Chitosan–polyelectrolyte complexation for the preparation of gel beads and controlled release of anticancer drug. II. Effect of pH‐dependent ionic crosslinking or interpolymer complex using tripolyphosphate or polyphosphate as reagent

Chitosangel beads were prepared using an in‐liquid curing method by ionotropic crosslinking or interpolymer linkage with tripolyphosphate (TPP) or polyphosphate (PP). The ionic interaction of chitosan with TPP or PP is pH‐dependent due to the transition of “ladder‐loop” complex structures. Chitosan gel beads cured in a pH value lower than 6 of a TPP solution was a controlled homogeneous ionic‐crosslinking reaction, whereas chitosan gel beads cured in a lower pH PP solution was a nonhomogeneous interpolymer complex reaction due to the mass‐transfer resistance for the diffusion of macromolecular PP. According to the results of FTIR and EDS studies, it was suggested that significantly increasing the ionic‐crosslinking density or interpolymer linkage of a chitosan–TPP or chitosan–PP complex could be achieved by transferring the pH value of curing agent, TPP or PP, from basic to acidic. The swelling behavior of various chitosan beads in acid medium appeared to depend on the ionic‐crosslinking density or interpolymer linkage of the chitosan–TPP or chitosan–PP complex, which were deeply affected by the in‐liquid curing mechanism of the chitosan gel beads. By the transition of the in‐liquid curing mechanism, the swelling degree of chitosan–TPP or chitosan–PP beads was depressed and the disintegration of chitosan–TPP or chitosan–PP beads did not occur in strong acid. The drug‐release patterns of the modified chitosan gel beads in simulated intestinal and gastric juices were sustained for 20 h. These results indicate that the sustained release of anticancer drugs could be achieved due to the variation of the reaction mechanism of a chitosan–polyelectrolyte pH‐dependent ionic interaction. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1093–1107, 1999     

Studies on semi‐interpenetrating polymer network beads of chitosan–poly(ethylene glycol) for the controlled release of drugs

Semi‐interpenetrating polymer network beads of chitosan and poly(ethylene glycol) were prepared and characterized for controlled release of drugs. A viscous solution of chitosan and poly(ethylene glycol) in 2% acetic acid was extruded as droplets with the help of a syringe and crosslinked using glutaraldehyde. The structural studies of the beads were performed by using a Fourier transform infrared spectrophotometer and scanning electron microscope. The swelling behavior, solubility, hydrolytic degradation, and loading capacity of the beads for isoniazid were investigated. The structural changes of the beads at pH 2.0 and 7.4 were put forward using the data obtained by infrared and ultraviolet spectroscopy. The prepared beads showed 82% drug‐loading capacity, which suggested that these semi‐interpenetrating polymer network beads are suitable for controlled release of drugs in an oral sustained delivery system. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 639–649, 2001     

Optimizing preparation of NaCS–chitosan complex to form a potential material for the colon‐specific drug delivery system

A novel polyelectrolyte complex (PEC) formed by sodium cellulose sulfate (NaCS) and chitosan was prepared as a candidate material for colon‐specific drug delivery system. It was found in experiments that the properties of two raw materials and the process parameters, such as the degree of substitution (DS) and concentration of NaCS, the viscosity and concentration of chitosan, were very important factors on the properties of the final product—NaCS–chitosan‐PEC. The preparation of NaCS–chitosan complex was optimized by using response surface methodology to evaluate the effects of these parameters on the degradation properties of NaCS–chitosan in the simulated colonic fluid (SCF). The DS of NaCS was in the range from 0.2 to 0.6, the concentration of NaCS from 2 to 4% (w/v), the viscosity of chitosan from 50 to 550 mPa s, and the concentration of chitosan from 0.5 to 1.5% (w/v). A mathematical model was developed to describe the effect of these parameters and their interactions on the degradation of NaCS–chitosan complex. The optimum operation conditions for preparing NaCS–chitosan complex were determined to DS of NaCS of 0.2, the concentration of NaCS of 4.0% (w/v), chitosan viscosity of 327 mPa s, and the concentration of chitosan 0.5% (w/v), respectively. Validation of experiments with 5 confirmatory runs indicated the high degree of prognostic ability of response surface methodology. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Properties of hybrid materials derived from hydroxy‐containing linear polyester and silica through sol–gel process. I. Effect of thermal treatment

The transparent hybrid material, HLP/SiO₂, was prepared by an in situ sol–gel process of tetraethoxysilane (TEOS) at 30°C in the presence of hydroxy‐containing linear polyester (HLP) obtained by ring‐opening reaction of diglycidyl ether of bisphenol A (DGEBA) with adipic acid under the catalyzation of triphenylphosphine (TPP). The hetero‐associated hydrogen bonds between the HLP and the residual silanol of silica in the hybrids were investigated by FTIR spectroscopy. Upon heating the hybrid, the interfacial force between the HLP matrix and the silica network changed from hydrogen bonds into covalent Si—O—C bonds through dehydration of hydroxy groups in HLP with residual silanol groups in the silica network. The existence of covalent Si—O—C bonds was proved by solid‐state ²⁹Si‐NMR spectra. Other properties such as tensile strength, glass transition temperature (T_g ), solubility, and thermal stability of the hybrids before and after heat treatment were studied in detail. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1179–1190, 2000     

