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John L. Brash - One of the best experts on this subject based on the ideXlab platform.
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dual surface modification with peg and corn trypsin inhibitor effect of peg cti ratio on Protein Resistance and anticoagulant properties
Journal of Biomedical Materials Research Part A, 2012Co-Authors: Sara Alibeik, Shiping Zhu, Jonathan W Yau, Jeffrey I Weitz, John L. BrashAbstract:The objective of this study was to investigate the bioactivity and Protein-resistant properties of dual functioning surfaces modified with PEG for Protein Resistance and corn trypsin inhibitor (CTI) for anticoagulant effect. Surfaces on gold substrate were prepared with varying ratios of free PEG to CTI-conjugated PEG. Two methods designated, respectively, “sequential” and “direct” were used. For sequential surfaces, PEG was first immobilized on gold and the surfaces were incubated with CTI at varying concentration. For direct surfaces, a PEG–CTI conjugate was synthesized and gold surfaces were modified using solutions of the conjugate of varying concentration. The CTI density on these surfaces was measured using radiolabeled CTI. Water contact angles were measured and the thickness of PEG–CTI layers was determined by ellipsometry. Fibrinogen adsorption from buffer and human plasma, and adsorption from binary solutions of fibrinogen and α-lactalbumin were investigated using radiolabeling methods. Bioactivity of the surfaces was evaluated via their effects on FXIIa inhibition and plasma clotting time. It was found that as the ratio of CTI-conjugated PEG to free PEG increased, bioactivity increased but Protein Resistance was relatively constant. It is concluded that on these surfaces conjugation of PEG to CTI does not greatly compromise the Protein Resistance of the PEG but results in improved interactions between the CTI and the “target” Protein FXIIa. At the same CTI density, sequential surfaces were more effective in terms of inhibiting FXIIa and prolonging clotting time. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A:, 2012.
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surface modification with peg and hirudin for Protein Resistance and thrombin neutralization in blood contact
Colloids and Surfaces B: Biointerfaces, 2010Co-Authors: Sara Alibeik, Shiping Zhu, John L. BrashAbstract:In this work, we hypothesize that a surface modified with both polyethylene glycol (PEG) and hirudin may provide a non-fouling, thrombin-neutralizing surface suitable for blood contacting applications. With gold as a model substrate we used two different approaches to the preparation of such a surface: (1) a "direct" method in which PEG was conjugated to hirudin and the conjugate was then immobilized on the gold; (2) a "sequential" method in which PEG was immobilized on the gold and hirudin then attached to the immobilized PEG. The surfaces were characterized by water contact angle, ellipsometry and XPS. The biological properties were investigated by measuring Protein adsorption (fibrinogen and thrombin) from buffer and plasma; thrombin inhibition was measured using a chromogenic substrate assay. Hirudin immobilization was found to be more efficient on surfaces prepared by the "direct" method. "Sequential" surfaces, however, despite having a lower density of hirudin, showed greater biological activity (thrombin binding and inhibition).
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Protein adsorption and cell adhesion detachment behavior on dual responsive silicon surfaces modified with poly n isopropylacrylamide block polystyrene copolymer
Langmuir, 2010Co-Authors: Yanxia Zhang, Hong Chen, Feng Zhou, He Huang, John L. BrashAbstract:Diblock copolymer grafts covalently attached to surfaces have attracted considerable attention because of their special structure and novel properties. In this work, poly(N-isopropylacrylamide)-block-polystyrene (PNIPAAm-b-PS) brushes were prepared via surface-initiated consecutive atom-transfer radical polymerization on initiator-immobilized silicon. Because of the inherent thermosensitivity of PNIPAAm and the hydrophobicity difference between the two blocks, the modified surfaces were responsive to both temperature and solvent. Moreover, the diblock copolymer brushes exhibited both Resistance to nonspecific Protein adsorption and unique cell interaction properties. They showed strong Protein Resistance in both phosphate-buffered saline and blood plasma. In particular, fibrinogen adsorption from plasma at either room temperature or body temperature was less than 8 ng/cm2, suggesting that the surfaces might possess good blood compatibility. In addition, the adhesion and detachment of L929 cells could be “...
