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Le Thi, Phuong,Lee, Yunki,Kwon, Ho Joon,Park, Kyung Min,Lee, Mi Hee,Park, Jong-Chul,Park, Ki Dong American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.24
<P>Thrombus and infections are the most common causes for the failure of medical devices, leading to higher hospitalization costs and, in some cases, patient morbidity. It is, therefore, necessary to develop novel strategies to prevent thrombosis and infection caused by medical devices. Herein, we report a simple and a highly efficient strategy to impart antithrombotic and antimicrobial properties to substrates, by simultaneously immobilizing heparin and in situ-synthesized silver nanoparticles (Ag NPs) via a tyrosinase-catalyzed reaction. This consists of tyrosinase-oxidized phenolic groups of a heparin derivative (heparin-grafted tyramine, HT) to catechol groups, followed by immobilizing heparin and inducing the in situ Ag NP formation onto poly(urethane) (PU) substrates. The successful immobilization of both heparin and in situ Ag NPs on the substrates was confirmed by analyses of water contact angles, XPS, SEM, and AFM. The sustained silver release and the surface stability were observed for 30 days. Importantly, the antithrombotic potential of the immobilized surfaces was demonstrated by a reduction in fibrinogen absorption, platelet adhesion, and prolonged blood clotting time. Additionally, the modified PU substrates also exhibited remarkable antibacterial properties against both Gram-positive and Gram-negative bacteria. The results of this work suggest a useful, effective, and time-saving method to improve simultaneous antithrombotic and antibacterial performances of a variety of substrate materials for medical devices.</P>
Le-Phuc Nguyen,Yen Thi Hai Pham,Phuong Thuy Ngo,Tri Van Tran,Loc Vinh Tran,Nam Thi Hoai Le,Luong Huu Nguyen,Tung Thanh Dang,Duc Anh Nguyen,Marco Wenzel,David Hartmann,Karsten Gloe,Jan J. Weigand,Klaus 한국화학공학회 2018 Korean Journal of Chemical Engineering Vol.35 No.5
Acid leaching and a two-step solvent extraction procedure were developed to produce high purity mixture of La and Ce from iron-rich spent FCC catalyst discharged from Dzung Quat refinery (Vietnam). Acid leaching of the spent catalyst with 2M HNO3 and a solid-to-liquid ratio of 1/3 at 80 oC in 1 h dissolved almost 90% of La while 12% of Al and 25% of Fe were transferred to the leachate. The extraction of RE metals and main impurities such as Al and Fe by a mixture of di-2-ethylhexyl phosphoric acid (D2EHPA) and tributyl phosphate (TBP) was investigated. Experiments showed that it was necessary to remove Fe before extracting RE and the optimum extraction conditions for a high recovery of RE while 0% of Al extraction were pH1, contact time=10min, and D2EHPA/TBP volume ratio= 4 : 1. At these conditions, the extraction yields of La(III) and Ce(III) were 72% and 89%, respectively. A two-step solvent extraction was developed to achieve a high purity of RE mixture, which included (1) the removal of impurity Fe by 25% (v/v) diisooctyl phosphinic acid (DiOPA) in n-octane for 140 min, (2) the extraction of rare earths by a mixture of di-2-ethylhexyl phosphoric acid (D2EHPA) and tributyl phosphate (TBP) in n-octane for 10 min without the need for adjusting the pH of the leaching solution.
Financing Decision and Labor Cost: Evidence from South Asian Countries
Thi Phuong Vy Le,Xuan Vinh Vo 중앙대학교 경제연구소 2020 Journal of Economic Development Vol.45 No.1
This study investigates the effect of financial leverage on labor costs using a data sample of listed companies from Southeast Asian countries covering the period from 2009 to 2015. Using several techniques for robust results, the results show that financial leverage has a negative effect on labor costs. In addition, the study finds that the negative impact of financial leverage on labor cost tends to be less in state-owned, foreign-owned, and large companies.
