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Hernández, Sara B., Sónia Castanheira, M. Graciela Pucciarelli, Juan J. Cestero, Gadea Rico-Pérez, Alberto Paradela, Juan A. Ayala, et al. "Peptidoglycan editing in non-proliferating intracellular Salmonella as source of interference with immune signaling." PLOS Pathogens 18, no. 1 (January 25, 2022): e1010241. http://dx.doi.org/10.1371/journal.ppat.1010241.
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Salmonella enterica causes intracellular infections that can be limited to the intestine or spread to deeper tissues. In most cases, intracellular bacteria show moderate growth. How these bacteria face host defenses that recognize peptidoglycan, is poorly understood. Here, we report a high-resolution structural analysis of the minute amounts of peptidoglycan purified from S. enterica serovar Typhimurium (S. Typhimurium) infecting fibroblasts, a cell type in which this pathogen undergoes moderate growth and persists for days intracellularly. The peptidoglycan of these non-proliferating bacteria contains atypical crosslinked muropeptides with stem peptides trimmed at the L-alanine-D-glutamic acid-(γ) or D-glutamic acid-(γ)-meso-diaminopimelic acid motifs, both sensed by intracellular immune receptors. This peptidoglycan has a reduced glycan chain average length and ~30% increase in the L,D-crosslink, a type of bridge shared by all the atypical crosslinked muropeptides identified. The L,D-transpeptidases LdtD (YcbB) and LdtE (YnhG) are responsible for the formation of these L,D-bridges in the peptidoglycan of intracellular bacteria. We also identified in a fraction of muropeptides an unprecedented modification in the peptidoglycan of intracellular S. Typhimurium consisting of the amino alcohol alaninol replacing the terminal (fourth) D-alanine. Alaninol was still detectable in the peptidoglycan of a double mutant lacking LdtD and LdtE, thereby ruling out the contribution of these enzymes to this chemical modification. Remarkably, all multiple mutants tested lacking candidate enzymes that either trim stem peptides or form the L,D-bridges retain the capacity to modify the terminal D-alanine to alaninol and all attenuate NF-κB nuclear translocation. These data inferred a potential role of alaninol-containing muropeptides in attenuating pro-inflammatory signaling, which was confirmed with a synthetic tetrapeptide bearing such amino alcohol. We suggest that the modification of D-alanine to alaninol in the peptidoglycan of non-proliferating intracellular S. Typhimurium is an editing process exploited by this pathogen to evade immune recognition inside host cells.
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Falchi, Federica A., Flaviana Di Lorenzo, Roberto Pizzoccheri, Gianluca Casino, Moira Paroni, Francesca Forti, Antonio Molinaro, and Federica Briani. "Overexpression of lpxT Gene in Escherichia coli Inhibits Cell Division and Causes Envelope Defects without Changing the Overall Phosphorylation Level of Lipid A." Microorganisms 8, no. 6 (May 30, 2020): 826. http://dx.doi.org/10.3390/microorganisms8060826.
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LpxT is an inner membrane protein that transfers a phosphate group from the essential lipid undecaprenyl pyrophosphate (C-55PP) to the lipid A moiety of lipopolysaccharide, generating a lipid A tris-phosphorylated species. The protein is encoded by the non-essential lpxT gene, which is conserved in distantly related Gram-negative bacteria. In this work, we investigated the phenotypic effect of lpxT ectopic expression from a plasmid in Escherichia coli. We found that lpxT induction inhibited cell division and led to the formation of elongated cells, mostly with absent or altered septa. Moreover, the cells became sensitive to detergents and to hypo-osmotic shock, indicating that they had cell envelope defects. These effects were not due to lipid A hyperphosphorylation or C-55PP sequestering, but most likely to defective lipopolysaccharide transport. Indeed, lpxT overexpression in mutants lacking the L,D-transpeptidase LdtD and LdtE, which protect cells with outer membrane defects from osmotic lysis, caused cell envelope defects. Moreover, we found that pyrophosphorylated lipid A was also produced in a lpxT deletion mutant, indicating that LpxT is not the only protein able to perform such lipid A modification in E. coli.
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Sanders, Akeisha N., Lori F. Wright, and Martin S. Pavelka. "Genetic characterization of mycobacterial l,d-transpeptidases." Microbiology 160, no. 8 (August 1, 2014): 1795–806. http://dx.doi.org/10.1099/mic.0.078980-0.
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l,d-Transpeptidases (Ldts) catalyse the formation of 3–3 cross-links in peptidoglycans (PGs); however, the role of these enzymes in cell envelope physiology is not well understood. Mycobacterial PG contains a higher percentage of 3–3 cross-links (~30–80 %) than the PG in most other bacteria, suggesting that they are particularly important to mycobacterial cell wall biology. The genomes of Mycobacterium tuberculosis and Mycobacterium smegmatis encode multiple Ldt genes, but it is not clear if they are redundant. We compared the sequences of the Ldt proteins from 18 mycobacterial genomes and found that they can be grouped into six classes. We then constructed M. smegmatis strains lacking single or multiple Ldt genes to determine the physiological consequence of the loss of these enzymes. We report that of the single mutants, only one, ΔldtC (MSMEG_0929, class 5), displayed an increased susceptibility to imipenem – a carbapenem antibiotic that inhibits the Ldt enzymes. The invariant cysteine in the active site of LdtC was required for function, consistent with its role as an Ldt. A triple mutant missing ldtC and both of the class 2 genes displayed hypersusceptibility to antibiotics, lysozyme and d-methionine, and had an altered cellular morphology. These data demonstrated that the distinct classes of mycobacterial Ldts may reflect different, non-redundant functions and that the class 5 Ldt was peculiar in that its loss, alone and with the class 2 proteins, had the most profound effect on phenotype.
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Genzen, Jonathan R., Jeffrey S. Mohlman, Jerry L. Lynch, Michael W. Squires, and Ronald L. Weiss. "Laboratory-Developed Tests: A Legislative and Regulatory Review." Clinical Chemistry 63, no. 10 (October 1, 2017): 1575–84. http://dx.doi.org/10.1373/clinchem.2017.275164.
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Abstract BACKGROUND Twenty-five years ago, the Food and Drug Administration (FDA) asserted in a draft document that “home brew” tests—now commonly referred to as laboratory-developed tests (LDTs)—are subject to the same regulatory oversight as other in vitro diagnostics (IVDs)4. In 2010, the FDA began work on developing a proposed framework for future LDT oversight. Released in 2014, the draft guidance sparked an intense debate over potential LDT regulation. While the proposed guidance has not been implemented, many questions regarding LDT oversight remain unresolved. CONTENT This review provides an overview of federal statutes and regulations related to IVDs and clinical laboratory operations, with a focus on those potentially applicable to LDTs and proposed regulatory efforts. Sources reviewed include the Code of Federal Regulations, the Federal Register, congressional hearings, guidance and policy documents, position statements, published literature, and websites. SUMMARY Federal statutes regarding IVDs were passed without substantive evidence of congressional consideration toward the concept of LDTs. The FDA has clear oversight authority over IVD reagents introduced into interstate commerce. A 16-year delay in publicly asserting FDA authority over LDTs, the pursuit of a draft guidance approach toward oversight, and establishment of regulations under the Clinical Laboratory Improvement Amendments of 1988 (CLIA'88) applicable to LDTs contributed to community uncertainty toward LDT oversight. Future regulatory and/or legislative efforts may be required to resolve this uncertainty.
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Lichtenberg, Steven, Oxana P. Trifonova, Dmitry L. Maslov, Elena E. Balashova, and Petr G. Lokhov. "Metabolomic Laboratory-Developed Tests: Current Status and Perspectives." Metabolites 11, no. 7 (June 26, 2021): 423. http://dx.doi.org/10.3390/metabo11070423.
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Laboratory-developed tests (LDTs) are a subset of in vitro diagnostic devices, which the US Food and Drug Administration defines as “tests that are manufactured by and used within a single laboratory”. The review describes the emergence and history of LDTs. The current state and development prospects of LDTs based on metabolomics are analyzed. By comparing LDTs with the scientific metabolomics study of human bio samples, the characteristic features of metabolomic LDT are shown, revealing its essence, strengths, and limitations. The possibilities for further developments and scaling of metabolomic LDTs and their potential significance for healthcare are discussed. The legal aspects of LDT regulation in the United States, European Union, and Singapore, demonstrating different approaches to this issue, are also provided. Based on the data presented in the review, recommendations were made on the feasibility and ways of further introducing metabolomic LDTs into practice.
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Skedros, John G., and Tanner R. Henrie. "Latissimus Dorsi Tendon Transfer with GraftJacket® Augmentation to Increase Tendon Length for an Irreparable Rotator Cuff Tear." Case Reports in Orthopedics 2017 (2017): 1–6. http://dx.doi.org/10.1155/2017/8086065.
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Massive irreparable rotator cuff tears can be reconstructed with latissimus dorsi tendon transfers (LDTT). Although uncommon, the natural length of the latissimus dorsi tendon (LDT) could be insufficient for transfer even after adequate soft tissue releases. Descriptions of cases where grafts were needed to lengthen the LDT are therefore rare. We located only two reports of the use of an acellular dermal matrix to increase effective tendon length in tendon transfers about the shoulder: (1) GraftJacket patch for a pectoralis major tendon reconstruction and (2) ArthroFlex® patch for LDTT. Both of these brands of allograft patches are obtained from human cadavers. These products are usually used to cover soft tissue repairs and offer supplemental support rather than for increasing tendon length. Extending the LDTT with GraftJacket to achieve adequate length, to our knowledge, has not been reported in the literature. We report the case of a 50-year-old male who had a massive, irreparable left shoulder rotator cuff tear that was reconstructed with a LDTT. The natural length of his LDT was insufficient for transfer. This unexpected situation was rectified by sewing two patches of GraftJacket to the LDT. The patient had greatly improved shoulder function at two-year follow-up.
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Gu, Henan, Jian Luo, Guofang Li, Yueling Yao, Yan Huang, and Dongjing Huang. "Spatial-Temporal Variations of Active Accumulated Temperature and Its Impact on Vegetation NDVI in the Source Region of China’s Yellow River." Water 14, no. 21 (October 29, 2022): 3458. http://dx.doi.org/10.3390/w14213458.
