1,720,973 research outputs found
Sustainable 3D Scaffolds Based on β-Chitin and Collagen I for Wound Dressing Applications
No full textThe development of greener substitutes for plastics is gaining massive importance in today’s society. This also involves the medical field, where disposable materials are used to grant sterility. Here, a novel protocol using only a water-based solvent for the preparation of bio-based composite foams of actual β-chitin and collagen type I is presented. The influence of the ratio of this chitin polymorph to the collagen on the final material is then studied. The samples with 50:50 and 75:25 ratios produce promising results, such as remarkable water absorption (up to 7000 wt.%), exposed surface (up to 7 m2·g−1), and total pore volume (over 80 vol.%). The materials are also tested using wet mechanical compression, exhibiting a Young’s modulus and tenacity (both calculated between 2% and 25% of deformation) of up to 20 Pa and 9 kPa, respectively. Fibroblasts, keratinocytes, and osteoblasts are grown on these scaffolds. The viability of fibroblasts and keratinocytes is observed for 72 h, whereas the viability of osteoblasts is observed for up to 21 days. Under the two conditions mentioned, cell activity and adhesion work even better than under its counterpart condition of pure collagen. In conclusion, these materials are promising candidates for sustainable regenerative medicine scaffolds or, specifically, as biodegradable wound dressings
Tunable Oxidized-Chitin Hydrogels with Customizable Mechanical Properties by Metal or Hydrogen Ion Exposure
Full text linkThis study focuses on the optimization of chitin oxidation in C6 to carboxylic acid and its use to obtain a hydrogel with tunable resistance. After the optimization, water-soluble crystalline β-chitin fibrils (β-chitOx) with a degree of functionalization of 10% were obtained. Diverse reaction conditions were also tested for α-chitin, which showed a lower reactivity and a slower reaction kinetic. After that, a set of hydrogels was synthesized from β-chitOx 1 wt.% at pH 9, inducing the gelation
by sonication. These hydrogels were exposed to different environments, such as different amounts of Ca2+, Na+ or Mg2+ solutions, buffered environments such as pH 9, PBS, pH 5, and pH 1, and pure water. These hydrogels were characterized using rheology, XRPD, SEM, and FT-IR. The notable feature of these hydrogels is their ability to be strengthened through cation chelation, being metal
cations or hydrogen ions, with a five- to tenfold increase in their storage modulus (G’). The ions were theorized to alter the hydrogen-bonding network of the polymer and intercalate in chitin’s crystal structure along the a-axis. On the other hand, the hydrogel dissolved at pH 9 and pure water. These bio-based tunable hydrogels represent an intriguing material suitable for biomedical applications
Synthesis and manufacturing of customizable β-chitin materials from sea food waste
No full textThis thesis explores the valorization of β-chitin, one of the three polymorphic forms of chitin, the second most abundant biopolymer on earth after cellulose. Despite its abundance, β-chitin remains underutilized due to challenges like poor solubility and handling. Derived primarily from squid pens, β-chitin offers advantages over α-chitin, such as higher reactivity and flexibility. The study developed innovative β-chitin-based materials through chemical and physical approaches. Oxidation with ammonium persulfate introduced carboxylic groups at the C6 position, significantly enhancing water solubility and enabling diverse applications. These included hydrogels with tunable mechanical properties at pH 1, 5, and 7.4, and in the presence of ions such as Ca²⁺, Na⁺, and Mg²⁺; chitin-chitosan composite films with improved stability in acidic environments; and encapsulation carriers for carotenoids that preserved their antioxidant activity through digestion. Additionally, physical methods were employed to create β-chitin foams with thermal insulation properties comparable to expanded polystyrene (EPS). Customizable foams with water-repellent and cushioning properties were achieved, expanding potential applications. The final chapter explored the amorphization and re-crystallization of β-chitin, successfully avoiding transformation into the thermodynamically stable α-polymorph through metal-ion treatments. This research underscores the potential of β-chitin as a sustainable and versatile resource for creating customizable materials. By leveraging waste-derived resources and integrating chemical and physical strategies, this study expands the practical applications of this underutilized biopolymer
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
Hierarchically organized chitin-based matrices
Full text linkChitin is the second most abundant biopolymer on Earth and the most diffused across the known species, being present in more than 70 % of them. It is present in a huge variety of different structures and morphologies being a massive pool of information for new material science approach. This thesis aims to study chitin at different level of organization using diverse approaches. Three main topics are discussed in this manuscript. The first is the use of a bottom-up approach to study chitin nanofibrils self-assembly in water triggering the assembly by pH increment. Successively, the assembly was studied in presence of another pH responsive biomacromolecule, the collagen, to get new composite materials and study how the assembly and the chitin/collagen ratio influence fibroblast’s viability. The second topic focuses on biogenic organized chitin-based matrices, in both Ariolimax californicus and Loligo vulgaris. This study aims to understand the features that give raise to the properties of those matrices. Finally, in the last section a top-up approach was used to exploit natural hierarchically organized chitinous matrices to obtain organized functional materials introducing a catechol on the free amino group of deacetylated chitin (DA 77 %). In conclusion, this study of chitin at different level of organization emphasized different novelties depending on the organization level studied. Moreover, this thesis gives many possibilities for future bioinspired routes to get highly organized materials, or for highly organized functional materials based on natural chitin-based matrices
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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