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Structural study on methacrylamide-grafted Tussah silk fibroin fibres
No full textTussah silk fibroin fibres were modified by grafting with methacrylamide (MAA), with weight gains ranging between 2.6% and 71.4%. Raman and IR spectroscopic analyses showed that upon grafting the fibres underwent slight conformational changes towards a more unordered state, due to the covalent and hydrogen bonds interactions occurring between the polymer (polyMAA) and the amorphous domains of silk fibres. To test the stability towards alkaline hydrolysis, the untreated and MAA-grafted silk fibres (weight gain of 71.4%) were immersed in NaOH 5% at 50 °C for different times; the IR and Raman spectroscopic techniques were utilized to elucidate the degradation mechanism as well as the rearrangements of the fibres induced by the treatment. Upon hydrolysis, both the untreated and grafted fibres underwent an enrichment in β-sheet conformation, due to the preferential removal of the unordered domains. As a result of the covalent interactions with silk fibroin, the polymer increased its stability towards alkaline hydrolysis, since its complete solubilization was avoided and the transformation of its CONH2 groups into COO- and COOH was delayed. Vibrational spectroscopy proved to be a valid technique to investigate the mechanism and the effects of the hydrolytic attack, which are both fundamental to design new-generation silk-based materials
Intermolecular interactions between B. mori silk fibroin and poly(L-lactic acid) in electrospun composite nanofibrous scaffolds
Full text linkIn this study, composite nanofibrous scaffolds were obtained by electrospinning a trifluoroacetic acid solution containing B. mori silk fibroin (SF) and poly(L-lactic acid) (PLLA) in a 1:1 weight ratio. SF, PLLA and SF/PLLA nanofibres were prepared with average diameter sizes of 360 ± 90 nm, 470 ± 240 nm and 580 ± 220 nm, respectively, as assessed by SEM analysis. Vibrational and thermal analyses showed that upon blending in the SF/PLLA nanofibres, the crystallisation of PLLA was hindered by the presence of SF, which crystallized preferentially and underwent conformational changes that did not significantly change its prevailing β-sheet structure. The two components were thermodynamically compatible and the intermolecular interactions between them were revealed for the first time. Human keratinocytes were cultured on nanofibres and their viability and proliferation were determined. Preliminary in vitro tests showed that the incorporation of SF into the PLLA component enhanced cell adhesion and proliferation with respect to the unfunctionalised material. SF has been successfully used to modify the biomaterial properties and confirmed to be an efficient bioactive protein to mediate cell-biomaterial interaction
Intermolecular interactions between B. mori silk fibroin and poly(L-lactic acid) in electrospun composite nanofibrous scaffolds
No full textStability toward alkaline hydrolysis of B. mori silk fibroin grafted with methacrylamide
No full textBombyx mori silk fibroin fibers were grafted with methacrylamide (MAA) and characterized by Raman and infrared (IR) vibrational spectroscopy before and after hydrolysis in NaOH 5% to elucidate the possible interactions between the two components and the stability of the fibers toward alkaline hydrolysis. Upon grafting, the fibers underwent conformational rearrangements toward a more unordered state and lost orientation at weight gains higher than 60%. Vibrational spectroscopy disclosed the occurrence of intermolecular interactions (mainly hydrogen bonds) between B. mori silk fibroin and polyMAA in the grafted fibers, and the formation of covalent bonds has been explored. These strong interactions made the grafted fibers as a whole more stable toward alkaline hydrolysis because they prevented the solubilization of the polymer upon hydrolysis and made slower the transformation of its CONH2 groups into COOH and COO− groups. Upon hydrolysis, silk fibroin underwent an enrichment in the β-sheet crystalline domains, because of the preferential removal of the unordered domains, which were more prone to the OH− attack. IR and Raman spectroscopy proved valid techniques to investigate the degradation mechanism and kinetics of grafted silk fibroin fibers and so for designing high-performing silk-based materials. The A731/A1004 Raman intensity ratio was proposed to spectroscopically evaluate the composition of the grafted samples; its value was found to linearly increase with weight gain (R2 = 0.998), envisaging the possibility of using Raman spectroscopy as a routine analytical technique for qualitative and quantitative characterization of grafted industrial samples. Copyright © 2016 John Wiley & Sons, Ltd
Influence of grafting with acrylate compounds on the conformational rearrangements of silk fibroin upon electrospinning and treatment with aqueous methanol
