Hydrogels composed of N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc) were prepared by redox polymerization with degradable chitosan cross-linkers.
Chitosan degradable cross-linkers were synthesized by the acrylation of the amine groups of glucosamine units within chitosan
and characterized with 1H NMR. With the chitosan cross-linkers, loosely cross-linked poly(N-isopropylacryamideco-acrylic acid) [P(NIPAAm-co-AAc)] hydrogels were prepared, and their phase transition behavior, lower critical solution temperature (LCST), water content
and degradation properties were investigated. The chitosan cross-linked P(NIPAAm-co-AAc) hydrogels were pliable and transparent at room temperature. The LCST could be adjusted at 32∼39°C by alternating the
feed ratio. Swelling was influenced by NIPAAm/AAc monomer ratio, cross-linking density, swelling media, and temperature. All
hydrogels with different feeding ratios contained more than 95% water at 25°C in the ultra pure water and phosphate-buffered
saline (PBS, pH = 7.4 ± 0.1), and had a prospective swelling in the simulated gastric fluids (SGF, pH = 1.2) > 72.54%. In
degradation studies, breakdown of the chitosan cross-linked P(NIPAAm-co-AAc) hydrogels was dependent on the cross-linking density. The chitosan cross-linked P(NIPAAm-co-AAc) hydrogels which can be tailored to create environmentally-responsive artificial extracellular materials have great potential
for future use.
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Biodegradable cross-linkers acryloyloxyethylaminopolysuccinimide (AEA-PSI) were obtained by microwave irradiation using maleic
anhydride as materials. With AEA-PSI cross-linker, cross-linked poly(N-isopropylacrylamide-co-acrylic acid) [P(NIPAAm-co-AAc)] hydrogels were prepared, and their phase transition behavior, lower critical solution temperature (LCST), water content,
thermodynamics stability, and enzymatic degradation properties were investigated. By alternating the NIPAAm/AAc molar ratio,
hydrogels were synthesized to have LCST in the vicinity of 37 °C. The LCST of AEA-PSI-cross-linked P(NIPAAm-co-AAc) hydrogels was significantly influenced by monomer ratio of the NIPAAm/AAc but not by the cross-linking density within
the polymer network. The water content of AEA-PSI-cross-linked P(NIPAAm-co-AAc) hydrogels was more than 90% even at 37 °C, which was controlled by the monomer molar ratio of NIPAAm/AAc, swelling media,
and the cross-linking density. The thermodynamics stability was also characterized by thermogravimetry. In enzymatic degradation
studies, breakdown of the AEA-PSI-cross-linked P(NIPAAm-co-AAc) hydrogels was dependent on the cross-linking density.
Submitted to Colloid and Polymer Science, 2007-1-28. 相似文献
Heterogeneous hydrogels were prepared by -ray irradiation of aqueous solutions of N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc) having various compositions above the lower critical solution temperature. The structures of the poly(N-isopropylacrylamide) (PNIPAAm) gel and poly(NIPAAm-co-AAc) gels in both their highly hydrated and their natural states were observed by environmental scanning electron microscopy. The heterogeneous structures of the homopolymer gel and the copolymer gels whose AAc contents were between 10–50% consisted of interconnected microspheres. In the copolymer gel with a high AAc content, the structure became a largely interconnected one which lacked micro-droplets. The hydrophobic interaction caused by hydrogen bonding between the unionized carboxylic acid groups of AAc and the amide groups of NIPAAm, the rates of polymerization, and the aggregation rates play important roles in the formation of interconnected microsphere gel structures. 相似文献
The temperature- and pH-sensitive hydrogels, poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-co-AAc)), were synthesized via frontal polymerization (FP). The reaction components have been varied in order to find their influences on frontal parameters and copolymer features. The results showed that front velocity and front temperature were dependent on the initiator concentration, reactant dilution, and NIPMA/AAc molar ratio. In addition, the morphology and sensitive behavior of the FP hydrogels were mainly affected by monomers’ ratio. Namely, the pore size, swelling abilities, LCST, and response kinetics of copolymer hydrogels obviously increased with the increasing acrylic acid concentration; however, they slightly changed with varying of amounts of initiator and solvent. Finally, in comparison with the hydrogels prepared by conventional batch polymerization, the ones synthesized by frontal polymerization exhibited more homogeneous chain composition and improved microstructure and response ability. 相似文献
