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A liberação de drogas solúveis em água a partir de matrizes de hidrogéis hidratados, geralmente envolve simultaneamente a absorção de água e a liberação da droga via mecanismo de difusão controlada. Foi analisado o comportamento difusional da fenobarbitona no hidrogel do copolímero 2-hidroxietil metacrilato (HEMA) e monoitaconato de metila (MMI). A liberação da droga no meio aquoso foi acompanhada por cromatografia líquida de alta pressão e os resultados mostraram que a liberação da fenobarbitona a partir dos hidrogéis estudados, considerando-se os valores dos coeficientes de difusão, não variou com a temperatura e com o método de polimerização. Os valores de energia de ativação sugerem um favorecimento na liberação da fenobarbitona a partir dos hidrogéis de p(HEMA-co-MMI) polimerizados em massa e em solução.

Research into how the triblock copolymer polystyrene-b-poly(ethylene/butylene)-b-polystyrene chains associate when dissolved in solvent mixtures of 4-methyl-2-pentanone and n-octane is described.

The impact of the external factors on the micellization process, as well as the structure of the poly(oxy)styrene-poly(oxy)ethylene block copolymers is determined. The high solubility of the SO blocks is shown to lead to an increase in the critical micelle concentration.

Polystyrene-b-poly(ethylene/butylene)-b-polystyrene copolymers show thermally reversible gelation in semidiluted solutions of the n-octane are studied. The mechanical properties of different gels were examined through oscillatory shear and compressive stress relaxation measurements.

ABSTRACT In this work, four polymerization mechanisms with flow are proposed where sustained oscillation can be present: (1) Polyaddition initiated by radicals produced by initiator decomposition, which is catalyzed by the polymer, first-order termination, a polymer disappears by a reaction with a third substance and by leaving the system in the exit flow. (2) Polycondensation where the polymer has catalytic activity upon H to produce a monomer, first-order termination and a monomer disappears by a reaction with a third substance, and there is exit flow for all the species. (3) Polycondensation with catalytic activity of the polymer upon A to produce a monomer, first-order termination, conformational transitions of the polymers, one of the polymer conformations disappears by a reaction with a monomer and exit flow for all the species. (4) Polycondensation combined with polyaddition where the polycondensation polymer product has catalytic activity on the monomer, first-order termination and exit flow of all the species. [ABSTRACT FROM AUTHOR]

Temperature-sensitive poly(N-isopropylacrylamide) (PNIPA) nanohydrogels were synthesized by nanoemulsion polymerization in water-in-oil systems. Several cross-linking degrees and the incorporation of acrylic acid as comonomer at different concentrations were tested to produce nanohydrogels with a wide range of properties. The physicochemical properties of PNIPA nanohydrogels, and their relationship with the swelling-collapse behaviour, were studied to evaluate the suitability of PNIPA nanoparticles as smart delivery systems (for active packaging). The swelling-collapse transition was analyzed by the change in the optical properties of PNIPA nanohydrogels using ultraviolet-visible spectroscopy. The thermodynamic parameters associated with the nanohydrogels collapse were calculated using a mathematical approach based on the van't Hoff analysis, assuming a two-state equilibrium (swollen to collapsed). A mathematical model is proposed to predict both the thermally induced collapse, and the collapse induced by the simultaneous action of two factors (temperature and pH, or temperature and organic solvent concentration). Finally, van't Hoff analysis was compared with differential scanning calorimetry. The results obtained allow us to solve the problem of determining the molecular weight of the structural repeating unit in cross-linked NIPA polymers, which, as we show, can be estimated from the ratio of the molar heat capacity (obtained from the van't Hoff analysis) to the specific heat capacity (obtained from calorimetric measurements). [ABSTRACT FROM AUTHOR]

ABSTRACT Two new kinetic mechanisms of polymerization are proposed (0Re-1,2 and 0Re-1) to study the instability of the steady states by the Lyapounov method. Both mechanisms take into account a reinitiation step in the polymerization process, but they are different because 0Re-1,2 considers two kinds of termination steps: a zero- and a second-order terminations. However, in the second mechanism, 0Re-1, only one of those termination steps (the zero-order one) is presented. In both proposed mechanisms, the nondiffusive and diffusive cases are studied. The results show that they are able to display arrangements in time (limit cycle oscillations) and space (order form fluctuations). [ABSTRACT FROM AUTHOR]

Poly( N-isopropylacrylamide) (PNIPA) and Poly( N-isopropylacrylamide-co-acrylic acid) (P(NIPA-co-AA)) microgels loaded with 5-aminolevulinic acid (ALA) were prepared by the spray-drying method. The amount of drug loaded was 290 µg ALA/mg microgel for PNIPA and 244 µg ALA/mg microgel for P(NIPA-co-AA) microgels. Maximum in vitro drug release took place within 15-30 min for PNIPA and 1-1.5 h for P(NIPA-co-AA) microgels as a function of pH, at 37°C. Transdermal delivery from microgels showed permeation fluxes 10 times higher than the passive diffusion flux. The cytotoxicity of microgels synthesized in HeLa cells after the application of photodynamic therapy (PDT) was superior compared with the administration of ALA in solution alone. Finally, the use of these microgels as a delivery vehicle for ALA constitutes a system capable of enhancing its topical administration and PDT effectiveness. [ABSTRACT FROM AUTHOR]

