1,720,963 research outputs found
Studio sulla struttura e sul comportamento dinamico di idrogel polisaccaridici per la formulazione di nuovi dispositivi biomedicali
Full text linkHyadd4-G è un derivato dell’acido ialuronico avente l’ 1÷3% di gruppi carbossilici legati a catene laterali di esadecilammina. L’introduzione di catene laterali esadeciliche sull’acido ialuronico (HA) porta alla formazione di un polisaccaride con nuove proprietà in grado di formare idrogel fisici, stabili a concentrazioni di polimero molto basse, mentre l’ HA nativo forma soluzioni viscose anche a concentrazioni dieci volte maggiori. Il comportamento strutturale e dinamico dell’idrogel Hyadd4-G riguarda diverse scale temporali e spaziali. Il fattore dinamico di struttura, f(Q,t), ottenuto con misure di DLS, è stato usato per ricavare i tempi microscopici caratteristici e le dimensioni della maglia del network. La metodologia del recupero di fluorescenza dopo photobleaching, FRAP, è stata usata per misurare i coefficienti di diffusione di sonde fluorescenti con diverse dimensioni. Le dimensioni idrodinamiche delle sonde, evidenziando un effetto di setaccio degli idrogel con gli esperimenti di FRAP, possono essere comparate con le dimensioni di maglia, δ, degli idrogel Hyadd4-G studiati con DLS. Misure di reologia nel regime viscoelastico lineare hanno mostrato che Hyadd4-G è un gel “soffice” viscoelastico. Tali misure hanno mostrato inoltre un particolare meccanismo di ricostituzione (“recupero di struttura”) dopo la distruzione del network del gel con misure in flusso e l’iniettabilità dell’idrogel è supportata da un pronunciato comportamento di “shear-thinning” sotto una deformazione non-lineare. La tecnica dello scattering dei neutroni ha fornito informazioni sulla microstruttura e sulle proprietà di diffusione dell’acqua nel network. La caratterizzazione dello Hyadd4-G ha mostrato che la formazione del gel è dovuta all’interazione tra le catene laterali idrofobiche che stabilizzano il network 3D con un’architettura di dimensioni nanoscopiche, nonostante il basso grado di sostituzione. Questa rappresentazione fornisce il necessario background per considerare Hyadd4-G come un potenziale nuovo idrogel utilizzabile per trattamenti di malattie osteoarticolari.
Lo xantano e il konjac glucomannano accoppiati forniscono uno dei sistemi di idrogel sinergici maggiormente studiati. Le zone di giunzione che stabilizzano una struttura 3D sono rappresentate da complessi macromolecolari in soluzione formati da catene polisaccaridiche parzialmente depolimerizzate. Le interazioni non-covalnti che stabilizzano la struttura del complesso polisaccaridico causano la distruzione di una struttura ordinata del complesso in soluzione e dell’idrogel. L’introduzione di legami chimici nella struttura 3D dell’idrogel sinergico rimuove questo comportamento, aggiungendo nuove caratteristiche al rigonfiamento e alle proprietà viscoelastiche dell’idrogel. L’utilizzo di epicloridrina come agente reticolante a basso peso molecolare non influisce sulla vitalità di fibroblasti NIH 3T3.Hyadd4-G is a derivatized hyaluronic acid having 1÷3% of the carboxyl groups grafted with a hexadecylic amide side-chains. The introduction of a hexadecyl side chain onto hyaluronic acid (HA) chains yields a polysaccharide with new properties, capable of forming physical hydrogels, stable at very low polymer concentrations, whereas native HA forms viscous solutions at ten times higher concentrations. We addressed the structural and dynamic behavior of Hyadd4-G hydrogels at different time and length scales. Dynamic structural factor, f(Q,t), obtained by DLS, was used to extract the microscopic characteristic times and pore size of the network. Fluorescence recovery after photobleaching methodology, FRAP, was used to measure diffusion coefficients of fluorescent probes with different size. The hydrodynamic coil dimensions of dextrans evidencing a sieving effect of the hydrogels by FRAP experiments can be compared with the mesh size, δ, of Hyadd4-G hydrogels studied by DLS. Rheology measurements in the linear viscoelastic regime show that Hyadd4-G is a soft viscoelastic gel. Rheological measurements showed an unusual self-healing mechanism (structure recovery) after destruction of the gel network in a shear flow and the injectability of the hydrogel is supported by a pronounced shear-thinning behavior under nonlinear deformations. Neutron scattering techniques can provide information about the microstructure and the diffusional properties of water within the pores of the network. Characterization of Hyadd4-G showed that the driving force for its gel-like behavior is the occurrence of hydrophobic interactions involving hydrophobic side-chains stabilizing a 3D-network with nano-sized architecture, despite the low degree of substitution. This picture provides the necessary background to assess Hyadd4-G as one of the potential new hydrogel systems suitable for treatment of osteoarticular diseases.
Xanthan and konjac glucomannan pair provides one of the most studied synergistic hydrogels. The junction zones stabilizing the 3D structure of this gel are present as macromolecular complexes in solution formed by the partially depolymerised polysaccharidic chains. The non-covalent interactions stabilizing the structure of the polysaccharidic complex cause the melting of the ordered structure of the complex in the solution and of the hydrogels. Introduction of chemical cross-links in the 3D structure of the synergistic hydrogel removes this behaviour, adding new features to the swelling and to the viscoelastic properties of the cured hydrogel. The use of epichlorohydrin as low molecular weight cross-linker does not impact on the viability of NIH 3T3 fibroblasts
Viscoelastic properties and elastic recovery of HYADD®4 hydrogel compared to crosslinked HA-based commercial viscosupplements
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
A new viscosupplement based on partially hydrophobic hyaluronic acid: A comparative study
No full textA novel partially hydrophobized derivative of hyaluronic acid (HYADD® 4), containing a low number of C16 side-chains per polysaccharide backbone, provides injectable hydrogels stabilized by side-chain hydrophobic interactions. The rheological properties of Hymovis®, a physical hydrogel based on the hyaluronic acid derivative HYADD® 4, were evaluated using as reference a solution of the parent natural polysaccharide, hyaluronic acid. The rheological measurements were performed both in flow and oscillation regimes at the physiological frequency values of the knee, typically spanning the range from 0.5 Hz (walking frequency) to 3 Hz (running frequency). Moreover, the viscoelastic features of Hymovis® were compared with the market-available viscosupplementation products in view of its use in joint diseases.The different behavior of the investigated materials in crossover frequency measurements and in structure recovery experiments can be explained on the basis of the structural and dynamic properties of the polymeric systems
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