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)

Layer-by-layer self-assembly was used to prepare thermoresponsive thin films of poly(N-isopropylacrylamide) (PNIPAAm) and poly(acrylic acid) (PAA) based on hydrogen bonding. The temperature of PNIPAAm adsorption was shown to significantly affect both the mass proportion of PNIPAAm in the film and the film surface morphology. When the adsorption was conducted at temperatures close to the lower critical solubility temperature of PNIPAAm, the amount of PNIPAAm in the film increased significantly (from 51 to 59%), and the total film mass increased by 30-40%. The films prepared at 30 degrees C also exhibited a lower surface roughness (1-2 nm) compared with 5-8 nm when prepared at 10 or 21 degrees C. The resulting multilayer films ([PAA/PNIPAAm]10) were capable of being reversibly loaded and unloaded with dye (Rhodamine B) by exposure to solutions at elevated temperatures. The rate of loading and release was shown to depend on both the solution temperature and film preparation temperature, leading to tunable loading/release properties.
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PMID:Facile tailoring of film morphology and release properties using layer-by-layer assembly of thermoresponsive materials. 1574 91

Block copolymers containing stimuli-responsive segments provide important new opportunities for controlling the activity and aggregation properties of protein-polymer conjugates. We have prepared a RAFT block copolymer of a biotin-terminated poly(N-isopropylacrylamide) (PNIPAAm)-b-poly(acrylic acid) (PAA). The number-average molecular weight (M(n)) of the (PNIPAAm)-b-(PAA) copolymer was determined to be 17.4 kDa (M(w)/M(n) = 1.09). The PNIPAAm block had an M(n) of 9.5 kDa and the poly(acrylic acid) (PAA) block had an M(n) of 7.9 kDa. We conjugated this block copolymer to streptavidin (SA) via the terminal biotin on the PNIPAAm block. We found that the usual aggregation and phase separation of PNIPAAm-SA conjugates that follow the thermally induced collapse and dehydration of PNIPAAm (the lower critical solution temperature (LCST) of PNIPAAm is 32 degrees C in water) is prevented through the shielding action of the PAA block. In addition, we show that the cloud point and aggregation properties (as measured by loss in light transmission) of the [(PNIPAAm)-b-(PAA)]-SA conjugate also depended on pH. At pH 7.0 and at temperatures above the LCST, the block copolymer alone was found to form particles of ca. 60 nm in diameter, while the bioconjugate exhibited very little aggregation. At pH 5.5 and 20 degrees C, the copolymer alone was found to form large aggregates (ca. 218 nm), presumably driven by hydrogen bonding between the -COOH groups of PAA with other -COOH groups and also with the -CONH- groups of PNIPAAm. In comparison, the conjugate formed much smaller particles (ca. 27 nm) at these conditions. At pH 4.0, however, large particles were formed from the conjugate both above and below the LCST (ca. 700 and 540 nm, respectively). These results demonstrate that the aggregation properties of the block copolymer-SA conjugate are very different from those of the free block copolymer, and that the outer-oriented hydrophilic block of PAA shields the intermolecular aggregation of the block copolymer-SA bioconjugate at pH values where the -COOH groups of PAA are significantly ionized.
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PMID:Controlling the aggregation of conjugates of streptavidin with smart block copolymers prepared via the RAFT copolymerization technique. 1702 47

Ultrathin fibers comprising 2-weak polyelectrolytes, poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) were fabricated using the electrospinning technique. Methylene blue (MB) was used as a model drug to evaluate the potential application of the fibers for drug delivery. The release of MB was controlled in a nonbuffered medium by changing the pH of the solution. The sustained release of MB in a phosphate buffered saline (PBS) solution was achieved by constructing perfluorosilane networks on the fiber surfaces as capping layers. Temperature controlled release of MB was obtained by depositing temperature sensitive PAA/poly(N-isopropylacrylamide) (PNIPAAM) multilayers onto the fiber surfaces. The controlled release of drugs from electrospun fibers have potential applications as drug carriers in biomedical science.
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PMID:Fabrication of ultrathin polyelectrolyte fibers and their controlled release properties. 1741 41