Poly(acrylamide-co-acrylic acid) nanocomposite physical (P(AAm-co-AAc)NCP) hydrogels have been prepared through the in situ free radical solution polymerization based on a “single network, dual cross-linkings” strategy. The P(AAm-co-AAc) NCP hydrogels are composed of nanobrushes of P(AAm-co-AAc) chains grafted on the surface of vinylhybrid silica nanoparticles (VSNPs). In the hydrogel system, the VSNPs act as the “analogous chemical cross-linking points” once the hydrogen bonds formed between the P(AAm-co-AAc) chains of the nanobrushes, thus leading to the fabrication of high-strength P(AAm-co-AAc) NCP hydrogels. Compared with conventional thermosensitive P(AAm-co-AAc) hydrogels, the P(AAm-co-AAc) NCP hydrogels have a broader range of phase transition temperature, which can be adjusted by altering the monomer ratio, the VSNPs concentration, the addition of urea and N,N-dimethylacrylamide (DMAAm). At the same time, the mechanical properties of the P(AAm-co-AAc) NCP hydrogels have been improved significantly by the introduction of VSNPs. Furthermore, both the phase transition and the tensile strength of the P(AAm-co-AAc) NCP hydrogels are largely influenced when Fe3+ ions are introduced as the ionic crosslinkers into the hydrogel networks. 相似文献
Fluorescent hydrogels have promising applications in biomedical and engineering fields. However, they are usually mechanically weak. Here, we report a fluorescent composite hydrogel with high toughness, which is facilely prepared by solution casting ethanol solution of poly(hydroxyurethane) (PHU) and poly(stearyl acrylate-co-acrylic acid) (P[SA-co-AAc]) followed by swelling the casted film in water. The composite hydrogels with water content of 62–78 wt% possess remarkable mechanical performances, with tensile breaking stress of 0.3–1.1 MPa, breaking strain of 280%–400%, Young's modulus of 0.2–0.7 MPa, and tearing fracture energy of 1250–2630 J/m2. The high toughness is attributed to the effective energy dissipation of the network with hydrophobic association of SA units and hydrogen bonds between PHU and P(SA-co-AAc) as the physical crosslinks. The intense aggregation of carbamates and the formation of carbamate clusters through intra- and intermolecular hydrogen bonds endow the composite hydrogel with strong fluorescence. These hydrogels with high toughness and strong fluorescence should find applications in flexible electronics, information display, and biomedical devices. 相似文献
In order to produce silica/polyelectrolyte hybrid materials the adsorption of the polyelectrolyte poly(vinyl formamide-co-vinyl amine), P(VFA-co-VAm) was investigated. The adsorption of the P(VFA-co-VAm) from an aqueous solution onto silica surface is strongly influenced by the pH value and ionic strength of the aqueous solution, as well as the concentration of polyelectrolyte. The adsorption of the positively charged P(VFA-co-VAm) molecules on the negatively charged silica particles offers a way to control the surface charge properties of the formed hybrid material. Changes in surface charges during the polyelectrolyte adsorption were studied by potentiometric titration and electrokinetic measurements. X-ray photoelectron spectroscopy (XPS) was employed to obtain information about the amount of the adsorbed polyelectrolyte and its chemical structure. The stability of the adsorbed P(VFA-co-VAm) was investigated by extraction experiments and streaming potential measurements. It was shown, that polyelectrolyte layer is instable in an acidic environment. At a low pH value a high number of amino groups are protonated that increases the solubility of the polyelectrolyte chains. The solvatation process is able to overcompensate the attractive electrostatic forces fixing the polyelectrolyte molecules on the substrate material surface. Hence, the polyelectrolyte layer partially undergoes dissolving process. 相似文献
To combine temperature and pH sensitive capabilities, N-isopropylmaleamic acid (NIPMMA), having isopropylamide group and weakly acidic group (–COOH), was synthesized and used as a precursor for fabrication of temperature and pH sensitive hydrogels. In this paper, a new class of intelligent hydrogel with pH and temperature sensitivity originated from only one precursor (NIPMMA) was designed and demonstrated. Resultant poly(NIPMMA-co-acrylonitrile) [P(NIPMMA-co-AN)] hydrogels were characterized by Fourier transform infrared spectroscopy for structural determination and scanning electron microscope for morphology observation. Their temperature and pH sensitive behaviors were also examined in detail. The data obtained exhibited that the magnitude of sensitive properties of P(NIPMMA-co-AN) hydrogels depended on the composition ratio of two precursors. By increasing the content of NIPMMA, the temperature and pH sensitive capabilities of P(NIPMMA-co-AN) hydrogels were improved correspondingly since AN has no sensitivity upon temperature or pH changes. 相似文献
