Mehrdad Yazdani-Pedram

Comparative studies on polyelectrolyte complexes and mixtures of chitosan-alginate and chitosan-carrageenan as prolonged diltiazem clorhydrate release systems.

The aim of this work was to evaluate the possibility of using mixtures and/or polyelectrolyte complexes from both chitosan-alginate and chitosan-carrageenan as prolonged drug release systems. Different dissolution profiles were obtained by changing the polymer matrix system (chitosan-alginate or chitosan-carrageenan) and the method used to include these polymers into the formulation (physical mixture or polyelectrolyte complex). Drug dissolution profiles from the matrices have been discussed by considering the swelling behavior of the polymers used. The swelling behavior of the chitosan-carrageenan and chitosan-alginate systems was analyzed by using the Hopfenberg model which permits to separate the diffusional contribution, kf, from the relaxational contribution, kr, involved in solvent penetration/sorption in glassy polymers. The chitosan-alginate system is better than the chitosan-carrageenan system as prolonged drug release matrix because the drug release is controlled at low percentage of the polymers in the formulation, the mean dissolution time is high, and different dissolution profiles could be obtained by changing the mode of inclusion of the polymers. Good agreement between td and kf/kr values for the system chitosan-alginate was found, which means that the swelling behavior of the polymers controlled the drug release from the matrix. In the case of the system chitosan-carrageenan, the high capacity of carrageenan promotes the entry of water into the tablet and therefore the main mechanism of drug release would be the disintegration instead of the swelling of the matrix.

Hydrogels based on modified chitosan, 1. Synthesis and swelling behavior of poly(acrylic acid) grafted chitosan

A large number of carboxylic groups were introduced onto chitosan by grafting with poly(acrylic acid) as an efficient way of modification. The reactions were carried out in a homogeneous aqueous phase by using potassium persulfate and ferrous ammonium sulfate as the combined redox initiator system. The efficiency of grafting was found to depend on monomer, initiator, and ferrous ion concentrations as well as reaction time and -temperature. It was observed that the level of grafting could be controlled to some degree by varying the amount of ferrous ion used as a co-catalyst in the reaction. Evidence of grafting was obtained by comparison of FTIR spectra of chitosan and the graft copolymer as well as solubility characteristics of the products. The swelling behavior of chitosan samples, grafted with 115% and 524% poly(acrylic acid), was studied as function of pH, in distilled water and in aqueous NaCl solution. The sample that has 115% grafting swells considerably more both in distilled water (pH 5.8) as well as higher pH values than the sample with 524% grafting. In contrast, an inverse swelling behavior at pH 2 was observed. An unusual swelling behavior at pH 2 was found for the sample with 524% grafting, which swells to a greater extent than in distilled water. This was attributed to the amphiphilic nature of the modified chitosan from which complex inter- and/or intramolecular interactions could originate.

Homogeneous grafting reaction of vinyl pyrrolidone onto chitosan

Modification of chitosan by grafting of vinyl pyrrolidone (VP) was carried out in homogeneous phase using potassium persulfate as redox initiator. The effect of the reaction variables on the extent of grafting was studied systematically. Values for grafting percentages up to 290% were reached. It was observed that the solubility of chitosan was markedly reduced after grafting with vinyl pyrrolidone. The grafted product is insoluble in common organic solvents as well in dilute organic and inorganic acids. However, the solubility of the grafted chitosan after adsorption of copper ions changed substantially, becoming completely soluble in dilute hydrochloric acid. This was attributed to the effect of complex formation produced by coordination of amino groups of chitosan with copper ions.

Melt functionalization of polypropylene with methyl esters of itaconic acid

Polypropylene (pp) was functionalized in the melt phase by grafting with itaconic acid derivatives. 2,5-dimethyl-2,5-bis(tert-buthylperoxy) hexane (lupersol 101) was used as radical initiator. A Brabender Plasticorder was used for all the experiments. The optimum conditions for the grafting reaction were 190°C, 75 rpm and 6 min. The itaconic acid derivatives used in this work were mono- and dimethyl esters. When dimethyl itaconate (DMI) was used as functional polar monomer, a maximum of 1.5% of grafting was reached. A similar value was found for grafting of monomethyl itaconate (MMI) where a maximum of 1.6% by weight of this monomer was incorporated in pp. The existence of grafted MMI and/or DMI in pp was confirmed by FT-IR spectroscopy. Carbonyl absorption bands from either MMI and/or DMI were observed in the FT-IR spectrum of the modified pp. The percentage of grafting attained was also followed by FT-IR analysis, where the amount of monomer incorporated in pp was estimated from a calibration curve established for the monomers used in this work. A systematic study of the reaction variables allowed the optimization of the grafting process. It was found that the percentage of grafting attained depends on the initial concentration of both monomer and initiator used in the reaction. Some properties of the modified pps were evaluated by employing dilute solution viscosity and differential scanning calorimetric (DSC) measurements. It was found that the molecular weight of the grafted polymer decreased with increasing percentage of grafting. DSC measurements indicated that functionalized pp samples have slightly higher crystallinity but show the same melting temperature as pp.

