Effect of experimental parameters on the formation of chitosan–poly(acrylic acid) nanofibrous scaffolds and evaluation of their potential application as DNA carrier

Gene delivery from tissue engineering scaffolds has demonstrated the ability to promote gene transfer and stimulate new tissue formation. In this article we report a novel nanofibrous scaffold based on polyelectrolyte complexes as a vehicle for delivery of DNA. When polycation chitosan (CS) was dropped into polyanion poly(acrylic acid) (PAA) suspension and freeze‐dried, CS‐PAA nanofibrous scaffold with diverse microstructure would be formed under different experimental conditions. The nanofiber size was affected by the CS molecular weight, the concentration of CS, the volume ratio of CS to PAA, the reaction temperature, the incubation time, and the final pH of the suspension as well. By using adipic acid as branch promoter, adjusting the pH value of the CS solution to 3, and then dropping CS into the PAA solution at a ratio of 3 : 1, a nanofibrous structure with average diameter 140 nm is obtained after the suspension is freeze‐dried. These nanofibrous scaffolds were nontoxic and can encapsulate plasmid DNA very well. Transgenic expression in human dermal fibroblasts seeded on the nanofibrous scaffolds was significant after 14 days compared to lipofectamine controls. This result indicates that CS‐PAA nanofibrous scaffold have favorable characteristics for nonviral gene delivery to mammalian cell, and have the potential to enhance gene transfer in tissue engineering. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Fabrication and characterization of CdTe nanoparticles attached to poly(4‐vinylpyridine) nanofibers

The major objective of this work was to characterize the status of CdTe nanoparticles attached to the surface of poly(4‐vinylpyridine) (P4VP) nanofibers. Scanning electron microscopy and transmission electron microscopy images indicated that the attachment of CdTe nanoparticles enlarged the diameter of P4VP nanofibers. Moreover, the results of the energy‐dispersive X‐ray spectrum and the electron diffraction pattern revealed that the deposition on the surface of P4VP nanofibers was CdTe in a cubic lattice. Furthermore, CdTe existed in its optical style according to photoluminescence spectra. X‐ray photoelectron spectroscopy verified Cd in CdTe nanoparticles combined with the N atom in P4VP nanofibers. Therefore, the obtained results provide some references for preparing coaxial nanofibers attached by other nanoparticles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis,characterization, and metal ions adsorption properties of chitosan–calixarenes (I)

Calixarene‐modified chitosans (CTS–CA‐I and CTS–CA‐II) were first synthesized by the reaction of chitosan (CTS‐NH₂) with 1,3‐bis‐chloroethoxyethoxy‐2,4‐dihydroxy‐p‐tert‐butylcalix[4]arene (CA‐I) or its benzoyl derivative (CA‐II). Their structures were characterized by infrared and X‐ray diffraction spectroscopy and scanning electron microscopy (SEM). The adsorption of Ni²⁺, Cd²⁺, Cu²⁺, Pd²⁺, Ag⁺, and Hg²⁺ by CTS–CA‐I and CTS–CA‐II was studied and the thermodynamic parameter of two calixarene‐modified chitosans toward Hg²⁺ was deduced. The adsorption properties of CTS–CA‐I and CTS–CA‐II were greatly varied compared with that CTS‐NH₂, especially with the adsorption capacity toward Ag⁺ and Hg²⁺, because of the presence of the calixarene moiety. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1139–1144, 2003     

Sorption/release of diclofenac sodium in/from free‐standing poly(acrylic acid)/poly(ethyleneimine) multilayer films