Antibacterial activity of chitosan–alginate sponges incorporating silver sulfadiazine: Effect of ladder‐loop transition of interpolyelectrolyte complex and ionic crosslinking on the antibiotic release

Hydrogel membranes prepared from polyelectrolyte complex (PEC) have been used for repair of wounds and controlled antibacterial release. A simple method, based on homogenizing interpolyelectrolyte complex, has been developed to prepare a chitosan–alginate sponge with high stability. The spongelike chitosan–alginate hydrogel can be used as a wound dressing for the sustained release of silver sulfadiazine (AgSD) in a controlled way. In this study, we evaluated the effect of electrolyteic properties of chitosan and alginate on the characteristics of the prepared chitosan–alginate PEC. All types of the spongelike chitosan–alginate hydrogels exhibited superabsorbent properties. However, only the chitosan–alginate hydrogel prepared by the interpolyelectrolyte complex of alginate with low pH of chitosan, and that prepared by the interpolyelectrolyte complex of chitosan with high pH of alginate, can keep their stability after swelling in PBS solution. FTIR analysis suggests that the protonated amino groups on chitosan and the ionized carboxylic groups on alginate should be responsible for the formation of a stable ladder‐type of chitosan–alginate PEC. Ionic crosslinking is helpful to increase the stability of the loop‐type of chitosan–alginate PEC. The release of AgSD from chitosan–alginate PEC sponges could be controlled by the variation of ladder‐loop structural transition of chitosan–alginate PEC and the ionic crosslinking of the chitosan–alginate complex. The antibacterial ability of AgSD‐incorporated PEC sponges was examined in agar plate against Pseudomonas aeruginosa and Staphylococcus aureus. The result suggests that the PEC sponges containing antimicrobial agents should effectively suppress bacterial proliferation to protect the wound from bacterial invasion. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 538–549, 2005     

Effect of preparation and reaction condition on the catalytic performance of Mo–V–Te–Nb catalysts for selective oxidation of propane to acrylic acid by high-throughput methodology

Combinatorial screening technique has been applied to investigate the catalytic activity and selectivity of quaternary Mo–V–Te–Nb mixed oxide catalysts treated with various chemicals during preparation for selective oxidation of propane to acrylic acid. The catalyst libraries were prepared by the slurry method and catalytic activities were examined in 32-channel high-throughput screening reactor system coupled with a mass spectrometer and/or gas chromatograph.The obtained results provided substantial evidence that the sample preparation condition would have strong effect on the catalytic performance for propane selective oxidation. Among screened samples, Mo–V–Te–Nb treated with HIO₃ solution presented a better performance. The reaction results of promising catalysts selected from the libraries were applied to further scale-up of the system and confirmed catalytic performance. Quantification of the result of Mo–V–Te–Nb treated with HIO₃ solution was realized by combination of GC and MS and relationship between the MS data and the GC results can be established.     

Effect of vegetable‐based polyols in unimodal glass‐transition polyurethane slabstock viscoelastic foams and some guidance for the control of their structure–property behavior. I

We investigated the synthesis and structure–property behaviors of two types of vegetable‐oil polyols (soy oil and castor oil) and their use in viscoelastic (VE) polyurethane foams (PUFs). This article is the first in a two‐part series. In this initial part, we principally address the dynamic mechanical analysis (DMA) behavior of these foams in conjunction with information on the cellular morphology, sol fraction, and rise and reaction temperature profile behavior (the latter two parameters were determined during the foaming process). Particular emphasis is placed on the DMA damping characteristics, which represent one of the most critical parameters in the application of VE PUFs. It is also shown that the damping characteristics could be modified in such foams by the variation of the isocyanate/hydroxyl (×100) index, the addition of plasticizer, and in the case of soy polyols, the soy content. The frequency dependence of the VE PUFs is also briefly addressed. In the second article in this series, which directly follows this article, we further address the details of other relevant physical properties of these same foams in view of their applied nature. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of strontium and cerium doping on the structural characteristics and catalytic activity for C3H6 combustion of perovskite LaCrO3prepared by sol–gel

Two series of Sr- or Ce-doped La_1−xM_xCrO₃ (x = 0.0, 0.1, 0.2 and 0.3) catalysts were prepared by thermal decomposition of amorphous citrate precursors followed by annealing at 800 °C in air atmosphere. The effect of Ce and Sr on the morphological/structural properties of LaCrO₃ was investigated by means of thermogravimetric/differential thermal analysis (TG/DTA) of the precursors decomposition under air, X-ray diffraction (XRD), electron paramagnetic resonance (EPR), transmission electron microscopy–X-ray energy dispersive spectroscopy (TEM–XEDS), S_BET determination, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) techniques. The characterization results are employed to explain catalytic activity results for C₃H₆ combustion. It is shown that the lanthanum chromite perovskite structure is obtained upon thermal treatment of the sol–gel derived precursors at T > ca. 800 °C. The presence of the dopant generally induces the formation of segregated oxide phases in the samples calcined at 800 °C although some introduction of the Sr in the perovskite structure is inferred from EPR measurements. The oxidation activity becomes maximised upon formation of such doped perovskite structure.