1,721,033 research outputs found
Highly ordered and tunable polyHIPEs by using microfluidics
No full textWe demonstrate how to generate highly ordered porous matrices from dextran-methacrylate (DEX-MA) using microfluidics. We use a flow focusing device to inject an aqueous solution of DEX-MA and surfactant to break the flow of an organic solvent (cyclohexane) into monodisperse droplets at a high volume fraction (above 74% v/v) to form an ordered high internal phase emulsion (HIPE). We collect the crystalline HIPE structure and freeze it by gelling. The resulting polyHIPEs are characterized by an interconnected and ordered morphology. The size of pores and interconnects ranges between hundreds and tens of micrometers, respectively. The technique that we describe allows for precise tuning of all the structural parameters of the matrices, including their porosity, the size of the pores and the lumen of interconnects between the pores. The resulting ordered and precisely tailored HIPE gels represent a new class of scaffolds for applications in tissue engineering.We demonstrate how to generate highly ordered porous matrices from dextran-methacrylate (DEX-MA) using microfluidics. We use a flow focusing device to inject an aqueous solution of DEX-MA and surfactant
to break the flow of an organic solvent (Cycle-Hexane) into monodisperse droplets at high volume fraction (above 74% v/v) to form an ordered high internal phase emulsion (HIPE). We collect the crystalline HIPE structure and freeze it by gelling. The resulting polyHIPEs are characterized by an interconnected and ordered morphology. The size of pores and interconnects ranges between hundreds and tens micrometers, respectively. The technique that we describe allows for precise tuning of all the structural parameters of the matrices, including their porosity, the size of the pores and the lumens of interconnects between the pores. The resulting ordered and precisely tailored HIPE gels represent a new
class of scaffolds for applications in tissue engineering
Highly Tailorable and Monodisperse Porous Beads via Microfluidics
No full textIn tissue engineering practice, a scaffold is often needed to deliver cells to the desired body site needing to be repaired. Scaffolds supporting cells can be either implanted through a surgical operation or injected through a laparoscopic device. The latter option is a first-choice in cases where a small and irregularly shaped defect needs to be regenerated. In such circumstances, the cell carrier has to be miniaturised while maintaining the morphological features that make a scaffold an efficient cell culture support, i.e. a uniform and adequate porous texture in terms of pore and interconnect dimensions. In this work, we illustrate a novel and powerful method for the manufacturing of monodisperse porous beads of tailorable dimension (in the range ~ 300÷1500 m) and with an internal porous texture characterised by uniformly sized and fully interconnected pores. The fabrication method relies on the use of a flow-focusing microfluidic chip that generates a monodisperse oil-in-water emulsion (panel b). The aqueous phase of the emulsion contains a biopolymer and an appropriate surfactant. Here, we demonstrate that by extruding the emulsion through a needle immersed in a perfluorinated oil on top of which a coagulating aqueous bath is stratified and by applying a pulsed electrical field (panel a), it is possible to precisely control the size of the emulsion droplets detached from the needle. As soon as the emulsion droplets reach the interface between the perfluorinated oil and coagulating bath, they instantaneously solidify. An inverse relationship exist between intensity of the applied voltage and beads dimension (panels c,d,e). The presented process is very repeatable and brings about to beads rigorously monodisperse in size (panel f). Finally, such microbeads demonstrated to be a successful cell carrier.In tissue engineering practice, a scaffold is often needed to deliver cells to the desired body site needing to be repaired. Scaffolds supporting cells can be either implanted through a surgical operation or injected through a laparoscopic device. The latter option is a first-choice in cases where a small and irregularly shaped defect needs to be regenerated. In such circumstances, the cell carrier has to be miniaturised while maintaining the morphological features that make a scaffold an efficient cell culture support, i.e. a uniform and adequate porous texture in terms of pore and interconnect dimensions. In this work, we illustrate a novel and powerful method for the manufacturing of monodisperse porous beads of tailorable dimension (in the range ~ 300÷1500 m) and with an internal porous texture characterised by uniformly sized and fully interconnected pores. The fabrication method relies on the use of a flow-focusing microfluidic chip that generates a monodisperse oil-in-water emulsion (panel b). The aqueous phase of the emulsion contains a biopolymer and an appropriate surfactant. Here, we demonstrate that by extruding the emulsion through a needle immersed in a perfluorinated oil on top of which a coagulating aqueous bath is stratified and by applying a pulsed electrical field (panel a), it is possible to precisely control the size of the emulsion droplets detached from the needle. As soon as the emulsion droplets reach the interface between the perfluorinated oil and coagulating bath, they instantaneously solidify. An inverse relationship exist between intensity of the applied voltage and beads dimension (panels c,d,e). The presented process is very repeatable and brings about to beads rigorously monodisperse in size (panel f). Finally, such microbeads demonstrated to be a successful cell carrier
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
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