1,720,985 research outputs found
Collagen/poly(ethylene glycol) diacrylate cryogels prepared by UV irradiation: tunable macroporous structures for tissue engineering applications.
No full textUV irradiation of acrylate-based precursors in water solutions is a fast and versatile method to obtain hydrogels with well-defined crosslink densities and mechanical properties, that show potential for cell encapsulation and tissue engineering. The formation of an interconnected, macroporous network within the hydrogel is fundamental to cell-material interactions and can be achieved by combining the UV crosslinking with several pore-forming strategies. In this work, macroporous poly(ethylene glycol) diacrylate (PEGDA)–based cryogels were synthesized by UV irradiation of frozen precursor solutions. PEGDA was chosen due to its peculiar non-fouling character, which allows the engineering of substrates with tunable bioactivity. In this regard, several cryogel formulations were prepared by adding different amounts of Type I collagen to the PEGDA solutions, with collagen providing extracellular matrix (ECM) mimicry. PEGDA solutions (700 Da, 10% w/v), containing VA-086 as a photoinitiator, were frozen under controlled freezing conditions (-20°C, with a freezing rate of -1°C/min) in a freeze-dryer (Virtis Advantage). After 1 hour at -20°C, the frozen samples were exposed to UV light (365 nm) for 3 minutes and finally swollen in distilled water for the removal of unreacted precursors. Cryogels containing collagen were synthesized as described above, by adding the appropriate amount of collagen (0.1 or 1% w/v) to the starting PEGDA solution. The gelation yield, the swelling ratio, the degradation rate and the mechanical properties of the cryogels were evaluated. Morphological analyses were also performed on both swollen and dry cryogels by means of fluorescence microscopy and/or micro-computed tomography, to analyse the effect of collagen on the cryogelation-induced porous structure. The experimental findings showed that the gelation yield was slightly increased for higher collagen concentrations, while the swelling ratio, the compressive elastic modulus of the cryogels and the weight loss after 28 days in PBS at 37°C seemed to be independent of the collagen amount. The morphological analysis demonstrated that a macroporous structure, with well-interconnected pores and robust pore walls, was formed for each cryogel formulation, and notably the pore size and pore size distribution were found to progressively decrease and get narrow as the collagen concentration was increased (Fig. 1). Preliminary cell seeding studies with 3T3 fibroblasts also showed the cytocompatibility of the developed cryogels, which thus hold promise for the development of 3D stiff microenvironments with tunable pore sizes, suitable for in vitro tissue engineering
Morphological and Mechanical Characterization of P-Scaffolds with Different Porosity
Get PDFThe aim of this paper is to model and to compare the results of the mechanical characterization, carried out on numerical models and real specimens, of uniform P-scaffolds with different porosity values. The analysis includes the morphological characterization of 3D printed specimens and the implementation of a FEM shell model to reproduce a compressive test suitable for mechanical properties evaluation of PLA scaffolds. Young modulus and yield strength were also obtained, in order to verify the numerical model accuracy, by experimental tests on 3D printed PLA scaffolds. Numerical results showed that the shell model was able to reproduce, more efficiently compared to a solid model proposed in a previous work, both elastic and plastic behavior of the scaffolds, providing elastic modulus values very close to the experimental ones. On the other hand, the not very high quality of the 3D printing, detected by MicroCT analysis, caused a significant dispersion in the yield strength numerical values respect to the real data. Anyway, an inverse correlation between mechanical properties and porosity was found as expected. The elastic modulus values were similar to the typical values of the trabecular bone for whose regeneration this kind of scaffolds is usually employed
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
A possible method to avoid skin effect in polymeric scaffold produced through thermally induced phase separation
Get PDFScaffold's morphology and in particular pore architecture is a key parameter for cell viability and tissue regeneration. Usually, morphology is managed through Thermally Induced Phase Separation (TIPS) consisting of controlled quenching and freeze-drying to remove ice crystals to create porosity. Nevertheless, the so-called skin effect, a less-/non-porous layer, usually occurring at scaffold's air–liquid or material-mold interface. Skin effect reduces scaffold's performance then the layer have to cut out with consequent loss of material and damage risks. Here, it is presented a possible method to avoid skin effect at mold-polymer interface in biopolymer-based scaffolds. It is based on producing scaffolds not directly in a mold but on a previously frozen distilled water surface. SEM analysis showed the absence of skinned surfaces and a uniform pore pattern in shape and size
Variations on the Author
Get PDF“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
Get PDFWe 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
Synthesis and characterization of macroporous poly(ethylene glycol)-based hydrogels for tissue engineering application
No full textPeptide activated poly(ethylene glycol) (PEG)-based hydrogels have received wide attention as material for tissue engineering application. However, the close structure of these materials may pose severe barriers to tissue invasion and nutrient transport. The aim of this work was to synthesize highly interconnected macroporous PEG hydrogels, suitable for use as tissue engineering scaffolds, by combining the photocrosslinking reaction with a foaming process. In particular, various porous samples, differing for both the polymer molecular weight and concentration in the starting precursor solution, have been prepared and characterized by means of scanning electron microscopy and mercury porosimetry. Moreover, water swelling properties have been evaluated and compared with those of the conventional nonporous ones, by performing both equilibrium and kinetic swelling measurements in distilled water. Results indicated that foamed hydrogels display a well-interconnected porous network, suitable for tissue invasion and free molecular trafficking within them. Pores dimension as well as swelling rate can be modulated by polymer concentrations and bubbling agent composition in the precursor solution
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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