Highly swelling P(2-acrylamido-2-methyl-1-propanesulfonic acid- co-acrylic acid) (P(AMPS-co-AAc)) superabsorbent hydrogel was synthesized in aqueous solution by a simple one-step using glow-discharge electrolysis plasma technique, in which N,N’-methylenebisacrylamide was used as a crosslinking agent. The structure, thermal stability and morphology of P(AMPS-co-AAc) superabsorbent hydrogel were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. A mechanism for synthesis of P(AMPS-co-AAc) superabsorbent hydrogel was proposed. The reaction parameters affecting the equilibrium swelling (i.e., discharge voltage, discharge time, macroscopic temperature of the liquid phase, mass ratio of AMPS to AAc, and content of crosslinker) were systematically optimized to achieve a superabsorbent hydrogel with a maximum swelling capacity. The hydrogel formed which absorbed about 1,685 g H2O/g dry hydrogel of the optimized product was used to study the influence of various pH values and salts solutions (NaCl, KCl, MgCl2, and CaCl2) on the equilibrium swelling. In addition, swelling kinetics in distilled water and on–off switching behavior were preliminarily investigated. The results showed that superabsorbent hydrogel was responsive to the pH and salts. 相似文献
Two thermo‐ and pH‐sensitive polypeptide‐based copolymers, poly(N‐isopropylacrylamide‐co‐N‐hydroxymethylacrylamide)‐b‐poly(L ‐lysine) (P(NIPAAm‐co‐HMAAm)‐b‐PLL, P1 ) and poly(N‐isopropylacrylamide‐co‐N‐hydroxymethylacrylamide)‐b‐poly(glutamic acid) (P(NIPAAm‐co‐HMAAm)‐b‐PGA, P2 ), have been designed and synthesized by the ring‐opening anionic polymerization of N‐carboxyanhydrides (NCA) with amino‐terminated P(NIPAAm‐co‐HMAAm). It was found that the block copolymers exhibit good biocompatibility and low toxicity. As a result of electrostatic interactions between the positively charged PLL and negatively charged PGA, P1 and P2 formed polyion complex (PIC) micelles consisting of polyelectrolyte complex cores and P(NIPAAm‐co‐HMAAm) shells in aqueous solution. The thermo‐ and pH‐sensitivity of the PIC micelles were studied by UV/Vis spectrophotometry, dynamic light scattering (DLS), and transmission electron microscopy (TEM). Moreover, fluorescent PIC micelles were achieved by introducing two fluorescent molecules with different colors. Photographs and confocal laser scanning microscopy (CLSM) showed that the fluorescence‐labeled PIC micelles exhibit thermo‐ and pH‐dependent fluorescence, which may find wide applications in bioimaging in complicated microenvironments. 相似文献
Nanoparticles are commonly stabilized through the adsorption of acidic/basic polyelectrolytes around the surface of the particle. One example of these nanoparticles is poly(ethylenimine) (PEI)-capped Au nanoparticles. In this work, we have examined by means of surface-enhanced Raman scattering (SERS) of 2,6-dimethylphenylisocyanide (2,6-DMPI) how much the surface potential of Au nanoparticles is affected by the solution pH through the mediation of the protonation and deprotonation of PEI in contact with Au nanoparticles. In fact, the surface-potential-dependent isocyanide (NC) stretching peak of 2,6-DMPI has shifted sharply around pH 8.5, close to the pK(a) value of the primary amine of PEI. When a negatively charged poly(acrylic acid) (PAA) was deposited onto the PEI, the peak shift of the NC stretching band took place around pH 6.5, close to the average pK(a) value of PEI and PAA. When additional PEI was deposited on PAA, the peak shift of the NC stretching band occurred once again around pH 8.5, indicative of the stronger interaction of upper two polyelectrolyte layers. These data clearly illustrate the usefulness of SERS in the elucidation of a delicate interaction of cationic and anionic polyelectrolytes, especially in layer-by-layer deposition. 相似文献
Based on a biodegradable cross-linker, acryloyloxyethylaminopolysuccinimide (AEA-PSI), a series of looser cross-linked poly(N-isopropylacrylamide-co-acrylic acid) [P(NIPAAm-co-AAc)] hydrogels were prepared, and their water content, swelling/deswelling
kinetics, and the morphology of the gels were investigated. The swelling behaviors of AEA-PSI-cross-linked P(NIPAAm/AAc) hydrogels
were investigated in Dulbecco’s phosphate-buffered saline (pH = 7.4), in the distilled water, and in the simulated gastric
