been proven using nanoindentation experiments. In order to quantify the effect of imperfect interface on the elastic properties of the composite, a Finite Element (FE) model is presented. Starting from the generation of typical 2D microstructures representing the result of a thermomoulding process, circular zein particles are embedded in a starch matrix. Particles are allowed to overlap in order to represent flowability of the filler into the matrix. Zein fraction in the composite is varied in the full range (0–100%). The generated microstructures are converted into a finite element model, where the influence of the interface is modelled thanks to a cohesive zone model. The predicted results show that Young's modulus of the composite is significantly affected by the spatial distribution of the interfaces. When the phase ratio is small enough, the interface effect is localized around filler clusters. Increasing further more the phase ratio leads to a percolation of the interface. In particular, interface percolation perpendicular to the loading direction predicts the lowest modulus. When the filler phase becomes predominant, the interface effect weakens. Based on the former discussion, an effective law is suggested using a simple non‐linear function between the effective modulus and the phase ratio.
A lattice Monte Carlo analysis on thermal diffusion in syntactic hollow‐sphere structures
Authors: Farnsworth J. , Murch G. E. , Belova I. V. , Öchsner A. , Fiedler T. 
Published: June 2010

AbstractThe Lattice Monte Carlo method [1] is a computationally intensive approach towards the study of thermal material properties. The Lattice Monte Carlo method has previously been used in the area of mass diffusion, and has more recently been applied towards the analysis of thermal diffusion in materials. Whilst previous studies have focused on two‐phase material consisting of component material and pore geometry only, this study applies the Lattice Monte Carlo method towards the investigation of three‐phase Metallic Hollow Sphere Structures (MHSS). MHSS consist of high‐conducting metallic shells, low‐conducting adhesive and non‐conducting pores. In the present study, three‐dimensional computerised models of the MHSS are built up from analysis of computed tomography (CT) scans. The results of this numerical analysis indicate a spatial variation of the thermal conductivity. However, MHSS can be considered as being isotropic to a good approximation.Die ‘Lattice Monte Carlo’ Methode [1] ist ein rechenintensiver Ansatz zur Bestimmung thermischer Materialeigenschaften. Die ‘Lattice Monte Carlo’ Methode hat sich für die Simulation der Diffusion in Festkörpern etabliert und wird seit kurzem auch für die Analyse thermischer Diffusion in Werkstoffen eingesetzt. Vorhergehende Studien konzentrierten sich auf Zwei‐Phasen‐Materialien bestehend aus Grundmaterial und Pooren. Die jetzige Analyse nutzt die ‘Lattice Monte Carlo’ Methode für die Untersuchung drei‐phasiger metallischer Hohlkugelstrukturen (abgekürzt aus dem Englischen ‘Metallic Hollow Sphere Structures’ als MHSS). MHSS bestehen aus hoch‐leitfähigen metallischen Schalen, thermisch‐isolierenden Kunststoff und nicht‐leitfähigen Poren. Drei‐dimensionale Rechenmodelle wurden in der vorliegenden Studie von computer‐tomographischen Daten abgeleitet. Die Ergebnisse der numerischen Analyse deuten eine räumliche Streuung der thermsichen Leitfähigkeit an. Die lokalen thermischen Leitfähigkeiten sind jedoch isotrop.
Static and fatigue behaviour of room temperature vulcanising silicone adhesives for high temperature aerospace applications
Authors: Banea M. D. , da Silva L. F. M. 
Published: June 2010