No full textSilk fabrics from Bombyx mori silkworm were grafted with 2-hydroxyethyl methacrylate (HEMA) as well as a binary system of HEMA and 4-hydroxybutyl acrylate (HBA) and then analysed by Raman and infrared (IR) spectroscopy to elucidate the interactions between the components and their possible conformational changes. The samples were then dissolved in trifluoroacetic acid and electrospun; the influence of the grafted polymers on the silk fibroin rearrangements upon these treatments was investigated by vibrational spectroscopy. Upon grafting, the fabrics underwent conformational rearrangements towards a more unordered state, although they kept their prevailing β-sheet conformation; also the polymeric component underwent hydrogen bonding and backbone rearrangements upon interaction with silk fibroin and the occurrence of strong covalent bonds cannot be excluded. By immersing the as-electrospun grafted and pure fibroin nanofibres (prevalently unordered) in aqueous methanol, they partially recovered the β-sheet content observed in the corresponding starting fabrics; the percentage of recovery decreased along the series: pure silk > HEMA-grafted silk > HEMA and HBA-grafted silk. This trend suggests that the presence of the polyHEMA grafted component hinders the silk fibroin recrystallization into β-sheet upon aqueous methanol treatment; moreover, the addition of the more sterically hindered HBA monomer in the grafting system further prevented this process. Copyright © 2016 John Wiley & Sons, Ltd
Silk fibres grafted with 2-hydroxyethyl methacrylate (HEMA) and 4-hydroxybutyl acrylate (HBA) for biomedical applications
Full text linkSilk fibroin may be chemically modified by grafting, with the purpose of improving its properties according to the desired function. In this study, silk fabrics from Bombyx mori silk fibres were grafted with 2-hydroxyethyl methacrylate (HEMA), as well as a binary mixture of HEMA and 4-hydroxybutyl acrylate (HBA). The samples were then electrospun from trifluoroacetic acid and treated with aqueous methanol. The% weight gains ascribable to HEMA and HBA were successfully determined through Raman spectroscopy. PolyHEMA made the fibres more hydrophilic and hindered crystallization into Î2-sheet only upon electrospinning and treatment with aqueous methanol; the presence of the HBA component in the grafting mixture did not further decrease the ability of silk fibroin to rearrange into Î2-sheet, due to its low contents (below 5%) under the used experimental conditions. Fibrillation partially occurred in the grafted fabrics; the electrospun samples maintained their nanostructured morphology. The surface of the substrates under investigation was compatible with cell attachment and growth, which were higher for the nanofibres. Cell adhesion and proliferation may be modulated by varying the surface chemistry and topography of the fabrics; grafting improved the surface properties of silk fibroin for enhanced functional performance in view of biomedical applications
GRAFTED SILK AND WOOL FABRICS WITH ENHANCED BIOACTIVITY
No full textSilk fibres have been used for centuries as suture materials. They have been considered functional biomaterials in the last decades, mainly as scaffolds for tissue engineering[1]. In this framework, silk fabrics from two different origin silkworms (one from Bombyx mori of Bombycidae and another from Antheraea yamamai (Tussah) of Saturniidae) were grafted with two monomers having phosphoric groups, i.e. phosmer M (2-phosphonooxyethyl 2-methylprop-2-enoate) and phosmer CL ((3-chloro-2-phosphonooxypropyl) 2-methylprop-2-enoate) at different concentrations. Our study aimed to evaluate the bioactivity of the fabrics, i.e. the ability to enucleate a calcium phosphate phase after immersion in Simulated Body Fluid solution (SBF). The same grafting was also applied to wool fabrics. Both phosmers were successfully studied as flame retarding agents[2] for silk fabrics, and their chemical composition suggested a possible application in the biomedical field.
IR and Raman spectroscopy were applied to study the degree of grafting and its influence on the structure and conformation of silk fibroins and wool keratins. The same techniques were used to characterize the fabrics after seven days of incubation in SBF at 37 °C to study possible structural variations and the enucleation of a calcium phosphate phase: interestingly, all samples showed to be bioactive.
The most bioactive samples contained the highest phosmers amounts, and, generally, the samples grafted with phosmer M appeared more bioactive. The IR technique, which is more sensitive to surface modifications, allowed a semiquantitative evaluation of calcium phosphate deposition but showed a certain inhomogeneity of the inorganic phase.
Although all samples enucleated a calcium phosphate phase, only some of them exhibited a mass increase (Bombyx mori: 0.4-8.5%; Tussah: 0.8-4%, wool: 0.4-3,5%), maybe because of the release of weakly bounded phosmers into the medium: therefore the mass of the newly formed calcium phosphate phase could be underestimated. Raman spectroscopy further confirmed these findings and evidenced that the inorganic deposit did not affect the structure of silk fibroins and wool keratins.
Long-lasting bioactivity testing in vitro is still in progress, together with cell adhesion and proliferation essays that would eventually confirm the improvement of silk and wool surfaces for future biomedical applications
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
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