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lysine peg modified polyurethane as a fibrinolytic surface effect of peg chain length on Protein interactions platelet interactions and clot lysis
Acta Biomaterialia, 2009Co-Authors: Hong Chen, Glenn W Mcclung, John L. BrashAbstract:Abstract Fibrinolytic polyurethane surfaces were prepared by conjugating lysine to the distal terminus of surface-grafted poly(ethylene glycol) (PEG). Conjugation was through the α-amino group leaving the e-amino group free. Lysine in this form is expected to adsorb both plasminogen and t-PA specifically from blood. It was shown in previous work that the PEG spacer, while effectively resisting nonspecific Protein adsorption, was a deterrent to the specific binding of plasminogen. In the present work, the effects of PEG spacer chain length on the balance of nonspecific and specific Protein binding were investigated. PEG–lysine (PEG-Lys) surfaces were prepared using PEGs of different molecular weight (PEG300 and PEG1000). The lysine-derivatized surfaces with either PEG300 or PEG1000 as spacer showed good Resistance to fibrinogen in buffer. The PEG300-Lys surface adsorbed plasminogen from plasma more rapidly than the PEG1000-Lys surface. The PEG300-Lys was also more effective in lysing fibrin formed on the surface. These results suggest that the optimum spacer length for Protein Resistance and plasminogen binding is relatively short. Immunoblots of Proteins eluted after plasma contact confirmed that the PEG–lysine surface adsorbed plasminogen while resisting most of the other plasma Proteins. The hemocompatibility of the optimized PEG–lysine surface was further assessed in whole blood experiments in which fibrinogen adsorption and platelet adhesion were measured simultaneously. Platelet adhesion was shown to be strongly correlated with fibrinogen adsorption. Platelet adhesion was very low on the PEG-containing surfaces and neither surface-bound lysine nor adsorbed plasminogen promoted platelet adhesion.
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Protein resistant poly ethylene oxide grafted surfaces chain density dependent multiple mechanisms of action
Langmuir, 2008Co-Authors: Larry D Unsworth, Heather Sheardown, John L. BrashAbstract:A clear understanding of the mechanisms responsible for the Protein-resistant nature of end-tethered poly(ethylene oxide) (PEO) surfaces remains elusive. A barrier to improved understanding is the fact that many of the factors involved (chain length, chain density, hydration, conformation, and distal chemistry) are inherently correlated. We hypothesize that, by comparing systems of variable but precisely known chain density, it should be possible to gain additional insight into the effects of the other factors. To evaluate this hypothesis, chain-end-thiolated PEOs were chemisorbed to gold-coated silicon wafers such that a range of chain densities was obtained. Three different PEOs were investigated: hydroxy-terminated chains of molecular weight 600 (600-OH), methoxy-terminated chains of molecular weight 750 (750-OCH3), and methoxy-terminated chains of molecular weight 2000 (2000-OCH3). In situ null ellipsometry was used to determine PEO chemisorption kinetics, ultimate PEO chain densities, Protein adsorption kinetics, and ultimate Protein adsorbed quantities. With this approach, it was possible to ascertain the effects of PEO distal chemistry (-OH, -OCH3), chain length, and layer hydration on Protein adsorption. The data obtained suggested that properties related to chain density (conformational freedom, hydration) were the main determinants of Protein Resistance at chain densities up to a critical value of approximately 0.5 chain/nm2; at this value, Protein adsorption was a minimum for the methoxy-terminated PEOs. For the hydroxyl-terminated PEO, adsorption leveled off at the critical value. Thus distal chemistry appears to be a major determinant of Protein Resistance at chain densities greater than the critical value.
Melissa A. Grunlan - One of the best experts on this subject based on the ideXlab platform.
