Browsing by Subject "Degradation"

Now showing 1 - 7 of 7
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    Degradation of bleaching agents under two different storage conditions
    (2016) Almutiri, Basil; Cook, Norman Blaine; Platt, Jeffrey A.; Lund, Melvin R.; Soto, Armando E.; Matis, Bruce A.
    This study was conducted in order to determine if there is any change in the active ingredient of tooth-whitening agents when the products are received from the manufacturer (Baseline), two months, four months, and six months after they are received, under two different storage conditions. Thirty-six products were received from multiple manufacturers: eight with hydrogen peroxide and 28 carbamide with peroxide products. All the bleaching syringes for a specific product were from the same lot. Once the products were received, one sample of each product was stored at room temperature and the other sample was stored in a refrigerator. Assays to determine the baseline concentration were performed within the first two weeks of their arrival and again 2 months, 4 months, and 6 months after receiving the products. All samples were analyzed for peroxide content by using the United States Pharmacopeia recommended method. The results obtained from this study show the following: 1. Bleaching products have different concentrations than what are indicated on the label. 2. Storage of bleaching products for an extended time at room temperature can cause bleaching products to lose some of their potency. 3. The preferable storage condition verified in this study is under refrigeration.
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    Effects of DCPD Cement Chemistry on Degradation Properties and Cytocompatibility: Comparison of MCPM/β-TCP and MCPM/HA Formulations
    (IOP, 2013) Alge, Daniel L.; Goebel, W. Scott; Chu, Tien-Min Gabriel; Pediatrics, School of Medicine
    Dicalcium phosphate dihydrate (DCPD) cements are attractive biomaterials for bone repair, and a number of different DCPD cement formulations have been proposed in the literature. In this study, we have specifically compared monocalcium phosphate monohydrate (MCPM)/hydroxyapatite (HA) and MCPM/β-tricalcium phosphate (β-TCP) formulations to test the hypothesis that DCPD cement chemistry affects the degradation properties and cytocompatibility of the cement. Using simple in vitro models we found that MCPM/β-TCP formulations degraded primarily by DCPD dissolution, which was associated with a slight pH drop and relatively low mass loss. Cytocompatibility testing of cement conditioned culture media revealed no significant change in cell viability relative to the negative control for all of the MCPM/β-TCP formulations. In contrast, the MCPM/HA formulations were prone to undergo rapid conversion of DCPD to HA, resulting in a sharp pH drop and extensive mass loss. A stoichiometric excess of HA in the cement was found to accelerate the conversion process, and significant cytotoxicity was observed for the MCPM/HA formulations containing excess HA. Collectively, these results show that, although the product of the setting reaction is the same, DCPD cements produced with MCPM/HA and MCPM/β-TCP formulations differ significantly in their degradation properties and cytocompatibility. These differences may have important implications for the selection of a DCPD cement formulation for clinical application.
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    Fundamental Investigation of Direct Recycling Using Chemically Delithiated Cathode
    (2022-12) Bhuyan, Md Sajibul Alam; Shin, Hosop; Zhu, Likun; Wei, Xiaoliang
    Recycling valuable cathode material from end-of-life (EOL) Li-ion batteries (LIBs) is essential to preserve raw material depletion and environmental sustainability. Direct recycling reclaims the cathode material without jeopardizing its original functional structures and maximizing return values from spent LIBs compared to other regeneration processes. This work employed two chemically delithiated lithium cobalt oxide (LCO) cathodes at different states of health (SOH), which are analogous to the spent cathodes but free of any impurities, to investigate the effectiveness of cathode regeneration. The material and electrochemical properties of both delithiated SOHs were systematically examined and compared to pristine LCO cathode. Further, those model materials were regenerated by a hydrothermal-based approach. The direct cathode regeneration of both low and high SOH cathode samples restored their reversible capacity and cycle performance comparable to pristine LCO cathode. However, the inferior performance observed in higher current density (2C) rate was not comparable to pristine LCO. In addition, the higher resistance of regenerated cathodes is attributed to lower high-rate performance, which was pointed out as the key challenge of the cathode recycling process. This study provides valuable knowledge about the effectiveness of cathode regeneration by investigating how the disordered, lithium-deficient cathode at different SOH from spent EOL batteries are rejuvenated without changing any material and electrochemical functional properties.