Thermo-responsive poly(N-isopropylacrylamide-co-acrylamide)-block-polyallylamine-conjugated albumin nanospheres (PAN), new thermal targeting anti-cancer drug carrier, was developed by conjugating poly(N-isopropylacrylamide-co-acrylamide)-block-polyallylamine (PNIPAM-AAm-b-PAA) on the surface of albumin nanospheres (AN). PAN may selectively accumulate onto solid tumors that are maintained above physiological temperature due to local hyperthermia. PNIPAM-AAm-b-PAA was synthesized by radical polymerization, and AN was prepared by ultrasonic emulsification. AN with diameter below 200 nm and narrow size distribution was obtained by optimizing the preparative conditions. Rose Bengal (RB) was used as model drug for entrapment into the AN and PAN during the particle preparation. The release rate of RB from PAN compared with AN in trypsin solution was slower, and decreased with the increase of PNIPAM-AAm-b-PAA molecular weight, which suggested that the existence of a steric hydrophilic barrier on AN made digestion of AN more difficult. Moreover, the release of RB from PAN above the cloud-point temperature (T(cp)) of PNIPAM-AAm-b-PAA became faster. This was because the density of temperature-responsive polymers on AN was not so high, so that the interspace between the polymer chains increased after they shrunk due to the high temperature. As a result, the biodegradable AN was attacked more easily by trypsin. The design of PAN overcame the disadvantages of temperature-responsive polymeric micelles.
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PMID:Preparation and characterization of thermo-responsive albumin nanospheres. 1765 29

We investigated the phase behavior and the microscopic structure of the colloidal complexes constituted from neutral/polyelectrolyte diblock copolymers and oppositely charged surfactant by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The neutral block is poly(N-isopropylacrylamide) (PNIPAM), and the polyelectrolyte block is negatively charged poly(acrylic acid) (PAA). In aqueous solution with neutral pH, PAA behaves as a weak polyelectrolyte, whereas PNIPAM is neutral and in good-solvent condition at ambient temperature, but in poor-solvent condition above approximately 32 degrees C. This block copolymer, PNIPAM-b-PAA with a narrow polydispersity, is studied in aqueous solution with an anionic surfactant, dodecyltrimethylammonium bromide (DTAB). For a low surfactant-to-polymer charge ratio Z lower than the critical value ZC, the colloidal complexes are single DTAB micelles dressed by a few PNIPAM-b-PAA. Above ZC, the colloidal complexes form a core-shell microstructure. The core of the complex consists of densely packed DTA+ micelles, most likely connected between them by PAA blocks. The intermicellar distance of the DTA+ micelles is approximately 39 A, which is independent of the charge ratio Z as well as the temperature. The corona of the complex is constituted from the thermosensitive PNIPAM. At lower temperature the macroscopic phase separation is hindered by the swollen PNIPAM chains. Above the critical temperature TC, the PNIPAM corona collapses leading to hydrophobic aggregates of the colloidal complexes.
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PMID:Electrostatic self-assembly of neutral and polyelectrolyte block copolymers and oppositely charged surfactant. 1788 Jan 99

Hybrid microgel particles were prepared by one step incubation of poly(N-isopropylacrylamide)-co-poly(acrylic acid) (PNIPAM-co-PAA) and gold nanoparticles (AuNPs). PNIPAM-co-PAA microgel particles were synthesized by surfactant-free emulsion polymerization with different crosslinking densities (4.5 wt.-%, 10 wt.-%, 15 wt.-%, MBA to NIPAM) and AuNPs obtained by trisodium citrate reduction method independently. The effect of crosslinking density of synthesized microgel particles on the loadings of AuNPs was investigated. The results showed that 18 +/- 2 nm AuNPs could be well entrapped in the loosely crosslinked (4.5 wt.-%, MBA to NIPAM) PNIPAM-co-PAA microgel particles with high loadings. The final hybrid microgel particles were well characterized by transmission electron microscopy (TEM), UV-vis spectra, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and FT-IR. In particular, the PNIPAM-co-PAA/AuNPs hybrid microgel particles were thermoresponsive and completely reversible with several heating/cooling cycles. Therefore, the PNIPAM-co-PAA/AuNPs hybrid microgel particles allow for combined surface plasmon and thermal switching applications.
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PMID:Incorporation of gold nanoparticles within thermoresponsive microgel particles: effect of crosslinking density. 1920 95