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anti Protein and anti bacterial behavior of amphiphilic silicones
Polymer Chemistry, 2017Co-Authors: Melissa L Hawkins, Samantha S Schott, Bagrat Grigoryan, Marc A Rufin, Bryan Khai D Ngo, Lyndsi Vanderwal, Shane J Stafslien, Melissa A. GrunlanAbstract:Silicones with improved water-driven surface hydrophilicity and anti-biofouling behavior were achieved when bulk-modified with poly(ethylene oxide) (PEO)-silane amphiphiles of varying siloxane tether length: α-(EtO)3Si-(CH2)2-oligodimethylsiloxanem-block-poly(ethylene oxide)8-OCH3 (m = 0, 4, 13, 17, 24, and 30). A PEO8-silane [α-(EtO)3Si-(CH2)3-PEO8-OCH3] served as a conventional PEO-silane control. To examine anti-biofouling behavior in the absence versus presence of water-driven surface restructuring, the amphiphiles and control were surface-grafted onto silicon wafers and used to bulk-modify a medical-grade silicone, respectively. While the surface-grafted PEO-control exhibited superior Protein Resistance, it failed to appreciably restructure to the surface–water interface of bulk-modified silicone and thus led to poor Protein Resistance. In contrast, the PEO-silane amphiphiles, while less Protein-resistant when surface-grafted onto silicon wafers, rapidly and substantially restructured in bulk-modified silicone, exhibiting superior hydrophilicity and Protein Resistance. A reduction of biofilm for several strains of bacteria and a fungus was observed for silicones modified with PEO-silane amphiphiles. Longer siloxane tethers maintained surface restructuring and Protein Resistance while displaying the added benefit of increased transparency.
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enhancing the Protein Resistance of silicone via surface restructuring peo silane amphiphiles with variable peo length
Journal of Materials Chemistry B, 2015Co-Authors: Marc A Rufin, Melissa L Hawkins, J A Gruetzner, M J Hurley, Elizabeth S Raymond, Jeffery E Raymond, Melissa A. GrunlanAbstract:Silicones with superior Protein Resistance were produced by bulk-modification with poly(ethylene oxide) (PEO)–silane amphiphiles that demonstrated a higher capacity to restructure to the surface–water interface versus conventional non-amphiphilic PEO–silanes. The PEO–silane amphiphiles were prepared with a single siloxane tether length but variable PEO segment lengths: α-(EtO)3Si(CH2)2-oligodimethylsiloxane13-block-poly(ethylene oxide)n-OCH3 (n = 3, 8, and 16). Conventional PEO–silane analogues (n = 3, 8, and 16) as well as a siloxane tether-silane (i.e. no PEO segment) were prepared as controls. When surface-grafted onto silicon wafer, PEO–silane amphiphiles produced surfaces that were more hydrophobic and thus more adherent towards fibrinogen versus the corresponding PEO–silane. However, when blended into a silicone, PEO–silane amphiphiles exhibited rapid restructuring to the surface–water interface and excellent Protein Resistance whereas the PEO–silanes did not. Silicones modified with PEO–silane amphiphiles of PEO segment lengths n = 8 and 16 achieved the highest Protein Resistance.
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direct observation of the nanocomplex surface reorganization of antifouling silicones containing a highly mobile peo silane amphiphile
Journal of Materials Chemistry B, 2014Co-Authors: Melissa L Hawkins, Marc A Rufin, Jeffery E Raymond, Melissa A. GrunlanAbstract:While nanocomplexity derived from surface reorganization in aqueous biofouling environments is known to give rise to antifouling behavior, quantification of this process is limited. In this work, the surface of an antifouling polymer matrix - a silicone modified with a highly mobile PEO-silane amphiphile - was characterized while undergoing dynamic surface reorganization in aqueous solution via off-resonance tapping mode atomic force microscopy (AFM) and while monitoring surface changes at a rate >25 μm2 min-1. Utilizing multimodal analysis during incubation in aqueous solution and surface force spectroscopic mapping before and after incubation, we directly observed the nanoscopically complex surface of the matrix and its five distinct stages of surface reorganization. Pre- and post-incubation nanomechanical mapping revealed a marked increase in Young's modulus and surface area, as well as increased adhesion and dissipative properties for the post-incubated surface. The observed topographic and viscoelastic changes are explained in terms of surface-air and surface-water interactions. These findings are compared to the bulk matrix reordering observed by immersion dynamic mechanical analysis (DMA) and enhanced Protein Resistance with increased submersion times as determined by confocal microscopy.