Polyelectrolyte multilayer films deposited onto various substrates have been used extensively as drug delivery systems. However, little attention has been paid to the release of drugs from free‐standing polymeric films. Herein, we report the construction of thermal crosslinked free‐standing poly(acrylic acid) (PAA)/branched poly(ethyleneimine) (PEI) multilayer films composed of 25 double layers [(PAA/PEI)₂₅] and their use in sorption/release of diclofenac sodium (DS). The (PAA/PEI)₂₅ multilayer films were characterized by scanning electron microscopy, potentiometric titrations and Fourier transform infrared spectroscopy, while the sorption/release of DS was monitored by UV – Vis spectroscopy. The DS sorption equilibrium data were fitted with five isotherm models (Langmuir, Freundlich, Sips, Dubinin–Radushkevich, and Temkin). The maximum equilibrium sorption capacity, q_m, given by the Langmuir model was 32.42 mg DS/g. The Korsmeyer–Peppas semiempirical equation showed that the release of DS from the free‐standing (PAA/PEI)₂₅ films proceeded by pseudo‐Fickian diffusion, irrespective of the releasing media. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43752.     

Preparation and properties of chitosan‐graft‐poly(methyl methacrylate) nanoparticles using potassium diperiodatocuprate (III) as an initiator

Graft copolymer nanoparticles prepared from chitosan (CS) and methyl methacrylate (MMA) monomer were synthesized in aqueous solution by using potassium diperiodatocuprate [Cu(III)] as an initiator and characterized in terms of particle size, zeta potential, transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, thermal stability, and X‐ray diffraction spectrometry. The results indicated that CS was covalently linked to poly(methyl methacrylate) (PMMA), and the resulting copolymers formed nanoparticles. These nanoparticles [prepared at 35°C, in a weight ratio of MMA/CS of 5 : 1 and with a Cu(III) concentration of 1.5 × 10⁻³ mol/L] were 54–350 nm in size, with a mean hydrodynamic diameter of 183 ± 3 nm and were highly uniform in particle‐size distribution, with a rather spherical shape and an obvious positive charge surface. The effect of reaction conditions such as Cu(III) concentration, reaction temperature, and the weight ratio of MMA/CS on the mean particle size was also investigated. Insulin‐loaded nanoparticles were prepared, and their maximal association efficiency was up to 85.41%. The experiment of release in vitro showed that the nanoparticles gave an initial burst release followed by a slowly sustained one. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Stability constants of amidoximated chitosan‐g‐poly(acrylonitrile) copolymer for heavy metal ions

Amidoximated chitosan‐g‐poly(acrylonitrile) (PAN) copolymer was prepared by a reaction between hydroxylamine and cyano group in chitosan‐g‐PAN copolymer prepared by grafting PAN onto crosslinked chitosan with epychlorohydrine. The adsorption and desorption capacities for heavy metal ions were measured under various conditions. The adsorption capacity of amidoximated chitosan‐g‐PAN copolymer increased with increasing pH values, and was increased for Cu²⁺ and Pb²⁺ but a little decreased for Zn²⁺ and Cd²⁺ with increasing PAN grafting percentage in amidoximated chitosan‐g‐PAN copolymer. In addition, desorption capacity for all metal ions was increased with increasing pH values in contrast to the adsorption results. Stability constants of amidoximated chitosan‐g‐PAN copolymer were higher for Cu²⁺ and Pb²⁺ but lower for Zn²⁺ and Cd²⁺ than those of crosslinked chitosan. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 469–476, 1999     

Preparation and swelling properties of semi‐IPN hydrogels based on chitosan‐g‐poly(acrylic acid) and phosphorylated polyvinyl alcohol

