The Experts below are selected from a list of 10698 Experts worldwide ranked by ideXlab platform
Cristina M L Martins - One of the best experts on this subject based on the ideXlab platform.
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dhvar5 antimicrobial peptide amp chemoselective Covalent Immobilization results on higher antiadherence effect than simple physical adsorption
2015Co-Authors: Fabiola Costa, Paula Gomes, Silvia Maia, Cristina M L MartinsAbstract:Bacterial colonization and subsequent biofilm formation is still one of the major problems associated with medical devices. Antimicrobial peptides (AMP) Immobilization onto biomaterials surface is a promising strategy to avoid bacterial colonization. However, a correct peptide orientation and exposure from the surface is essential to maintain AMP antimicrobial activity. This work aims to evaluate the effect of the Immobilization on antibacterial activity of Dhvar5 (LLLFLLKKRKKRKY), an AMP with a head-to-tail amphipathicity. Dhvar5 was linked to thin chitosan coatings in i) a controlled orientation and exposure, testing Covalent Immobilization of its N- or C-terminus and using spacers with different lengths and flexibilities or in ii) a random orientation by physical adsorption. Chitosan coating was chosen due to its antimicrobial properties and readiness to be functionalized. Surface characterization demonstrated the chemoselective Immobilization of the peptide with different spacers in a similar concentration (∼2 ng/cm2). Efficacy assays demonstrated that Covalent Immobilization of Dhvar5 exposing its cationic end, improves the chitosan coating antimicrobial effect by decreasing Methicillin-resistant Staphylococcus aureus (MRSA) colonization. This effect was enhanced when longer spacers were used independently of their flexibility. In opposite, immobilized Dhvar5 exposing its hydrophobic end has no effect on bacterial adhesion to chitosan, and when adsorbed in a random orientation even induces bacterial adhesion to chitosan coating.
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Covalent Immobilization of antimicrobial peptides amps onto biomaterial surfaces
2011Co-Authors: Fabiola Costa, Isabel Carvalho, Ronald C Montelaro, Paula Gomes, Cristina M L MartinsAbstract:Bacterial adhesion to biomaterials remains a major problem in the medical devices field. Antimicrobial peptides (AMPs) are well-known components of the innate immune system that can be applied to overcome biofilm-associated infections. Their relevance has been increasing as a practical alternative to conventional antibiotics, which are declining in effectiveness. The recent interest focused on these peptides can be explained by a group of special features, including a wide spectrum of activity, high efficacy at very low concentrations, target specificity, anti-endotoxin activity, synergistic action with classical antibiotics, and low propensity for developing resistance. Therefore, the development of an antimicrobial coating with such properties would be worthwhile. The Immobilization of AMPs onto a biomaterial surface has further advantages as it also helps to circumvent AMPs’ potential limitations, such as short half-life and cytotoxicity associated with higher concentrations of soluble peptides. The studies discussed in the current review report on the impact of Covalent Immobilization of AMPs onto surfaces through different chemical coupling strategies, length of spacers, and peptide orientation and concentration. The overall results suggest that immobilized AMPs may be effective in the prevention of biofilm formation by reduction of microorganism survival post-contact with the coated biomaterial. Minimal cytotoxicity and long-term stability profiles were obtained by optimizing Immobilization parameters, indicating a promising potential for the use of immobilized AMPs in clinical applications. On the other hand, the effects of tethering on mechanisms of action of AMPs have not yet been fully elucidated. Therefore, further studies are recommended to explore the real potential of immobilized AMPs in health applications as antimicrobial coatings of medical devices.
Fabiola Costa - One of the best experts on this subject based on the ideXlab platform.
