Determination of the Mark-Houwink equation for chitosans with different degrees of deacetylation

Peroxide chitosan derivatives and their application

Via radical reactions of chitosan and 5-tert-butylperoxy-5-methyl-1-hexen-3-in peroxychitosanes with ditertiary peroxide fragments were synthesized. They can be used as macroinitiator and coemulsifiers for emulsion polymerization of vinyl monomers. Latex polymers obtained antibacterial properties. Polymeranalogical interaction of chitosan with tert-butylperоxymethyl ester of butendicarbon acid yields in peroxychitosanes with controlled quantity of primary-tertiary peroxide fragments. New pH-sensitive smart hydrogels with antibacterial properties were created on their basis.

Low molecular weight chitosans—Preparation with the aid of pronase, characterization and their bactericidal activity towards Bacillus cereus and Escherichia coli

The homogeneous low molecular weight chitosans (LMWC) of molecular weight 9.5-8.5 kDa, obtained by pronase catalyzed non-specific depolymerization (at pH 3.5, 37 degrees C) of chitosan showed lyses of Bacillus cereus and Escherichia coli more efficiently (100%) than native chitosan (<50%). IR and (1)H-NMR data showed decrease in the degree of acetylation (14-19%) in LMWC compared to native chitosan ( approximately 26%). Minimum inhibitory concentration of LMWC towards 10(6) CFU ml(-1) of B. cereus was 0.01% (w/v) compared to 0.03% for 10(4) CFU ml(-1) of E. coli. SEM revealed pore formation as well as permeabilization of the bacterial cells, as also evidenced by increased carbohydrate and protein contents as well as the cytoplasmic enzymes in the cell-free supernatants. N-terminal sequence analyses of the released proteins revealed them to be cytoplasmic/membrane proteins. Upon GLC, the supernatant showed characteristic fatty acid profiles in E. coli, thus subscribing to detachment of lipopolysaccharides into the medium, whereas that of B. cereus indicated release of surface lipids. The mechanism for the observed bactericidal activity of LMWC towards both Gram-positive and Gram-negative bacteria has been discussed.

Polyelectrolyte Microstructure in Chitosan Aqueous and Alcohol Solutions

This work deals with chain ordering in aqueous and water-alcohol solutions of chitosan. The so-called polyelectrolyte peak is investigated by small-angle synchrotron X-ray scattering. The polyelectrolyte microstructure was characterized by the position of the maximum of the polyelectrolyte scattering peak qmax, which scales with the polymer concentration cp as qmax approximately cp alpha. An evolution of the power law exponent alpha is observed as a function of the degree of acetylation (DA) of chitosan, which is responsible for changes of both the charge density (f) and the hydrophobicity of the polymer chains. The results highlighted the two organization regimes of the theory of Dobrynin and Rubinstein, investigated here for the first time for a natural polymer. At low DAs, alpha approximately 1/2, in agreement with a pearl necklace organization where the structure is controlled by the string between pearls. For higher DA, alpha approximately 1/3, and the correlation revealed by the polyelectrolyte peak is controlled by the pearls. This analysis offers a way to study quantitatively the balance between solvophobic-solvophilic interactions that play an important role in the solution properties of natural polymers. In addition, the role of several parameters acting on the interaction balance were evidenced, such as the nature of the counterion, the composition of the solvent (amount of alcohol in the aqueous solution), and the screening of Coulombic forces by salt addition. Finally, the nanostructure transition from a polyelectrolyte solution to a physical gel is discussed. The gel state is reached when the solvophobic interactions are favored, but depending on the gelation route the polyelectrolyte ordering could be preserved or not.

A novel hydrogel crosslinked hyaluronan with glycol chitosan

A novel hydrogel was prepared by crosslinking hyaluronan with glycol chitosan in aqueous solution using water soluble carbodiimide at nearly neutral pH and room temperature. The products can be easily formulated into injectable gels, various films, membranes and sponges for soft tissue augmentation, viscosupplementation, drug delivery, preventing adhesion of post operation, wound dressing and tissue engineering scaffolds. The said hydrogel has high water adsorption property and biostability. Rheololgical results of the gel showed a soft and viscoelastic structure. FTIR further confirmed the formation of amide bonds between carboxyl groups of hyaluronan and amine groups of glycol chitosan and no N-acylurea and other derivatives were identified.

Synthesis, characterization and thermal sensitivity of chitosan-based graft copolymers

Novel chitosan-based graft copolymers (CECTS-g-PDMA) were synthesized through homogeneous graft copolymerization of (N,N-dimethylamino)ethyl methacrylate (DMA) onto N-carboxyethylchitosan (CECTS) in aqueous solution by using ammonium persulfate (APS) as the initiator. The effect of polymerization variables, including initiator concentration, monomer concentration, reaction time and temperature, on grafting percentage was studied. XRD, FTIR, DSC and TGA were used to characterize the graft copolymers. Surface-tension measurements, turbidity measurements and temperature-variable (1)H NMR analysis were combined to investigate the thermal sensitivity of CECTS-g-PDMAs in aqueous solution.

