Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0267964 (PAA)
 2,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In aqueous solutions at room temperature, poly( N-methyl-2-vinyl pyridinium iodide)- block-poly(ethylene oxide), P2MVP 38- b-PEO 211 and poly(acrylic acid)- block-poly(isopropyl acrylamide), PAA 55- b-PNIPAAm 88 spontaneously coassemble into micelles, consisting of a mixed P2MVP/PAA polyelectrolyte core and a PEO/PNIPAAm corona. These so-called complex coacervate core micelles (C3Ms), also known as polyion complex (PIC) micelles, block ionomer complexes (BIC), and interpolyelectrolyte complexes (IPEC), respond to changes in solution pH and ionic strength as their micellization is electrostatically driven. Furthermore, the PNIPAAm segments ensure temperature responsiveness as they exhibit lower critical solution temperature (LCST) behavior. Light scattering, two-dimensional 1H NMR nuclear Overhauser effect spectrometry, and cryogenic transmission electron microscopy experiments were carried out to investigate micellar structure and solution behavior at 1 mM NaNO 3, T = 25, and 60 degrees C, that is, below and above the LCST of approximately 32 degrees C. At T = 25 degrees C, C3Ms were observed for 7 < pH < 12 and NaNO 3 concentrations below approximately 105 mM. The PEO and PNIPAAm chains appear to be (randomly) mixed within the micellar corona. At T = 60 degrees C, onion-like complexes are formed, consisting of a PNIPAAm inner core, a mixed P2MVP/PAA complex coacervate shell, and a PEO corona.
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PMID:Temperature responsive complex coacervate core micelles with a PEO and PNIPAAm corona. 1869 10

Two-dimensional NMR and small-angle neutron scattering experiments were performed on comicelles of poly(N-methyl-2-vinyl pyridinium iodide)-block-poly(ethylene oxide), P2MVP-b-PEO, and poly(acrylic acid)-block-poly(acryl amide), PAA-b-PAAm, in aqueous solutions to study whether a transition between a heterogeneous (Janus-type) and homogeneous corona can be observed upon a variation of parameters that are anticipated to affect the miscibility of the PEO and PAAm coronal blocks. Investigated were the effect of a salt-induced decrease in micellar aggregation number, P agg for 1<or=[NaNO3]<or=279 mM, a temperature increase for 25<or=T<or=80 degrees C, a variation of the fraction of EO monomers in the corona, fEO, at a fixed corona block length, N corona, for 0<or=fEO<or=1, a decrease in the PEO block length, N PEO, at a fixed PAAm block length, NPAAm, for 200<or=NPEO<or=450, and finally, upon a decrease in corona block length at NPAAm=NPEO for 100<or=N corona<or=400. These parameters should affect the mixing/demixing transition via their effect on the PEO/PAAm interfacial area (e.g., as in the case of f EO and P agg) or the relevant Flory-Huggins interaction parameters (e.g., as in the case of temperature). None of the above parameters was shown to yield a transition toward a homogeneous corona wherein the polymer chains are randomly mixed; i.e., the segregation of PAAm and PEO chains within the micellar corona of comicelles of PAA-b-PAAm and P2MVP-b-PEO appears to be rather robust.
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PMID:On the transition between a heterogeneous and homogeneous corona in mixed polymeric micelles. 1882 17

Uricase (UOx) and polyelectrolyte were used for preparation of a permselective multilayer film and enzyme multilayer films on a platinum (Pt) electrode, allowing the detection of uric acid amperometrically. The polyelectrolyte multilayer (PEM) film composed of poly(allylamine) (PAA) and poly(vinyl sulfate) (PVS) were prepared via layer-by-layer assembly on the electrode, functioning as H(2)O(2)-selective film. After deposition of the permselective film (PAA/PVS)(2)PAA, UOx and PAA were deposited via layer-by-layer sequential deposition up to 10 UOx layers to prepare amperometric sensors for uric acid. Current response to uric acid was recorded at +0.6 V vs. Ag/AgCl to detect H(2)O(2) produced from the enzyme reaction. The response current increased with increasing the number of UOx layers. Even in the presence of ascorbic acid, uric acid can be detected over the concentration range 10(-6)-10(-3) M. The response current and deposited amount of UOx were affected by deposition bath pH and the addition of salt. The deposition of PAA/UOx film prepared in 2 mg ml(-1) solution (pH 11) of PAA with NaCl (8 mg ml(-1)) and 0.1 mg ml(-1) solution (pH 8.5) of UOx with borate (100 mM) resulted in an electrode which shows the largest response to uric acid. The response of the sensor to uric acid was decreased by 40% from the original activity after 30 days.
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PMID:Amperometric uric acid sensors based on polyelectrolyte multilayer films. 1896 95

