1,721,065 research outputs found
Design of semi-interpenetrating networks based on poly(ethyl-2-cyanoacrylate) and oligo(ethylene glycol) diglycidyl ether
Full text linkThe synthesis of semi-interpenetrating networks (SIPN) based on linear poly(ethyl 2- cyanoacrylate) (PECA) and oligo(ethylene glycol) diglycidyl ether (OEGDG) based polymer networks was motivated by the hypothesis that the brittleness of polycyanoacrylates may be overcome by incorporating them into a polymer network architecture. A sequential synthetic route was applied, in which first PECA was prepared by anionic polymerization. Subsequently, OEGDG was crosslinked with different anhydrides and curing catalysts to form networks with hydrolyzable ester bonds and interpenetrating PECA. These SIPNs showed a low water uptake compared to other polyether based networks. Some of the obtained materials were transparent and exhibited a great flexibility, which was maintained also after 24 h of immersion in water and subsequent drying. Such networks could be components of future stimuli-sensitive material systems
Highly flexible poly(ethyl-2-cyanoacrylate) based materials obtained by incorporation of oligo(ethylene glycol)diglycidylether
Full text linkHydrolytic Degradation Behavior of Poly(rac-lactide)-block-poly(propylene glycol)-block-poly(rac-lactide) Dimethacrylate Derived Networks Designed for Biomedical Applications
Full text linkFor polymer-based degradable implants, mechanical performance and degradation behavior need to be precisely controlled. Based on a rational design, this work comprehensively describes the properties of photo-crosslinked polymer networks prepared from poly(rac-lactide)-block-poly(propylene glycol)-block-poly(rac-lactide) dimethacrylate precursors during degradation. By varying the length of poly(rac-lactide) blocks connected to a central 4?kDa polyether block, microphase separated networks with adjustable crosslinking density, hydrophilicity/hydrophobicity ratio, thermal, and mechanical properties are obtained. The materials are characterized by a low water uptake, controlled mass loss, and slowly decreasing wet-state E moduli in the kPa range
Efficient synthesis of pure monotosylated beta-cyclodextrin and its dimers
Full text link6-O-Monotosyl-β-cyclodextrin (mono-Ts-βCD) is one of the most important intermediates in the production of substituted βCD. So far, performing the monotosylation reaction and, in particular, the purification steps was challenging, relied on toxic solvents, and resulted in long and expensive procedures at, importantly, low yields. Here, the reaction of cyclodextrin with p-toluenesulfonyl chloride in aqueous environment is described to obtain a highly pure mono-Ts-βCD, for which a single-step purification with a cation exchange resin was applied. With this synthetic route and purification, yields could be increased from typically 98 mol %. From mono-Ts-βCD, β-cyclodextrin dimers linked by ethylenediamine (bis-Et-βCD) were successfully prepared (yield 93%, purity 96 mol %) in a one-step approach using an anion exchange resin to trap leaving groups that typically interfere in the reaction. This synthesis procedure with a direct collection of side-products may be a general strategy applicable for nucleophilic substitution of tosylated cyclodextrins
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
Erste Ergebnisse der Mukosarekonstruktion im Tiermodell mittels eines neuartigen Formgedächtnispolymers
No full textHintergrund: Die Verfügbarkeit polymerer Biomaterialen, die hochspezifisch an anatomische, physiologische und chirurgische Anforderungen angepasst werden können, erfährt wachsende Bedeutung bei der Entwicklung neuer therapeutischer Optionen in verschiedenen Bereichen der Medizin. Bioabbaubare, stimuli-sensitive Implantatmaterialien haben dabei großes Anwendungspotenzial, insbesondere im Bereich der rekonstruktiven Chirurgie. Die Pharynxrekonstruktion mit einem polymeren Biomaterial wäre eine neuartige Therapieoption in der onkologischen Kopf-Halschirurgie, insbesondere wenn durch eine rasche und vollständige Integration des Materials in das umgebende Gewebe das Risiko einer Fistelbildung minimiert werden könnte.Material und Methoden: In dieser prospektiven Studie wurde ein kovalentes Polymernetzwerk zur Rekonstruktion eines im Durchmesser 10 mm großen durchgreifenden Gewebedefektes in die Magenwand von Sprague-Dawley Ratten implantiert. Durch die Implantation in die Magenwand sollten die chemische Stabilität und die Degradationseigenschaften des Copolymers unter extremen enzymatischen, chemischen und mechanischen Bedingungen untersucht werden. In der Kontrollgruppe wurde die Magenwand primär ohne Biomaterialimplantation verschlossen. Die Explantation erfolgte nach 1 Woche, 4 Wochen und 6 Monaten. Ein wichtiger klinischer Parameter war die Dichtigkeit zwischen dem implantierten Polymer und der umgebenden Magenwand.Ergebnisse: Der intra- und postoperative Verlauf war bei allen operierten Tieren (n=63) komplikationslos. Die Untersuchung der Dichtigkeit, eines Adhäsionsindexes und der mikrobiologischen Parameter ergab keine signifikanten Unterschiede zwischen der Polymer- und der Kontrollgruppe.Diskussion: Weitere Untersuchungen zur Biokompatibilität und -funktionalität sowie Methoden zur Oberflächenmodifizierung der Polymersystems zur Induktion der Angiogenese und einer Optimierung der Gewebeintegration sind derzeit Gegenstand aktueller Untersuchungen. In einem nächsten Schritt ist der Einsatz des polymeren Biomaterials zur Mukosarekonstruktion im Kopf-Halsbereich im Großtiermodell geplant.Fazit: Um die funktionellen Aspekte bei der Entwicklung neuartiger Therapieoptionen in der onkologischen Kopf-Halschirurgie adäquat zu berücksichtigen, sollte die Phoniatrie von Beginn an in das interdisziplinäre Forschungsprojekt eingebunden sein
Synthesis of Biomedical, Fluorescence-Labeled Polyesterurethanes for the Investigation of Their Degradation
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