1,720,968 research outputs found
Complex polymeric architectures self-assembling in unimolecular micelles: Preparation, characterization and drug nanoencapsulation
Full text linkUnimolecular polymeric micelles are a class of single-molecule amphiphilic core-shell polymeric architectures, where the hydrophobic core is well stabilized by the hydrophilic shell, avoiding intermolecular core-core interactions. Multi-arm copolymers with a dendritic core, as well as hyperbranched and comb-like polymers, can form unimolecular micelles easily. In this review, examples of polymers able to form detectable unimolecular micelles will be presented, summarizing the analytical techniques used to characterize the unimolecular micelles and discriminate them from other supramolecular aggregates, such as multi-micelle aggregates. Unimolecular micelles are suitable for the nanoencapsulation of guest molecules. Compared to traditional supramolecular micelles, unimolecular micelles do not disassemble under dilution and are stable to environmental modifications. Recent examples of their application as drug delivery systems, endowed with increased stability and transport properties, will be discussed
PROGETTAZIONE DI MACROMOLECOLE AD ARCHITETTURA COMPLESSA PER LA NANOMEDICINA
No full textPolimeri ad architettura complessa vengono sempre più utilizzati in nanomedicina, grazie alla loro capacità di attraversare barriere biologiche e di trasportare farmaci. Polimerizzazioni controllate e tecniche di “click chemistry” permettono una sintesi di macromolecole biocompatibili con peso molecolare, topologia e funzionalità regolabili
Mannosylated brush copolymers based on poly(ethylene glycol) and poly(ε-caprolactone) as multivalent lectin-binding nanomaterials
Full text linkA class of linear and four-arm mannosylated brush copolymers based on poly(ethylene glycol) and poly(ε-caprolactone) is presented here. The synthesis through ring-opening and atom transfer radical polymerizations provided high control over molecular weight and functionality. A post-polymerization azide–alkyne cycloaddition allowed for the formation of glycopolymers with different mannose valencies (1, 2, 4, and 8). In aqueous media, these macromolecules formed nanoparticles that were able to bind lectins, as investigated by concanavalin A binding assay. The results indicate that carbohydrate–lectin interactions can be tuned by the macromolecular architecture and functionality, hence the importance of these macromolecular properties in the design of targeted anti-pathogenic nanomaterials
Engineered polyester-PEG nanoparticles prepared through a “grafting through” strategy and post-functionalization via Michael type addition
No full textFree radical polymerization (FRP) is widely used in industrial processes as an efficient and versatile method to engineer polymeric nanoparticles (PNPs) of controlled size, narrowly distributed, and of well-defined surface properties. Functional Poly(ε-caprolactone) (PCL) and poly(lactic acid) (PLA) can be utilized as macromonomers in FRP in combination with a co-polymerizable poly(ethylene glycol) (PEG), to achieve aqueous dispersions of PNPs composed of a hydrophobic polyester core and a hydrophilic PEG shell of tuneable size. For several industrial and biological applications, PNPs also need surface functionalization to provide specific physicochemical characteristics, including stimuli-responsiveness, and bioactivity. In this work, a flexible “grafting through” strategy based on Ring opening polymerization (ROP) and FRP was proposed to obtain engineered polyester-PEG nanoparticles functionalized with acrylate groups on the hydrophilic shell. The presence of acrylates allows a versatile surface functionalization through Michael-type addition with a thiolated ligand (peptide), in aqueous solution under physiological pH, with the advantage of high conversion and absence of reaction side products. A cysteine-containing cyclic RGD was used as model peptide for conjugation, due to its potential application as ligand for endothelial cells. Results indicated that active cell targeting can be achieved by using this surface functionalization approach
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
Study and characterization of amphiphilic copolymers with complex architecture for biomedical applications
No full textLAUREA MAGISTRALELa nanomedicina `e un recente e promettente campo di ricerca che utilizza la nanotecnologia per sviluppare innovazione nel campo della sanita`. Una delle applicazioni della nanomedicina `e il drug delivery; infatti, la progettazione di nanostrutture puo` essere utilizzata per incapsulare e trasportare farmaci o agenti biologicamente attivi nel corpo umano, aumentandone la loro emivita e solubilita`. La funzionalizzazione dei nanocarrier, inoltre, permette di ottenere una veicolazione specifica nei tessuti che sono interessati dalla malattia e che devono essere curati, ottimizzando i dosaggi del principio attivo e riducendone gli effetti collaterali.