The phosphorylated poly(vinyl alcohol) (P‐PVA) samples with various substitution degrees were prepared through the esterification reaction of PVA and phosphoric acid. By using chitosan (CTS), acrylic acid (AA) and P‐PVA as raw materials, ammonium persulphate (APS) as an initiator and N,N‐methylenebisacrylamide as a crosslinker, the CTS‐g‐PAA/P‐PVA semi‐interpenetrated polymer network (IPN) ssuperabsorbent hydrogel was prepared in aqueous solution by the graft copolymerization of CTS and AA and followed by an interpenetrating and crosslinking of P‐PVA chains. The hydrogel was characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) techniques, and the influence of reaction variables, such as the substitution degree and content of P‐PVA on water absorbency were also investigated. FTIR and DSC results confirmed that PAA had been grafted onto CTS backbone and revealed the existence of phase separation and the formation of semi‐IPN network structure. SEM observations indicate that the incorporation of P‐PVA induced highly porous structure, and P‐PVA was uniformly dispersed in the polymeric network. Swelling results showed that CTS‐g‐PAA/P‐PVA semi‐IPN superabsorbent hydrogel exhibited improved swelling capability (421 g·g^?1 in distilled water and 55 g·g^?1 in 0.9 wt % NaCl solution) and swelling rate compared with CTS‐g‐PAA/PVA hydrogel (301 g·g^?1 in distilled water and 47 g·g^?1 in 0.9 wt % NaCl solution) due to the phosphorylation of PVA. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of different dopants on the adsorption,morphology, and properties of self‐assembled films of poly(o‐ethoxyaniline)

Self‐assembled films of poly(o‐ethoxyaniline)—POEA alternated with sulfonated lignin (SL)—were successfully produced, and their kinetics of formation and growth investigated for different dopants (hydrochloric acid, methanesulfonic acid, p‐toluenesulfonic acid, and camphorsulfonic acid). These films were characterized by ultraviolet‐visible spectroscopy, atomic force microscopy, surface potential, and electrical resistance measurements. It has been observed that the bulkiest dopants led to a greater time for the polymer deposition and greater amount of material adsorbed. This can be explained by the lower mobility and lower solvation of the bulkiest dopant counterions, which led to a higher screening effect of the charges present in the POEA chains and therefore to a more compact molecular conformation. The morphology of the POEA films were also greatly affected by the type of dopant used, being rougher for the bulkiest dopants. The POEA films also exhibited different electrical responses upon ethylene exposure depending on the dopant, indicating a promising use for gas sensor applications. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1309–1316, 2002     

Synthesis of double‐hydrophilic poly(methylacrylic acid)–poly(ethylene glycol)–poly(methylacrylic acid) triblock copolymers and their micelle formation

The aim of the work reported was to synthesize a series of double‐hydrophilic poly(methacrylic acid)‐block‐poly(ethylene glycol)‐block‐poly(methacrylic acid) (PMAA‐b‐PEG‐b‐PMAA) triblock copolymers and to study their self‐assembly behavior. These copolymeric self‐assembly systems are expected to be potential candidates for applications as carriers of hydrophilic drugs. Bromo‐terminated difunctional PEG macroinitiators were used to synthesize well‐defined triblock copolymers of poly(tert‐butyl methacrylate)‐block‐poly(ethylene glycol)‐block‐poly(tert‐butyl methacrylate) via reversible‐deactivation radical polymerization. After the removal of the tert‐butyl group by hydrolysis, double‐hydrophilic PMAA‐b‐PEG‐b‐PMAA triblock copolymers were obtained. pH‐sensitive spherical micelles with a core–corona structure were fabricated by self‐assembly of the double‐hydrophilic PMAA‐b‐PEG‐b‐PMAA triblock copolymers at lower solution pH. Transmission electron microscopy and laser light scattering studies showed the micelles were of nanometric scale with narrow size distribution. Solution pH and micelle concentration strongly influenced the hydrodynamic radius of the spherical micelles (48–310 nm). A possible reason for the formation of the micelles is proposed. Copyright © 2010 Society of Chemical Industry     

Synthesis and properties of chitosan‐modified poly(acrylic acid)

