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ABSTRACT: Graft copolymerization of amino group-terminated poly((2-dimethylamino) ethyl methacrylate) (PDMAEMA-NH2) onto oxidized sodium alginate (OSA) was reacted without using a catalyst. The structure of the graft was investigated by Fourier transform infrared (FT-IR) spectroscopy. The OSA-g-PDMAEMA gel beads were prepared by dropping the aqueous solution of the graft copolymer into CaCl2 aqueous solution. The effects of pH and ionic strength on the swelling behaviors of the gel beads were studied. The results indicate that the gel beads have pH and ionic strength sensitivity. Bovine serum albumin (BSA) was entrapped in the beads and the in vitro drug release profiles were established in buffer solution with pH 1.8 (HCl), pH 7.4 (KH2PO4-NaOH), and 0.9% (w/v) NaCl at 37 degrees C. The results showed that the oral delivery of proteins can be controlled by adjusting the graft percentage (G, %), pH and ionic strength. According to this study, the OSA-g-PDMAEMA gel beads could be suitable for the oral delivery of proteins.
International journal of pharmaceutics 01/2009; 371(1-2):16-24. · 2.96 Impact Factor
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ABSTRACT: BACKGROUND: The objective of the work reported was to investigate the effect of gel microstructure on the swelling mechanism. A series of porous gels with various pore sizes were prepared by freeze-treating a conventional hydrogel that contained various amounts of water at − 20 °C. Scanning electron microscopy and differential scanning calorimetry were used to characterize the microstructure of the porous gels.RESULTS: The experimental results showed that the water content during freezing was the key factor controlling the microstructure. Measurement of swelling kinetics showed that a greater amount of water during the freezing process would lead to a rapid swelling rate. The apparent diffusion coefficients (Dp) at all times during the swelling process were obtained by fitting the experimental data to the diffusion equation. The values of Dp suggested that the swelling mechanism of the gels depends on the pore size. The diffusion exponent (n) obtained by fitting the fractional mass change (Mt/M∞) to equation of Fick's law further confirmed that the swelling mechanism of the gels is determined by the pore size.CONCLUSION: The swelling mechanism of the gels is determined by the microstructure related to the pore size and the thickness of struts. The microstructure can be controlled by adjusting the water content of the hydrogels by changing the pH of the swelling medium prior to freezing. Copyright © 2008 Society of Chemical Industry
Polymer International 12/2008; 58(2):142 - 148. · 1.90 Impact Factor
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ABSTRACT: BACKGROUND: A considerable amount of research has been focused on smart hydrogels that can respond to external environmental stimuli, especially temperature and pH. In this study, fast responsive thermo- and pH-sensitive poly[(N,N-diethylacrylamide)-co-(acrylic acid)] hydrogels were prepared by free radical copolymerization in aqueous solution using poly(ethylene glycol) (PEG) as a pore-forming agent.RESULTS: Swelling studies showed that the hydrogels produced had both temperature and pH sensitivity. The deswelling kinetics at high temperature demonstrated that the shrinking rates were influenced by the addition of the pore-forming agent and the amount of acrylic acid in the initial total monomers. The deswelling curves in low-buffer solutions had two stages. Pulsatile swelling studies indicated that the PEG-modified hydrogels were superior to the normal ones. These different swelling properties were further confirmed by the results of scanning electron microscopy.CONCLUSION: Such fast responsive thermo- and pH-sensitive hydrogels are expected to be useful in biomedical fields for stimuli-responsive drug delivery systems. Copyright © 2008 Society of Chemical Industry
Polymer International 08/2008; 57(10):1165 - 1173. · 1.90 Impact Factor
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ABSTRACT: A series of thermo- and pH-sensitive poly (N,N-diethylacrylamide-co-acrylic acid) (P(DEA-co-AA)) hydrogels were prepared in NaCl aqueous solutions with different concentrations. Swelling and deswelling studies showed that in comparison with conventional P(DEA-co-AA) hydrogels (prepared in distilled water), the P(DEA-co-AA) hydrogels thus prepared had almost the same volume phase transition temperature (VPTT), but exhibited much faster response rates as the temperature was raised above their VPTT. Besides, the hydrogels prepared by this method had faster response rates in low pH buffer solutions, and the response rates increased with the increased concentration of the NaCl solutions used during the polymerization. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Journal of Applied Polymer Science 05/2008; 109(5):3037 - 3043. · 1.29 Impact Factor
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ABSTRACT: Drug-loaded chitosan (CS) beads were prepared under simple and mild condition using trisodium citrate as ionic crosslinker. The beads were further coated with poly(methacrylic acid) (PMAA) by dipping the beads in PMAA aqueous solution. The surface and cross-section morphology of these beads were observed by scanning electron microscopy and the observation showed that the coating beads had core-shell structure. In vitro release of model drug from these beads obtained under different reaction conditions was investigated in buffer medium (pH 1.8). The results showed that the rapid drug release was restrained by PMAA coating and the optimum conditions for preparing CS-based drug-loaded beads were decided through the effect of reaction conditions on the drug release behaviors. In addition, the drug release mechanism of CS-based drug-loaded beads was analyzed by Peppa's potential equation. According to this study, the ionic-crosslinked CS beads coated by PMAA could serve as suitable candidate for drug site-specific carrier in stomach.