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

Chemically cross-linked poly(N-isopropylacrylamide) (PNIPAM) microgels and PNIPAM with different amounts of acrylic acid groups (PNIPAM-co-PAA) were synthesized and the temperature-induced aggregation behaviors of aqueous suspensions of these microgels were investigated mainly with the aid of dynamic light scattering (DLS) and turbidimetry. The DLS results show that the particles at all conditions shrink at temperatures up to approximately the lower critical solution temperature (LCST), but the relative contraction effect is larger for the microgels without acid groups or for microgels with added anionic surfactant (SDS). A significant depression of the cloud point is found in suspensions of PNIPAM with very low concentrations of SDS. The compression of the microgels cannot be traced from the turbidity results, but rather the values of the turbidity increase in this temperature interval. This phenomenon is discussed in the framework of a theoretical model. At temperatures above LCST, the size of the microgels without attached charged groups in a very dilute suspension is unaffected by temperature, while the charged particles (pH 7 and 11) continue to collapse with increasing temperature over the entire domain. In this temperature range, low-charged particles of higher concentration and particles containing acrylic acid groups at low pH (pH 2) aggregate, and macroscopic phase separation is approached at higher temperatures. This study demonstrates how the stabilization of microgels can be affected by factors such as polymer concentration, addition of ionic surfactant to particles without charged acid groups, amount of charged groups in the polymer, and pH.
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PMID:Effects of temperature and pH on the contraction and aggregation of microgels in aqueous suspensions. 1961 21

Polymeric micelles with a polystyrene core, poly(acrylic acid)/poly(4-vinyl pyridine) (PAA/P4VP) complex shell and poly(ethylene glycol) & poly(N-isopropylacrylamide) (PEG & PNIPAM) mixed corona were synthesized and used as the supporter for the gold nanoparticles (GNs). It was concluded from the result of (1)H NMR characterization that hydrophilic channels formed around PEG chains when PNIPAM collapsed above its lower critical solution temperature. The density of the channels in the corona can be tuned by changing the weight ratios of PEG chains to PNIPAM chains. The GNs were set in the PAA/P4VP complex layer and the catalytic activity of the GNs can be modulated by the channels. The catalytic activity increased with increasing the density of the channels in the corona. Meanwhile, the whole Au/micelle nanoparticles were stabilized by the extended PEG chains.
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PMID:Modulating the catalytic activity of Au/micelles by tunable hydrophilic channels. 1985 48

Using surface initiated atomic transfer radical polymerization (ATRP) and an injection method, a poly(N-isopropylacrylamide)-b-poly(acrylic acid)-g-RGD (PNIPAAm-b-PAA-g-RGD) gradient surface was prepared. First, a thermoresponsive surface with a constant thickness of PNIPAAm was fabricated, onto which the AA monomers were block copolymerized using the PNIPAAm macromolecules as initiators. During this process, a continuous injection method was employed to yield a molecular weight gradient of PAA on the underlying uniform PNIPAAm layer. RGD peptide was finally covalently immobilized onto the PAA gradient by carbodiimide chemistry. In vitro culture of HepG2 cells showed that immobilization of the RGD peptide could accelerate cell attachment, while the thermoresponsive layer beneath could effectively release the cells by simply lowering temperature. Thus, the PNIPAAm-b-PAA-g-RGD gradient surface, combining the thermal response with cell affinity properties, can well regulate the cell adhesion and detachment, which may thus be useful for investigation of cell-substrate interactions with a smaller number of samples.
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PMID:Gradient immobilization of a cell adhesion RGD peptide on thermal responsive surface for regulating cell adhesion and detachment. 2103 59


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