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Query: UMLS:C0267964 (PAA)
 2,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A new photografting method to micropattern a covalent surface modification on poly(dimethylsiloxane) (PDMS) provides advantages in simplicity and efficiency. To accomplish the entire process on the benchtop, the PDMS was initially treated with benzophenone dissolved in a water/acetone mixture. This process permitted limited diffusion of the photoinitiator into the PDMS surface. Polymerization of acrylic acid was initiated by exposure of the benzophenone-implanted PDMS to UV radiation through a photomask with a thin aqueous layer of acrylic acid sandwiched between the PDMS and photomask. This procedure resulted in patterned poly(acrylic acid) (PAA) on the PDMS surface. In the modified regions, PAA and PDMS formed an interpenetrating polymer network extending 50 microm into the PDMS with an X-Y spatial resolution of 5 microm. The carboxyl groups of the PAA graft could be derivatized to covalently bond other molecules to the patterned PAA. Two bioanalytical applications of this micropatterned surface were demonstrated: (1) a guide for cell attachment and growth and (2) a substrate for immunoassays. 3T3 cells were shown to selectively localize to modified surface regions where they could be cultured for up to 7 days. Additionally, the micropatterned surface was used to immobilize either protein A or antibody for heterogeneous immunoassays.
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PMID:Covalent micropatterning of poly(dimethylsiloxane) by photografting through a mask. 1631 60

Infection of implanted materials by bacteria constitutes one of the most serious complications following prosthetic and implant surgery. In the present study, a new strategy for confering stainless steel with antibacterial property via the alternate deposition of quaternized polyethylenimine (PEI) or quaternized polyethylenimine-silver complex and poly(acrylic acid) (PAA) was investigated. The success of the deposition of the polyelectrolyte multilayers (PEM) and its chemical nature was investigated by static water contact angle and X-ray photoelectron spectroscopy (XPS), respectively. The antibacterial activity was assessed using Escherichia coli (E. coli, a gram-negative bacterium) and Staphylococcus aureus (S. aureus, a gram-positive bacterium). The inhibition of E. coli and S aureus growth on the surface of functionalized films was clearly shown using the LIVE/DEAD Baclight bacterial viability kits and fluorescence microscopy. The cytotoxicity of the PEM to mammalian cells, evaluated by the MTT assay, was shown to be minimal and long-term antibacterial efficacy can be maintained. These results indicate new possibilities for the use of such easily built and functionalized architectures for the functionalization of surfaces of implanted medical devices.
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PMID:In vitro antibacterial and cytotoxicity assay of multilayered polyelectrolyte-functionalized stainless steel. 1634 94

A two-step "grafting from" method has been successfully carried out, which is based on the electrografting of polyacrylate chains containing an initiator for the atom transfer radical polymerization (ATRP) of 2-(tert-butylamino)ethyl methacrylate (TBAEMA) or copolymerization of TBAEMA with either monomethyl ether of poly(ethylene oxide) methacrylate (PEOMA) or acrylic acid (AA) or styrene. The chemisorption of this type of polymer brushes onto stainless steel surfaces has potential in orthopaedic surgery. These films have been characterized by ATR-FTIR, Raman spectroscopy, atomic force microscopy (AFM), and measurement of contact angles of water. The polymer formed in solution by ATRP and that one detached on purpose from the surface have been analyzed by size exclusion chromathography (SEC) and (1)H NMR spectroscopy. The strong adherence of the films onto stainless steel has been assessed by peeling tests. AFM analysis has shown that addition of hydrophilic comonomers to the grafted chains decreases the surface roughness. According to dynamic quartz crystal microbalance experiments, proteins (e.g., fibrinogen) are more effectively repelled whenever copolymer brushes contain neutral hydrophilic (PEOMA) co-units rather than negatively charged groups (PAA salt). Moreover, a 2- to 3-fold decrease in the fibrinogen adsorption is observed when TBAEMA is copolymerized with either PEOMA or AA rather than homopolymerized or copolymerized with styrene. Compared to the bare stainless steel surface, brushes of polyTBAEMA, poly(TBAEMA-co-PEOMA) and poly(TBAEMA-co-AA) decrease the bacteria adhesion by 3 to 4 orders of magnitude as revealed by Gram-positive bacteria S. aureus adhesion tests.
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PMID:Combination of electrografting and atom-transfer radical polymerization for making the stainless steel surface antibacterial and protein antiadhesive. 1637 29