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Global climate change has greatly influenced the ecosystems in the Tibetan Plateau. Many studies focused on the direct effects of climate warming on the headwater regions by mean temperature, while less investigating its implication for the eco-environment. To address this, the study discussed the spatial-temporal variations of the bio-related climate indicators ≥0 °C annual accumulated temperature AAT0 and its lasting days LDT0, and corresponding ≥5 °C indicators AAT5 and LDT5 on the source region of the Yellow River (SRYR). The stationarity of indicators during 1979–2018 were tested by Pettitt test, and trends checked by linear regression analysis and Mann-Kendall test. Normalized difference vegetation index NDVI (2001–2016) was adopted to detect the correlation between vegetation activities and indicators. Results show that the AAT and LDT0 exhibited significant increasing trend over the SRYR, while the LDT5 significantly increased mainly under 4000 m. Most LDT extended due to the combined efforts of the early onset and late termination of the given temperature. 1997 was detected in the abrupt change analysis of AAT0 both on the basin scale and most area, and was adopted to divide the period into two stages. The regional mean AAT0 linearly grew at a rate of 96 °C decade−1 during the entire period, and 104 °C decade−1 during the second stage. Except for a drastic jump in the areal mean values, there was a distinct upward-shift of isoline in elevation between stages. NDVI showed strong correlativity with ≥0 °C indicators on the basin scale, according to the Pearson, Spearman and Kendall correlation coefficients, ranging from 0.5 to 0.7. Spatially, the overlap area between Pearson’s γ ≥ 0.5 and linearly rising AAT0 reached 50%, which was fully covered with significantly increasing AAT0 during the recent stage. Thus the rapid growth of ≥0 °C indicators would effectively accelerate NDVI over this major alpine grasslands, especially around the eastern low regions, where indicators are higher and grow faster.
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Stiggins, Chuck, and Dr Phil Allsen. "EXERCISE METHODS NOTEBOOK #30: Lying dumbbell triceps extension." National Strength & Conditioning Association Journal 9, no. 3 (1987): 79. http://dx.doi.org/10.1519/0744-0049(1987)009<0079:ldte>2.3.co;2.
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Vermeersch, Pieter, Tobias Van Aelst, and Elisabeth M. C. Dequeker. "The new IVD Regulation 2017/746: a case study at a large university hospital laboratory in Belgium demonstrates the need for clarification on the degrees of freedom laboratories have to use lab-developed tests to improve patient care." Clinical Chemistry and Laboratory Medicine (CCLM) 59, no. 1 (January 26, 2021): 101–6. http://dx.doi.org/10.1515/cclm-2020-0804.
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AbstractObjectivesThe new European In Vitro Diagnostic (IVD) Regulation 2017/746 (IVDR) restricts the use of lab-developed tests (LDT) after 26th May 2022. There are no data on the impact of the IVDR on laboratories in the European Union.MethodsLaboratory tests performed in UZ Leuven were divided in four groups: core laboratory, immunology, special chemistry, and molecular microbiology testing. Each test was classified as Conformité Européenne (CE)-IVD, modified/off-label CE-IVD, commercial Research Use Only (RUO) or LDT. Each matrix was considered a separate test.ResultsWe found that 97.6% of the more than 11.5 million results/year were generated with a CE-IVD method. Of the 922 different laboratory tests, however, only 41.8% were CE-IVD, 10.8% modified/off-label CE-IVD, 0.3% RUO, and 47.1% LDT. Off-label CE-IVD was mainly used to test alternative matrices not covered by the claim of the manufacturer (e.g., pleural or peritoneal fluid). LDTs were mainly used for special chemistry, flow cytometry, and molecular testing. Excluding flow cytometry, the main reasons for the use of 377 LDTs were lack of a CE-IVD method (71.9%), analytical requirements (14.3%), and the fact the LDT was in use before CE-IVD available (11.9%).ConclusionsWhile the large majority of results (97.6%) were generated with a CE-IVD method, only 41.8% of laboratory tests were CE-IVD. There is currently no alternative on the market for 71.5% of the 537 LDTs performed in our laboratory which do not fall within the scope of the current IVD directive (IVDD). Compliance with the IVDR will require a major investment of time and effort.
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DE JESÚS, ANTONIO J., and RICHARD C. WHITING. "Modeling the Physiological State of the Inoculum and CO2 Atmosphere on the Lag Phase and Growth Rate of Listeria monocytogenes." Journal of Food Protection 71, no. 9 (September 1, 2008): 1915–18. http://dx.doi.org/10.4315/0362-028x-71.9.1915.
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In previous studies, the growth of L. monocytogenes has been modeled under different CO2 headspace concentrations; however, the inoculum cells were always in the stationary phase. In this study, the growth of L. monocytogenes under different CO2 concentrations as affected by the physiological state of the cells was investigated. Exponential-growth-phase, stationary-phase, dried, and starved cells were prepared and inoculated at 5°C into brain heart infusion broths that had been preequilibrated under atmospheres of 0, 20, 40, 60, or 80% CO2 (the balance was N2). Lag-phase duration times (LDTs) and exponential growth rates were determined by enumerating cells at appropriate time intervals and by fitting the data to a three-phase linear function that has a lag period before the initiation of exponential growth. Longer LDTs were observed as the CO2 concentration increased, with no growth observed at 80% CO2. For example, the LDTs for exponential-phase, stationary-phase, starved, and dried cells were 2.21, 8.27, 9.17, and 9.67 days, respectively, under the 40% CO2 atmosphere. In general, exponential-growth-phase cells had the shortest LDT followed by starved cells and stationary-phase cells. Dried cells had the longest LDT. Exponential growth rates decreased as the CO2 concentrations increased. Once exponential growth was attained, no retained differences among the various initial physiological states of the cells for any of the atmospheres were observed in the exponential growth rates. The exponential growth rates under 0, 20, 40, 60, and 80% CO2 averaged 0.39, 0.37, 0.23, 0.23, and 0.0 log CFU/day, respectively. Dimensionless factors were calculated that describe the inhibitory action of CO2 on the LDTs and exponential growth rates for the various physiological states.
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Peters, Katharina, Manuel Pazos, Zainab Edoo, Jean-Emmanuel Hugonnet, Alessandra M. Martorana, Alessandra Polissi, Michael S. VanNieuwenhze, Michel Arthur, and Waldemar Vollmer. "Copper inhibits peptidoglycan LD-transpeptidases suppressing β-lactam resistance due to bypass of penicillin-binding proteins." Proceedings of the National Academy of Sciences 115, no. 42 (October 1, 2018): 10786–91. http://dx.doi.org/10.1073/pnas.1809285115.
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The peptidoglycan (PG) layer stabilizes the bacterial cell envelope to maintain the integrity and shape of the cell. Penicillin-binding proteins (PBPs) synthesize essential 4–3 cross-links in PG and are inhibited by β-lactam antibiotics. Some clinical isolates and laboratory strains ofEnterococcus faeciumandEscherichia coliachieve high-level β-lactam resistance by utilizing β-lactam–insensitive LD-transpeptidases (LDTs) to produce exclusively 3–3 cross-links in PG, bypassing the PBPs. InE. coli, other LDTs covalently attach the lipoprotein Lpp to PG to stabilize the envelope and maintain the permeability barrier function of the outermembrane. Here we show that subminimal inhibitory concentration of copper chloride sensitizesE. colicells to sodium dodecyl sulfate and impair survival upon LPS transport stress, indicating reduced cell envelope robustness. Cells grown in the presence of copper chloride lacked 3–3 cross-links in PG and displayed reduced covalent attachment of Braun’s lipoprotein and reduced incorporation of a fluorescentd-amino acid, suggesting inhibition of LDTs. Copper dramatically decreased the minimal inhibitory concentration of ampicillin inE. coliandE. faeciumstrains with a resistance mechanism relying on LDTs and inhibited purified LDTs at submillimolar concentrations. Hence, our work reveals how copper affects bacterial cell envelope stability and counteracts LDT-mediated β-lactam resistance.
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Kulis-Horn, Robert K., and Carsten Tiemann. "Evaluation of a laboratory-developed test for simultaneous detection of norovirus and rotavirus by real-time RT-PCR on the Panther Fusion® system." European Journal of Clinical Microbiology & Infectious Diseases 39, no. 1 (September 10, 2019): 103–12. http://dx.doi.org/10.1007/s10096-019-03697-7.
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Abstract The Hologic Panther Fusion® Open Access™ functionality allows implementation of laboratory-developed tests (LDTs), with fully automated sample extraction, real-time PCR, and result interpretation. We report the development and validation of a multiplex LDT for norovirus G1, norovirus G2, and rotavirus from stool samples on this system. The LDT was optimized for primer and probe sequences, salt concentration, and PCR annealing temperature. Reproducibility of the PCR and extraction process was assessed. Performance of the multiplex LDT assay was evaluated with external quality assessment (EQA) samples and compared to a commercial multiplex assay (Allplex™ GI-Virus Assay, Seegene) in clinical samples. Salt concentrations and annealing/extension temperature were optimized to 4 mM MgCl2, 70 mM KCl, 20 mM Tris, and 60 °C, respectively. The user-prepared part of the LDT PCR mix (containing salts, probes, and primers) was stable for ≥ 11 days onboard the instrument. We observed reproducible results of PCR and the extraction process. The LDT had a sensitivity comparable to or greater than the commercial Allplex™ assay and showed excellent linearity. Forty-five EQA samples yielded the expected result with the LDT. There was 100% concordance between LDT and Allplex™ results in 160 clinical samples. Results from the suspension and direct swab stool sample preparation methods were highly concordant in the LDT. We report the successful development and validation of a multiplex PCR LDT for detection of norovirus G1, norovirus G2, and rotavirus from stool samples on the Panther Fusion® system.
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Gonzalez-Aguirre, Adrian, and Etay Ziv. "Liver-Directed Therapy for Gastroenteropancreatic NETs in the Era of Peptide Receptor Radionuclide Therapy." Digestive Disease Interventions 04, no. 03 (September 2020): 282–90. http://dx.doi.org/10.1055/s-0040-1718388.
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AbstractGastroenteropancreatic neuroendocrine tumors (GEP-NETs) represent a heterogeneous group of tumors. Current treatment algorithms for these tumors are complex and often require a multidisciplinary approach. Recently, peptide receptor radionuclide therapy (PRRT) was granted Food and Drug Administration approval, making this treatment widely available in the United States. PRRT is now another therapeutic option for patients with GEP-NETs. To date there are no consensus guidelines about how to sequence multiple treatment options. Moreover, there is concern of potential liver toxicity when PRRT is used before or after liver-directed therapies (LDTs). In this review, we describe the characteristics of the most commonly used LDT and their potential interactions with PRRT, as well as specific clinical scenarios that are relevant when deciding on the use of LDT. We also review the limited case series that have been published involving patients treated with different combinations of LDT and PRRT. Finally, we discuss some of the future directions for GEP-NET treatments.