International Journal of Pharmaceutics 03/2008; 349(1-2):180-7. · 3.35 Impact Factor
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Macromolecular Chemistry and Physics 12/2007; 209(4):410 - 416. · 2.36 Impact Factor
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ABSTRACT: The structure and properties of the polyelectrolyte complex composed of chitosan (CS) and poly(methacrylic acid) (PMAA) were studied in aqueous solutions using UV-visible transmittance measurements, a fluorescence probe technique, and transmission electron microscopy. The thermal properties of the solid complex were measured using differential scanning calorimetry. The results showed that the complex optimum molar ratio (in monomer unit) of CS to PMAA is 1:4 at pH = 4.0, that is, there is an optimum complex between CS and PMAA when the feed ratio (in molar monomer unit) of CS to PMAA is 1:4 and an ionic bond between the amino ion group and carboxylate group can be formed on average every four carboxylate (or carboxyl) groups. The conformation of PMAA changed from a hypercoiled to a loose coil on complexation, and the pH- and salt-sensitive range of the polyelectrolyte complex was obviously different from that of CS or PMAA. The formation process of the complex under various external conditions is discussed in detail. Transmission electron microscopy revealed that the sizes of CS–PMAA complex particles increased with increasing pH or salt concentration, and a change in morphology of the complex was observed. Thermal analysis further revealed that there was a change of structure and properties on blending in aqueous solutions. Copyright © 2007 Society of Chemical Industry
Polymer International 06/2007; 56(10):1305 - 1312. · 1.90 Impact Factor
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ABSTRACT: A series of interpenetrating polymer networks of poly(acrylic acid) (PAA)/triazole modified poly(vinyl alcohol) (TMIPNs) were synthesized by radical polymerization in methanol at room temperature with l-ascorbic acid (Vc) and peroxide hydrogen (H2O2) as initiators and trihydroxymethyl propane glycidol ether (6360) as a crosslinker. The structures of the gels were characterized by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The swelling/deswelling behavior of hydrogels was studied in different pH and different concentrations of NaCl aqueous solutions. The results showed that the TMIPNs hydrogels had excellent pH- and salt-sensitivity in the range of the investigation. The mechanism of the swelling and the deswelling was discussed and the results were confirmed further by scanning electron microscope (SEM). In addition, the controlled release behavior of TMIPNs in vitro was also studied. The effects of physical stimulus (ultraviolet ray and ultrasonic wave), salt concentration, pH value and the swelling/deswelling on the controlled released behavior were also explored.
