Biomedical subjects

A Domard

Publications and source records attributed to A Domard.

At least 19 recordsLinked to original sources

PubMed2006

A material decoy of biological media based on chitosan physical hydrogels: application to cartilage tissue engineering.

The cartilage tissue has a limited self-regenerative capacity. Tissue-engineering represents a promising trend for cartilage repair. The present study was aimed to develop a biomaterial formulation by combining fragments of chitosan hydrogel with isolated rabbit or human chondrocytes. We first reported the properties of the constructs elaborated with rabbit chondrocytes and pure chitosan physical hydrogels with defined molecular weight, acetylation degree and polymer concentration. Morphological data showed that chondrocytes were not penetrating the hydrogels but tightly bound to the surface of the fragments and spontaneously formed aggregates of combined cell/chitosan. A significant amount of neo-formed cartilage-like extracellular matrix (ECM) was first accumulated in-between cells and hydrogel fragments and furthermore was widely distributed within the neo-construct. The optimal biological response was obtained with hydrogel fragments concentrated at 1.5% (w/w) of polymer made from a chitosan with a degree of acetylation between 30 and 40%. Such hydrogels were then mixed with human chondrocytes. The phenotype of the cells was analyzed by using chondrocytic (mRNA expression of mature type II collagen and aggrecan as well as secretion of proteoglycans of high molecular weight) and non chondrocytic (mRNA expression of immature type II collagen and type I collagen) molecular markers. As compared with human chondrocytes cultured without chitosan hydrogel which rapidly dedifferentiated in primary culture, cells mixed with chitosan rapidly loose the expression of type I and immature type II collagen while they expressed mature type II collagen and aggrecan. In these conditions, chondrocytes maintained their phenotype for as long as 45 days, thus forming cartilage-like nodules. Taken together, these data suggest that a chitosan hydrogel does not work as a scaffold, but could be considered as a decoy of cartilage ECM components, thus favoring the binding of chondrocytes to chitosan. Such a biological response could be described by the concept of reverse encapsulation.

Acetylation↗

PubMed2006

Interactions study between the copper II ion and constitutive elements of chitosan structure by DFT calculation.

Molecular modeling is particularly useful to understand interactions between various kinds of molecules and ions. This study is aimed at studying the interactions between one Cu(2+) ion and one or several glucosamine residues. The geometries and the interaction energies of all of the complexes involving all of the dimers obtained from glucosamine and N-acetylglucosamine were computed by means of density functional theory (DFT) methods. In a first step, for the two dimers A-A and A-B (A for glucosamine and B for N-acetyl glucosamine), a starting geometry was built, and the energies were calculated using a rigid rotation of 30 degrees intervals for each of the dihedral angles (Phi and Psi) of the glycosidic bond, spanning the whole angular range. These calculations allowed us to retrieve the minimal energy conformation and investigate all possible conformations. The results were compared to some experimental data. In a second step, we investigated the interactions of Cu(2+) with the different possible coordination sites of A. For all complexes considered, the Cu(2+) site was completed with H(2)O and/or OH(-) ligands to have a global neutral charge. The calculations confirmed that the most stable interactions involved the free amino site in a "pending complex". Another pending form was possible considering the participation of the heterocyclic O site, but the latter was less favored. On the other hand, we also showed that glucosamine could not act as a bidentate ligand and that N-acetyl glucosamine was not coordinating with Cu(2+). Finally, our results evidenced a cooperative fixation of Cu(2+) ions when considering the complexation of two successive metal ions on the two consecutive glucosamine residues of the dimer A-A.

Cations, Divalent↗

PubMed2001

Sorption and desorption studies on chitin gels.