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Taylor, Kirsten I., Peter Brugger, Dorothea Weniger, and Marianne Regard. "Effects of Task Instructions on Visual Field Language Asymmetries." Zeitschrift für Neuropsychologie 15, no. 2 (June 2004): 91–98. http://dx.doi.org/10.1024/1016-264x.15.2.91.
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Abstract: Lexical decision tasks (LDTs) are often employed to implicitly measure each hemisphere's capacity to process semantic information. Different hemispheric patterns may result from tasks with explicit semantic demands (semantic decision tasks, SDTs). We administered healthy subjects two different lateralized tasks, one LDT and one SDT (category matching task). The target word pairs were identical in both tasks and either closely or distantly semantically related. Overall, the fastest RTs were evidenced in the RVF/LH. However, individual analyses revealed a single main effect of hemifield in the LDT (RVF/LH faster than LVF/RH) and a single main effect of semantic distance (shorter latencies with closely related words) in the SDT. These findings indicate that hemispheric asymmetries depend on task demands.
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Zandi, Trevor A., and Craig A. Townsend. "Competing off-loading mechanisms of meropenem from an l,d-transpeptidase reduce antibiotic effectiveness." Proceedings of the National Academy of Sciences 118, no. 27 (June 29, 2021): e2008610118. http://dx.doi.org/10.1073/pnas.2008610118.
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The carbapenem family of β-lactam antibiotics displays a remarkably broad spectrum of bactericidal activity, exemplified by meropenem’s phase II clinical trial success in patients with pulmonary tuberculosis, a devastating disease for which β-lactam drugs historically have been notoriously ineffective. The discovery and validation of l,d-transpeptidases (Ldts) as critical drug targets of bacterial cell-wall biosynthesis, which are only potently inhibited by the carbapenem and penem structural classes, gave an enzymological basis for the effectiveness of the first antitubercular β-lactams. Decades of study have delineated mechanisms of β-lactam inhibition of their canonical targets, the penicillin-binding proteins; however, open questions remain regarding the mechanisms of Ldt inhibition that underlie programs in drug design, particularly the optimization of kinetic behavior and potency. We have investigated critical features of mycobacterial Ldt inhibition and demonstrate here that the covalent inhibitor meropenem undergoes both reversible reaction and nonhydrolytic off-loading reactions from the cysteine transpeptidase LdtMt2 through a high-energy thioester adduct. Next-generation carbapenem optimization strategies should minimize adduct loss from unproductive mechanisms of Ldt adducts that reduce effective drug concentration.
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Caliendo, Angela M., and Kimberly E. Hanson. "Point-Counterpoint: The FDA Has a Role in Regulation of Laboratory-Developed Tests." Journal of Clinical Microbiology 54, no. 4 (January 20, 2016): 829–33. http://dx.doi.org/10.1128/jcm.00063-16.
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Since the Food and Drug Administration (FDA) released its draft guidance on the regulation of laboratory-developed tests (LDTs) in October 2014, there has been a flurry of responses from commercial and hospital-based laboratory directors, clinicians, professional organizations, and diagnostic companies. The FDA defines an LDT as an “in vitrodiagnostic device that is intended for clinical use and is designed, manufactured, and used within a single laboratory.” The draft guidance outlines a risk-based approach, with oversight of high-risk and moderate-risk tests being phased in over 9 years. High-risk tests would be regulated first and require premarket approval. Subsequently, moderate-risk tests would require a 510(k) premarket submission to the FDA and low-risk tests would need only to be registered. Oversight discretion would be exercised for LDTs focused on rare diseases (defined as fewer than 4,000 tests, not cases, per year nationally) and unmet clinical needs (defined as those tests for which there is no alternative FDA-cleared or -approved test). There was an open comment period followed by a public hearing in early January of 2015, and we are currently awaiting the final decision regarding the regulation of LDTs. Given that LDTs have been developed by many laboratories and are essential for the diagnosis and monitoring of an array of infectious diseases, changes in their regulation will have far-reaching implications for clinical microbiology laboratories. In this Point-Counterpoint, Angela Caliendo discusses the potential benefits of the FDA guidance for LDTs whereas Kim Hanson discusses the concerns associated with implementing the guidance and why these regulations may not improve clinical care.
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Cordillot, Mathilde, Vincent Dubée, Sébastien Triboulet, Lionel Dubost, Arul Marie, Jean-Emmanuel Hugonnet, Michel Arthur, and Jean-Luc Mainardi. "In VitroCross-Linking of Mycobacterium tuberculosis Peptidoglycan by l,d-Transpeptidases and Inactivation of These Enzymes by Carbapenems." Antimicrobial Agents and Chemotherapy 57, no. 12 (September 16, 2013): 5940–45. http://dx.doi.org/10.1128/aac.01663-13.
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ABSTRACTTheMycobacterium tuberculosispeptidoglycan is cross-linked mainly byl,d-transpeptidases (LDTs), which are efficiently inactivated by a single β-lactam class, the carbapenems. Development of carbapenems for tuberculosis treatment has recently raised considerable interest since these drugs, in association with the β-lactamase inhibitor clavulanic acid, are uniformly active against extensively drug-resistantM. tuberculosisand kill both exponentially growing and dormant forms of the bacilli. We have purified the fivel,d-transpeptidase paralogues ofM. tuberculosis(Mt1 to -5) and compared their activities with those of peptidoglycan fragments and carbapenems. The five LDTs were functionalin vitrosince they were active in assays of peptidoglycan cross-linking (Mt5), β-lactam acylation (Mt3), or both (Mt1, Mt2, and Mt4). Mt3 was the only LDT that was inactive in the cross-linking assay, suggesting that this enzyme might be involved in other cellular functions such as the anchoring of proteins to peptidoglycan, as shown inEscherichia coli. Inactivation of LDTs by carbapenems is a two-step reaction comprising reversible formation of a tetrahedral intermediate, the oxyanion, followed by irreversible rupture of the β-lactam ring that leads to formation of a stable acyl enzyme. Determination of the rate constants for these two steps revealed important differences (up to 460-fold) between carbapenems, which affected the velocity of oxyanion and acyl enzyme formation. Imipenem inactivated LDTs more rapidly than ertapenem, and both drugs were more efficient than meropenem and doripenem, indicating that modification of the carbapenem side chain could be used to optimize their antimycobacterial activity.
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Genzen, Jonathan R. "Regulation of Laboratory-Developed Tests." American Journal of Clinical Pathology 152, no. 2 (June 26, 2019): 122–31. http://dx.doi.org/10.1093/ajcp/aqz096.
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Abstract Objectives To provide a clinical laboratory perspective on the Verifying Accurate Leading-edge IVCT Development Act (VALID) discussion draft. This potential legislative effort, if enacted, would overhaul the regulatory oversight of in vitro diagnostics (IVDs) in the United States and create a single system for regulation of conventional IVDs and laboratory-developed tests (LDTs). Methods A concise literature-based review of LDT regulation is presented followed by a discussion of key concerns pertinent to clinical laboratories that should be considered in future IVD regulatory reform efforts. Results Key issues identified include the importance of fostering innovation, preserving patient safety, protecting the practice of laboratory medicine, and minimizing undue regulatory burden. Clinical laboratories are not equivalent to manufacturing facilities and would therefore encounter challenges in implementing device-centric regulatory oversight models. Conclusions It is imperative that a clinical laboratory perspective on LDTs is understood and incorporated prior to advancement of future legislative proposals.
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Vance, Gail H. "College of American Pathologists Proposal for the Oversight of Laboratory-Developed Tests." Archives of Pathology & Laboratory Medicine 135, no. 11 (November 1, 2011): 1432–35. http://dx.doi.org/10.5858/arpa.2011-0304-sa.
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Context.—The US Food and Drug Administration (FDA) announced it will exercise authority over laboratory-developed tests (LDTs). Laboratory-developed tests have traditionally been developed and offered in laboratories as a service to patients and regulated under the Clinical Laboratory Improvement Amendments of 1988 (Clinical Laboratory Improvements Act). Laboratories now face potential dual regulatory oversight from both the Centers for Medicare and Medicaid Services (CMS) and the FDA. The College of American Pathologists (CAP) constructed a proposal to minimize redundancy of agency oversight and burden to laboratories. Modifications to the proposal continue while the laboratory community awaits release of the guidance documents that will stipulate FDA requirements. Objective.—To describe the historical context framing the entry of FDA into the oversight of LDTs and outline the CAP LDT Proposal in its current form. Data Sources.—PubMed review of published literature; United States Constitution; and online information resources from the National Institutes of Health, FDA, and US Government. Conclusion.—The College of American Pathologists is a leader in laboratory quality and has unique insights into the benefits and risks to patients presented by LDTs. Continued dialog with officials from the FDA and CMS will promote public and private collaborative efforts to assure innovation of diagnostic testing, public information, and patient safety for clinical diagnostic testing.
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Trosman, Julia R., Christine B. Weldon, Gregory J. Tsongalis, and Kathryn A. Phillips. "A Standardized BCR-ABL Monitoring Test: Assessment of Potential Adoption Impacts In Healthcare In the United States." Blood 116, no. 21 (November 19, 2010): 4754. http://dx.doi.org/10.1182/blood.v116.21.4754.4754.