Processing and Characterization of Porous Structures from Chitosan and Starch for Tissue Engineering Scaffolds

Natural biodegradable polymers were processed by different techniques for the production of porous structures for tissue engineering scaffolds. Potato, corn, and sweet potato starches and chitosan, as well as blends of these, were characterized and used in the experiments. The techniques used to produce the porous structures included a novel solvent-exchange phase separation technique and the well-established thermally induced phase separation method. Characterization of the open pore structures was performed by measuring pore size distribution, density, and porosity of the samples. A wide range of pore structures ranging from 1 to 400 microm were obtained. The mechanisms of pore formation are discussed for starch and chitosan scaffolds. Pore morphology in starch scaffolds seemed to be determined by the initial freezing temperature/freezing rate, whereas in chitosan scaffolds the shape and size of pores may have been determined by the processing route used. The mechanical properties of the scaffolds were assessed by indentation tests, showing that the indentation collapse strength depends on the pore geometry and the material type. Bioactivity and degradation of the potential scaffolds were assessed by immersion in simulated body fluid.

Novel injectable calcium phosphate/chitosan composites for bone substitute materials

In this study, a novel injectable bone substitute material was developed which consists of chitosan, citric acid and glucose solution as the liquid phase, and tricalcium phosphate powder as the solid phase. This material was moldable because of its paste consistency after mixing. We used four groups of cement to investigate the mechanical properties and biocompatibility of the new biomaterial in vitro, which were named group A (10% citric acid), B (15% citric acid), C (20% citric acid) and D (25% citric acid). The setting times of the cements were 5-30 min. X-ray diffraction analysis showed that the products were hydroxyapatite (HA) and dicalcium phosphate anhydrous. When the concentration of citric acid was increased, the compressive strength of specimen increased. Through the simulated body fluid test, we observed the material was bioactive. Group D could induce Ca and P ions to deposit the surface group D quickly. These results indicated that the concentration of citric acid in the liquid component affected the mechanical properties and bioactivity of cements. The cell cultivation test showed that the cytocompatibility of the new biomaterial was good. The method for preparing the novel bone substitute material is simple. The starting material is more readily available and cheaper than HA, poly(methyl methacrylate), and so on. The cement could have good prospects for medical application.

Three-dimensional culture of human osteoblastic cells in chitosan sponges: the effect of the degree of acetylation

In this investigation, the effect of the degree of acetylation (DA) of chitosan on the behavior of human osteoblastic MG-63 cells cultured in three-dimensional chitosan matrices was assessed. Chitosan sponges with DAs in the range of 4 to 49% were prepared and characterized in terms of microstructure, porosity, and pore size. Collagen sponges were used as 3D control. Cell proliferation was determined using the MTT assay while the retention of the osteoblastic phenotype was monitored by assaying alkaline phosphatase activity. Cell morphology, cytoskeletal organization, and viability were assessed using different microscopy techniques. Chitosan sponges showed a similar microstructure regardless the DA, except for the highest DA used, where a more heterogeneous pore distribution was observed. In terms of cell proliferation, alkaline phosphatase activity and cell viability, cells cultured in chitosan scaffolds performed as well as in the 3D control regardless the DA, except for the highest DA used, where an inhibitory effect on cell proliferation was found. However, while in sponges with DAs < or = 13% cells attached and spread displaying long cell filopodia and numerous cell-to-cell contacts, in sponges with higher DAs cells tended to remain spherical and grow into spheroid-like cellular aggregates. In the present study, the DA played a key role in determining the affinity of osteoblastic cells towards the substrates, possibly by influencing the nature of the initial adsorbed protein layer.

Chemical modification of chitosan by phosphorylation: an XPS, FT-IR and SEM study

In the present work, the surface of chitosan membranes was modified using a phosphorylation method carried out at room temperature. Phosphorylation may be of particular interest in materials for orthopaedic applications, due to the cation-exchange properties of phosphate functionalities. Phosphate groups chelate calcium ions, thus inducing the deposition of an apatite-like layer known to improve the osteoconduction of polymer-based implants. Additionally, the negatively charged phosphate functionalities, together with the positively charged amine groups from chitosan, are expected to provide chitosan with an amphoteric character, which may be useful as a combinatorial therapeutic strategy, by simultaneously allowing the immobilization of signalling molecules like growth factors. Phosphorylation was carried out at room temperature using the H3PO4/Et3PO4/P2O5/butanol method. Surface characterization was performed by XPS, ATR-FT-IR, and SEM. Cross-sections were analyzed by SEM fitted with EDS. The phosphate content increased with the reaction time, as shown by XPS and ATR-FT-IR, a P/N atomic ratio of 0.73 being obtained after 48 h of treatment. High-resolution XPS spectra regarding C1s, O1s, N1s and P2p are discussed. The introduction of a neutralization step led to a reduction of P content, which pointed out to the presence of phosphates ionically bound to protonated amines, in addition to phosphate esters. EDS analysis of cross-sections revealed a gradual P reduction up to 50% towards the inner part of the membrane.