Lo scopo della tesi `e di caratterizzare copolimeri anfifilici con architetture differenti, sintetizzati in precedenza nel gruppo di ricerca del Prof. Cellesi, adatti per applicazioni biomediche. I copolimeri anfifilici, in ambiente acquoso, formano micelle/nanoparticelle con un nucleo idrofobico, capace di incapsulare farmaci insolubili in acqua, e una corona idrofila, che accresce la stabilit`a delle nanoparticelle nell’ambiente biologico eludendo il riconoscimento da parte del sistema immunitario ed evitando una rapida biodegradazione. I copolimeri anfifilici studiati sono composti di policaprolattone (PCL) idrofobico e glicole polietilenico (PEG) idrofilo; tre architetture differenti sono state caratterizzate: lineare, a quattro braccia e multi-ramificata. La nanoprecipitazione, un diffuso processo per la formazione di sospensioni di nanoparticelle in mezzo acquoso, `e stata studiata valutando quali parametri del processo influenzano l’incapsulamento di farmaci e le distribuzioni delle dimensioni delle particelle. Sono stati incapsulati due tipi di farmaci non solubili in acqua, che hanno mostrato promet- tenti risultati nel trattamento di patologie renali: il desametasone, un corticosteroide, e il Bis-T-23, un attivatore della dinamina. Inoltre, `e stato studiato l’assemblaggio spontaneo dei polimeri in ambiente acquoso; infatti, `e importante conoscere come i polimeri si comportano nella sospensione colloidale, se possiedono una concentrazione micellare critica e formano aggregati, oppure esistono come entita` unimolecolari mantenendo una buona stabilita` anche se soggetti a diluizione.
Entrambi i farmaci sono stati incapsulati con successo in tutti i polimeri. Solo i polimeri con struttura lineare e multi-ramificata hanno registrato un miglioramento significa- tivo dell’incapsulamento del farmaco riducendo la concentrazione di polimero e farmaco nella nanoprecipitazione. Le distribuzioni delle dimensioni non hanno mostrato alcuna differenza significativa o andamento regolare cambiando le condizioni sperimentali. Sono suggerite ulteriori modifiche nelle condizioni sperimentali della nanoprecipitazione e il supporto di simulazioni computazionali per ulteriori miglioramenti delle capacita` di caricamento del farmaco e l’ottimizzazione della progettazione dei polimeri.Nanomedicine is a quite recent and promising research field that uses nanotechnology to achieve innovation in healthcare. One of the application in nanomedicine is the drug delivery; in fact, the design of nanostructures can be used as carriers that encapsulate and transport drugs or biological active agents in the human body increasing their half-lives and solubility. Moreover, the functionalization of the nanocarriers is used to achieve the targeting in specific tissues that need to be treated, optimizing the dosage and reducing the side effects of the active agents.
The aim of the thesis is to characterize amphiphilic copolymers, previously synthe- sized by Prof. Cellesi’s research group, with different architectures that are suit- able for biomedical applications. Amphiphilic copolymers, in aqueous media, form micelles/nanoparticles with an hydrophobic core, which is able to encapsulate water- insoluble drugs, and a hydrophilic corona, that increase the nanoparticle stability in the biological environment avoiding recognition by the immune system and fast biodegra- dation. The amphiphilic copolymers studied are made of hydrophobic polycaprolactone (PCL) and hydrophilic polyethylene glycol (PEG); three different architectures were characterized: linear, arm and multi-branch copolymers.
The nanoprecipitation, a widespread process to form nanoparticle suspensions in the aqueous media, was studied by evaluating which parameters affect the encapsulation of drugs and particle size distributions. Two types of water-insoluble drugs, that had showed promising results in treating kydney diseases, were encapsulated: dex- amethasone, a corticosteroid, and Bis-T-23, a dynamin activator. Moreover, the self- assembling of the polymers was studied in aqueous media; in fact, it is important to understand how polymers behave once in the colloidal suspensions, if they have a crit- ical micelle concentrations and form aggregates or they exist as unimolecular entities maintaining a good stability even upon dilution.
Both drugs were successfully encapsulated in all the polymers. Only the polymers with linear and multi-branched structures had a significant improvement of the drug
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loading reducing the polymer-drug concentrations during the nanoprecipitation. The size distributions did not show any significant difference or regular trends changing the experimental conditions.
Further changes in the experimental conditions in the nanoprecipitation and the sup- port of computational simulations are suggested to further improve the loading capac- ities and optimized the polymers designed
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
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