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Abstract Abstract 4754 Background. BCR-ABL transcript monitoring is a guideline recommended component of Chronic Myeloid Leukemia (CML) management. BCR-ABL monitoring in the U.S. is mainly done using laboratory developed tests (LDTs). Studies found accuracy and reliability problems with LDTs which may lead to undesirable health and economic impacts (Gabert et al, Leukemia, 2003, Zhang et al, J Mol Diagn 2007, Muller et al, Leukemia 2008). There are ongoing efforts to standardize BCR-ABL LDTs in the U.S. and globally (Hughes et al, Blood 2006, Branford et al Blood 2006). A standardized BCR-ABL monitoring test (SBAT) may be an effective method to propagate standardization and improve quality of BCR-ABL testing. A standardized BCR-ABL monitoring test is one which minimizes operator error, and is stringently reviewed and shown to be validated under health authorities’ quality systems regulations (principally Food and Drug Administration's Quality Systems Regulations and European Union's In-Vitro Diagnostics Directive), ensuring the safety and effectiveness of the test, as well as its reliable performance across multiple operators and labs through a thorough examination of its initial design, manufacturing, and associated processes. Our study qualitatively assessed potential benefits and drawbacks of adopting a SBAT, compared to current LDTs. Methods. We conducted peer-reviewed and grey literature review to answer questions: (1) How may the shortcomings of current BCR-ABL LDTs be impacting patient care, outcomes and quality of life? (2) How may adoption of a SBAT address the LDT shortcomings and propagate standardization? (3) What are potential health, economic and care process benefits and drawbacks of SBAT adoption for healthcare stakeholders? Results. We identified BCR-ABL LDT shortcomings: (a) methodologic shortcomings resulting in suboptimal test accuracy; (b) process shortcomings (e.g. operator error; batch to batch variation in materials) leading to suboptimal reproducibility and (c) variability in methods across labs leading to incomparability of results. Three key results are: (1) Inaccurate over-quantitation of BCR-ABL results may lead to unnecessary further testing (e.g. mutation testing; bone marrow cytogenetic testing) and misinformed therapy decisions, e.g. drug dose escalation. False under-quantitation may lead to missed indications of relapse, resistance to therapy, or problems with therapy compliance. Due to result incomparability, patients often cannot change providers without losing testing history which may impact life decisions such as relocation. (2) A SBAT may address most LDT process shortcomings and important methodologic shortcomings. Consequently, if a SBAT is adopted broadly it may reduce inter- and intra-lab variability. It may also address limitations of standardization efforts, such as minimizing operator error and increasing compliance with harmonization guidelines. (3) SBAT adoption is likely to provide substantial benefits in health outcomes and quality of life to patients who may otherwise receive inaccurate results. Benefits in care process are anticipated to outweigh drawbacks. Benefits include faster results, increased confidence in results, ability to get a second opinion or transition patient care to different providers. Drawbacks may include implementation efforts, and getting used to new report formats by patients and physicians. BCR-ABL testing history may potentially be incomparable for some existing patients if laboratories do not implement effective data transition. We anticipate that the economic impact of SBAT adoption on the healthcare system will be limited due to the relatively small CML patient population. A significant financial impact may be on labs. Some labs may benefit by bringing BCR-ABL test in-house, but this may reduce test volume for labs that provide this as a centralized service. Conclusions. Implementing a standardized BCR-ABL monitoring test (SBAT) is likely to significantly benefit CML patients’ health and quality of life and provide better utility to providers than LDTs. A SBAT will contribute to addressing the broader quality of diagnostics challenge recognized by payers, providers, guideline bodies and government authorities. A SBAT represents an incremental improvement in a field that has relatively few patients, but potentially paves the way to similar developments in other blood cancers and beyond. Disclosures: Trosman: Novartis: Consultancy. Weldon:Novartis: Consultancy. Tsongalis:Novartis: Consultancy. Phillips:Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees.
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Bjekić-Macut, Jelica, Vojislav Radosavljević, Zoran Andrić, Dušan Ilić, Olivera Stanojlović, Danijela Vojnović Milutinović, Ivana Božić Antić, et al. "Cortisol Response to Low-Dose (1 μg) ACTH Stimulation for the Prediction of Outcome in Patients with Systemic Inflammatory Response Syndrome." Journal of Medical Biochemistry 35, no. 4 (October 1, 2016): 428–35. http://dx.doi.org/10.1515/jomb-2016-0015.
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Summary Background: Systemic inflammatory response syndrome (SIRS) changes cortisol dynamics and indicates dissociation between the adrenal cortex and the hypothalamo-pituitary unit. The aim of this study was to assess the cortisol response after stimulation with ACTH1-24 in patients with SIRS at admission to the Respiratory Intensive Care Unit (RICU) and seven days later. Methods: Fifty-four subjects were included in the study, and SIRS was defined according to the Consensus Conference criteria from 1992. Severity of the disease was determined using the APACHE II score, and organ dysfunction using the SOFA score. Low-dose (1 μg) ACTH test (LDT) was performed in all patients, and cortisol was determined along with basal ACTH. Data were analyzed using parametric and nonparametric tests and regression analysis. The results are presented as mean ± standard deviation, and P<0.05 was considered statistically significant. Results: There were no differences in cortisol values between the two LDTs. Cortisol increment lower than 250 nmol/L during the LDT was found in 14/54 (25.9%) subjects at the onset of SIRS. Five out of 54 (9.6%) patients died within 7 days from the onset of SIRS. Female sex and maximal cortisol response (Δ max) on LDT predicted the duration of hospitalization in RICU, while APACHE II and SOFA scores best predicted the duration of hospitalization, mortality outcome as well as overall survival outcome. Conclusions: A difference was found in Δ max at the diagnosis of SIRS and seven days later. Δ max, and primarily the clinical scores APACHE II and SOFA predicted the outcomes of hospitalization and overall survival.
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Vainer, Gilad, Ghadeer Zatara, Lingkang Huang, Shanthy Nuti, Shanthy Nuti, and Kenneth Emancipator. "7 Analytical comparison of a PD-L1 22C3 antibody laboratory-developed test protocol on the Benchmark XT and PD-L1 IHC 22C3 pharmDx: pan-tumor and triple-negative breast cancer samples." Journal for ImmunoTherapy of Cancer 9, Suppl 2 (November 2021): A7. http://dx.doi.org/10.1136/jitc-2021-sitc2021.007.
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BackgroundPD-L1 IHC 22C3 pharmDx is an FDA-approved companion diagnostic for pembrolizumab across multiple tumor types designed for use on the Autostainer Link 48 (AL48). Many pathology laboratories do not have access to the AL48 and therefore do not use PD-L1 IHC 22C3 pharmDx but instead assess PD-L1 using laboratory-developed tests (LDTs) on the Ventana BenchMark platform. We compared our PD-L1 22C3 antibody-based LDT on the BenchMark XT platform with PD-L1 IHC 22C3 pharmDx using cervical cancer (CC), head and neck squamous cell carcinoma (HNSCC), urothelial carcinoma (UC), esophageal SCC (ESCC), and triple-negative breast cancer (TNBC) samples.MethodsTumor specimens from patients with CC, HNSCC, UC, ESCC, and TNBC were stained with the 22C3 antibody, scored using the LDT on the BenchMark XT as previously described,1 and compared with PD-L1 IHC 22C3 pharmDx scored by a trained pathologist, who measured PD-L1 with the use of combined positive score (CPS) and standard cutoffs (HNSCC and CC, ≥1; UC, ESCC, and TNBC, ≥10). Agreement in PD-L1 CPS as determined using the LDT and the PD-L1 IHC 22C3 pharmDx was evaluated.Results423 samples with CC (n = 77), HNSCC (n = 126), UC (n = 121), ESCC (n = 80), and TNBC (n = 19) were evaluated in this study. The pan-tumor (CC, HNSCC, UC, and ESCC) intraclass correlation coefficient (ICC) of PD-L1 CPS as a continuous variable was 0.95 (95% CI, 0.94%–0.96%); Spearman correlations were 0.95. ICC (95% CI) was 0.92 (0.88–0.95) for CC, 0.97 (0.96–0.98) for HNSCC, 0.95 (0.92–0.97) for UC, and 0.92 (0.88–0.95) for ESCC; Spearman correlation was 0.93, 0.96, 0.92, and 0.89, respectively. The overall percentage agreement at the respective CPS cutoff was 96% (CC), 96% (HNSCC), 96% (UC), and 90% (ESCC). Staining patterns by 22C3 LDT and PD-L1 IHC 22C3 pharmDx were also very similar in our TNBC pilot study; however, correlation was not calculated because of the small sample numbers.ConclusionsThe PD-L1 22C3 antibody-based LDT on the BenchMark XT demonstrated high concordance with PD-L1 IHC 22C3 pharmDx. These findings suggest the comparability of PD-L1 IHC 22C3 pharmDx with an LDT based on the 22C3 antibody across several tumor types. Further validation for TNBC is ongoing to confirm the data from the pilot run.ReferenceNeuman T, et al. J Thorac Oncol. 2016;11:1863–1868.
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Benlloch, Susana, Miquel Taron, Maria Luisa Botero, Jordi Bertran-Alamillo, Clara Mayo, Ana Gimenez Capitan, Itziar de Aguirre, et al. "Retrospective EGFR mutation testing of clinical specimens from the EURTAC trial of erlotinib in non-small cell lung cancer (NSCLC) using a novel allele-specific PCR (AS-PCR) assay." Journal of Clinical Oncology 30, no. 15_suppl (May 20, 2012): 10596. http://dx.doi.org/10.1200/jco.2012.30.15_suppl.10596.
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10596 Background: Anti-EGFR inhibitors are superior to chemotherapy in first-line therapy of advanced EGFR-mutant NSCLC. The EURTAC trial was a randomized Phase III trial of erlotinib vs. chemotherapy in patients with EGFR-mutant NSCLC. Interim results showed significant improvement in progression-free survival (R. Rosell, ASCO 2011). An accurate rapid in vitro diagnostic for EGFR mutations is needed to select patients for this therapy. Methods: Prospective EGFR mutation testing for the trial was performed on laser-capture microdissected tumor cells using a combination of 3 lab-developed tests (LDTs), including a Length Analysis of Fluorescently-labeled PCR (Genescan) method for exon 19 deletions, a Taqman-based PCR assay for exon 21 mutation with laser-capture macrodissected tumor cells, and secondary Sanger sequencing. A subset of samples from the trial was retrospectively tested with an AS-PCR assay (cobas EGFR mutation test) which detects L858R and > 29 exon 19 deletions. The test provides automated results within 8 h; the DNA required can be isolated from one 5-micron tissue section. Four methods were compared: AS-PCR assay, LDT, direct Sanger sequencing and massively parallel sequencing (MPS; 454, Branford, CT). Results: LDT results were obtained for 1044 screened patients. Residual tumor blocks were available for 487 patients (47%), including 303 wild-type, 172 mutant (135 enrolled on the trial) and 12 inconclusive cases by the LDT. Comparison of AS-PCR and LDT results showed a positive percent agreement (PPA) – 93.7% (CI 88.8%, 96.5%), and negative percent agreement (NPA) – 97.5% (94.9%, 98.8%). Comparison of AS-PCR and Sanger results showed a PPA of 96.6% (91.7%, 98.7%) but an NPA of 88.3% (84.1%, 91.5%). Among 34 AS-PCR+/Sanger- case, MPS confirmed the presence of exon 19 deletions in 25 cases and L858R mutations in 7. Direct comparison of AS-PCR and MPS results showed a PPA of 93.1% (88.1%, 96.1%) and NPA of 97.7% (95.0%, 98.9%). Clinical outcomes for cases with mutations detected by the AS-PCR test will be presented. Conclusions: The AS-PCR assay was highly concordant with the LDT and MPS, and more sensitive than Sanger sequencing.