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dhvar5 antimicrobial peptide amp chemoselective Covalent Immobilization results on higher antiadherence effect than simple physical adsorption
2015Co-Authors: Fabiola Costa, Paula Gomes, Silvia Maia, Cristina M L MartinsAbstract:Bacterial colonization and subsequent biofilm formation is still one of the major problems associated with medical devices. Antimicrobial peptides (AMP) Immobilization onto biomaterials surface is a promising strategy to avoid bacterial colonization. However, a correct peptide orientation and exposure from the surface is essential to maintain AMP antimicrobial activity. This work aims to evaluate the effect of the Immobilization on antibacterial activity of Dhvar5 (LLLFLLKKRKKRKY), an AMP with a head-to-tail amphipathicity. Dhvar5 was linked to thin chitosan coatings in i) a controlled orientation and exposure, testing Covalent Immobilization of its N- or C-terminus and using spacers with different lengths and flexibilities or in ii) a random orientation by physical adsorption. Chitosan coating was chosen due to its antimicrobial properties and readiness to be functionalized. Surface characterization demonstrated the chemoselective Immobilization of the peptide with different spacers in a similar concentration (∼2 ng/cm2). Efficacy assays demonstrated that Covalent Immobilization of Dhvar5 exposing its cationic end, improves the chitosan coating antimicrobial effect by decreasing Methicillin-resistant Staphylococcus aureus (MRSA) colonization. This effect was enhanced when longer spacers were used independently of their flexibility. In opposite, immobilized Dhvar5 exposing its hydrophobic end has no effect on bacterial adhesion to chitosan, and when adsorbed in a random orientation even induces bacterial adhesion to chitosan coating.
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Covalent Immobilization of antimicrobial peptides amps onto biomaterial surfaces
2011Co-Authors: Fabiola Costa, Isabel Carvalho, Ronald C Montelaro, Paula Gomes, Cristina M L MartinsAbstract:Bacterial adhesion to biomaterials remains a major problem in the medical devices field. Antimicrobial peptides (AMPs) are well-known components of the innate immune system that can be applied to overcome biofilm-associated infections. Their relevance has been increasing as a practical alternative to conventional antibiotics, which are declining in effectiveness. The recent interest focused on these peptides can be explained by a group of special features, including a wide spectrum of activity, high efficacy at very low concentrations, target specificity, anti-endotoxin activity, synergistic action with classical antibiotics, and low propensity for developing resistance. Therefore, the development of an antimicrobial coating with such properties would be worthwhile. The Immobilization of AMPs onto a biomaterial surface has further advantages as it also helps to circumvent AMPs’ potential limitations, such as short half-life and cytotoxicity associated with higher concentrations of soluble peptides. The studies discussed in the current review report on the impact of Covalent Immobilization of AMPs onto surfaces through different chemical coupling strategies, length of spacers, and peptide orientation and concentration. The overall results suggest that immobilized AMPs may be effective in the prevention of biofilm formation by reduction of microorganism survival post-contact with the coated biomaterial. Minimal cytotoxicity and long-term stability profiles were obtained by optimizing Immobilization parameters, indicating a promising potential for the use of immobilized AMPs in clinical applications. On the other hand, the effects of tethering on mechanisms of action of AMPs have not yet been fully elucidated. Therefore, further studies are recommended to explore the real potential of immobilized AMPs in health applications as antimicrobial coatings of medical devices.
Yakup M Arica - One of the best experts on this subject based on the ideXlab platform.
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Covalent Immobilization of lipase onto amine functionalized polypropylene membrane and its application in green apple flavor ethyl valerate synthesis
2011Co-Authors: Gulay Bayramoglu, Baki Hazer, Begum Altintas, Yakup M AricaAbstract:Abstract In this study, a functionalized hydrophobic polypropylene chloride membrane (PPC) was prepared by the amination of chlorinated polypropylene with hexamethylene diamine (APP). The PPC and APP membranes were characterized using SEM, FTIR and contact angle studies. The aminated polypropylene (APP) membrane was used for Covalent Immobilization of Candida rugosa lipase via glutaraldehyde coupling. The retained activity of the immobilized lipase was 76%. Kinetic analysis shows that the dependence of lipolytic activity of both free and immobilized lipase on tributyrin substrate concentration can be described by Michaelis–Menten model. The estimated apparent K m values for the free and immobilized lipase were 2.9 and 8.4 mM, respectively. The V max values of free and immobilized enzymes were calculated as 926 and 741 U/mg enzyme, respectively. Optimal temperature was 5 °C higher for immobilized enzyme than that of the free enzyme. Thermal and storage stabilities were found to be increased upon Immobilization. Finally, the immobilized lipase was used for the production of green apple flavor (i.e., ethyl valerate) in hexane medium.