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the Protein Resistance of silicones prepared with a peo silane amphiphile
Journal of Materials Chemistry, 2012Co-Authors: Melissa L Hawkins, Melissa A. GrunlanAbstract:Silicone coatings with improved Resistance to plasma Proteins were prepared by incorporating a PEO-silane amphiphile: α-(EtO)3Si-(CH2)2-oligodimethylsiloxane13-block-poly(ethylene oxide)8-OCH3. The oligodimethylsiloxane tether imparts amphiphilicity and molecular mobility to the chain thereby enhancing Protein Resistance. Using a medical grade, silica-filled acetoxy-cure silicone, the PEO-silane amphiphile was introduced at varying levels (0, 1, 5, 10, 15 and 20 wt%) and films prepared via solvent-casting. Increased PEO-silane amphiphile content led to increased surface hydrophilicity and improved Resistance to bovine serum albumin (BSA) and human fibrinogen (HF). When maintained in air, the surfaces of the coatings did not display hydrophobic recovery.
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Protein resistant silicones incorporation of poly ethylene oxide via siloxane tethers
Biomacromolecules, 2007Co-Authors: Ranjini Murthy, Casey D Cox, Mariah S Hahn, Melissa A. GrunlanAbstract:Silicones with enhanced Protein Resistance were prepared by introducing poly(ethylene oxide) (PEO) chains via siloxane tethers (a−c) of varying lengths. Three unique ambifunctional molecules (a−c) having the general formula α-(EtO)3Si(CH2)2-oligodimethylsiloxanen-block-poly(ethylene oxide)8-OCH3 (n = 0 (a), 4, (b), and 13 (c)) were prepared via regioselective Rh-catalyzed hydrosilylation. Nine films were subsequently produced by the H3PO4-catalyzed sol−gel cross-linking of a−c each with α,ω-bis(Si−OH)polydimethylsiloxane (P, Mn = 3000 g/mol) in varying ratios (1:1, 1:2, and 2:3 molar ratio a, b, or c to P). Films prepared with a 2:3 molar ratio (a−c to P) contained the least amount of un-cross-linked materials, which may migrate to the film surface. For this set of films, surface hydrophilicity and Protein Resistance increased with siloxane tether length (a−c). These results indicate that PEO was more effectively mobilized to the surface if incorporated into silicones via longer siloxane tethers.
Shaoyi Jiang - One of the best experts on this subject based on the ideXlab platform.
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photoiniferter mediated polymerization of zwitterionic carboxybetaine monomers for low fouling and functionalizable surface coatings
Macromolecules, 2011Co-Authors: Jordan E Krause, Norman D Brault, Hong Xue, Yibo Zhou, Shaoyi JiangAbstract:Surface-initiated photoiniferter-mediated polymerization (SI-PIMP) offers great promise for many applications primarily due to it lacking the requirement of a toxic catalyst as well as not being limited to specific types of monomers. In this work, zwitterionic carboxybetaine (pCB) polymer thin films with uniform and controlled thicknesses at high surface packing densities were achieved via SI-PIMP. It was found that the polymerization proceeded linearly with both UV-irradiation time and monomer concentration. Subsequent studies using a surface plasmon resonance biosensor showed pCB films to be ultralow fouling to undiluted human blood plasma. Antibody immobilization combined with excellent postfunctionalized Protein Resistance enabled the detection of an antigen down to 1 ng/mL from undiluted human plasma. These results demonstrate SI-PIMP as an attractive alternative to other commonly used polymerization techniques for zwitterionic monomers, such as atom transfer radical polymerization.
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nonfouling behavior of polycarboxybetaine grafted surfaces structural and environmental effects
Biomacromolecules, 2008Co-Authors: Zheng Zhang, Hong Xue, Hana Vaisocherova, Gang Cheng, Wei Yang, Shaoyi JiangAbstract:Zwitterionic carboxybetaine (CB) has unique dual functionality for ligand immobilization on a nonfouling background. The properties of CB groups depend on their spacer groups between the positive quaternary amine groups and the negative carboxyl groups and environmental factors (e.g., ionic strengths and pH values). In this work, five polycarboxybetaines were prepared, including one polycarboxybetaine methacrylate (polyCBMA) and four polycarboxybetaine acrylamides (polyCBAAs) with different spacer groups. The polymers were grafted from a gold surface covered with initiators using surface-initiated atom transfer radical polymerization. Fibrinogen adsorption was measured as a function of ionic strengths and pH values using surface plasmon resonance sensors. The responsive Protein adsorption on four polyCBAAs was mapped out. Results show that most of these surfaces exhibit high Protein Resistance in a wide range of ionic strengths and are more effective than zwitterionic self-assembled monolayers. Although Protein adsorption tends to increase at low ionic strength and low pH value, it is still very low for polycarboxybetaines with a methylene, an ethylene, or a propylene spacer group but is more evident for polyCBAA with a longer spacer group (i.e., a pentene group). The response to ionic strengths and pH values can be attributed to the antipolyelectrolyte and protonation/deprotonation properties of polycarboxybetaines, respectively. Both of these properties are related to the spacer groups of CBs.