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Zhang, Ye, Yating Song, Tianshi Feng, and Yanyan Chen. "Comparative Analysis of Emission Characteristics of In-Use China II–V Gasoline, Hybrid, Diesel-Fueled Vehicles." Atmosphere 14, no. 2 (January 29, 2023): 272. http://dx.doi.org/10.3390/atmos14020272.
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Increasingly stringent regulations regarding vehicle emissions have contributed to the diversification of vehicle technologies, resulting in the increasing complexity of typical vehicles that make up a fleet. In order to investigate the real gas emissions of different typical vehicles, tests were conducted using a portable emission measurement system (PEMS) in Beijing and emission studies were conducted on eight light-duty passenger vehicles (LDPVs, including light-duty gasoline passenger vehicles and hybrid electric vehicles), eight heavy-duty passenger vehicles (HDPVs), and four light-duty trucks (LDTs). The results show that the emissions of relevant pollutants from LDPV meet the emission standard limits. The emission factors of CO2, CO, NOX, and HC of China IV and China V hybrid electric vehicles (HEVs) are much smaller than the emission standard limits and the emission factors of other vehicles, which have better emission reduction effects. Among LDPV, heavy-duty passenger vehicles (HDPVs), and LDT, the emissions of HDPV and LDT are extremely high. Emission characteristics vary on different types of roads, with the highest emission factors generally occurring on secondary roads. The micro-trip method was used to explore the influence of speed on emission factors. HEV are less sensitive to speed changes and can still maintain a low emission level at low speeds. The average speed and emission factors of HDPV in micro-trip has a strong correlation.
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Zhao, Hong, Si Yuan Peng, and Jia Ming Yang. "Improving the Dispersity and DC Breakdown of MgO/LDPE Nanocomposite by Adding EVA." Advanced Materials Research 833 (November 2013): 339–42. http://dx.doi.org/10.4028/www.scientific.net/amr.833.339.
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To improve the agglomerate phenomena of polarity nanosized MgO-filler in non-polar low density polyethylene (LDPE) matrix, in the composite (MgO/LDPE) master batch preparation process, adding a certain amount of ethylene-vinyl acetate copolymer (EVA), in order to improve the compatibility of nanoparticles and matrix materials. The dispersion states of MgO in the MgO/LDPE and EVA/MgO/LDPE composite material was evaluated by using scanning electron microscope (SEM), results shown that compared with MgO/LDPE nanocomposite, the dispersion of EVA modified MgO/LDPE is better and the agglomerate phenomena is not seen. DC breakdown tests shown that EVA modified MgO/LDPE compared with other several kinds of materials (LDPE; EVA/LDPE; MgO/LDPE and EVA/MgO/LDPE); the DC breakdown strength has improved significantly.
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Kalia, Arun, and M. S. Dhanya. "Evaluation of Biodegradation Efficiency of Xylene Pretreated Polyethylene Wastes by Isolated Lysinibacillus fusiformis." Nature Environment and Pollution Technology 21, no. 3 (September 1, 2022): 1375–80. http://dx.doi.org/10.46488/nept.2022.v21i03.045.
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The ability of the bacterial degradation of low-density polyethylene (LDPE) waste by Lysinibacillus fusiformis isolated from hydrocarbon-contaminated soil was investigated in the present study. The potential of the bacterial isolate to utilize LDPE waste bags of two different thicknesses in a month as a sole carbon source in mineral salt media was assessed. Further, the effect of pretreatment by xylene on the bacterial degradation of LDPE waste bags (0.5 percent w/v) in 30 days was investigated. The isolated Lysinibacillus fusiformis was able to degrade 9.51 percent of LDPE with 30 μm thickness but able to degrade only 1.45 percent of LDPE having 50 μm thickness. The bacterial biomass was 1.77 times higher on LDPE- 30 μm containing media in comparison to LDPE- 50 μm. The xylene pretreatment of LDPE wastes enhanced the biodegradation efficiency of isolated Lysinibacillus fusiformis to 12.09 and 1.97 percent respectively in 30 μm and 50 μm thick LDPE bags. The xylene pre-treatment improved the bacterial growth on media with LDPE of both thicknesses. The adherence of bacterium on the surface of LDPE was found more on 50 μm thick xylene treated LDPE compared to its untreated LDPE than 30 μm thick LDPE films. The xylene pre-treatment of polyethylene waste had an additive effect on the biodegradation of waste LDPE films with a significant effect on thickness.
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Novello, Vittorino, Laura De Palma, Luigi Tarricone, and Giuliano Vox. "Effects of different plastic sheet coverings on microclimate and berry ripening of table grape cv "Matilde"." OENO One 34, no. 2 (June 30, 2000): 49. http://dx.doi.org/10.20870/oeno-one.2000.34.2.1011.
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<p style="text-align: justify;">Two types of plastic cover (LDPE + EVA and LDPE + HDPE) were tested to assess their radiometric properties and the influence on the vegetative and reproductive performances of ‘Matilde’ table grape. Films showed the same transmittance to short infrared waves, but LDPE + EVA had a higher transmissivity to visible, PAR and short infrared wavelength ranges of solar radiation, especially as for the « direct » light component. In comparison to the open field, covering increased GDD accumulation and advanced budbreak by 12 days (LDPE + HDPE) or 20 days (LDPE + EVA). Commercial ripening (14 °Brix) was advanced by 8 and 22 days, respectively. Must acidity was higher in open field than under LDPE + EVA. Yield per vine increased under LDPE + EVA, although not at a significant level; bunch mass was higher under LDPE + EVA than in open field. Berry mass was maximum under LDPE + EVA and progressively decreased under LDPE + HDPE and in open field. Under covering, the pruning cane mass increased by 63% with LDPE + EVA and 43% with LDPE + HDPE.</p>
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Sabet, Maziyar, and Hassan Soleimani. "Broad studies of graphene and low-density polyethylene composites." Journal of Elastomers & Plastics 51, no. 6 (October 3, 2018): 527–61. http://dx.doi.org/10.1177/0095244318802608.
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Graphene (Gr) distribution in low-density polyethylene (LDPE) considerably increased thermal stability, thermal conductivity, mechanical properties, and flexural properties of LDPE/Gr composites. Addition of Grs to LDPE postponed the time for making the polymer brittle. High specific surface area and superior properties of Gr improved thermal stability, conductivity, storage modulus, and mechanical properties of composites. The electrical conductivity of LDPE/Grs composites upgraded owing to the thermal stability of Grs in LDPE matrix. In terms of rheology, the addition of Grs augmented viscosity of the LDPE matrix. Addition of Grs to LDPE nucleates crystallization by reducing the activation energy along with rising crystallization onset temperature. Adding Gr facilitated decreasing aggregation, expanded crystallinity, improved the local lattice order of LDPE/Grs, and advanced Grs contact with LDPE. Thus, on a macroscopic scale, Gr constrains mobility of polymer chains, causing a growth in stiffness and strength of the composite. The distribution of Grs in LDPE at micron size scale was verified by atomic force microscopy and other microscopic testers. With further Grs inclusions to LDPE, the activation energy reduced, Grs proceeded as nucleating agents throughout the crystallization of composites, and increased the enhancement of relative crystallinity of LDPE/Gr compounds. The percolation phenomenon of LDPE/Gr composite occurred about 0.5 wt% of Gr loading. Due to further addition of Gr to LDPE, the impermeability of oxygen through the conduit raised somehow the LDPE/Gr sample with 0.5 wt% Gr content, generated a sharp improvement, and dropped fuel permeation with about 37% in comparison with pure LDPE.
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Tang, Ying, Yun Wang, and Xian Ping Xia. "Influence of the Particle Size of LDPE on the Performance of Cu/LDPE Composites." Advanced Materials Research 833 (November 2013): 330–34. http://dx.doi.org/10.4028/www.scientific.net/amr.833.330.
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The Cu/LDPE composites were characterized through the tests of micro-structure, mechanical property, surface hydrophilicity and releasing rate of cupric ions, in order to study the influence of the particle size of LDPE on the performance of Cu/LDPE composites. The results indicate that, with decreasing of the particle size of LDPE, Cu/LDPE composites have greater value of elongation at break and releasing rate of cupric, but smaller value of tensile strength and elasticity modulus, and the influence on surface hydrophilicity and crystalline is little. It is considered that the influence of the particle size of LDPE on the performance of Cu/LDPE composites results from the difference of both the molecular weight of LDPE and the dispersion uniformity of copper in LDPE.
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Zhao, Xue Yan, Xue Gang Luo, Xiao Yan Lin, and Xiao Qi. "Rheological and Thermal Properties of Blends of Recycled LDPE and Virgin LDPE." Advanced Materials Research 734-737 (August 2013): 2501–4. http://dx.doi.org/10.4028/www.scientific.net/amr.734-737.2501.
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Blends of recycled LDPE and LDPE were prepared by the twin-screw extruder at different ratios. Recycled LDPE was used as matrix in this work, LDPE was used to improve the properties of RLDPE. Thermal and rheological properties of the blends were carefully evaluated and compared with pure LDPE. DSC measurements indicates that the RLDPE/LDPE blends are miscible in the crystalline phase and LDPE can increase the crystallization of the blends. Rheological analysis shows that virgin LDPE will promote the normal flow of RLDPE and improve the mobility of chain segments in flow. Consequently, the rheological and processing properties of the blends have improved compared to RLDPE. The blends show potential applications in high-value products.
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Liu, Jun, Youyuan Wang, Kun Xiao, and Zhanxi Zhang. "Research on the Thermal Aging Behaviors of LDPE/TiO2 Nanocomposites." Journal of Nanomaterials 2017 (2017): 1–11. http://dx.doi.org/10.1155/2017/5048382.