Potassium persulfate (K₂S₂O₈) was used to initiate the polymerization of acrylic acid (AA) monomer in a chitosan (CS) solution. Both a poly(acrylic acid) (PAA) homopolymer and a CS‐co‐PAA copolymer were produced. When the amount of AA was increased from 5 to 40 g with 5 g of CS, the total monomer conversion was found to increase from 89 to 98% after 2 h of reaction at 70°C. In addition, the percentage of reacted AA monomer being converted to the CS‐co‐PAA copolymer (copolymerization efficiency) and the weight composition of the PAA portion in the copolymer (copolymer composition) both increased with the amount of AA added. The structures and properties of the synthesized CS‐modified PAA polymers were studied. In Fourier transform infrared spectra, the formation of a polyelectrolyte complex between CS chains and PAA chains could be observed. From the thermograms obtained via differential scanning calorimetry, we found that the presence of rigid CS chains increased the glass‐transition temperature of PAA. Thermogravimetric analysis revealed three stages of degradation of the synthesized CS‐modified PAA polymers. The swelling ratio of the CS‐modified PAA polymers depended on the pH value and had a maximum value in a buffer solution at pH 7. This was due to the changes in the morphological structure with the pH value. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Water‐dispersible porous polyisoprene‐block‐poly(acrylic acid) microspheres

Two polyisoprene‐block‐poly(tert‐butyl acrylate) (PI‐b‐PtBA) samples and a poly(tert‐butyl acrylate) (PtBA) homopolymer (hPtBA) were prepared by anionic polymerization and characterized by light scattering, size exclusion chromatography, and NMR. The tert‐butyl groups were removed from one of the diblocks to yield amphiphilic polyisoprene‐block‐poly(acrylic acid) (PI‐b‐PAA). PI‐b‐PAA was then used as the surfactant to disperse dichloromethane containing PI‐b‐PtBA and hPtBA at different weight ratios as oil droplets in water. Solid microspheres containing segregated polyisoprene (PI) and PtBA/hPtBA domains were obtained after dichloromethane evaporation. Permanent microspheres were obtained after PI domain crosslinking with sulfur monochloride. Porous microspheres were produced after the hydrolysis of PtBA and the extraction of the homopoly(acrylic acid) chains. The shape and connectivity of the poly(acrylic acid)‐lined pores were tuned by changes in the PtBA/hPtBA content in the precursor microspheres. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2785–2793, 2003     

Synthesis and adsorption properties for metal ions of mesocyclic diamine‐grafted chitosan‐crown ether

A new type of grafted chitosan‐crown ether was synthesized using mesocyclic diamine crown ether as the grafting agent. The C2 amino group in chitosan was protected from the reaction between benzaldehyde and chitosan to form N‐benzylidene chitosan (CTB). After reaction with mesocyclic diamine crown ether of the epoxy propane group to give mesocyclic diamine‐N‐benzalidene chitosan (CTBA), the Schiff base was removed in a dilute ethanol hydrochloride solution to obtain chitosan‐crown ether (CTDA). Its structure was confirmed by FTIR spectra analysis and X‐ray diffraction analysis. Its static adsorption properties for Pb(II), Cu(II), Cd(II), and Cr(III) were studied. The experimental results showed that the grafted chitosan‐crown ether has high selectivity for the adsorption of Cu(II) in the presence of Pb(II), Cu(II), and Cd(II) and its adsorption selectivity is better than that of chitosan. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1255–1260, 2000     

Emulsifier‐free synthesis and self‐assembly of an amphiphilic poly(styrene‐co‐acrylic acid) copolymer

A poly(styrene‐co‐acrylic acid) copolymer was synthesized by surfactant‐free polymerization with the assistance of power ultrasound in water. Fourier transform infrared, NMR, and differential scanning calorimetry measurements revealed that the copolymer was random. Atomic force microscopy and laser light scattering were used to investigate the self‐assembly of the copolymer, and it was found that the copolymer chains formed micelles or other self‐assemble structures in solution. Atomic force microscopy also indicated that the self‐assembled structures developed into nanospheres with a poly(acrylic acid)‐rich or polystyrene‐rich surface in a film, depending on the solvent used for the preparation of the film. In particular, a wheel‐like structure could resulted in a film when the copolymer film was prepared in a moist environment; it resulted from heterogeneous aggregates of poly(acrylic acid) at the rim of water bubbles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100:3718–3726, 2006     