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Covalent Immobilization of chloroperoxidase onto magnetic beads catalytic properties and stability
2008Co-Authors: Gulay Bayramoglu, Senem Kiralp, Meltem Yilmaz, Levent Toppare, Yakup M AricaAbstract:Abstract Amino groups containing magnetic beads were used in Covalent Immobilization of the enzyme “chloroperoxidase (CPO)” which is one of a few enzymes that can catalyse the peroxide dependent oxidation of a wide spectrum of organic and inorganic compounds. The magnetic poly(glycidylmethacrylate-methylmethacrylate-ethyleneglycol dimethacrylate), magnetic p(GMA-MMA-EGDMA) beads were prepared via suspension polymerization in the presence of ferric ions. The magnetic beads were characterized with scanning electron microscope (SEM), Fourier transform infrared (FTIR), Mossbauer spectroscopy and vibrating sample magnetometer (VSM). The magnetic beads were derivatized sequentially with ammonia and glutaraldehyde, and CPO was Covalently immobilized on the support via reaction of the amino groups of the enzyme under mild conditions. The effect of various parameters including pH, temperature and enzyme concentration on the Immobilization efficiency of CPO onto glutaric dialdhyde activated magnetic beads was evaluated. Magnetic measurement revealed that the resultant CPO-immobilized magnetic beads were superparamagnetic with a saturation magnetization of 18.2 emu/g. The analysis of FTIR spectra confirmed the binding of CPO on the magnetic beads. The maximum amount of immobilized CPO on the magnetic beads was 2.94 mg/g support. The values of Michaelis constants Km for immobilized CPO was significantly larger, indicating decreased affinity by the enzyme for its substrate, whereas Vmax values were smaller for the immobilized CPO. However, the CPO immobilized on the magnetic beads resulted in an increase in enzyme stability with time.
K G Neoh - One of the best experts on this subject based on the ideXlab platform.
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biomimetic deposition of calcium phosphate minerals on the surface of partially demineralized dentine modified with phosphorylated chitosan
2011Co-Authors: Zhang Xu, K G Neoh, Anil KishenAbstract:The aim of this study is to remineralize partially demineralized dentine sections using phosphorylated chitosan (P-chi) based on mimicking the nucleating role of the phosphorylated noncollagenous proteins in the biomineralization of dentine. The surface of partially demineralized dentine sections, mainly composed of type I collagen, were modified by Covalent Immobilization of P-chi on the collagen surface. The dentine sections were subsequently put into remineralizing solution for remineralization, and then the remineralizing effect was investigated. The remineralization effect of this methodology was compared with that of fluoride. Moreover, the influence of surface properties of samples on remineralizing effect was investigated. The experimental results indicated that the effect of fluoride on remineralization of dentine was limited when residual crystals were lacking on the surface of partially demineralized dentine, whereas the Covalent Immobilization of P-chi can significantly induce deposition of calcium phosphate minerals on the surface of the partially demineralized dentine. This biomimetic methodology resulted in favorable surface properties (i.e., highly negative charge and low interfacial free energy between substrate and remineralizing medium) for crystal nucleation. Thus, P-chi can facilitate surface remineralization of dentine and thereby could find application in the minimally invasive management of dentine caries and dentine hypersensitivity.
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Covalent Immobilization of glucose oxidase on well defined poly glycidyl methacrylate si 111 hybrids from surface initiated atom transfer radical polymerization
2005Co-Authors: Fujian Xu, Yali Li, E T Kang, K G NeohAbstract:A simple one-step procedure was employed for the Covalent Immobilization of an atom-transfer radical polymerization (ATRP) initiator, via the robust Si−C bond, on the hydrogen-terminated Si(111) surface (Si−H surface). Well-defined poly(glycidyl methacrylate) [P(GMA)] brushes, tethered directly on the (111)-oriented single-crystal silicon surface, were prepared via surface-initiated ATRP. Kinetics study on the surface-initiated ATRP of glycidyl methacrylate revealed that the chain growth from the silicon surface was consistent with a “controlled” process. A relatively high concentration of glucose oxidase (GOD; above 0.2 mg/cm2) could be coupled directly to the well-defined P(GMA) brushes via the ring-opening reaction of the epoxide groups with the amine moieties of the enzyme. The resultant GOD-functionalized P(GMA) brushes, with the accompanying hydroxyl groups from the ring-opening reaction of the epoxide groups, serves as an effective spacer to provide the GOD with a higher degree of conformational fr...
