1,721,118 research outputs found
Tailoring the surface of polymeric nanofibres generated by pressurized gyration
Full text linkPolymeric nanofibres with smooth, rough and porous surfaces were prepared by pressurised gyration, which is a novel method for producing nanofibres, utilising the combination of centrifugal spinning and solution blowing. A series of fibres were prepared by using polyacrylonitrile (Pan), poly(methyl methacrylate) (PMMA) and 50:50 Pan–PMMA polymer solutions without pressure and with 0·2 MPa working pressure. The surface morphology of the nanofibres was analysed by scanning electron microscopy, and their thermal properties were studied by thermogravimetry and hot-stage microscopy. Nanofibres with a smooth surface were generated at 0·2 MPa working pressure, and those with a rough surface were generated without any working pressure. Porous Pan nanofibres were prepared by using PMMA as a sacrificial polymer. The 50:50 Pan–PMMA blend fibres were subjected to heat treatment to obtain porous fibres. The less thermally stable PMMA decomposes when heated, generating pores on the surface of the Pan fibres. The porous nanofibres have a higher surface area-to-volume ratio compared to smooth fibres, and these fibres could be useful in a variety of applications, such as tissue engineering, filtering and purification
The Tailored Production of Small Diameter Fibres and Their Applications in Wound Healing
Full text linkThinner fibres benefit from a high surface area to volume ratio which is valuable in many biomedical applications ranging from tissue engineering to drug delivery and wound healing. Fibre forming technologies such as electrospinning and pressurised gyration rely on the careful manipulation of solution properties as well as working parameters to obtain the most optimal fibre morphology for their intended applications. In deeply understanding how these fibre manufacturing technologies work, there can be highly optimised and tailored production of polymeric biomaterials.
Natural substances represent a class of materials that fail to be forgotten for use in health-related applications. Honey and cinnamon have gained significant interest not only for their physical and chemical properties but also for their antibacterial activity. Manuka Honey UMF 20+ was examined for its antibacterial properties against Escherichia coli and Staphylococcus epidermidis using flow cytometry where the active agent is thought to be the high methylglyoxal content. The inhibitory effect of manuka honey on bacterial growth was evident at concentrations ranging from 10 to 30 v/v%, where higher concentrations benefited from additional honey loading. The incorporation of Manuka honey as an antibacterial agent was explored as a potential route for manufacturing wound dressing components. Using pressurised gyration, scaffolds of sub-micrometre fibres were formed from 10, 20 and 30 v/v% Manuka honey which were incorporated into the polycaprolactone polymer solutions. The composite fibres were analysed for their morphology and topography using scanning electron microscopy. The average fibre diameter of the Manuka honey-polycaprolactone scaffolds was found to be in the range of 437 to 815 nm. The antibacterial activity of the most potent 30 v/v% scaffolds was studied against S. epidermidis. The scaffolds showed strong antibacterial activity with a bacterial reduction rate of over 90%. The results here show that honey composite fibres can be considered a natural therapeutic agent for wound healing applications.
Fibrous bandage-like constructs made with incorporated cinnamon extract have been previously shown to have potent antifungal abilities which surpass even the raw material itself. The question remains as to whether these constructs are useful in the prevention of bacterial infections and what the antimicrobial effect means in terms of toxicity to native physiological cells. In this work cinnamon-extracted fibres are tested against Staphylococcus epidermidis to assess their antibacterial capacity; it was found that the fibres were able to successfully kill the bacteria. The constructs were also tested under indirect MTT cytotoxicity tests involving the L929 mouse fibroblast cell line, where they showed no variation from the control groups in terms of toxicity. Additionally, cell viability imaging showed no significant toxicity issues with the fibres, even at their tested highest concentration. Here I present a viable method to produce wound healing products made from non-toxic and abundant naturally occurring materials such as cinnamon.
Two fibre forming techniques, pressurised gyration and electrospinning have been combined to create a manufacturing process where advanced wound healing bandages can be created. This new hybrid process leverages the rapid production rate of pressurised gyration to create the bulk portion of the bandages and exploits the precise nature of electrospinning to directly print a bioactive fibrous patch onto the active site of the bandages. Polycaprolactone bandages have thus been created which have a bioactive patch consisting of collagen and chitosan with a poly(ethylene oxide) support. The patches have an average fibre diameter of 173 ± 27 nm and closely resemble the extracellular matrix in its structure, together with the active collagen and chitosan, this will be crucial in their ability to facilitate advanced wound healing. Additionally, synthetic materials such as antimicrobial nanoparticles can be added to the patches which demonstrate that the manufacturing technique is not limited to only using natural materials. Patches with these nanoparticles had an average fibre diameter of 142 ± 31 nm and demonstrated that very uniform and thin fibres could be created with these materials. The process has a great degree of automation and has potential for industrial scalability.