The effects of the addition of random copolymers of poly(styrene-co-methacrylic acid) [P(S-co-MAA)] on the self-assembly of block copolymers of poly(styrene-b-acrylic acid) (PS-b-PAA) are described. The effects of variation of five factors, including the MAA content, the weight fraction and molar mass of the P(S-co-MAA), the initial concentration of the mixture, and the length of the PAA segment in the block copolymer, were investigated. With increasing MAA content, the localization of the random copolymer in the aggregate changed from the core to the interface, which led to a morphological transition from spheres to vesicles. Vesicles, mixtures of vesicles and large spheres, and large spheres alone were formed with increasing weight fraction of the random copolymer. When the molar mass of the random copolymer was high, both rods and vesicles were observed at low water contents; otherwise, only vesicles were observed. The vesicle size increased (from 100 to 140 nm) with increasing initial polymer concentration, whereas the vesicle membrane thickness remained constant. The size of the vesicles prepared from the mixtures increased with water content but decreased with the length of PAA in the diblock.
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PMID:Self-assembly of mixtures of block copolymers of poly(styrene-b-acrylic acid) with random copolymers of poly(styrene-co-methacrylic acid). 1637 54

Hydroxyapatite (HAP) was mineralized in poly(vinyl alcohol) (PVA)/poly(acrylic acid) (PAA) complex hydrogel immersed in a salt solution containing PAA. The transparent HAP/polymer composite swelled in water depending on the HAP content; high HAP content gave small swelling and vice versa. The HAP content reached about 80 wt % at most. Observation of the cross section of the composite by energy-dispersive analysis of X-ray (EDAX) revealed that the composite consisted of two phases, i.e., a hard HAP-rich phase and a soft polymer-rich phase. In the HAP-rich phase, the space inside the hydrogel was occupied by HAP, while HAP was not mineralized in the polymer-rich phase. The nucleation seemed to take place, at first, at the middle depth of the hydrogel where the HAP-rich phase was formed. The HAP-rich phase grew its size toward the surface of the hydrogel at the cost of the polymer-rich phase. The presence of phosphorus, P, in the polymer-rich phase indicated the adsorption of HPO(4)(2-) on the polymer chain of the hydrogel via hydrogen bonding, accompanied with Ca(2+) because of electrostatic constraints. This adsorption of ions in addition to Donnan distribution of ions leads to the formation of a hypercomplex that can be regarded as a precursor of the HAP-rich phase. The change of the hypercomplex into the HAP-rich phase is discontinuous and hence concluded as a phase transition. By comparison of our mineralization system with the biomineralization system of HAP and CaCO(3), the physicochemical mechanism of the mineralization process in the present system was found to be similar to that in biological systems. In this sense, we termed the present system an artificial biomineralization system.
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PMID:Construction of a new artificial biomineralization system. 1639 3

Interaction between ethoxylated nonionic surfactants and poly(acrylic acid) (PAA) in aqueous solutions is well-documented in the literature. In the present study, pure ethoxylated surfactant solution in a hydrophobic solvent was permeated through a partially cross-linked PAA composite membrane to quantify the surfactant-PAA interaction in the heterogeneous system. Partitioning of the mixture of the surfactants (15-S-5) between the hydrophobic solvent and aqueous solution of PAA was also studied. The role of ethylene oxide group variation in the surfactant-PAA interaction for the heterogeneous system was established by performing experiments with pure surfactants having the same alkyl chain length but varying ethoxylate chain lengths. It was observed that the surfactants with a higher number of ethylene oxide groups per molecule exhibit stronger interaction with PAA. The literature data for adsorption of pure ethoxylated surfactants (C12E(n)) on a hydrophobic solid-water interface was correlated and compared with the data obtained in our study. It was calculated that resistance in terms of transfer of surfactant molecules from a hydrophobic solvent domain to PAA domain lowers the extent of PAA-surfactant interaction by an order of magnitude. Only 40% of available carboxyl groups were accessible for interaction with the ethoxylated nonionic surfactants due to diffusion limitations. Finally the pH sensitivity of the PAA-surfactant complex was verified by successful regeneration of the membrane on permeation of slightly alkaline water. The regeneration and reuse of membrane is especially attractive in terms of process development for nonionic surfactant separation from hydrophobic solvents.
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PMID:Ethoxylated nonionic surfactants in hydrophobic solvent: interaction with aqueous and membrane-immobilized poly(acrylic acid). 1640 Nov 9