In situ forming gelatin hydrogels by dual-enzymatic cross-linking for enhanced tissue adhesiveness
Le Thi, Phuong,Lee, Yunki,Nguyen, Dai Hai,Park, Ki Dong The Royal Society of Chemistry 2017 Journal of materials chemistry. B, Materials for b Vol.5 No.4
<P><I>In situ</I> forming hydrogels show promise as therapeutic implants and carriers in a wide range of biomedical applications. They can easily seal or fill damaged tissue, thereby functioning as cell/drug delivery vehicles or hemostats. In this regard, strong and stable adhesion to the surrounding tissue is considered an important parameter to improve the <I>in vivo</I> performance of <I>in situ</I> forming hydrogels. In this study, tissue-adhesive gelatin-based hydrogels were prepared by dual-enzymatic cross-linking, where horseradish peroxidase (HRP) and tyrosinase (Tyr) were used. Tyr was employed to convert phenol groups of gelatin derivatives into <I>o</I>-quinone, which can readily react with nucleophiles (<I>e.g.</I>, amines or thiols) on tissue surfaces, thereby resulting in strong tissue adhesion. Incorporating Tyr (0.25 kU mL<SUP>−1</SUP>) did not affect the gelation rate or mechanical strength of HRP-cross-linked hydrogels. Importantly, the dual-enzymatically cross-linked hydrogels (GH/HRP/Tyr) exhibited significantly improved adhesive strength (34 kPa), which was superior to single HRP-cross-linked hydrogels (GH/HRP; 19 kPa) and commercially available fibrin glues (7 kPa). These dual-enzymatically cross-linked gelatin-based hydrogels with strong adhesiveness could act as promising bio-adhesives for tissue-regeneration applications.</P>
Le Thi, Phuong,Lee, Yunki,Hoang Thi, Thai Thanh,Park, Kyung Min,Park, Ki Dong Elsevier 2018 Materials science & engineering. C, Materials for Vol.92 No.-
<P><B>Abstract</B></P> <P>Recently, the interest in antimicrobial hydrogels with impregnated antibacterial agents has significantly increased because of their ability to combat infection in biomedical applications, including wound management, tissue engineering, and biomaterial surface coating. Among these antibacterial reagents, silver nanoparticles (AgNP) show good antibacterial activity against both gram-negative and gram-positive bacteria, including highly multi-resistant strains. However, the entrapment of AgNP within a hydrogel matrix is often associated with toxicity issues because of the use of chemical reductants (<I>e.g.</I>, commonly sodium borohydride), burst leaching, or unwanted agglomeration of AgNP in the absence of surfactants or stabilizers. In this study, we present catechol-rich gelatin hydrogels with <I>in situ</I> hybridization of AgNP for enhanced antimicrobial activities. AgNP were formed through a redox reaction between silver ions and the catechol moieties of a gelatin derivative polymer, without the addition of any chemical reductants. The AgNP with an average size of 20 nm were entrapped within hydrogel matrices and showed sustained release from the hydrogel matrix (8.7% for 14 days). The resulting hydrogels could kill both gram-negative and gram-positive bacteria, depending on the amount of AgNP released from the hydrogels and did not have a significant influence on mammalian cell viability. We believe that our catechol-rich hydrogels <I>in situ</I> hybridizations with AgNP have great potential for biomedical applications, such as wound management and surface coating, because of their excellent antibacterial activities and biocompatibility.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Silver nanoparticles incorporation (AgNP) impart the antimicrobial properties to injectable gelatin hydrogel. </LI> <LI> AgNP was <I>in situ</I> synthesized within the hydrogel matrix, with controllable size and sustained release. </LI> <LI> The nanocomposite hydrogels significantly inhibited bacterial growth without affecting viability of mammalian cells. </LI> <LI> These <I>in situ</I> forming GHD/AgNP hydrogels are potential for a wide range of biomedical applications. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>A simple method using catecholic chemistry to prepare an injectable nanocomposite hydrogel with excellent antimicrobial activities. Silver nanoparticles (AgNP) were <I>in situ</I> synthesized within the gelatin hydrogel matrix, during the hydrogelation without use of toxic reductants. The hydrogels inhibited bacterial growth while not affected the viability of mammalian cells. This injectable hydrogel is easy to fabricate <I>in vivo</I> with promising potential for biomedical applications, where advantageous antibacterial activities are required to reduce the infection rates, for example wound dressing, tissue adhesives, biomaterial surface coatings …</P> <P>[DISPLAY OMISSION]</P>