This body of work describes the development of a porous hydrogel for wound healing applications. In the present study poly (vinyl alcohol) (PVA) and poly (acrylic acid) (PAA) based hydrogels were prepared, and their properties were examined. Varying concentrations of the polymers and distilled water were used to prepare the hydrogels. The use of a high shear mixer, for foaming the PVA and PVA/PAA gels, and how this physical change can affect the structure and porosity of the hydrogel in question, represents a key feature of this work. The mechanical and thermal properties were determined by parallel plate rheometry and modulated differential scanning calorimetry (MDSC) respectively. The results indicated that the hydrogels containing low concentration of PVA and high volume of H(2)O are significantly weaker than those synthesised with higher concentrations of PVA. The thermal analysis shows distinct endotherms and provides evidence of crystallisation. The chemical structure of the hydrogels was confirmed by means of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR).
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PMID:Development of a novel porous cryo-foam for potential wound healing applications. 1911 91

The diffusion mechanism of vitamin B12 in two types of crosslinked hydrogels, poly(acrylic acid) (cPAA) and copolymers of acrylic acid and N-vinyl pyrrolidinone (cP(AA-NVP)) was studied. The PAA and P(AA-NVP) synthesized by three different degrees of crosslinking have limited water absorption capabilities ranging from 3% to 18%. In the copolymers permeability of B12 is controlled by both intramolecular and intermolecular hydrogen-bonding between the pyrrolidinone and carboxylic acid side chains. The diffusion kinetic data in two types of polymers were best described by Peppas models instead of Higuchi models. Permeation from both crosslinked PAA and P(AA-co-NVP) copolymers followed a Super Case II transport mechanism, most likely driven by macromolecular chain relaxation and swelling of hydrophilic polymers. A special FTIR spectroscopic method for drug binding study, FTIR difference spectroscopy, is used to probe the strong interactions between vitamin B12 and the side chains of the hydrogels. The FTIR differential spectra of B12 in PAA hydrogels revealed dramatic changes of the spectral marker bands of B12 after binding in the crosslinked gels, indicating significant interactions occurring in the amide and phosphate moieties of B12. Such interactions retard the diffusion of vitamin B12.
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PMID:Vitamin B12 diffusion and binding in crosslinked poly(acrylic acid)s and poly(acrylic acid-co-N-vinyl pyrrolidinone)s. 1913 32

Au clusters smaller than 1.5 nm and stabilized by poly(N-vinyl-2-pyrrolidone) (PVP) showed higher activity for aerobic oxidation of alcohol than those of larger size or stabilized by poly(allylamine) (PAA). X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy of adsorbed CO, and X-ray absorption near edge structure measurements revealed that the catalytically active Au clusters are negatively charged by electron donation from PVP, and the catalytic activity is enhanced with increasing electron density on the Au core. Based on similar observations of Au cluster anions in the gas phase, we propose that electron transfer from the anionic Au cores of Au:PVP into the LUMO (pi*) of O(2) generates superoxo- or peroxo-like species, which plays a key role in the oxidation of alcohol. On the basis of these results, a simple principle is presented for the synthesis of Au oxidation catalysts stabilized by organic molecules.
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PMID:Effect of electronic structures of Au clusters stabilized by poly(N-vinyl-2-pyrrolidone) on aerobic oxidation catalysis. 1940 34

Physically cross-linked hydrogels composed of 75% poly(vinyl alcohol) PVA and 25% poly(acrylic acid) were prepared by a freeze/thaw treatment of aqueous solutions. Between 0.5 and 1wt% of aspirin was incorporated into the systems. The purpose of the research was the development of a novel pH-sensitive hydrogel composite for the delivery of aspirin to wounds. Extensive research has being conducted on freeze/thaw poly(vinyl alcohol) hydrogels for use in active pharmaceutical ingredient (API) delivery. However very little research has been reported on the effects of an API on the overall properties of a freeze/thaw hydrogel. From the rheological analysis undertaken it was apparent that aspirin has a limiting effect on the formation of hydrogen bonding leading to hydrogels with reduced mechanical strength. To counteract this, a novel hydrogel system was developed encompassing a reinforcing film in the centre of the hydrogels. Freezing profiles were obtained to gain a better knowledge of the freezing behaviour of the hydrogels during the formation stage. Thermograms obtained from modulated differential scanning calorimetry (MDSC) indicated that the aspirin lowered the glass transition temperatures (T(g)) of the constituent polymers. The pH-sensitive nature of the hydrogels was apparent from solvent uptake studies carried out. Increasing alkaline media led to a greater degree of swelling due to increased ionisation of PAA. The hydrogels exhibited non-Fickian release kinetics. The release rates were relatively slow with total release achieved at between 30 and 40 h. The quantity of drug incorporated was found to influence the release rates considerably.
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PMID:The synthesis of novel pH-sensitive poly(vinyl alcohol) composite hydrogels using a freeze/thaw process for biomedical applications. 1942 75