Amphipols are short amphilic polymers designed for applications in membrane biochemistry and biophysics and used, in particular, to stabilize membrane proteins in aqueous solutions. Amphipol A8-35 was obtained by modification of a short-chain parent polymer (poly(acrylic acid); PAA) with octyl- and isopropylamine, to yield an amphiphilic product with an average molar mass of 9-10 kg x mol(-1) (sodium salt form) and a polydispersity index of 2.0 to 3.1, depending on the source of PAA. The behavior of A8-35 in aqueous buffers was studied by size exclusion chromatography, static and dynamic light scattering, equilibrium and sedimentation velocity analytical ultracentrifugation, and small angle neutron scattering. Despite the variable length of the chains and the random distribution of hydrophobic groups along them, A8-35 self-organizes into well-defined assemblies. The data are best compatible with most of the polymer forming compact assemblies (particles) with a molar mass of approximately 40 kg x mol(-1), a radius of gyration of approximately 2.4 nm, and a Stokes radius of approximately 3.15 nm. Each particle contains, on average, four A8-35 macromolecules and 75-80 octyl chains. Neutron scattering reveals a sharp interface between the particles and water. A minor (approximately 0.1%) mass fraction of the material forms much larger aggregates, whose proportion may increase under certain conditions of preparation or handling, such as low pH. They can be removed by gel filtration.
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PMID:Well-defined nanoparticles formed by hydrophobic assembly of a short and polydisperse random terpolymer, amphipol A8-35. 1643 Feb 95

Particles of amorphous calcium carbonate (ACC), formed in situ from calcium chloride by the slow release of carbon dioxide by alkaline hydrolysis of dimethyl carbonate in water, are stabilized against coalescence in the presence of very small amounts of double hydrophilic block copolymers (DHBCs) composed of poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) blocks. Under optimized conditions, spherical particles of ACC with diameters less than 100 nm and narrow size distribution are obtained at a concentration of only 3 ppm of PEO-b-PAA as additive. Equivalent triblock or star DHBCs are compared to diblock copolymers. The results are interpreted assuming an interaction of the PAA blocks with the surface of the liquid droplets of the concentrated CaCO3 phase, formed by phase separation from the initially homogeneous reaction mixture. The adsorption layer of the block copolymer protects the liquid precursor of ACC from coalescence and/or coagulation.
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PMID:Nanosized amorphous calcium carbonate stabilized by poly(ethylene oxide)-b-poly(acrylic acid) block copolymers. 1646 Jan 21

We present a novel route to assemble perpendicular cylinders by converting an asymmetric diblock copolymer from poly(styrene-b-tert-butyl acrylate) (PS-b-PtBA) to poly(styrene-b-acrylic acid) (PS-b-PAA) using an autocatalytic reaction. Upon exposure of the films of PS-b-PAA to water, PAA cylinders constrained by the continuous, glassy PS phase protrude 10 nm above the surface and swell laterally to form mushroom caps, rendering the entire surface hydrophilic. Upon annealing, the original nanostructures re-form demonstrating reversibility of swelling. Because of their stimuli-responsive behavior, these nanoscale materials are excellent candidates for sensors and microfluidic applications.
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PMID:Reversible stimuli-responsive nanostructures assembled from amphiphilic block copolymers. 1646 51

A study of proton diffusion across membranes of block copolymer vesicles in dilute solution is described. The vesicles were formed by the self-assembly of a diblock copolymer of poly(styrene-b-acrylic acid) (PS(310)-b-PAA(36), where the numbers represent the degree of polymerization for individual blocks). A pH gradient was created across the vesicle membrane with the interior pH (pH(in)) of ca. 2.9 and the exterior pH (pH(out)) of ca. 8.5. The permeability of the polystyrene (PS) membrane was tuned by the addition of different amounts of dioxane (0-40 wt %) to the external aqueous solution. Proton concentrations in the solution outside of the vesicles were followed by monitoring the spectrum of a pH-sensitive fluorescent dye, namely 8-hydroxypyrene-1,3,6-trisulfonate. After the start of the experiment, the proton concentrations increase linearly with the square root of time, while the slopes of the lines increase with dioxane content. To calculate the diffusion coefficients of the protons across the vesicular membrane, the concentration data were fitted using a model, which describes the diffusion of species across the membrane of a reservoir. The apparent diffusion coefficient (D*, which equals the true diffusion coefficient multiplied by the partition coefficient of protons between PS and water) increases from 1.1 x 10(-18) cm(2)/s at 7 wt % dioxane in the external solution to 1.2 x 10(-14) cm(2)/s at 40 wt %. The increase of D* with dioxane content is related to its plasticization of the PS membrane, which can be used as a gating mechanism.
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PMID:Proton diffusion across membranes of vesicles of poly(styrene-b-acrylic acid) diblock copolymers. 1650 66


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