On the Modification of Chitosan Through Grafting

Abstract The feasibility of grafting poly(methyl acrylate) and poly[1-(methoxycarbonyl) ethylene] onto chitosan, poly-β(1←-4)-2-amino-2-deoxy-d-glucose, was investigated. The grafting reaction was carried out in aqueous solution by using ferrous ammonium sulfate (FAS) in combination with H2O2 as redox initiator. The effects of such reaction variables as chitosan, monomer and initiator concentrations, reaction time, and reaction temperature were determined. Through this study the grafting reaction could be optimized. The grafting yield reached its maximum value of 332% when 0.3 g chitosan was copolymerized with 3 mL monomer at 70°C for 120 minutes with [FAS] = 6 × 10−5 M, [H2O2] = 6 × 10−3 M, and 8 mL water. The grafted chitosan was found to be insoluble in solvents for chitosan and solvents for poly(methyl acrylate), but did show swelling in dilute acetic acid, methanol, acetone, and in an ethanol/2% acetic acid 1:1 mixture. The thermal stability of chitosan and grafted chitosan were studied by dynamic th...

Cocatalyst effect in potassium persulfate initiated grafting onto chitosan

Methyl methacrylate and methyl acrylate were grafted onto chitosan by using potassium persulfate alone as redox initiator and in combination with MnCl2 and CuCl2, as inorganic, and both ammonium tartrate and oxalate as organic cocatalysts. The extent of grafting was found to depend mainly on the nature of the cocatalysts used.

Porous silica derived from chitosan-containing hybrid composites

In this paper, we report the preparation by the sol-gel technique of organic-inorganic hybrid composites containing the biopolymer chitosan incorporated in a siloxane-based inorganic network. The hybrid xerogels were transformed into porous silica particles by elimination of the organic phase. Surface characteristics of the silica samples can be easily tailored. In this way Brunauer-Emmett-Teller areas, pore volume, and pore diameter of the prepared silica can be predetermined within a wide range. Morphology of the particles at longer length scales can be designed to obtain either irregularly shaped particles with layered morphology or spherical particles. The results are explained on the basis of the cationic polyelectrolytic properties of chitosan, which allows easy association with siloxane oligomers, the precursors of silica in forming hybrid nanocomposites.

Viscoelastic relaxations in poly(ethylene-co-1-octadecene) synthesized by a metallocene catalyst

Abstract The viscoelastic relaxations of four copolymers of ethylene and 1-octadecene, with different comonomer contents, synthesized with a metallocene catalyst, have been analysed and compared to those of the corresponding polyethylene homopolymer. Similar to other ethylene copolymers, the temperature for α relaxation decreases with the increase in the comonomer content, attributed to the reduction of the crystal size. In fact, a linear relation has been found between the temperature location of α relaxation and the crystal thickness estimated from the SAXS long spacing. However, the position of β relaxation experiences very little dependence with the comonomer content and it overlaps to α relaxation for the higher comonomer contents. As to γ relaxation, there is also a clear effect of the comonomer content on the breadth and on the location of this relaxation.

Comparison of redox initiators reactivities in the grafting of methyl methacrylate onto chitin

Abstract Relative reactivities of potassium persulfate (KPS) and ferrous ammonium sulfate-potassium persulfate (FAS-KPS) systems, in aqueous medium, as initiators for grafting of methyl methacrylate (MMA) onto chitin, were studied. Evidence of grafting was obtained from IR spectroscopic measurements of the grafted and ungrafted chitin. To compare the efficiency of both redox initiators, a systematic study was carried out to optimize the grafting yield by varying reaction conditions such as initiator, monomer and chitin concentrations as well as reaction time and temperature. Under optimum polymerization conditions 94.5% grafting was obtained by using KPS while up to 352% grafting was reached when FAS-KPS redox system was used. The apparent activation energy, in the case of the FAS-KPS initiated grafting, was estimated to be 23 Kcal/mol. The grafted chitin is insoluble in most solvents, as chitin, but show enhanced affinity for some organic solvents.

Preparation and bioactive properties of novel bone-repair bionanocomposites based on hydroxyapatite and bioactive glass nanoparticles †

Bionanocomposites based on ceramic nanoparticles and a biodegradable porous matrix represent a promising strategy for bone repair applications. The preparation and bioactive properties of bionanocomposites based on hydroxyapatite (nHA) and bioactive glass (nBG) nanoparticles were presented. nHA and nBG were synthesized with nanometric particle size using sol-gel/precipitation methods. Composite scaffolds were prepared by incorporating nHA and nBG into a porous alginate (ALG) matrix at different particle loads. The ability of the bionanocomposites to induce the crystallization of the apatite phase from simulated body fluid (SBF) was systematically evaluated using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray analysis, and Fourier transform infrared spectroscopy. Both nHA/ALG and nBG/ALG composites were shown to notably accelerate the process of crystallization and growth of the apatite phase on the scaffold surfaces. For short immersion times in SBF, nBG (25%)-based nanocomposites induced a higher degree of apatite crystallization than nHA (25%)-based nanocomposites, probably due to the more reactive nature of the BG particles. Through a reinforcement effect, the nanoparticles also improve the mechanical properties and stability in SBF of the polymer scaffold matrix. In addition, in vitro biocompatibility tests demonstrated that osteoblast cells are viable and adhere well on the surface of the bionanocomposites. These results indicate that nHA- and nBG-based bionanocomposites present potential properties for bone repair applications, particularly oriented to accelerate the bone mineralization process.