A major problem which hinders the applications of neural prostheses is the inconsistent performance caused by tissue responses during long-term implantation. The study investigated a new approach for improving the electrode-neural tissue interface. Hydrogel poly(vinyl alcohol)/poly(acrylic acid) interpenetrating polymer networks (PVA/PAA IPNs) were synthesized and tailored as coatings for poly(dimethylsiloxane) (PDMS) based neural electrodes with the aid of plasma pretreatment. Changes in the electrochemical impedance and maximum charge injection (Q(inj)) limits of the coated iridium oxide microelectrodes were negligible. Protein adsorption on PDMS was reduced by approximately 85% after coating. In the presence of nerve growth factor (NGF), neurite extension of rat pheochromocytoma (PC12) cells was clearly greater on PVA/PAA IPN films than on PDMS substrates. Furthermore, the tissue responses of PDMS implants coated with PVA/PAA IPN films were studied by 6-week implantation in the cortex of rats, which found that the glial fibrillary acidic protein (GFAP) immunoreactivity in animals (n=8) receiving coated implants was significantly lower (p<0.05) compared to that of uncoated implants (n=7) along the entire distance of 150 microm from the outer skirt to the implant interface. The coated film remained on the surface of the explanted implants, confirmed by scanning electron microscopy (SEM). All of these suggest the hydrogel coating is feasible and favorable to neural electrode applications.
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PMID:Poly(vinyl alcohol)/poly(acrylic acid) hydrogel coatings for improving electrode-neural tissue interface. 1946 2

A hydrogen-bonded layer-by-layer (LbL) technique was used to build multilayers of neutral, temperature-responsive polymers such as poly(N-isopropylacrylamide) (PNIPAM), poly(N-vinylcaprolactam) (PVCL), poly(vinyl methyl ether) (PVME), or poly(acrylamide) (PAAm) with a polycarboxylic acid such as poly(acrylic acid) (PAA), poly(methacrylic acid) (PMAA), or poly(ethacrylic acid) (PEAA). For all multilayers involving temperature-responsive polymers, the temperature used during or after self-assembly had a significant effect on film stability with pH changes. The proximity of the self-assembly or post-self-assembly temperature to the critical temperature of phase separation of a neutral polymer from solution resulted in a higher pH stability of multilayers. However, for polymers with a lower critical solution temperature (LCST) such as PNIPAM, PVCL, or PVME within PNIPAM/PMAA, PVCL/PMAA, or PVME/PMAA multilayers, the critical pH of film disintegration (pH(crit)) increased in the temperature range from 10 to 37 degrees C, whereas for polymer films with an upper critical solution temperature (UCST), such as PAAm within PAAm/PMAA, the film showed the opposite trend. Using a hydrogen-bonded polyvinylpyrrolidone (PVPON)/PMAA system, which is not responsive to temperature changes, we constructed hybrid films with lower [PNIPAM/PMAA](n) and higher [PVPON/PMAA](m) strata and obtained free-floating [PVPON/PMAA](m) films by temperature-triggered dissolution of the PNIPAM/PMAA layers at a constant pH value. The kinetics of [PVPON/PMAA](m) film release was strongly dependent on the number of bilayers within the PNIPAM/PMAA stratum, indicating significant interpenetration between PNIPAM/PMAA and PVPON/PMAA bilayers. Importantly, the use of PEAA instead of PAA or PMAA in film assembly enabled the construction of hydrogen-bonded LbL films that can be released by applying temperature as a trigger at near-physiological pH values. This feature makes such release layers attractive candidates for future tissue engineering applications.
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PMID:Hydrogen-bonded layer-by-layer temperature-triggered release films. 1957 3

The current study involves the development of a hydrogel carrier for a H(2)O(2) delivery system. In this work poly (vinyl alcohol) (PVA) and poly (acrylic acid) (PAA) based hydrogels were prepared, and their mechanical and physical properties examined. The novel aspect of this research is the differing functionality created by varying the concentration of H(2)O(2). The mechanical and thermal properties were determined by parallel plate rheometry and modulated differential scanning calorimetry (MDSC) respectively. The results indicated that the hydrogels containing H(2)O(2) are significantly weaker than those synthesised using water alone at test temperatures of 30 and 45 degrees C. MDSC analysis suggested that thermal transitions occur at temperatures that may make these hydrogels useful as temperature sensitive drug delivery systems. The chemical structure of the hydrogels was confirmed by means of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), while swelling experiments in distilled water indicate that the swelling of the gels is temperature dependent.
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PMID:The rheological and thermal characteristics of freeze-thawed hydrogels containing hydrogen peroxide for potential wound healing applications. 1962 31


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