AbstractThis paper focuses on the mechanical properties of room temperature vulcanising (RTV) silicone adhesives for aerospace applications. In view of the very limited amount of published data on this subject, we analyzed the performances of two RTV silicone rubber adhesives through adhesive joint tests. The standard Thick Adherend Shear Test (TAST) was performed in order to measure the shear properties of the adhesives. Single lap joints (SLJs) were fabricated and tested to assess the adhesive performance in a joint. The influence of temperature on the lap‐shear strength of the adhesives was investigated. It is shown that the lap‐shear strength of both adhesives decreased with increasing of temperature. The effect of bondline thickness and overlap length on the lap‐shear strength of the adhesives was also studied. The reduction of failure load with an increase of the bondline thickness is a very common situation when dealing with structural adhesives. However, for the tested RTV silicone adhesives the failure loads increased as the bondline was made thicker. Also, the failure loads of RTV silicone adhesive joints increased almost proportionally with increasing the overlap length. Fatigue tests were also performed and show a low dispersion of the results.
Optimal design of rear chassis components for lightweight automobile using design of experiment
Authors: Park J.‐H. , Kim S.‐K. , Choi B.‐I. , Lee H.‐J. , Lee Y.‐H. , Kim J.‐S. , Kim K.‐J. 
Published: June 2010

AbstractWith growing public concerns on the rising price of fossil fuel and the greenhouse gas emissions, the automotive industry is once again faced with the increased demand to develop more fuel‐efficient vehicles. Savings in weight using lightweight materials such as aluminum can lead to increased fuel economy and reduction in pollution. Aluminum material has a weak point compared to the steel material in strength for life cycle. In this study, to design a lighter and more reliable chassis component using aluminum material as compared with existing steel chassis components, a new link shape was suggested by adding vertical ribs to an existing I‐beam type link and to investigate how each design parameter makes an effect on the reliability and component weight. The design of experiment (DOE) was performed with six design parameters and two levels. Through the analysis of variance, three parameters which were the most influential on weight were selected. And then the response surface analysis was performed with two levels to find out the optimal dimensions. The weight of the aluminum link was 64% that of the steel link. The stiffness of the optimized aluminum link under all loads was more than 100% that of the steel link. The maximum von Mises stresses of the optimized aluminum link under all loads was equal or less than 20% of the ultimate tensile strength (58 MPa).
Transcriptomic analysis of tubular carcinomas of the breast reveals similarities and differences with molecular subtype‐matched ductal and lobular carcinomas
Authors: Lopez‐Garcia Maria A , Geyer Felipe C , Natrajan Rachael , Kreike Bas , Mackay Alan , Grigoriadis Anita , Reis‐Filho Jorge S , Weigelt Britta 
Published: June 2010

AbstractTubular carcinoma (TC) is an uncommon special type of breast cancer characterized by an indolent clinical course. Although described as part of a spectrum of related lesions named ‘low‐grade breast neoplasia family’ due to immunophenotypical and genetic similarities, TCs, low‐grade invasive ductal carcinomas of no special type (IDC‐NSTs), and classic invasive lobular carcinomas (ILCs) significantly differ in terms of histological features and clinical outcome. The aim of this study was to investigate whether pure TCs constitute an entity distinct from low‐grade IDC‐NSTs and from classic ILCs. To define the transcriptomic differences between TCs and IDC‐NSTs and ILCs whilst minimizing the impact of histological grade and molecular subtype on their profiles, we subjected a series of grade‐ and molecular subtype‐matched TCs and IDC‐NSTs and molecular subtype‐matched TCs and classic ILCs to genome‐wide gene expression profiling using oligonucleotide microarrays. Unsupervised and supervised analysis revealed that TCs are similar at the transcriptomic level to grade‐ and molecular subtype‐matched IDC‐NSTs. However, subtle yet significant differences were detected and validated by quantitative reverse transcriptase‐PCR, which may in part explain the reported more favourable outcome of TCs. Transcriptomic differences between TCs and molecular subtype‐matched classic ILCs were more overt, predominantly due to lower expression of proliferation and cell cycle genes in TCs and down‐regulation of cell adhesion/extracellular matrix‐related genes in classic ILCs. Our results support the existence of a ‘low‐grade breast neoplasia family’; however, the transcriptomes of these lesions display small, yet important differences, which, together with their distinct biological behaviour, warrant their separation as discrete entities. Copyright © 2010 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.