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      • Stabilization of Polymer-Hydrogel Capsules via Thiol–Disulfide Exchange

        Chong, Siow-Feng,Chandrawati, Rona,Stä,dler, Brigitte,Park, Jeongju,Cho, Jinhan,Wang, Yajun,Jia, Zhongfan,Bulmus, Volga,Davis, Thomas P.,Zelikin, Alexander N.,Caruso, Frank WILEY-VCH Verlag 2009 Small Vol.5 No.22

        <P>Polymer hydrogels are used in diverse biomedical applications including drug delivery and tissue engineering. Among different chemical linkages, the natural and reversible thiol–disulfide interconversion is extensively explored to stabilize hydrogels. The creation of macro-, micro-, and nanoscale disulfide-stabilized hydrogels commonly relies on the use of oxidizing agents that may have a detrimental effect on encapsulated cargo. Herein an oxidization-free approach to create disulfide-stabilized polymer hydrogels via a thiol–disulfide exchange reaction is reported. In particular, thiolated poly(methacrylic acid) is used and the conditions of polymer crosslinking in solution and on colloidal porous and solid microparticles are established. In the latter case, removal of the core particles yields stable, hollow, disulfide-crosslinked hydrogel capsules. Further, a procedure is developed to achieve efficient disulfide crosslinking of multilayered polymer films to obtain stable, liposome-loaded polymer-hydrogel capsules that contain functional enzymatic cargo within the liposomal subcompartments. This approach is envisaged to facilitate the development of biomedical applications of hydrogels, specifically those including fragile cargo.</P> <B>Graphic Abstract</B> <P>Polymer-hydrogel capsules are stabilized via disulfide linkages whereby crosslinking relies on the thiol–disulfide exchange without the use of oxidizing agents (see image). The method permits the formation of hollow capsules as well as functional capsosomes, hydrogel capsules subcompartmentalized with enzyme-loaded liposomes, without the loss of activity of liposome-encapsulated enzymes. <img src='wiley_img/16136810-2009-5-22-SMLL200900906-content.gif' alt='wiley_img/16136810-2009-5-22-SMLL200900906-content'> </P>

      • KCI등재

        Bridging Thrombolysis versus Direct Mechanical Thrombectomy in Stroke Due to Basilar Artery Occlusion

        Isabel Siow,Benjamin Y.Q. Tan,Keng Siang Lee,Natalie Ong,Emma Toh,Anil Gopinathan,Cunli Yang,Pervinder Bhogal,Erika Lam,Oliver Spooner,Lukas Meyer,Jens Fiehler,Panagiotis Papanagiotou,Andreas Kastrup 대한뇌졸중학회 2022 Journal of stroke Vol.24 No.1

        Background and Purpose Mechanical thrombectomy (MT) is an effective treatment for patients with basilar artery occlusion (BAO) acute ischemic stroke. It remains unclear whether bridging intravenous thrombolysis (IVT) prior to MT confers any benefit. This study compared the outcomes of acute BAO patients who were treated with direct MT versus combined IVT plus MT. Methods This multicenter retrospective cohort study included patients who were treated for acute BAO from eight comprehensive stroke centers between January 2015 and December 2019. Patients received direct MT or combined bridging IVT plus MT. Primary outcome was favorable functional outcome defined as modified Rankin Scale 0–3 measured at 90 days. Secondary outcome measures included mortality and symptomatic intracranial hemorrhage (sICH). Results Among 322 patients, 127 (39.4%) patients underwent bridging IVT followed by MT and 195 (60.6%) underwent direct MT. The mean±standard deviation age was 67.5±14.1 years, 64.0% were male and median National Institutes of Health Stroke Scale was 16 (interquartile range, 8 to 25). At 90-day, the rate of favorable functional outcome was similar between the bridging IVT and direct MT groups (39.4% vs. 34.4%, P=0.361). On multivariable analyses, bridging IVT was not associated with favorable functional outcome, mortality or sICH. In subgroup analyses, patients with underlying atherosclerosis treated with bridging IVT compared to direct MT had a higher rate of favorable functional outcome at 90 days (37.2% vs. 15.5%, P=0.013). Conclusions Functional outcomes were similar in BAO patients treated with bridging IVT versus direct MT. In the subgroup of patients with underlying large-artery atherosclerosis stroke mechanism, bridging IVT may potentially confer benefit and this warrants further investigation.