This study reports on the synthesis and characterization of interpenetrating polymeric network (IPN) and polyelectrolyte complexes (PEC) produced by ion-complex formation between natural and synthetic polymer bearing opposed charge. PEC of sodium alginate (NaAlg) and poly(acryloxyethyl-trimethylammonium chloride- co-2-hydroxyethyl methacrylate) (poly(Q- co-H)) were formed by addition of 2.0 wt % sodium alginate solution to 1.5 wt % poly(Q- co-H) solution, and by adding the poly(Q- co-H) solution to the NaAlg solution under magnetic agitation. The IPN were prepared using the sequential method with three different compositions, in which Q and H monomers were mixed in the 95/5 proportions in presence of NaAlg. The mixture was polymerized at 60°C using potassium persulfate as initiator. The characterizations of scaffolds were investigated by Fourier-transform infrared spectroscopy and thermogravimetric analysis. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]

Copolymeric nanohydrogels based on N-isopropylacrylamide, N-(pyridin-4-ylmethyl)acrylamide and tert-butyl-2-acrylamidoethyl carbamate, synthesized by microemulsion polymerization, were characterized using Fourier transform infrared spectroscopy and their size (38-52 nm) determined using quasielastic light scattering. Folic acid was covalently attached to the nanohydrogels (1.40 ± 0.07 mmol g−1). Tamoxifen (6.7 ± 0.2-7.3 ± 1.2 µg TMX mg−1 nanohydrogel), a hydrophobic anticancer drug, and 5-fluorouracil (7.7 ± 0.7-10.14 ± 1.75 µg 5-FU mg−1 nanohydrogel), a hydrophilic anticancer drug, were loaded into the nanohydrogels. Maximum in vitro TMX release (77-84% of loaded drug) depended on interactions of the drug with hydrophobic clusters of the nanogels; however, no nanogel/5-FU interactions allowed total release of the loaded drug. The cytotoxicity of unloaded nanohydrogels in MCF7, T47D and HeLa cells was low. Cell uptake of nanogels without bound folic acid took place in the three cell types by unspecific internalization in a time-dependent process. Cell uptake increased for folic acid-targeted nanohydrogels in T47D and HeLa cells, which have folate receptors. The administration of 10 and 30 µmol L−1 TMX by TMX-loaded nanogels and 10 µmol L−1 5-FU by 5-FU-loaded nanogels was effective on the three cell types, and the best results were obtained for folic acid-targeted nanohydrogels. Copyright © 2012 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

We used temperature-sensitive poly(Nisopropylacrylamide) hydrogels as drug delivery systems, so changes in body temperature induced by pathogens could act like external stimuli to activate controlled release of the drugs incorporated in the hydrogel. In the distilled water combined release studies, we chose two model drugs: aminophylline and triamterene. The amount of drug released was measured by UV-Vis spectroscopy following the evolution of the absorption peaks of aminophylline (271 nm) and triamterene (365 nm). The maximum release time was greater for triamterene than for aminophylline at 37 °C, so these time-release profiles enabled the active ingredients to work over different periods of time. By increasing molar mass or solubility of the drug, we observed that the diffusion coefficient decreased. On the contrary, increasing hydrophobicity of the drug leads to a diffusion coefficient increase. The evolution of pore size distribution of hydrogels during loading and releasing was measured by quasi-elastic light scattering and by environmental electronic scanning microscope. When loading and releasing the drugs, the pore size of the hydrogel decreased and increased again without reaching the initial pore size of the hydrogel, respectively. We observed that the greater the concentration of drug loaded into the hydrogel, the greater the reduction in pore size. [ABSTRACT FROM AUTHOR]

Folate-targeted poly[(p-nitrophenyl acrylate)-co-(N-isopropylacrylamide)] nanohydrogel (F-SubMG) was loaded with 5-fluorouracil (5-FU) to obtain low (16.3 ± 1.9 μg 5-FU/mg F-SubMG) and high (46.8 ± 3.8 μg 5-FU/mg F-SubMG) load 5-FU-loaded F-SubMGs. The complete in vitro drug release took place in 8 h. The cytotoxicity of unloaded F-SubMGs in MCF7 and HeLa cells was low; although it increased for high F-SubMG concentration. The administration of 10 μM 5-FU by 5-FU-loaded F-SubMGs was effective on both cellular types. Cell uptake of F-SubMGs took place in both cell types, but it was higher in HeLa cells because they are folate receptor positive. After subcutaneous administration (28 mg 5-FU/kg b.w.) in Wistar rats, F-SubMGs were detected at the site of injection under the skin. Histological studies indicated that the F-SubMGs were surrounded by connective tissue, without any signs of rejections, even 60 days after injection. Pharmacokinetic study showed an increase in MRT (mean residence time) of 5-FU when the drug was administered by drug-loaded F-SubMGs. [ABSTRACT FROM AUTHOR]

Here, we present the oil/water (O/W) microemulsion polymerization in three-component microemulsions of n-butyl acrylate, ethyl acrylate, and methyl acrylate, monomers with similar chemical structures but different water solubilities using the cationic surfactant dodecyl trimethyl ammonium bromide. The effects of monomer water solubility, initiator type and initial monomer concentration on the polymerization kinetics were studied. Reaction rates were high with final conversions between 70 and 98% depending on the monomer and reaction conditions. The final latexes were bluish, with a particle size ranging between 20 and 50 nm and polymer with molar masses in the order of 106 g mol−1. Increasing monomer water solubility resulted in a slower reaction rate, larger particles and a lower number density of particles. A higher reaction rate, larger average particle size and higher particle number density were obtained by increasing the monomer concentration. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 [ABSTRACT FROM AUTHOR]