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    Hydrolytically Degradable PEG-Based Inverse Electron Demand Diels-Alder Click Hydrogels
    (American Chemical Society, 2022) Dimmitt, Nathan H.; Arkenberg, Matthew R.; de Lima Perini, Mariana Moraes; Li, Jiliang; Lin, Chien-Chi; Biomedical Engineering, School of Engineering and Technology
    Hydrogels cross-linked by inverse electron demand Diels-Alder (iEDDA) click chemistry are increasingly used in biomedical applications. With a few exceptions in naturally derived and chemically modified macromers, iEDDA click hydrogels exhibit long-term hydrolytic stability, and no synthetic iEDDA click hydrogels can undergo accelerated and tunable hydrolytic degradation. We have previously reported a novel method for synthesizing norbornene (NB)-functionalized multiarm poly(ethylene glycol) (PEG), where carbic anhydride (CA) was used to replace 5-norbornene-2-carboxylic acid. The new PEGNBCA-based thiol-norbornene hydrogels exhibited unexpected fast yet highly tunable hydrolytic degradation. In this contribution, we leveraged the new PEGNBCA macromer for forming iEDDA click hydrogels with [methyl]tetrazine ([m]Tz)-modified macromers, leading to the first group of synthetic iEDDA click hydrogels with highly tunable hydrolytic degradation kinetics. We further exploited Tz and mTz dual conjugation to achieve tunable hydrolytic degradation with an in vitro degradation time ranging from 2 weeks to 3 months. Finally, we demonstrated the excellent in vitro cytocompatibility and in vivo biocompatibility of the new injectable PEGNBCA-based iEDDA click cross-linked hydrogels.
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    Molybdopterin biosynthesis pathway contributes to the regulation of SaeRS two-component system by ClpP in Staphylococcus aureus
    (Taylor & Francis, 2022) Zhao, Na; Wang, Yanan; Liu, Junlan; Yang, Ziyu; Jian, Ying; Wang, Hua; Ahmed, Mahmoud; Li, Min; Bae, Taeok; Li, Qian; Biology, School of Science
    In Staphylococcus aureus, the SaeRS two-component system is essential for the bacterium's hemolytic activity and virulence. The Newman strain of S. aureus contains a variant of SaeS sensor kinase, SaeS L18P. Previously, we showed that, in the strain Newman, SaeS L18P is degraded by the membrane-bound protease FtsH. Intriguingly, the knockout mutation of clpP, encoding the cytoplasmic protease ClpP, greatly reduces the expression of SaeS L18P. Here, we report that, in the strain Newman, the positive regulatory role of ClpP on the SaeS L18P expression is due to its destabilizing effect on FtsH and degradation of MoeA, a molybdopterin biosynthesis protein. Although the transcription of ftsH was not affected by ClpP, the expression level of FtsH was increased in the clpP mutant. The destabilizing effect appears to be indirect because ClpXP did not directly degrade FtsH in an in vitro assay. Through transposon mutagenesis, we found out that the moeA gene, encoding the molybdopterin biosynthesis protein A, suppresses the hemolytic activity of S. aureus along with the transcription and expression of SaeS L18P. In a proteolysis assay, ClpXP directly degraded MoeA, demonstrating that MoeA is a substrate of the protease. In a murine bloodstream infection model, the moeA mutant displayed reduced virulence and lower survival compared with the WT strain. Based on these results, we concluded that ClpP positively controls the expression of SaeS L18P in an FtsH and MoeA-dependent manner, and the physiological role of MoeA outweighs its suppressive effect on the SaeRS TCS during infection.
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    Monitoring compositional changes of the lipid fraction of fingermark residues deposited on paper during storage
    (Forensic Chemistry, 2016-11-01) Frick, A.A.; Chidlow, G.; Goodpaster, John V.; Lewis, S.W.; van Bronswijk, W.
    Characterising the changes in fingermark composition as a function of time is of great value for improving fingermark detection capabilities by understanding the processes and circumstances under which target compounds become degraded. In this study, gas chromatography-mass spectrometry was used to monitor relative changes in the lipids from latent fingermarks over 28 days. Principal component analysis of the relative composition of 15 lipids in fingermarks showed that fingermark age was a significant contributor to the variability observed in the data, but that inter-donor variability was also significant. This was attributed principally to changes in the relative amounts of squalene, which rapidly decreased in the fingermarks. It was also observed, however, that most fingermarks exhibited relatively small changes in composition during the first seven days, followed by more rapid changes up to 28 days. Significant inter-donor variation of both initial fingermark composition and the rates and nature of loss processes was observed, which was reflected in the relative projection of samples from different donors. Finally, samples stored with no exposure to light or airflow for 28 days were projected significantly closer to the samples analysed on the day of deposition than those exposed to light, due to the reduced photodegradation rate of squalene.
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    The influence of matrix degradation and functionality on cell survival and morphogenesis in PEG-based hydrogels
    (Wiley, 2013) Raza, Asad; Lin, Chien-Chi; Biomedical Engineering, Purdue School of Engineering and Technology
    Two norbornene-functionalized PEG macromers are synthesized to render hydrogels with different hydrolytic degradability. Dithiol-containing linkers such as dithiothreitol or biscysteine-containing peptides are used to control proteolytic degradability. The influence of thiol-ene gel degradability on cell survival and morphogenesis in 3D is assessed using hMSCs and pancreatic MIN6 β cells. The initial cell viability can be negatively affected in highly crosslinked thiol-ene hydrogels. When cells are encapsulated in thiol-ene gels lacking cell-adhesive motifs, their survival and proliferation are promoted in more hydrolytically labile hydrogels. The degree of 3D cell spreading in encapsulated hMSCs is enhanced when the matrices are immobilized with cell-adhesive motifs.