1,720,961 research outputs found
Functionalized nanostructured chitosan-based devices for peripheral nerve regeneration
No full textPeripheral nerve injuries (PNIs) are a common global issue lacking definitive treatments. Regenerative medicine introduces promising methods to bridge nerve gaps, with a strong focus on biocompatible, biodegradable, and mechanically compliant materials. Chitosan, an FDA-approved biopolymer, stands out for its biocompatibility and biodegradability. Its regenerative potential improves with nano/micro-structuring, which guides cells through biomimetic topographical signals, and blending with other materials enhances its mechanical compatibility with host tissues.This thesis focuses on developing chitosan-based scaffolds for peripheral nerve regeneration. A method to create micro-structured chitosan films with reproducible patterns was designed, producing three directional micro-grooved patterns: gratings (GR), isosceles triangles (ISO), and scalene triangles (SCA). These structured films were tested in vitro with Schwann cells, showing variations in cell migration across the patterns.To address chitosan’s rigidity, soft chitosan membranes were created using glycerol as a bioplasticizer, reducing stiffness and enhancing suitability for clinical use. My work revealed that membrane flexibility and surface structures influence neural cell responses, with softer, micro-structured membranes leading to improved cell behavior compared to stiffer versions.Further evaluations employed an in vitro nerve model with primary Schwann cells and nociceptive neurons, developed in collaboration with the MERLN Institute (University of Maastricht) to study the effects of micro-structured glycerol-chitosan membranes. Additionally, these membranes were tested ex vivo with dorsal root ganglia (DRGs) from rats and in vivo in a cavernous nerve injury model in collaboration with the University of Turin.Finally, to develop even smaller features, glycerol-plasticized chitosan nanofibers were developed and characterized, demonstrating promising potential for use in nerve regeneration applications.In summary, this thesis highlights chitosan’s potential for peripheral nerve repair, showcasing its micro and nanostructurability, biocompatibility, and suitability in supporting nerve regeneration. This research demonstrates chitosan’s capacity to advance regenerative medicine, offering valuable biomaterials for peripheral nerve injury treatment
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
Chitosan Micro-Grooved Membranes with Increased Asymmetry for the Improvement of the Schwann Cell Response in Nerve Regeneration
Full text linkPeripheral nerve injuries are a common condition in which a nerve is damaged, affecting more than one million people every year. There are still no efficient therapeutic treatments for these injuries. Artificial scaffolds can offer new opportunities for nerve regeneration applications; in this framework, chitosan is emerging as a promising biomaterial. Here, we set up a simple and effective method for the production of micro-structured chitosan films by solvent casting, with high fidelity in the micro-pattern reproducibility. Three types of chitosan directional micro-grooved patterns, presenting different levels of symmetricity, were developed for application in nerve regenerative medicine: gratings (GR), isosceles triangles (ISO) and scalene triangles (SCA). The directional patterns were tested with a Schwann cell line. The most asymmetric topography (SCA), although it polarized the cell shaping less efficiently, promoted higher cell proliferation and a faster cell migration, both individually and collectively, with a higher directional persistence of motion. Overall, the use of micro-structured asymmetrical directional topographies may be exploited to enhance the nerve regeneration process mediated by chitosan scaffolds
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
Development and testing of chitosan micro-structured substrates for nerve regeneration
No full textPeripheral nerve injuries are a common type of injury around the world, affecting more than 1 million people every year. Even though the intrinsic capacity of regeneration of the peripheral nervous system (PNS), the effective repair depends on the extent of the cut and the distance between the two ends of the nerve. In response to nerve injury, the Schwann cells undergo rapid changes in their phenotype, proliferate and migrate and provide a “pathway” (i.e. the Bungner bands) for the following axonal regrowth. This is a critical process for nerve regeneration.
Nowadays there are still no efficient therapeutic treatments for this kind of condition and nerve grafts remain the gold standard in clinics. Recently, the use of hollow nerve guidance conduits has started. Chitosan, a chitin derived polymer, is a good biomaterial for tissue engineering applications and, in fact, basic plain chitosan nerve conduits have been approved for clinical use in Europe.
In our body, cells can perceive physico-mechanical stimuli around them, and regulate their morphology, behaviour and fate in response to these stimuli. This process is generally referred to as mechanotransduction, where integrin receptors and focal adhesion pathway are the major molecular players. Several studies in vitro have demonstrated that neural cells cultured on nano/micro-structured substrates, such as directional gratings (GRs), respond to them, modifying their morphology and migration behaviour.
The ability of anisotropic substrates to tune neural cells can be useful in the PNS regeneration framework, as devices patterned with directional micro-topographies could be used to orientate cells in the right direction and to achieve a more rapid and effective repair of the injured nerve. In this sense, patterning the inner part of hollow nerve guidance conduits can be an optimal way to enhance the effectiveness of these devices.
In this thesis, chitosan based micro-structured substrates are produced and tested in vitro, with the aim to develop improved scaffolds for peripheral nerve regeneration.
Here, we developed micro-structured substrates, made of chitosan, an FDA approved and biodegradable material, and enhanced with topography modifications, at micrometer level. We used three types of anisotropic patterns, presenting different levels of symmetricity: gratings (GRs), isosceles triangles (ISO) and scalene triangles (SCA), with a Flat surface as control. Line dimensions were 4 µm in width and 370 nm in depth. We developed an improved solvent casting method for the micro-structured chitosan films production. Moreover, we characterized their water absorption capacity and topography stability, showing overall good reproducibility levels for the procedure.
The chitosan directional topographies were then tested in vitro with the RT4-D6P2T-GFP glial Schwann cells (a Schwannoma cell line). In general, the topographical modifications of the chitosan showed to improve Schwann cell adhesion and proliferation. We performed wound healing experiments (i.e. collective migration), in which cells showed an increased capacity to collectively migrate on the SCA pattern. Furthermore, cytoskeleton organization and cell-cell junctions were evaluated via immunostaining for actin fibres and N-cadherin.
In general, we set up an improved method for the production of micro-structured chitosan films by solvent casting, with considerably reduced costs in term of time and materials used in the process and high fidelity in micro pattern reproducibility. In addition, films resulted more durable and their manipulation in the further biological experiments resulted easier.
The cell experiments showed the impact of the directional patterns on the Schwann cells, showing that the directional asymmetric topographies (ISO and SCA) promote a faster migration of cells, both singularly and collectively. This effect was particularly enhanced on SCA patterns.
In conclusion, the use of micro-structured directional topographies, such as SCA, may be exploited to enhance the nerve regeneration process mediated by chitosan scaffolds
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