Synthesis and characterization of poly(dimethylamino ethyl methacrylate)–poly(ethylene oxide)–poly(dimethylamino ethyl methacrylate) triblock copolymers

Novel, monodispersed, and well‐defined ABA triblock copolymers [poly(dimethylamino ethyl methacrylate)–poly(ethylene oxide)–poly(dimethylamino ethyl methacrylate)] were synthesized by oxyanionic polymerization with potassium tert‐butanoxide as the initiator. Gel permeation chromatography and ¹H‐NMR analysis showed that the obtained products were the desired copolymers with molecular weights close to calculated values. Because the poly(dimethylamino ethyl methacrylate) block was pH‐ and temperature‐sensitive, the aqueous solution behavior of the polymers was investigated with ¹H‐NMR and dynamic light scattering techniques at different pH values and at different temperatures. The micelle morphology was determined with transmission electron microscopy. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and adsorption properties of poly(N‐vinylformamide/acrylonitrile) chelating fiber for heavy metal ions

In this article we report a new chelating fiber that was prepared from a hydrolyzate of poly(N‐vinylformamide/acrylonitrile) by a wet‐spinning method. This fiber contains chelating groups, such as amidine groups, amino groups, cyano groups, and amide groups, with high densities. We examined the chelating abilities for several metal ions with this fiber, and present the morphological merit of the fibrous product compared with the globular resin. Based on the research results, it is shown that the fiber has higher binding capacities and better adsorption properties for heavy metal ions than the resin. The pH value of the metal ion solution shows strong influences on the adsorption of the metal ions. The maximum adsorption capacities of the fiber for Cu²⁺, Cr³⁺, Co²⁺, Ni²⁺, and Mn²⁺ are 112.23, 88.11, 141.04, 108.06, and 73.51 mg/g, respectively. In mixed metal ions solution, the fiber adsorbs Cr³⁺, Cu²⁺ and Co²⁺ efficiently. The adsorbed metal ions can be quantitatively eluted by hydrochloric acid. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1378–1386, 2002     

Alternative procedure for the incorporation of quantum dots into poly(N‐isopropyl acrylamide‐co‐acrylic acid) microgels based on multiple interactions

Monodisperse fluorescent poly(N‐isopropyl acrylamide‐co‐acrylic acid) microgels doped with quantum dots (QDs) were fabricated as follows. First, cysteamine‐capped cadmium telluride (CA–CdTe) QDs were introduced into the microgels at pH 7 by electrostatic interactions. Afterward, the CA–CdTe QDs were further immobilized in the microgels by the collapse of the polymer network when the pH of solution was adjusted to 4. In this system, there existed multiple interactions between the CA–CdTe QDs and the microgels, including hydrogen bonds, electrostatic interactions, and coordination bonds. The photoluminescence intensity and maximum emission wavelength of the resulting microgels could be easily adjusted by changes in the content of the CA–CdTe QDs in the hybrid microgels (HMs) and with differently sized QDs, respectively. We found that the lower the addition of CA–CdTe QDs was, the bigger the blueshift of the photoluminescence spectra of the HMs was and the weaker the photoluminescence intensity was. Finally, temperature‐responsive emission of the HMs was examined. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43227.     

Preparation and characterization of porous chitosan–tripolyphosphate beads for copper(II) ion adsorption