      • KCI등재

        The Relative Efficacy of Recasts and Prompts on Past Tense Use of ESL Learners

        Choo Siow Chin,Siti Zaidah Zainuddin,Stefanie Pillai 아시아테플 2019 The Journal of Asia TEFL Vol.16 No.2

        The objective of the study is twofold: to investigate the effects of corrective feedback (CF) on the accuracy of past tense use, and to compare the relative effectiveness of recasts and prompts on the accuracy of past tense use. The participants of the study consisted of 105 secondary school ESL learners in Malaysia. The target structure of CF was the regular and irregular past forms. CF was provided contingent upon the occurrence of past tense errors according to the type of corrective feedback (i.e., recasts, prompts and no corrective feedback) assigned to participants. By employing a pre-post- and delayed- post-test design, learning outcomes were measured by means of an oral production test (OPT), a written production test (WPT) and an untimed grammaticality judgment test (GJT). The results revealed that participants, regardless of type of corrective feedback, showed both short-term and long-term gains in accuracy of past tense use. However, on the delayed effects of CF, the findings suggest that the effects of prompts may be more durable compared to recasts or control. It was found that the effectiveness of corrective feedback was also affected by other mediating factors, including learners’ proficiency level, prior knowledge and the morphological structure of the target linguistic feature.

      • KCI등재

        Thermal Ageing Studies of Sintered Micron-Silver (Ag) Joint as a Lead-Free Bonding Material

        K. S. Siow,S. T. Chua 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.9

        The sintered silver (Ag) joint has proven to be a suitable die-attach material to be used under the operating conditions of widebandgap semiconductors because of its high melting point and high thermal and electrical conductivities. However, to bondreliably, a sintered Ag joint needs a suitable metallized substrate (e.g. gold or silver) and the application of pressure duringsintering. Hence, we investigated the evolving microstructure (i.e. the importance of pore shape factor) and shear strengthof micron-Ag joints bonded without pressure on copper, Ag-plated substrate, and direct-bond copper (DBC) thermally agedat 300 °C for 1000 h. The DBC substrate maintained die-shear strength better because its coefficient of thermal expansionmatched those of the sintered Ag and Si dies. Regardless of substrate, micron-Ag joints showed a decrease of large pores(> 0.16 μm2) and an increase of spherical pore shapes during the aging period. These favourable changes maintained themechanical integrity of the micron-Ag joints. This evolving microstructure of the sintered Ag joint provides guidelines forpackaging engineers to consider as part of their selection of metallizations and substrates for power electronic packaging.

      • KCI등재후보

        A Review of Brain-derived Neurotrophic Factor as a Candidate Biomarker in Schizophrenia

        Milawaty Nurjono,Jimmy Lee,Siow-Ann Chong 대한정신약물학회 2012 CLINICAL PSYCHOPHARMACOLOGY AND NEUROSCIENCE Vol.10 No.2

        Brain-derived neurotrophic factor (BDNF), a neurotrophin known to be responsible for development, regeneration, survival and maintenance of neurons has been implicated in the pathophysiology of schizophrenia. This review seeks to complement previous reviews on biological roles of BDNF and summarizes evidence on the involvement of BDNF in the pathophysiology of schizophrenia with an emphasis on clinical relevance. The expressions of BDNF were altered in patients with schizophrenia and were found to be correlated with psychotic symptomatology. Antipsychotics appeared to have differential effects on expression of BDNF but did not restore BDNF expression of patients with schizophrenia to normal levels. In addition, evidence suggests that BDNF is involved in the major neurotransmitter systems and is associated with disruptions in brain structure, neurodevelopmental process, cognitive function, metabolic and immune systems commonly associated with schizophrenia. Besides that, BDNF has been demonstrated to be tightly regulated with estrogen which has also been previously implicated in schizophrenia. Evidence gathered in this review confirms the relevance of BDNF in the pathophysiology of schizophrenia and the potential utility of BDNF as a suitable biomarker for diagnostic and prognostic purposes for disease outcome and other co-morbidities. However, further investigations are warranted to examine the specificity of BDNF in schizophrenia compared to other neurodegenerative disorders and other neuropsychiatric illness. Longitudinal prospective studies will also be of added advantage for evaluation of prognostic utility of BDNF in schizophrenia.

      • SCIESCOPUSKCI등재

        Initial Study of a Wire Mesh Tomography Sensor for Liquid/Gas Component Investigation

        Rahiman, M.H.F.,Siow, L.T.,Rahim, R.A.,Zakaria, Z.,Ang, Vernoon The Korean Institute of Electrical Engineers 2015 Journal of Electrical Engineering & Technology Vol.10 No.5

        Experimental studies have been carried out to study the principle operation of the conductive type wire-mesh tomography sensor and analyse the wire-mesh tomography sensor for the liquid/gas two-phase flow interface and void fraction distribution in a process column. The measurement of the two-phase flows in the process column is based on the cross-sectional local instantaneous conductivity. The sensor consists of two planes of parallel electrode wires with 16 electrodes each and was placed orthogonally with each plane. The sensor electrode wires were made of tinned copper wire with an outer diameter of 0.91 mm which stretched over the sensor fixture. Therefore, this result in the mesh grid size with 5.53×5.53mm<sup>2</sup>. The wire-mesh sensor was tested in a horizontal liquid/gas two-phase flows process column with nominal diameter of 95.6 mm and the sampling frequency of 5882.3529 Hz. The tomogram results show that the wire-mesh tomography provides significant results to represent the void fraction distribution in the process column and estimation error was found in the liquid/gas interface level

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