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development of biocompatible interpenetrating polymer networks containing a sulfobetaine based polymer and a segmented polyurethane for Protein Resistance
Biomacromolecules, 2007Co-Authors: Yung Chang, Shengfu Chen, Zheng Zhang, Matthew T Bernards, Shaoyi JiangAbstract:Interpenetrating polymer networks (IPNs) were prepared by the modification of a segmented polyurethane (SPU) with a cross-linked sulfobetaine methacrylate (SBMA) polymer. The IPN films that were prepared can effectively resist nonspecific Protein adsorption when the distribution of SBMA units within the SPU film is well controlled, and they retain high mechanical strengths inherent from the base SPU films. Furthermore, the zwitterionic and biomimetic nature of sulfobetaine and the ease of SBMA preparation make SBMA-based materials very attractive for a wide range of applications. It is challenging to control the diffusion of highly polar SBMA into the hydrophobic network of SPU. In this study, various parameters governing the formation of IPNs containing SBMA were studied. The chemical composition depth profile of the IPN films was determined by confocal Raman microscopy. The morphology and thickness of these IPN films were examined by atomic force microscopy and scanning electron microscopy. The amount of adsorbed Proteins on the IPN films was determined by an enzyme-linked immunosorbent assay. Results show that the amount of adsorbed Proteins on the IPN films depends on the incubation conditions, including solvent polarity, incubation time, SBMA monomer ratio, and incubation concentration. It appears that the IPN films prepared in a mixed solvent of higher polarity with long incubation time lead to very low Protein adsorption. This study not only introduces a new IPN system containing SBMA, but also provides a fundamental understanding of various parameters governing the formation of IPNs.
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strong Resistance of a thin crystalline layer of balanced charged groups to Protein adsorption
Langmuir, 2006Co-Authors: Shengfu Chen, Shaoyi JiangAbstract:Resistance of mixed self-assembled monolayers (SAMs) with various counter-charged terminal groups of different valence and protonation/deprotonation states to nonspecific Protein adsorption is investigated. It is demonstrated that excellent nonfouling surfaces can be readily constructed from mixed positively and negatively charged components of equal valence in a wide range of thiol solution compositions. Furthermore, the lattice structure of one of the mixed SAM systems studied is revealed by atomic force microscopy (AFM) to be (5.2 ± 0.2 A × 5.2 ± 0.2 A)60°. Results indicate that the packing structure of mixed charged SAMs is determined by strong charge−charge interactions of the terminal groups rather than S−Au and chain−chain interactions. This work provides direct evidence that conformational flexibility is not required for Protein Resistance of a surface and even a single compact layer of charged groups of balanced charge with a crystalline structure can resist nonspecific Protein adsorption, sugges...
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Protein adsorption on oligo ethylene glycol terminated alkanethiolate self assembled monolayers the molecular basis for nonfouling behavior
Journal of Physical Chemistry B, 2005Co-Authors: Shengfu Che, Jie Zheng, Uddy D Ratne, Shaoyi JiangAbstract:A study of Protein Resistance of oligo(ethylene glycol) (OEG), HS(CH2)11(OCH2CH2)nOH (n = 2, 4, and 6), self-assembled monolayers (SAMs) on Au(111) surfaces is presented here. Hydroxyl-terminated OEG-SAMs are chosen to avoid the hydrophobic effect observed with methyl-terminated OEG-SAMs, particularly at high packing densities. The structure of the OEG-SAM surfaces is controlled by adjusting the assembly solvent. These SAMs were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Protein adsorption on these surfaces was investigated by surface plasmon resonance (SPR). OEG-SAMs assembled from mixed ethanol and water solutions show higher packing density on gold than those from pure ethanol solution. For EG2OH- and EG4OH-SAMs, Proteins (i.e., fibrinogen and lysozyme) adsorb more on the densely packed SAMs prepared from mixed ethanol and water solutions, while EG6OH-SAMs generally resist Protein adsorption regardless of the assembly solvent used.