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Covalent Immobilization of invertase onto the surface modified polyaniline from graft copolymerization with acrylic acid
2000Co-Authors: Yongjun Chen, K G Neoh, E T Kang, K L TanAbstract:Abstract Invertase was Covalently immobilized on the emeraldine (EM) base form of polyaniline (PAN) films and powders with surface-grafted acrylic acid (AAc) polymer. The Immobilization proceeded via the amide linkage formation between the amino groups of invertase and the carboxyl groups of the grafted AAc polymer chains on EM in the presence of a water-soluble carbodiimide. The surface structure and composition of the grafted–modified and enzyme-functionalized EM base were characterized by X-ray photoelectron spectroscopy (XPS). It was found that the amount of immobilized invertase increased linearly with the concentration of surface-grafted AAc polymer chains. EM powders could be graft-modified and enzyme-functionalized more effectively than EM films. The decrease in activity of the immobilized invertase was considered to be due to, among other factors, the reduced accessibility of substrate molecules to the active sites of the enzyme and the conformational change of the invertase molecules as a result of the Covalent Immobilization. However, the immobilized enzyme was less sensitive to temperature deactivation below the optimum temperature as compared to that of the free form. The optimum pH value of invertase was not affected by the Immobilization reaction, but the pH stability range was broadened. The immobilized invertase also exhibited a significantly improved stability during storage in buffer solution over that of the free enzyme.
Tripta Kamra - One of the best experts on this subject based on the ideXlab platform.
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Covalent Immobilization of molecularly imprinted polymer nanoparticles on a gold surface using carbodiimide coupling for chemical sensing
2016Co-Authors: Tripta Kamra, Shilpi Chaudhary, Lars Montelius, Joachim SchnadtAbstract:One challenging task in building (bio)chemical sensors is the efficient and stable Immobilization of receptor on a suitable transducer. Herein, we report a method for Covalent Immobilization of molecularly imprinted core-shell nanoparticles for construction of robust chemical sensors. The imprinted nanoparticles with a core-shell structure have selective molecular binding sites in the core and multiple amino groups in the shell. The model Au transducer surface is first functionalized with a self-assembled monolayer of 11-mercaptoundecanoic acid. The 11-mercaptoundecanoic acid is activated by treatment with carbodiimide/N-hydroxysuccinimide and then reacted with the core-shell nanoparticles to form amide bonds. We have characterized the process by studying the treated surfaces after each preparation step using atomic force microscopy, scanning electron microscopy, fluorescence microscopy, contact angle measurements and X-ray photoelectron spectroscopy. The microscopy results show the successful Immobilization of the imprinted nanoparticles on the surface. The photoelectron spectroscopy results further confirm the success of each functionalization step. Further, the amino groups on the MIP surface were activated by electrostatically adsorbing negatively charged Au colloids. The functionalized surface was shown to be active for surface enhanced Raman scattering detection of propranolol. The particle Immobilization and surface enhanced Raman scattering approach described here has a general applicability for constructing chemical sensors in different formats.
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Covalent Immobilization of molecularly imprinted polymer nanoparticles using an epoxy silane
2015Co-Authors: Tripta Kamra, Shilpi Chaudhary, Lars Montelius, Joachim Schnadt, Changgang Xu, Niclas Johansson, Lei YeAbstract:Molecularly imprinted polymers (MIPs) can be used as antibody mimics to develop robust chemical sensors. One challenging problem in using MIPs for sensor development is the lack of reliable conjugation chemistry that allows MIPs to be fixed on transducer surface. In this work, we study the use of epoxy silane to immobilize MIP nanoparticles on model transducer surfaces without impairing the function of the immobilized nanoparticles. The MIP nanoparticles with a core-shell structure have selective molecular binding sites in the core and multiple amino groups in the shell. The model transducer surface is functionalized with a self-assembled monolayer of epoxy silane, which reacts with the core-shell MIP particles to enable straightforward Immobilization. The whole process is characterized by studying the treated surfaces after each preparation step using atomic force microscopy, scanning electron microscopy, fluorescence microscopy, contact angle measurements and X-ray photoelectron spectroscopy. The microscopy results show that the MIP particles are immobilized uniformly on surface. The photoelectron spectroscopy results further confirm the action of each functionalization step. The molecular selectivity of the MIP-functionalized surface is verified by radioligand binding analysis. The particle Immobilization approach described here has a general applicability for constructing selective chemical sensors in different formats.
