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PLGA Copolymerization Kinetic Parameter Estimation with Stochastic Modeling
Get PDFKinetic parameters for the reversible copolymerization of poly(lactide-co-glycolide) (PLGA) provide insight into the resulting sequence, which can affect the performance of PLGA in some pharmaceutical applications such as long-acting implants. The effects of synthesis conditions on kinetic parameters and resulting sequences for PLGA have not yet been fully studied. Because existing reactivity ratio models such as Meyer-Lowry or Beckingham-Sanoja-Lynd are insufficient for copolymerization reactions which include reversibility and transesterification, and complete deterministic descriptions of reversible copolymerization are impractical, a stochastic model was used to determine kinetic parameters from experimental data collected using Fourier-transform infrared (FTIR) spectroscopy. The effect of temperature and reaction volume on rate constants and reactivity ratios were investigated. Preliminary results reveal that individual rate constants increase with increasing temperature. No clear trend was observed for reaction volume. Neither temperature nor reaction volume clearly impacted reactivity ratios. Average reactivity ratios across all experiments were r_G=3.93, r_L=0.23. More iterations of fitting need to be carried out, and experiments need to be repeated for better accuracy. These results are significant because it allows a better understanding of the various reactions during PLGA copolymerization, and the method itself can be modified to determine kinetic parameters for other complex copolymers.Chemical Engineerin
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Carboxylate-functional Poly(methyl glycidyl sulfoxide) Synthesis and Applications in Cryopreservation
Get PDFCryopreservation enables the possibilities of biological and medical applications such as
organ/blood transplant, in vitro fertilization, endangered plant tissues, animal oocytes and
semen preservation. However, it is also a practice facing many challenges such as ice
nucleation and recrystallization upon thawing and the cytotoxicity nature of
cryoprotectants that negatively impact the vitality of cells. Of all cryoprotective agents,
polymers are historically proven to be one of the most versatile and advantageous
materials due to their high molecular weight. In this study, a carboxylate-functional poly
(methyl glycidyl sulfoxide) (PMGS) was synthesized and studied, aiming to lower the
cytotoxicity. However, post-thaw cell metabolic activity of 20% and 30% carboxylate
content anionic-functional PMGS is very similar to that of the regular PMGS, at 30%
relative cell activity. Furthermore, ice nucleation was studied by designing a water-in-oil
emulsion to eliminate the effect of impurities acting like ice nucleating agent (INA) and
achieve near homogenous ice nucleation in cryopreservation. The images acquired on
the optical microscope were analyzed in combination with the w/o emulsion design to
provide a foundation for the most optimal testing environment of a new polymeric
cryoprotectant.Chemical Engineerin
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
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
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Membrane selectivity and fouling : insights from advanced characterization techniques
Get PDFMembrane-based separations have emerged as efficient and low-cost methods for the treatment of complex wastewater streams. The efficient and effective use of membranes relies on their selectivity and resistance to fouling. The selectivity of porous membranes is typically characterized using solute rejection tests, where membranes are challenged with dilute aqueous solutions of neutral solutes. Since single solute methods are time-intensive, mixed solute tests have become more common. In this work, mixed solute filtration experiments showcased the presence of co-solute interactions, which increase with size and weight percent of large solutes in the mixture. Mixed solute filtration experiments at varying operating conditions were conducted to determine operating conditions that alleviate co-solute interactions. Low flux conditions can effectively minimize co-solute interactions, leading to pore size distributions that closely resemble results observed in ideal single solute filtrations. Laboratory fouling experiments are typically run such that the transmembrane pressure (TMP) is fixed, and the permeate flux decreases over time as fouling progresses. However, this change in flux means that the hydrodynamic conditions at the membrane surface are continuously changing, which affects fouling. Industrial filtrations may start at a constant TMP, but feed pressure may be periodically adjusted to maintain permeate production. In this work, the evolution of the fouling layer resistance due to scaling was investigated in both constant TMP and constant flux reverse osmosis (RO) crossflow filtration. It was determined that scaling in both operational modes is mechanistically different, where scaling in self-reinforcing and self-limiting under constant flux and constant TMP conditions, respectively. Membrane researchers use macroscopic performance metrics as an indicator of fouling (i.e. flux decline). However, this approach does not capture the membrane and fouling layer in their operational states, therefore potentially overlooking the true mechanisms of fouling. In this work, a remotely controlled crossflow membrane system and a custom membrane cell were designed and constructed for operando fouling characterization using synchrotron-based transmission small/wide X-ray scattering (SAXS/WAXS) measurements. The system's capability was demonstrated by examining nanoparticle fouling in ultrafiltration using SAXS and mineral scaling in RO using WAXS.Chemical Engineerin
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
Deposition of Electroactive Polymers onto Polymer Nanofibers for Nerve Regeneration
No full textAlthough peripheral nerves can regenerate after an injury through the Wallerian degeneration process, the degree of regeneration is often not efficient enough to achieve full return of functionality. To overcome the disadvantages of current nerve repair approaches, peripheral nerve tissue engineering strategies have been proposed by developing synthetic graft alternatives for long-gap nerve injuries. Nerve tissue engineering approach relies on mimicking the microenvironment of nerve tissue.
This study reports the successful fabrication of an alternative for nerve tissue engineering. Electrospinning of the biocompatible polymer polycaprolactone (PCL) is used to produce porous and ordered nanofibers that resemble the structure and organization of the extracellular matrix, providing a suitable environment to promote the adhesion and directional growth of nerves. These oriented nanofibers are conformally coated with the inherently conducting polymer (ICP) polypyrrole (PPy) to provide an electrically conductive medium enabling the application of external stimuli to enhance cellular growth and connectivity. Furthermore, the scaffold is engineered with magnetic nanoparticles (MNPs) to provide a remote-controlled option for the delivery of electrical inputs through the generation of eddy currents when exposed to alternating magnetic fields.
The biocompatibility of the fabricated composite has been proven using C2C12 and ND7/23 mouse cells. The growth of these cells has been shown to coincide with the alignment of the nanofibers. On highly aligned composites, there is evidence of neuroblastoma differentiation.
While adhesion of the PPy coating onto the electrospun polymer has been demonstrated to be strong by tape test, it can potentially be enhanced by the formation of covalent bonds between the electrospun substrate and the modifier ICP. This study also preliminarily reports the success of reacting modified monomers of poly(3,4-ethylenedioxythiophene) (PEDOT) onto polyacryonitrile (PAN) and poly(methyl methacrylate) (PMMA). Aminomethyl EDOT (EDOT-MeNH2) was potentially successfully grafted onto PAN, alkaline hydrolyzed PAN , and PMMA. Hydroxymethyl EDOT (EDOT-MeOH) was also potentially successfully grafted onto alkaline hydrolyzed PAN. These would then be polymerized on the electrospun substrates, forming graft copolymers.
The results of this study not only provide the foundations for a device for enhanced nerve regeneration, but also would be an enabling technology for the fabrication of improved composites of electrospun polymers and ICPs with applications in biomedical engineering and, potentially, energy storage, water purification, sensors, and wearable electronics.Chemistry and Biochemistr
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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