Michael Grunze - One of the best experts on this subject based on the ideXlab platform.
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settlement and adhesion of algal cells to hexa ethylene glycol containing self assembled monolayers with systematically changed wetting properties
Biointerphases, 2007Co-Authors: Soeren Schilp, Michala E Pettitt, Maureen E Callow, Michael Grunze, Alexander Kueller, Axel Rosenhahn, James A CallowAbstract:Protein Resistance of self-assembled monolayers (SAMs) of hexa(ethylene glycols) (EG6) has previously been shown to be dependent on the alkoxyl end-group termination of the SAM, which determines wettability [S. Herrwerth, W. Eck, S. Reinhardt, and M. Grunze, J. Am. Chem. Soc. 125, 9359 (2003)]. In the present study, the same series of hexa(ethylene glycols) was used to examine the correlation between Protein Resistance and the settlement and adhesion of eukaryotic algal cells, viz., zoospores of the macroalga Ulva and cells of the diatom Navicula, which adhere to the substratum through the secretion of Protein-containing glues. Results showed that the initial settlement of Ulva zoospores was highest on the hydrophilic EG6OH but that cells were only weakly adhered. The number of Ulva zoospores and Navicula cells firmly adhered to the SAMs systematically increased with decreasing wettability, as shown for the Protein fibrinogen. The data are discussed in terms of hydration forces and surface charges in the SAMs.
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factors that determine the Protein Resistance of oligoether self assembled monolayers internal hydrophilicity terminal hydrophilicity and lateral packing density
Journal of the American Chemical Society, 2003Co-Authors: Sascha Herrwerth, Wolfgang Eck, Sven Reinhardt, Michael GrunzeAbstract:Protein Resistance of oligoether self-assembled monolayers (SAMs) on gold and silver surfaces has been investigated systematically to elucidate structural factors that determine whether a SAM will be able to resist Protein adsorption. Oligo(ethylene glycol) (OEG)-, oligo(propylene glycol)-, and oligo(trimethylene glycol)-terminated alkanethiols with different chain lengths and alkyl termination were synthesized as monolayer constituents. The packing density and chemical composition of the SAMs were examined by XPS spectroscopy; the terminal hydrophilicity was characterized by contact angle measurements. IRRAS spectroscopy gave information about the chain conformation of specific monolayers; the amount of adsorbed Protein as compared to alkanethiol monolayers was determined by ellipsometry. We found several factors that in combination or by themselves suppress the Protein Resistance of oligoether monolayers. Monolayers with a hydrophobic interior, such as those containing oligo(propylene glycol), show no p...
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temperature dependence of the Protein Resistance of poly and oligo ethylene glycol terminated alkanethiolate monolayers
Langmuir, 2001Co-Authors: Dirk Schwendel, Sascha Herrwerth, Wolfgang Eck, R Dahint, Matthias Schloerholz, Michael GrunzeAbstract:Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS) has been used to study the Protein Resistance of poly- and oligo(ethylene glycol) (PEG and OEG) terminated alkanethiolate self-assembled monolayers (SAMs) on Au and Ag in the temperature range from 0 to 85 °C. These experiments extend previous room-temperature studies by Harder et al.1 who related the Protein adsorption characteristics of OEG-SAMs to the lateral density and corresponding molecular conformation of the ethylene glycol (EG) moieties in the film. In addition to the short oligomer OEG-SAMs, we investigated PEG-derivatized alkanethiolate monolayers with an average chain length of 45 EG units and a mean molecular mass of 2000 g/mol (PEG2000). We observe that films, which are Protein resistant at room temperature, maintain their Protein repulsive characteristics up to 85 °C but may adsorb significant amounts of Protein if the temperature is lowered.