The advancement of manufacturing processes needs to be supported by the discovery of novel materials and novel combinations of existing materials. Graphene possesses many properties that have predominately been investigated for commercial applications. For the first time, porous graphene (PG) has been incorporated into polymer matrices produced by a high-output manufacturing process. Graphene and its other derivates such as graphene oxide have been shown to provide an antibacterial surface that can mechanically kill pathogens that encounter it. For this reason, graphene nanopores presents itself as a viable additive for wound healing materials. This overarching work focuses on the production of small diameter fibres via multiple techniques to achieve the most control over the final fibre morphology for uses in advanced wound healing materials
Experimental and theoretical investigation of the fluid behavior during polymeric fiber formation with and without pressure
Full text linkThe fabrication of polymeric micro/nanofibers is gaining attention due to their use in an array of applications including tissue engineering scaffolds, nanosensors, and fiber-reinforced composites. Despite their versatile nature, polymeric fibers are widely underutilized due to the lack of reliable, large-scale production techniques. Upon the discovery of centrifugal spinning and, recently, pressurized gyration techniques, new research directions have emerged. Here, we report a comprehensive study detailing the optimal conditions to significantly improve the morphology, homogeneity, and yield of fibers of varying diameters. A series of polymeric fibers was created using a 21 wt.% solution of polyethylene oxide in distilled water and the fluid behavior was monitored inside a transparent reservoir using a high-speed camera. Fabrication of the fibers took less than 1 s. Using centrifugal spinning, we studied the formation of the fibers at three different rotational speeds, and for pressurized gyration, one rotational speed was studied with three different nitrogen gas pressures. Using the pressurized gyration technique at a gas pressure of 0.3 MPa, there was significant improvement in the production yield of the fibers. We found a strong correlation between the variation of pressure and the rate of the solution leaving the reservoir with the improved morphology of the fibers. The use of reduced power techniques, like centrifugal spinning and pressured gyration, to yield high-quality nonwoven nanofibers and microfibers in large quantities is important due to their use in rapidly expanding markets. (C) 2019 Author(s)
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
Core-sheath polymer nanofiber formation by the simultaneous application of rotation and pressure in a novel purpose-designed vessel
No full textForming polymeric core-sheath nanofibers is gaining prominence owing to their numerous potential applications, most notably in functional scenarios such as antiviral filtration, which is attracting significant attention due to the current COVID pandemic. This study has successfully designed and constructed a novel pressurized gyration vessel to fabricate core-sheath polymer nanofibers. Several water-soluble and water-insoluble polymer combinations are investigated. Both polyethylene oxide and polyvinyl alcohol were used as the core while both poly(lactic acid) (PLA) and poly(caprolactone) (PCL) were used as the sheath; PLA and PCL were used as core and sheath, in different instances; respectively. The fluid behavior of the core-sheath within the vessel was studied with and without applied pressure using computational fluid dynamics to simulate the core-sheath flow within the chamber. A high-speed camera was used to observe the behavior of jetted solutions at core-sheath openings, and the best scenario was achieved using 6000 rpm spinning speed with 0.2 MPa (twice atmospheric) applied pressure. The surface morphology of core-sheath fibers was studied using a scanning electron microscope, and focused ion beam milling assisted scanning electron microscopy was used to investigate the cross-sectional features of the produced fibers. Laser confocal scanning microscopy was also used to verify the core-sheath structure of the fibers, which were further characterized by Fourier transform infrared spectroscopy and differential scanning calorimetry. Thus, using a variety of polymer combinations, we show, both theoretically and experimentally, how core-sheath fibers evolve in a vessel that can serve as a scalable manufacturing pressurized gyration production process
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
A novel reusable anti-COVID-19 transparent face respirator with optimized airflow
No full textThis novel face mask is designed to be a reusable respirator with a small and highly efficient disposable fabric filter. Respirator material requirements are reduced by 75% compared to traditional designs and allow repeated cleaning or sterilization. The probability of virus particle inhalation is reduced using novel air filtration pathways, through square-waveform design to increase filter airflow. Air enters the mask from right and left side filters, while the area in front of the mouth is isolated. Clear epoxy is used for a transparent frame, allowing lip-reading, and mask edges contain a silicone seal preventing bypass of the filters. The mask is manufactured using silicone molds, eliminating electricity requirements making it economical and viable in developing countries. Computational fluid dynamics numerical studies and Fluent ANSYS software were used to simulate airflow through the filter to optimize filter air path geometry and validate mask design with realistic human requirements. The breathing cycle was represented as a transient function, and N95 filter specifications were selected as a porous medium. The novel design achieved 1.2 x 10(-3)kg s(-1), 20% higher than human requirements, with air streamlines velocity indicating local high speed, forcing and trapping virus particles against filter walls through centrifugal forces
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
- …