Preparation and antimicrobial activity of hydroxypropyl chitosan

Water-soluble hydroxypropyl chitosan (HPCS) derivatives with different degrees of substitution (DS) and weight-average molecular weight (Mw) were synthesized from chitosan and propylene epoxide under basic conditions. Their structure was characterized by IR spectroscopy, NMR spectroscopy, and elemental analysis, which showed that both the OH groups at C-6 and C-3 and the NH2 group of chitosan were alkylated. The DS value of HPCS ranged from 1.5 to 3.1 and the Mw was between 2.1x10(4) and 9.2x10(4). In vitro antimicrobial activities of the HPCS derivatives were evaluated by the Kirby-Bauer disc diffusion method and the macrotube dilution broth method. The HPCS derivatives exhibited no inhibitory effect on two bacterial strains (Escherichia coli and Staphylococcus aureus); however, some inhibitory effect was found against four of the six pathogenic fruit fungi investigated. Some derivatives (HPCS1, HPCS2, HPCS3, HPCS3-1, and HPCS4) were effective against C. diplodiella and F. oxysporum. HPCS3-1 is the most effective one with MIC values of 5.0, 0.31, 0.31, and 0.16mg/mL against A. mali, C. diplodiella, F. oxysporum, and P. piricola, respectively. Antifungal effects were also observed for HPCS2 and HPCS3-1 against A. mali, as well as HPCS3 and HPCS3-1 against P. piricola. The results suggest that relatively lower DS and higher Mw value enhances the antifungal activity of HPCS derivatives.

Pharmacological activity of peroral chitosan-insulin nanoparticles in diabetic rats

The objective of the present study was to evaluate the effects of formulation parameters on the in vivo pharmacological activity of the chitosan-insulin nanoparticles. Chitosan-insulin nanoparticles were prepared by ionotropic gelation at pH 5.3 and 6.1 and denoted as F5.3 np and F6.1 np, respectively. F5.3 np and F6.1 np administered orally at insulin doses of 50 U/kg and/or 100 U/kg were effective at lowering the serum glucose level of streptozotocin-induced diabetic rats. The 100 U/kg-dose F5.3 np sustained the serum glucose at pre-diabetic levels for at least 11 h. In comparison, F6.1 np had a faster onset of action (2h versus 10h) but lower efficiency. The effectiveness of peroral F5.3 np and F6.1 np in lowering the serum glucose level of streptozotocin-induced diabetic rats was ascribed to the local effect of insulin in intestine. Confocal micrographs showed strong interaction between rat intestinal epithelium and chitosan nanoparticles 3h post-oral administration.

β-Galactosidase from Penicillium canescens. Properties and immobilization

β-galactosidase from Penicillium canescens was immobilized on chitosan, sepharose-4B, foamable polyurethane and some other carriers. The highest yield of immobilization (up to 98%) was obtained by using chitosan as a carrier. The optimum pH and temperature were not significantly altered by immobilization. High stability of immobilized β-galactosidase during storage was demonstrated. Efficient lactose saccharification (over 90%) in whey was achieved by using immobilized β-galactosidase.

Monitoring the self-assembly of chitosan/glutaraldehyde/cysteamine/Au-colloid and the binding of human serum albumin with hesperidin

A new method for monitoring, in real-time, the self-assembly of chitosan/glutaraldehyde/cysteamine (CGC) on the gold surface and the immobilization of Au-colloid on CGC membrane with piezoelectric quartz crystal impedance (PQCI) are firstly proposed. Cyclic voltammogram and electrochemical impedance spectroscopy were also use to investigate the formation of Au-colloid/CGC. The viscosity-average molecular weight of chitosan used was firstly estimated as 16.8 x 10(5) with piezoelectric quartz crystal (PQC) sensor. On the basis of the analysis of the multi-dimensional information provided by PQCI, two stages existed in chitosan drying course: the frequency shift of the first stage was controlled by viscoelastic of the liquid, while the total frequency shift was due to mass change. The cross-link ratio of glutaraldehyde with chitosan was about 0.13, while for glutaraldehyde with cysteamine was about 0.217. PQCI also showed that the Au-colloid immobilization is a first-order reaction, while the HSA immobilization is a sum of two exponential functions, e.g., adsorption and re-arrangement. The association of the immobilized HSA with the purified hesperidin was monitored, and the association constant was estimated as 3.42 ml mg(-1) by Scatchard analysis.