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low energy configurations of methoxy triethylene glycol terminated alkanethiol self assembled monolayers and their relevance to Protein adsorption
Journal of Physical Chemistry B, 1998Co-Authors: A J Pertsin, Michael Grunze, I A GarbuzovaAbstract:Methoxy triethylene glycol terminated alkanethiol monolayers self-assembled on Au and Ag have recently been found to exhibit a striking difference in Protein Resistance, which has been interpreted in terms of the transition of the ethylene glycol tails from a helical to an all-trans conformation (Harder, P.; Grunze, M.; Dahint, R.; Whitesides, G. M.; Laibinis, P. E. J. Phys. Chem. 1998, 102, 426−436. Wang, R. L. C.; Kreuzer, H. J.; Grunze, M. J. Phys. Chem. 1997, 101, 9767−9773). To gain further arguments in favor of such a conformational transition, we undertake a search for the lowest energy monolayer configurations on Au and Ag by combining the methods of stochastic global search and static energy minimization. The conformational and intermolecular contributions to the monolayer lattice energy are calculated using a classical atomistic force field fitted to ab initio MP2 level calculation results for 1,2-dimethoxyethane. It is found that in the lowest energy monolayer configuration on Au the methoxy tr...
Youyi Xu - One of the best experts on this subject based on the ideXlab platform.
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Amphiphilic ABA copolymers used for surface modification of polysulfone membranes, Part 1: Molecular design, synthesis, and characterization
Polymer, 2008Co-Authors: Jian-yu Wang, Youyi Xu, Jianhua LiAbstract:Abstract Two kinds of novel amphiphilic ABA copolymers, which are suitable for surface modification of polysulfone membranes, were successfully synthesized via the atom transfer radical polymerization (ATRP) technique, using a bromo-terminated difunctional polysulfone as macroinitiator. Firstly, the difunctional polysulfone macroinitiator was prepared by esterifying the phenolic end groups of polysulfone to α-haloesters. Secondly, the macroinitiator was used to initiate the polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA) and 3-O-methacryloyl-1,2:5,6-di-O-isopropylidene- d -glucofuranose (MAIpG), resulting in two kinds of ABA copolymers, i.e., P(PEGMA)-b-PSF-b-P(PEGMA) and PMAIpG-b-PSF-b-PMAIpG, respectively. In the case of PMAIpG-b-PSF-b-PMAIpG, the isopropylidenyl groups of the protected sugar residues were removed by acidolysis treatment, thus the amphiphilic ABA copolymer, PMAG-b-PSF-b-PMAG, was obtained. The resultant copolymers were characterized by FT-IR, 1H NMR, GPC, and TGA. Semipermeable polysulfone membranes prepared via the standard immersion precipitation phase inversion process, using the synthesized amphiphilic ABA copolymers as additives, display enhanced hydrophilicity and Protein Resistance compared to unmodified polysulfone membranes.
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porous membranes modified by hyperbranched polymers ii effect of the arm length of amphiphilic hyperbranched star polymers on the hydrophilicity and Protein Resistance of poly vinylidene fluoride membranes
Journal of Membrane Science, 2007Co-Authors: Yonghong Zhao, Dongxu Pang, Baoku Zhu, Yanling Qian, Youyi XuAbstract:Amphiphilic hyperbranched-star polymers (HPE-g -MPEG) with different arm length were synthesized by grafting methoxy poly(ethylene glycol)s (MPEGs, M¯n=350,750 and 2000, respectively) to the hyperbranched polyester (HPE) molecule using terephthaloyl chloride (TPC) as the coupling agent, and blended with PVDF to fabricate porous membranes via phase inversion process. Membrane morphologies were observed by scanning electron microscopy (SEM) and atomic force microscope (AFM), and chemical composition changes of the membrane surfaces were measured by X-ray photoelectron spectroscopy (XPS). Water contact angle, static Protein adsorption, and filtration experiments were used to evaluate the hydrophilicity and anti-fouling properties of the membranes. It was found that, with the increase in MPEG arm length, the MPEG segments of HPE-g-MPEG enriched at the membrane surfaces substantially, resulting in a significant decrease in water contact angle. Furthermore, the blend membranes containing longer arm HPE-g-MPEGs showed lower static Protein adsorption, higher Protein solution fluxes, and better Protein solution flux recovery than the pure PVDF membrane.