Porous chitosan–tripolyphosphate beads, prepared by the ionotropic crosslinking and freeze‐drying, were used for the adsorption of Cu(II) ion from aqueous solution. Batch studies, investigating bead adsorption capacity and adsorption isotherm for the Cu(II) ion, indicated that the Cu(II) ion adsorption equilibrium correlated well with Langmuir isotherm model. The maximum capacity for the adsorption of Cu(II) ion onto porous chitosan–tripolyphosphate beads, deduced from the use of the Langmuir isotherm equation, was 208.3 mg/g. The kinetics data were analyzed by pseudo‐first, pseudo‐second order kinetic, and intraparticle diffusion models. The experimental data fitted the pseudo‐second order kinetic model well, indicating that chemical sorption is the rate‐limiting step. The negative Gibbs free energy of adsorption indicated a spontaneous adsorption, while the positive enthalpy change indicated an endothermic adsorption process. This study explored the adsorption of Cu(II) ion onto porous chitosan–tripolyphosphate beads, and used SEM/EDS, TGA, and XRD to examine the properties of adsorbent. The use of porous chitosan–tripolyphosphate beads to adsorb Cu(II) ion produced better and faster results than were obtained for nonporous chitosan–tripolyphosphate beads. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Selected properties of pH‐sensitive,biodegradable chitosan–poly(vinyl alcohol) hydrogel

Chitosan and poly(vinyl alcohol) (PVA) were used to form a semi‐interpenetrating polymeric network with glutaraldehyde as the cross‐linker. The molecular weight and degree of deacetylation of the chitosan were 612 kDa and 72 %, respectively. The chemical bonds formed by the cross‐linking reaction and transition of these bonds in different pH media were investigated. The gelation property of the chitosan–PVA pregel solution and mechanical properties of the hydrogel were studied. The FTIR spectra of the hydrogel before and after swelling at pH 3 and pH 7 indicated formation of Schiff's base (C?N) and ? NH₃⁺. They also showed pH‐induced transition of C?N to C? N, and ? NH₃⁺ to ? NH₂, as well as the instability of the Schiff's base. The chitosan is essential for hydrogel formation through Schiff's base reaction between the amino groups of the chitosan and the aldehyde groups of the glutaraldehyde. The addition of PVA improved the mechanical properties of the hydrogel. However, PVA tends to leach out at longer swelling times in the acidic medium due to hydrolysis of the gel networks, Schiff's base. Copyright © 2004 Society of Chemical Industry     

Self‐assembly of bovine serum albumin and poly(acrylic acid) induced by noncovalent bonds

Bovine serum albumin/poly(acrylic acid), BSA/PAA, nano‐scaled particles were produced by noncovalent bonds induced self‐assembly method at acid pH area. Proper conditions during preparation process, such as pH value, BSA/PAA weight ratio(WR), PAA molecular weight, were researched by studying the hydrodynamic diameter, polydispersity index, and ζ potential of the nanoparticles. Complex formation between BSA and PAA was studied by FT‐IR, AFM, and TEM. BSA chains are supposed to be partly trapped in the nanoparticles core after interaction with PAA because of the electrostatic attractions and hydrogen bonds interactions between BSA and PAA, while the rest of the BSA chains should form the shell of the nanoparticles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Facile synthesis of amphiphilic chitosan‐g‐poly(lactic acid) derivatives and the study of their controlled drug release

We report here a simple and green procedure for the synthesis of amphiphilic chitosan (CS) derivatives with poly(lactic acid) (PLA) side chains, without the use of high pure lactide, high temperatures, or large amounts of organic solvent. The chemical structure and physical properties of these CS derivatives were characterized by Fourier transform infrared spectroscopy, ¹H‐NMR, thermogravimetric analysis, and X‐ray diffraction. The formation and characteristics of polymeric micelles based on these CS derivatives were studied by fluorescence spectroscopy and dynamic light scattering. The critical aggregation concentration in water varied from 0.048 to 0.021 mg/mL, and the mean diameter was in the range 169.8–260.7 nm in aqueous solution at 25°C when the PLA grafting percentage increased from 92 to 132%. Transmission electron microscopy showed that the micelles exhibited a nanospheric morphology within a size range of 60–120 nm. For the resulting micellar aggregates, the drug loading and in vitro drug‐release characteristics were studied with indomethacin as the model drug. We found that such micellar aggregates could be potentially used as nanocarriers for drug delivery. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 908‐915, 2013