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The ability of antithermal aging of LDPE/TiO2 nanocomposites was investigated through SEM, FTIR, DSC, and dielectric properties in this paper. The results of SEM images showed that the thermal aging had a significant influence on the structure of Pure-LDPE and LDPE/TiO2 samples. The measurement of FTIR showed that the content of hydroxyl and carboxyl increased with thermal aging, but the time of emerging aging characteristic peaks for the LDPE/TiO2 samples was delayed. The DSC measurement indicated that filling TiO2 nanoparticles changed the crystallization behavior of LDPE, played a role of heterogeneous nucleation during the process of recrystallization, and improved the crystallinity of LDPE/TiO2. Similarly, the aged LDPE/TiO2 samples had lower permittivity and dissipation factor compared to the aged Pure-LDPE samples. All the results had indicated the LDPE/TiO2 samples had the significant ability of antithermal aging, especially the LDPE/TiO2-0.5 samples with good dispersion of nanoparticles. A new model was proposed to illustrate the antithermal aging behaviors of LDPE/TiO2 samples, which shows that the TiO2 nanoparticles play a role of “crosslinking points” between LDPE molecular chains, increasing the density of crystal structure and reducing oxygen diffusion into materials to break molecular structure.
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Zhu, Nianqing, Hailong Chen, Xinxing Gao, Rongjie Hou, Zhongbing Ni, and Mingqing Chen. "Fabrication of LDPE/PS interpolymer resin particles through a swelling suspension polymerization approach." e-Polymers 20, no. 1 (July 6, 2020): 361–68. http://dx.doi.org/10.1515/epoly-2020-0031.
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AbstractA facile method to prepare low-density polyethylene (LDPE)/polystyrene (PS) interpolymer resin particles by swelling suspension polymerization without addition of extra swelling agent was developed. The polymerization temperature, polymerization time, and initiator concentration were investigated. Fourier transform infrared spectroscopy analysis confirmed that the LDPE/PS interpolymer resin particles were successfully prepared and a small amount of PS-g-LDPE existed in the resin. Scanning electron microscopy revealed that PS was uniformly distributed in the LDPE matrix, indicating excellent compatibility between PS and LDPE. The mechanical properties of LDPE/PS interpolymer resin were intermediate between PS and LDPE polymers.
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Jai, Junaidah, Siti Fatma Abd Karim, Nurul Asyikin Md Zaki, Rabiatul Adawiyah Abdol Aziz, Farhana Wahet, and Nadiah Shafiqah Shaharuddin. "Physico-mechanical and water absorption properties of LDPE/cassava starch film." Malaysian Journal of Chemical Engineering and Technology (MJCET) 4, no. 2 (October 31, 2021): 103. http://dx.doi.org/10.24191/mjcet.v4i2.13825.
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Plastic waste is a global crisis, and Malaysia is the 8th worst country worldwide for plastic waste. With this trend, growing market demands for green product have imposed pressure on industries to find an alternative to petroleum-based plastic. Degradable plastic is introduced to overcome this limitation. The present work investigates degradable plastic film of low-density polyethylene incorporated with cassava starch (LDPE-CS). The compounding of the LDPE-CS was prepared via pre-mixing, blending, resin crushing, and film hot pressing. Film thickness, tensile strength, elongation, water absorption, and field test were conducted on the LDPE-CS and commercial LDPE (control). Experimental data of LDPE-CS and commercial LDPE films were evaluated and compared. Thickness of LDPE-CS film was 0.18 mm which was 51% thicker than the control film. Tensile strength and elongation of the LDPE-CS were 7.04 MPa and 5.39%, while control film was 12.77 MPa and 921.5%, respectively. The tensile strength and elongation of the LDPE-SC were significantly lower than the control film, which may be due to the weak interface between LDPE and starch. The water absorption test revealed that the LDPE-CS film absorbed water by 4.8%, which indicates its degradability in the water. The field test shows that the LDPE-CS is biodegradable and comparable with the commercial plant polybag in terms of its capability in planting.
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Tee, Tiam Ting, Soo Tueen Bee, Tin Sin Lee, Chantara Thevy Ratnam, and Haraveen Kaur Jogindar Singh. "Hot Set Characterization of Electron Beam Irradiated-Copper (II) Oxide Added LDPE Composites under Acidic Aging." Applied Mechanics and Materials 786 (August 2015): 63–67. http://dx.doi.org/10.4028/www.scientific.net/amm.786.63.
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In this research study, the effect of aging duration time and electron beam irradiation dosages on the hot set results of copper (II) oxide added LDPE composites have been investigated. The addition of copper (II) oxide particles in LDPE matrix has significantly reduced the formation of crosslinking networks in LDPE matrix by blocking the mobility of free radicals generated by electron beam irradiation. At lower irradiation dosages (< 100 kGy), all the copper (II) oxide added LDPE composites were immediately failed the hot set test when subjected to static load of 20 N/cm2 under high temperature. Besides, the occurrence of copper (II) oxide particles in LDPE matrix also reduced the matrix continuities of copper (II) oxide added LDPE composites and caused the matrix resistance ability of LDPE matrix to be decreased. The increasing of irradiation dosages has significantly delayed the failing time of all LDPE composites when under static load at high temperature. This is because the increasing of electron beam irradiation could further induce the generation of free radicals to form higher degree of crosslinking networks in LDPE matrix. At higher irradiation dosage up to 250 kGy, the pristine LDPE was observed able to withstand the applied static load under high temperature more than 15 minutes. This is due to higher degree of crosslinking networks formed in LDPE matrix could effectively restrict the mobility of LDPE chains under static load and thus delay the failing of sampels. When the aging duration time increased from 4 days to 14 days, the resistance ability of all LDPE has been significantly weakened due to the occurrence of chain scissioning process in LDPE matrix by delaying the failing time of samples.
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Cheng, Yujia, Guang Yu, Xiaohong Zhang, and Boyang Yu. "The Research of Crystalline Morphology and Breakdown Characteristics of Polymer/Micro-Nano-Composites." Materials 13, no. 6 (March 21, 2020): 1432. http://dx.doi.org/10.3390/ma13061432.
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In this article, low-density polyethylene (LDPE) was used as a matrix polymer, the Micro-ZnO and Nano-ZnO particles were used as the inorganic filler. With the melt blending method, the Nano-ZnO/LDPE(Nano-ZnO particles doping into LDPE), Micro-ZnO/LDPE(Micro-ZnO particles doping into LDPE) and Micro-Nano-ZnO/LDPE (Nano-ZnO and Micro-ZnO particles doping into LDPE in the same time) composites were prepared. Then, the inorganic filler and the composites were dealt with structural characterizations and analysis by Fourier transform infrared (FTIR), Polarization microscope (PLM), and Differential scanning calorimeter (DSC). Besides, these samples were dealt with (alternating current) AC breakdown performance test. The micro-experimental results showed that the Micro-ZnO and Nano-ZnO particles doping reduced the crystal size and increased the crystallization rate. With the change of cell structure, the crystallinity of composites increased. The crystallinity order of different samples was as follows: LDPE < Micro-ZnO/LDPE < Nano-ZnO/LDPE < Micro-Nano-ZnO/LDPE. From the breakdown of the experimental result, with the same mass fraction of the different inorganic doping of particles, the breakdown strength of these composites was different. The Nano-ZnO particle doping could improve the breakdown strength of composites effectively. Among them, the breakdown strength of Nano-ZnO/LDPE and Micro-Nano-ZnO/LDPE were 11% higher and 1.3% lower than that of pure LDPE, respectively. Meanwhile, the breakdown strength of Micro-composite was the lowest but its Weibull shape coefficient was the highest. Therefore, the Micro-ZnO doping was helpful for the Nano-ZnO dispersing in the matrix, which produced the Micro-Nano-synergy effects better.
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Yap, E. P., S. C. Koay, M. Y. Chan, H. L. Choo, T. K. Ong, and K. Y. Tshai. "Recycling Polymer Blend made from Post-used Styrofoam and Polyethylene for Fuse Deposition Modelling." Journal of Physics: Conference Series 2120, no. 1 (December 1, 2021): 012021. http://dx.doi.org/10.1088/1742-6596/2120/1/012021.
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Abstract Styrofoam is widely used as packaging material for many applications like home furniture and electrical appliance. Styrofoam is a non-biodegradable material which its disposal causes serious environment issues. This research demonstrates an alternate recycling method of Styrofoam waste by converting it into 3D printing filament for Fused Deposition Modelling (FDM). For this research, the recycled polystyrene (rPS) was extracted from Styrofoam waste and blended with low-density polyethylene (LDPE), then extruded into filament using a filament extruder. The formulated rPS/LDPE blend with different blend ratio exhibited a good printability when the printing temperature and extrusion rate fixed at 240°C and 120%. However, the tensile strength of printed specimens with rPS/LDPE blends were lower than printed specimen with neat rPS. The tensile strength and modulus of printed specimens with rPS/LDPE were decreased due to the increase of LDPE content. The decrease of tensile strength mainly caused by the incompatibility between the rPS and LDPE phases. However, the addition of more LDPE content in the blend enhanced the ductility of rPS/LDPE blends. Furthermore, the increase of LDPE content also increased the thermal stability of rPS/LDPE blends. Overall, the rPS/LDPE blend is a potential alternate material for producing FDM filament.
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Sarker, Ranojit Kumar, Payel Paul, Sharmistha Das, Sudipta Chatterjee, Poulomi Chakraborty, and Prosun Tribedi. "Exploration of Strategies for the Enhanced Biodegradation of Low-Density Polyethylene (LDPE) by A Soil Bacterium Enterobacter Cloacae AKS7." Journal of Pure and Applied Microbiology 15, no. 3 (July 2, 2021): 1266–78. http://dx.doi.org/10.22207/jpam.15.3.16.