fluids (pH = 1.2), respectively. The water contents of the hydrogels were controlled by the monomer molar ratio of NIPAAm/AAc,
swelling media, and the temperature. In the swelling kinetics, all the dried hydrogels exhibited fast swelling behavior, and
the swelling ratios were influenced significantly by the amounts of AEA-PSI and AAc content. The deswelling kinetics of the
hydrogel were independent of the content of AAc and cross-linker. Lastly, the morphology of the hydrogels was estimated by
the field scan electron microscopy. 相似文献
Adsorption of proteins onto film surfaces built up layer by layer from oppositely charged polyelectrolytes is a complex phenomenon, governed by electrostatic forces, hydrogen bonds, and hydrophobic interactions. The amounts of the interacting charges, however, both in polyelectrolytes and in proteins adsorbed on such films are a function of the pH of the solution. In addition, the number and the accessibility of free charges in proteins depend on the secondary structure of the protein. The subtle interplay of all these factors determines the adsorption of the proteins onto the polyelectrolyte film surfaces. We investigated the effect of these parameters for polyelectrolyte films built up from weak "protein-like" polyelectrolytes (i.e., polypeptides), poly(L-lysine) (PLL), and poly(glutamic acid) (PGA) and for the adsorption of human serum albumin (HSA) onto these films in the pH range 3.0-10.5. It was found that the buildup of the polyelectrolyte films is not a simple function of the pure charges of the individual polyelectrolytes, as estimated from their respective pKa values. The adsorption of HSA onto (PLL/PGA)n films depended strongly on the polyelectrolyte terminating the film. For PLL-terminated polyelectrolyte films, at low pH, repulsion, as expected, is limiting the adsorption of HSA (having net positive charge below pH 4.6) since PLL is also positively charged here. At high pH values, an unexpected HSA uptake was found on the PGA-ending films, even when both PGA and HSA were negatively charged. It is suggested that the higher surface rugosity and the decrease of the alpha-helix content at basic pH values (making accessible certain charged groups of the protein for interactions with the polyelectrolyte film) could explain this behavior. 相似文献
Acrylamide (AAm)/Acrylic Acid (AAc) copolymers have been prepared by gamma irradiation of binary mixtures at three different compositions where the acrylamide/acrylic acid mole ratios varied around 15, 20, and 30%. Threshold dose for 100% conversion of monomers into hydrogels was found to be 8.0 kGy. Poly(Acrylamide‐co‐Acrylic Acid) (poly(AAm‐co‐AAc)) hydrogels have been considered for the removal of uranyl ions from aqueous solutions. Swelling behavior of these hydrogels was determined in distilled water at different pH values and in aqueous solutions of uranyl ions. The results of swelling tests at pH 8.0 indicated that poly(AAm‐co‐AAc) hydrogel, containing 15% acrylamide showed maximum % swelling. Diffusion of water and aqueous solutions of uranyl ion into hydrogels was found to be non‐Fickian in character and their diffusion coefficients were calculated. The effect of pH, composition of hydrogel, and concentration of uranyl ions on the adsorption process were studied at room temperature. It was found that one gram of dry poly(AAm‐co‐AAc) hydrogel adsorbed 70–320 mg and 70–400 mg uranyl ions from aqueous solutions of uranyl nitrate and uranyl acetate in the initial concentration range of 50–1500 mg UO22+L?, depending on the amount of AAc in the hydrogels, respectively. Adsorption isotherms were constructed for poly(AAm‐co‐AAc)–uranyl ion system indicating an S type of adsorption in the Giles classification system. It is concluded that crosslinked poly(AAm‐co‐AAc) hydrogels can be successfully used for the removal of uranyl ions from their aqueous solutions. 相似文献
We report on the modification of the polyelectrolytes poly(L ‐glutamic acid) (PGA), poly(acrylic acid) (PAA), and poly(L ‐lysine) (PLL) with side groups bearing phosphorylcholine (PC) groups. Two different side chains were synthesized from monoamino tri‐ or tetraethylene glycol, both with PC group linked to the OH end: the tert‐butyloxycarbonyl protected compounds BOCNH(EO)nPC (n = 2, 3) and the succinylated compound SucNH(EO)3PC. BOCNH(EO)nPC was deprotected and the resulting amine was condensed with PGA or PAA and SucNH(EO)3PC was directly coupled to PLL. Degrees of substitution as high as 80% were obtained with the method described. These polyelectrolytes are potential candidates to fabricate multilayers with protein repellent properties.