International Journal of Pharmaceutics 03/2007; 331(1):19-26. · 3.35 Impact Factor
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ABSTRACT: A novel salts- and pH-responsive copolymer, poly(acrylic acid-co-ethyl 1-(4-chlorophenyl)-5-acrylamino-1,2,3-triazol-4-carboxylate), poly(AA-co-ECATC), was prepared by radical polymerization in methanol at room temperature with L-ascorbic acid (Vc) and peroxide hydrogen (H2O2) as initiators. The copolymer was characterized by Fourier Transform Infrared (FTIR) spectroscopy and Differential Scanning Calorimetry (DSC). The copolymer possessed excellent fluorescence properties. The effects of metal ions with different charges, radius and outer-layer electron constructions and pH values on the conformation transition of copolymer chains were systematically investigated by the fluorescence intensity and the fluorescence anisotropy. It was found that fluorescence intensity and fluorescence anisotropy curves waved with the change of metal ions concentrations and pH values. Additionally, FTIR Subtraction spectroscopy was also carried out to confirm our results. The work provided a theory basis for the study of salts- and pH-sensitive smart hydrogels, which were always used in the slow- or controlled-release drugs. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1714–1722, 2007
Journal of Applied Polymer Science 02/2007; 104(3):1714 - 1722. · 1.29 Impact Factor
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ABSTRACT: A novel semi-interpenetrating polymer network (semi-IPN) hydrogel composed of chitosan and poly(methacrylic acid) was synthesized using formaldehyde as a crosslinker. The amount of crosslinker was searched and optimized. The structure of the hydogel was investigated by Fourier transform infrared (FTIR) spectroscopy. The spectrum shows that a structure of polyelectrolyte complex exists in the hydrogel. The effects of pH, ionic strength, and inorganic salt on the swelling behaviors of the hydrogel were studied. The results indicate the hydrogel has excellent pH sensitivity in the range of pH 1.40 to 4.50, pH reversible response between pH 1.80 and 6.80, and ionic strength reversible response between ionic strength 0.2 and 2.0M. The results also show that the hydrogel has a bit higher swelling capacity in a mix solution of calcium chloride (CaCl2) and hydrochloric acid (HCl) solution than in a mix solution of sodium chloride (NaCl) and HCl. These results were further confirmed through morphological change measured by scanning electron microscope (SEM). © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1720–1726, 2005
Journal of Applied Polymer Science 08/2005; 98(4):1720 - 1726. · 1.29 Impact Factor
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ABSTRACT: In this study, a novel semi-interpenetrating polymer network (semi-IPN) hydrogel of kappa-carrageenan-g-poly(methacrylic acid)/poly(N,N-diethylacrylamide) (KC-g-PMAA/PDEA) was prepared using ammonium persulfate as an initiator and N,N,N′,N′-tetramethylethylenediamide as an accelerator at 25 °C. The structure of the hydrogels was characterized by Fourier transform infrared spectroscopy and scanning electron microscope. The effects of the feed components, temperature and pH on the swelling behavior of the hydrogels were studied. The results showed that the introduction of KC-g-PMAA did not change the lower critical solution temperature of the semi-IPN hydrogels, which was the same to the PDEA hydrogel (at 28 °C). With the increase of KC-g-PMAA content, the thermo- and pH-sensitivity of the hydrogel improved, which the swelling rate increased with the increasing content of KC-g-PMAA. The semi-IPN hydrogels showed a fast deswelling and swelling rate. The swelling dynamic transport of the hydrogels was analyzed based on the Fickian equation.
Materials Chemistry and Physics 115(1):339-346. · 2.23 Impact Factor
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ABSTRACT: Poly(acrylic acid) (PAA) with different molecular weight and poly(vinylpyrrolidone) (PVP) were prepared by free radical polymerization using 2,2′-azoisobutyronitrile (AIBN) as initiator in anhydrous methanol for PAA, and in distilled water for PVP. Then, the complexation between PAA and PVP in aqueous solution was studied by UV transmittance measurement and fluorescence probe technique. The result shows that (1) at low pH, the formation of complexation between PAA and PVP bases on the intermacromolecular hydrogen bond and the composition of the formed complex is around 3:2 (the unit molar ratio of PAA to PVP) at pH 2.60 over the range of pH investigated. (2) The cooperative interaction through the formation of hydrogen bond among active sites plays an important role in complex formation, and depends on the pH of solution, the required minimum chain length of poly(acrylic acid). (3) The hydrogen bond is not affected by small molecular salt, which only affects those carboxylic groups without forming hydrogen bond on the PAA chain.
European Polymer Journal.
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ABSTRACT: In this study, a poly(N-vinylpyrrolidone)-graft-poly(N-isopropylacrylamide) hydrogel (PVP-g-PNIPAM) was synthesized through the “grafting from” process. Grafting of temperature responsive poly(N-isopropylacrylamide) (PNIPAM) brushes was carried out from the poly(N-vinylpyrrolidone) (PVP) synthesized with free radical polymerization and functionalized with ATRP initiator, PVP–Br, which was performed through a bromination reaction between pendant allylic groups of the PVP and N-bromosuccinimide (NBS). The structure of the initiator and PVP-g-PNIPAM was characterized by ultraviolet and visible (UV/Vis) absorption, nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared (FTIR) measurements. Scanning electron microscope (SEM) morphology measurement displayed some dendritic grafted chains dangling onto the pore wall of the hydrogel.The characteristic in response to the change in environmental temperature was investigated by the fluorescence anisotropy and UV/Vis transmittance measurements. The results showed that the PVP-g-PNIPAM hydrogel exhibited rapid response to the change in environmental temperature due to free and mobile graft chains compared with the P(VP-co-NIPAM) hydrogel, which was prepared by free radical copolymerization in this work.
European Polymer Journal.