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In the context of sustainable bioremediation of Low-density polyethylene (LDPE), in this study, several strategies were explored to enhance the LDPE degradation by the bacterium Enterobacter cloacae AKS7. Initially, Mineral oil and Tween 80 were used to test whether they could modulate microbial colonization and polymer degradation by AKS7. Results indicated Mineral oil could increase microbial colonization and LDPE degradation whereas Tween 80 compromised the same. Since LDPE holds hydrophobic characteristics, the organism showing higher cell-surface hydrophobicity could adhere efficiently to the polymer. Thus, the organism AKS7 was grown in media with different concentrations of glucose and ammonium sulphate to exhibit differences in cell-surface hydrophobicity. We noticed that with increasing cell-surface hydrophobicity, the microbial colonization and LDPE degradation got enhanced considerably. The observations indicated that cell-surface hydrophobicity promoted microbial colonization to LDPE that increased the degree of biodegradation. Besides, LDPE films were photo-oxidized before microbial exposure which showed that AKS7 could degrade ultra-violet (UV) treated LDPE more proficiently compared to the UV-untreated polymer. Moreover, AKS7 could colonize more effectively to the UV-treated LDPE in contrast to the untreated LDPE. Furthermore, it was observed that UV exposure increased the carbonyl bond index of the polymer which got utilized by the organism efficiently thereby increasing the polymer degradation. Hence, the observations indicated that effective microbial colonization to UV-treated LDPE films exhibited a promising metabolic activity that could show an enhanced degradation of LDPE. Therefore, AKS7 warrants to be considered as a promising organism for enhanced degradation of LDPE.
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Pham, Nga Thi-Hong. "Characterization of Low-Density Polyethylene and LDPE-Based/Ethylene-Vinyl Acetate with Medium Content of Vinyl Acetate." Polymers 13, no. 14 (July 18, 2021): 2352. http://dx.doi.org/10.3390/polym13142352.
Full textAbstract:
Low-density polyethylene (LDPE) and ethylene vinyl acetate copolymer (EVA), which are non-polar and polar polymers, are immiscible and form a polyphase system. In this study, LDPE was mixed with 2.5%, 5%, 7.5%, 10%, 12.5% Ethylene-vinyl acetate (EVA-28) with a medium content of vinyl acetate (28% VA), respectively by injection molding machine and LDPE. Tensile strength and flexural strength were tested according to ASTM D638-02 standard and ISO 178 standard. The results showed that adding EVA-28 increased the elongation at break of the LDPE/2.5% EVA, LDPE/5% EVA and LDPE/10% EVA blend samples. In addition, the tensile and flexural strength of the LDPE/EVA blend decreases gradually as the EVA-28 content in the blend increases. The hardness decreases with the increasing EVA-28 content. EVA-28 spherical particles appeared scattered on the surface of the LDPE matrix, in the highest EVA-28 percent sample (12.5% EVA-28), the number of particles appeared to be quite a lot, and was dispersed quite evenly on the surface. The LDPE/EVA-28 blend achieved a higher elongation at the break than LDPE, in which 10% EVA-28 gives the highest elongation at break.
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Yang, Jiaming, Congji Liu, Changji Zheng, Hong Zhao, Xuan Wang, and Mingze Gao. "Effects of Interfacial Charge on the DC Dielectric Properties of Nanocomposites." Journal of Nanomaterials 2016 (2016): 1–11. http://dx.doi.org/10.1155/2016/2935202.
Full textAbstract:
The interfacial charge phenomenon of MgO/low-density polyethylene (LDPE) and SiO2/LDPE nanocomposites was measured by synchrotron radiation small-angle X-ray scattering. Based on the Porod theory, the Porod curve of SiO2/LDPE nanocomposite shows negative divergence but the LDPE and MgO/LDPE do not, which reveals that interfacial charge may exist in the SiO2/LDPE nanocomposite. The DC dielectric properties of the nanocomposites are closely related to the interfacial charge. Experimental results show that the SiO2/LDPE nanocomposite has lower DC conductivity, less space charge, and higher DC breakdown strength than the MgO/LDPE nanocomposite. It is thought that the interfacial charge has a positive effect on the DC dielectric performance of nanocomposites, and the mechanism could be attributed to the scattering effects of the interfacial charge on the carrier migration. There is no obvious interfacial charge in the MgO/LDPE nanocomposite, but it still has excellent DC dielectric properties compared with LDPE, which indicates that the interfacial charge is not the only factor affecting the dielectric properties; the dipole interface layer and the reduction of free volume can also inhibit the migration of carriers and decrease electrons free path, improving the dielectric performance.
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Trong, Vu Minh, and Bui Dinh Hoan. "Infrared Spectrum and Thermal Properties of LDPE, EVA and Fly Ash Composites." Key Engineering Materials 869 (October 2020): 69–75. http://dx.doi.org/10.4028/www.scientific.net/kem.869.69.
Full textAbstract:
The polymer composites based on low-density polyethylene (LDPE), ethylene vinyl acetate copolymer (EVA) and fly ash (FA) without and with vinyltrimetoxysilan (VTMS) modification were prepared by melt mixing in a Haake Rheomixer. The FT-IR spectra indicated the bonds between LDPE/EVA and FA modified by vinyltrimetoxysilan were dipole - dipole interaction and hydrogen bonding. Thermal oxidation stability of the LDPE/EVA/VFA composites are higher than those of the LDPE/EVA/FA composites. Thermal oxidation stability of the LDPE/EVA/VFA composites and the LDPE/EVA/FA composites were higher than the LDPE/EVA blends. Putting fly ash into polymers, thermal oxidation stability of composites increased and significantly increased when using modified fly ash (MFA).
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Yu, Guang, and Yujia Cheng. "Effects of Inorganic ZnO Particle Doping on Crystalline Polymer Morphology and Space Charge Behavior." Coatings 10, no. 10 (September 29, 2020): 932. http://dx.doi.org/10.3390/coatings10100932.
Full textAbstract:
This study further investigated the synergistic effect of micro- and nanofiller doping on matrix material space charges and breakdown characteristics. Accordingly, low-density polyethylene (LDPE) was used as the matrix material, and spherical ZnO particles with sizes of 30 nm and 1 µm were used as additives. Micro-ZnO/LDPE, nano-ZnO/LDPE, and micro-nano-ZnO/LDPE composites were prepared through melt blending. The crystalline morphologies of the composites were observed via polarized light microscopy. The composite crystallinity and melting peak temperature were measured via differential scanning calorimetry, and the micro- and nanoparticle dispersions in the matrix were observed via scanning electron microscopy. The test results showed that the particles were uniformly dispersed in the polyethylene matrix. The filler acted as a heterogeneous nucleation agent in the matrix. The crystal size decreased, thereby increasing the crystal quantity. The doping of inorganic ZnO particles improved the composite crystallinity. The ZnO/LDPE composites were subjected to DC breakdown, space charge, and dielectric spectrum tests. When the crystal arrangement of the sample was loose and its size was large, the breakdown process developed along a shorter path, and the field strength of the composite breakdown decreased. The order of AC and DC breakdown field strengths of the samples was as follows: micro-ZnO/LDPE < pure LDPE < micro-nano-ZnO/LDPE < nano-ZnO/LDPE. The DC and AC breakdown field strengths of the micro- and nano-ZnO/LDPE were 4.7% and 3.2% higher than those of the pure LDPE, respectively. Moreover, the DC and AC breakdown field strengths of the nano-ZnO/LDPE were 11.02% and 15.8% higher than those of the pure LDPE, respectively. The doping of inorganic ZnO particles restrained the space charge accumulation, and the residual charges decreased after short-circuit treatment. The dielectric constant of all nanocomposites was lower than that of LDPE, and the dielectric loss of all composites was higher than that of LDPE.
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Song, Wei, Yu Sun, Tian-Jiao Yu, Yu-Zhang Fan, Zhi Sun, and Bai Han. "Investigation of Electrical Properties of BiFeO3/LDPE Nanocomposite Dielectrics with Magnetization Treatments." Polymers 13, no. 16 (August 6, 2021): 2622. http://dx.doi.org/10.3390/polym13162622.
Full textAbstract:
The purpose of this paper is to study the effect of nano-bismuth ferrite (BiFeO3) on the electrical properties of low-density polyethylene (LDPE) under magnetic-field treatment at different temperatures. BiFeO3/LDPE nanocomposites with 2% mass fraction were prepared by the melt-blending method, and their electrical properties were studied. The results showed that compared with LDPE alone, nanocomposites increased the crystal concentration of LDPE and the spherulites of LDPE. Filamentous flake aggregates could be observed. The spherulite change was more obvious under high-temperature magnetization. An agglomerate phenomenon appeared in the composite, and the particle distribution was clear. Under high-temperature magnetization, BiFeO3 particles were increased and showed a certain order, but the change for room-temperature magnetization was not obvious. The addition of BiFeO3 increased the crystallinity of LDPE. Although the crystallinity decreased after magnetization, it was higher than that of LDPE. An AC test showed that the breakdown strength of the composite was higher than that of LDPE. The breakdown strength increased after magnetization. The increase of breakdown strength at high temperature was less, but the breakdown field strength of the composite was higher than that of LDPE. Compared with LDPE, the conductive current of the composite was lower. So, adding BiFeO3 could improve the dielectric properties of LDPE. The current of the composite decayed faster with time. The current decayed slowly after magnetization.
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Tee, Tiam Ting, Soo Tueen Bee, Tin Sin Lee, Chantara Thevy Ratnam, Haraveen Kaur Jogindar Singh, and Chong Yu Low. "Effect of Aging in Acidic Condition on Mechanical Properties of Copper (II) Oxide Added LDPE Composites." Applied Mechanics and Materials 786 (August 2015): 8–12. http://dx.doi.org/10.4028/www.scientific.net/amm.786.8.
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In this work, the effect of aging duration time and copper (II) oxide loading level on the physico-mechanical properties of copper (II) oxide added LDPE composites have been investigated. The addition of copper (II) oxide particles in LDPE matrix has significantly decreased the tensile strength of LDPE composites. The occurrence of copper (II) oxide particles in LDPE matrix could reduce the matrix continuities of copper (II) oxide added LDPE composites by the agglomeration of copper (II) oxide particles. This could further cause the applied straining stress unable to be effectively transferred throughout the whole polymer matrix. The increasing of aging time duration up to 8 days has slightly reduced the tensile strength of all copper (II) oxide added LDPE composites. The increasing of copper (II) oxide loading level has significantly decreased the elongation at break of LDPE composites. This is due to poor interfacial adhesion between copper (II) oxide particles and LDPE matrix could further restrict the mobility of LDPE chains under straining stress and thus decrease the elongation at break.
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AbdulKadir, H. K., and Abdulkader M. Alakrach. "Effects of Hydrolytic and Oxidizing Agents on the Properties of Low Density Polyethylene/Halloysite Nanocomposites for Biomedical Applications." INTERNATIONAL JOURNAL OF DRUG DELIVERY TECHNOLOGY 12, no. 03 (June 30, 2022): 990–95. http://dx.doi.org/10.25258/ijddt.12.3.12.
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Low density polyethylene (LDPE) nanocomposites reinforced with natural halloysite nanotubes (HNTs) were synthesized and evaluated as a prospective material for biomedical applications via in vitro biostability studies in this work. A twin-screw extruder machine was used to fabricate the examined LDPE and LDPE/HNTs nanocomposites (NCs), followed by in vitro treatment of the prepared NCs via immersion in oxidizing and hydrolytic chemicals for four weeks at 37°C. The materials’ in vitro mechanical characteristics were evaluated under these harsh conditions. The analysis showed that the LDPE with 3 wt% HNTs exhibited the best nanofiller dispersion characteristics. This NC also presented smoother surface degradation characteristics compared to the plain LDPE and other LDPE NCs. Furthermore, as compared to plain LDPE, the LDPE NCs showed enhanced mechanical capabilities, and these qualities were less impacted by the in vitro conditions. The introduction of 3 wt% HNTs into the LDPE gave the best in vitro mechanical characteristics. Furthermore, the existence of a better-scattered nanotube structure was thought to offer a more sinuous pathway for the propagation of H2O and the oxidants, thereby reducing their penetration across the matrix chains. Hence, the kinetics of disintegration inside the LDPE molecular chains were slower, resulting in improved biostability.
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Canales, Daniel, Lissette Montoille, Lina M. Rivas, J. Andrés Ortiz, Mauricio Yañez-S, Franco M. Rabagliati, Maria Teresa Ulloa, Eduardo Alvarez, and Paula A. Zapata. "Fungicides Films of Low-Density Polyethylene (LDPE)/Inclusion Complexes (Carvacrol and Cinnamaldehyde) Against Botrytis Cinerea." Coatings 9, no. 12 (November 26, 2019): 795. http://dx.doi.org/10.3390/coatings9120795.
Full textAbstract:
Low density polyethylene (LDPE) films were prepared with the incorporation of natural agents (carvacrol and trans-cinnamaldehyde) by the melting process. The co-precipitation method was used successfully to complex the carvacrol or trans-cinnamaldehyde with β-cyclodextrin (β-CD). The active compounds encapsulated in β-CD achieved ca. 90% encapsulation efficiency (E.E.). The inclusion complex studied by scanning electron microscopy (SEM) found particles of different sizes, ca. 4 μm. The active compounds were added directly (1 and 5 wt %) into the polymer matrix, yielding LDPE + carvacrol and LDPE + cinnamaldehyde films. The active compounds encapsulated in β-cyclodextrin (β-CD) were added to LDPE, yielding LDPE + β-CD-carvacrol and LDPE + β-CD-cinnamaldehyde films. The incorporation of carvacrol and trans-cinnamaldehyde, and their corresponding inclusion complexes with β-cyclodextrin, did not affect the thermal properties of LDPE. The microcapsules distributed in all polymer matrices had sizes of 5–20 μm as shown by scanning electron microscopy (SEM). In terms of mechanical properties, the polymers showed a slight decrease of Young’s modulus (12%) and yield stress compared (14%) to neat LDPE. This could be due to the essential oil acting as a plasticizer in the polymer matrix. The LDPE + carvacrol and LDPE + cinnamaldehyde films had the capacity to inhibit fungi by 99% compared to neat LDPE. The effectiveness against fungi of LDPE+β-CD + active agent was slower than by the direct incorporation of the essential oil in the LDPE in the same amount of active agent. The biocidal properties were related to the gradual release of active compound from the polymer. The results confirm the applicability of carvacrol, trans-cinnamaldehyde, and their corresponding inclusion complexes in active packaging, as well as their use in the food delivery industry.
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CN Mefo, BA Ezeonuegbu, JB Ameh, SA Ado, and US Ishiaku. "Biodegradation of cassava starch modified low density polyethylene by Bacillus cereus and Pseudomonas aeruginosa isolated from waste dumpsite." GSC Biological and Pharmaceutical Sciences 19, no. 2 (May 30, 2022): 149–57. http://dx.doi.org/10.30574/gscbps.2022.19.2.0170.
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Low density polyethylene (LDPE) is used for packaging and other industrial application is a significant source of environmental pollution. The present study was aimed at testing the ability of bacterial strains identified as Bacillus cereus and Pseudomonas aeruginosa to degrade LDPE. These strains were isolated from soil samples collected from dump site. All bacterial isolates were screened for their ability to degrade synthetic LDPE. Bacillus cereus and Pseudomonas aeruginosa produced weight loss percentages of 0.18% and 0.17% respectively and were used for further studies. The biodegradation was further enhanced by blending pellets of the LDPE (90, 80 and 70 %) with cassava starch (10, 20 and 30%). The screened bacteria isolates were incubated along with the cassava starch modified LDPE for a period of 60 days. Degradation was observed in terms of weight loss and tensile strength of the modified LDPE. Bacillus cereus and Pseudomonas aeruginosa achieved a maximum weight loss reduction of 42.01 % and 51.03 % respectively in LDPE modified with 30 % cassava starch. However, the highest weight loss reduction of 54.03 % in 30 % Cassava starch modified LDPE by the bacterial consortium. Tensile strength of 42.01% was achieved in LDPE containing 30% starch. Therefore these results show that the bacteria used in this study can colonize, utilize and modify LDPE as a sole carbon source, signifying the potential of Bacillus and Pseudomonas spp. to degrade LDPE film. This work would also pave way for future studies on biodegradation to resolve the universal pollution issues.
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Tee, Tiam Ting, Soo Tueen Bee, Azman Hassan, Chantara Thevy Ratnam, Tin Sin Lee, and Chong Yu Low. "Full Factorial Design Analysis on Mechanical Properties of Electron Beam Irradiated-Flame Retarded LDPE/EVA Composites." Applied Mechanics and Materials 786 (August 2015): 58–62. http://dx.doi.org/10.4028/www.scientific.net/amm.786.58.
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This study aims to investigate the effect of three factors, namely alumina trihydrate (ATH), montmorillonite (MMT) and irradiation dosage on the mechanical properties (tensile strength and elongation at break) of flame-retarded LDPE-EVA composites. In this study, full factorial design analysis was used to examine the effects of factors and their combination interactions on mechanical properties. ATH is the most significant factor in affecting the tensile strength of LDPE-EVA blends due to the poor compatibility effect between ATH particles and LDPE-EVA matrix. However, MMT is the least significant factor on tensile strength of LDPE-EVA composites. ATH was the most significant in affecting the elongation at break of LDPE-EVA blends. This is because the increasing of ATH amount in LDPE-EVA matrix could restrict the mobolity of polymer chains in LDPE-EVA matrix. However, the factor of irradiation dosage was found to be insignificant in affecting the elongation at break of LDPE-EVA blends.
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Wang, Ni Na, Ding Han Xiang, Pin Shu Mo, and Yi Lu. "Flame Retardant Low Density Polyethylene with Aluminium Hydroxide/ Commercial Fire Retardants FR01 Synergistic System." Advanced Materials Research 652-654 (January 2013): 485–89. http://dx.doi.org/10.4028/www.scientific.net/amr.652-654.485.
Full textAbstract:
Low density polyethylene (LDPE) was modified by the addition of commercial fire retardants FR01 and aluminium hydroxide (ATH). ATH/FR01/LDPE composites were prepared by melt blending and extrusion in a twin-screw extruder. ATH was first modified by a silane coupling agent KH550 then added to LDPE. The flame retardancy, electrical property and thermal behavior of the LDPE composites were investigated by limiting oxygen index (LOI), volume resistivity and thermogravimetric analysis (TGA), respectively. The results indicated that the surface modification of ATH (M-ATH) could greatly improve the dispersibility and compatibility with LDPE matrix. The mechanical property tests showed good mechanical properties of composite, compared with unmodified one, tensile strength and elongation of M-ATH/LDPE were all improved, and the addition of FR01 improved the flame retardancy of ATH/LDPE remarkably. TGA results demonstrate that char yield of M-ATH/FR01/LDPE (30/15/70) reaches 27 wt% at 600 °C in Ar atmosphere.
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Li, Changming, Sixu Duan, Chengcheng Zhang, Jian Zhang, and Baozhong Han. "Research on DC dielectric properties of polyaniline nanofibers/LDPE composites." High Performance Polymers 30, no. 1 (December 22, 2016): 76–81. http://dx.doi.org/10.1177/0954008316680278.
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In this article, polyaniline (PANI) nanofibers were prepared and added to low-density polyethylene (LDPE) to produce PANI nanofibers/LDPE composites. LDPE and the composites were tested for direct current (DC) conductivity, breakdown strength, and space charge characteristics. The results suggested that DC breakdown strength of PANI nanofibers/LDPE composites significantly declined once PANI was added, and the decline was more evident with the increase of PANI nanofibers. Meanwhile, the addition of PANI nanofibers contributed to a decrease in the conductivity of LDPE. As the content of PANI nanofibers increased, the conductivity of the composites declined first and then raised. DC conductivity properties of LDPE could be improved by adding an appropriate amount of PANI nanofibers. Compared with LDPE, the space charge distribution was changed in LDPE due to the addition of PANI nanofibers. With the increase of content of PANI nanofibers, the amount of space charges close to the electrodes decreased gradually.
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Yan, Zhiyu, Hong Zhao, Baozhong Han, Jiaming Yang, and Junqi Chen. "The suppression of space charge accumulation in CB/LDPE nanocomposites and its association with molecule relaxation." e-Polymers 18, no. 1 (January 26, 2018): 49–56. http://dx.doi.org/10.1515/epoly-2017-0111.
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AbstractSpace charge accumulation within insulating material poses a threat to the reliability in the operation of DC power cables. To investigate the influence of carbon black (CB) on the space charge accumulation of low density polyethylene (LDPE), both conductive carbon black (C-CB) and insulating carbon black (I-CB) were employed as filler particles. The space charge distributions of LDPE and CB/LDPE nanocomposites were obtained by the pulsed electro-acoustic (PEA) method. Additionally, dynamic mechanical analysis (DMA) and thermally stimulated current (TSC) spectroscopy were applied to explore the mechanism of improving space charge performance. Both the C-CB/LDPE and I-CB/LDPE nanocomposites can effectively suppress space charge accumulation. It was concluded that the improvement in space charge characteristics of CB/LDPE nanocomposites was attributable to the interaction between the CB particles and the LDPE, which reduces the number of defects formed from molecules participating in α relaxation and decreases the density of traps within the LDPE.