The aim of this work was to study various transport phenomena in chitin gels obtained by N-acetylation of chitosan in a water-alcohol mixture. Three kinds of transport were investigated: the sorption of solutes interacting with chitin, the desorption of solutes without significant interaction with the polymer, and osmosis phenomena. In the case of interactive sorption, dyes having different chemical structures such as C.I. Acid Blue 74, C.I. Reactive Violet 5 or C.I. Direct Red 28 were tested. Sorptions of C.I. Acid Blue 74 and C.I. Reactive Violet 5 depend on the charge density of the polymer network and, as a consequence, on DA, pH and the dielectric constant of the media. This result reveals the importance of electrostatic interactions. On the other hand, the sorption of C.I. Direct Red 28 is mainly due to hydrophobic interactions and H-bonding, it is limited to the extreme surface of the gel. Concerning the non-interactive desorption, solutes of different steric hindrance such as PP vitamin, B1 vitamin and caffeine exhibit similar diffusion coefficients located within 3.7-5.6x10(-6) cm(2) s(-1). Finally, the osmotic behaviour of the gel immersed in a concentrated solution of gelatin allows us to multiply by 25 the concentration of chitin in the gel without any penetration of gelatin.

Absorption↗

PubMed2001

Influence of the degree of acetylation on some biological properties of chitosan films.

In this study, we investigated in vitro the role of the degree of acetylation (DA) on some biological properties of chitosan films. We noticed that, whatever the DA, all chitosan films were cytocompatible towards keratinocytes and fibroblasts. We also demonstrated that the higher the DA of chitosan, the lower was the cell adhesion on the films. Fibroblasts appear to adhere twice as much as keratinocytes on these materials. We observed that keratinocyte proliferation increases when the DA of chitosan films decreases. Thus, DA influences the cell growth in the same way as cell adhesion. On the other hand, although they remain alive, fibroblasts do not proliferate on chitosan films. This behaviour is related to an extremely high adhesion on this kind of material, which certainly inhibits cell growth. In conclusion, DA plays a key role in cell adhesion and proliferation, but does not change the cytocompatibility of chitosan. In parallel, it is also important to notice the role played by the surface morphology of the material, a second major parameter which influences the mechanism of adhesion.

Acetylation↗

PubMed2001

Preparation of chitosan gel beads by ionotropic molybdate gelation.

A new process is described for the preparation of chitosan gel beads using molybdate as the gelling agent. This new gelation technique leads to a structure different from that produced during alkaline coagulation of a chitosan solution. Instead of a morphology characterized by large open pores, gel beads produced in a molybdate solution, under optimum conditions (pH 6; molybdate concentration, 7 g x L(-1)), have a double layer structure corresponding to a very compact 100-microm thick external layer and an internal structure of small pores. Experimental conditions, especially pH and molybdate concentration, were selected to optimize molybdate content and the stability of the bead shape.

Biocompatible Materials↗

PubMed2001

Relation between the degree of acetylation and the electrostatic properties of chitin and chitosan.

A series of chitosan/chitin samples with DA's varying between 5.2 and 89% was prepared from the reacetylation under soft conditions of a unique chitosan sample allowing the preservation of the chain distribution. The study of the variation of pH for the same concentration of amine groups, at different ionic strengths, on the scale of DA's allows us to extrapolate the variation of pKa at dissociation degrees (alpha) 0 and 1. A modeling of all the curves was obtained by means of only one equation. Then, for given concentration of chitosan and ionic strength, it is possible to predict the pH of the solution whatever the DA and alpha. The role of DA through the participation of hydrophobic interactions and hydrogen bondings on the electrostatic parameters is discussed. The results allow a better understanding of some physicochemical and biological properties of chitosan and chitin.

Acetylation↗

PubMed2001

Physicochemical properties of physical chitin hydrogels: modeling and relation with the mechanical properties.

In this work, we were interested in the modeling of syneresis of physical chitin hydrogels by a mathematic law allowing us to predict the variation of the weight of the gel as a function of time. The variation of the weight of the gel during syneresis can be described by W(t)()/W(0) = (t(1/2) + (W(infinity)/W(0))t)/(t(1/2)) + t) where W(0), W(infinity), and W(t)() are the weights of the gel at the beginning of syneresis, for infinite time and for a time t, respectively. t(1/2) corresponds to the half-time of syneresis. W(infinity)/W(0) and t(1/2) were studied in relation with several parameters such as the ionic strength, pH, degree of acetylation of chitin and the initial concentration of polymer. The mechanical properties of chitin hydrogels maintained during syneresis in media of different pH's and ionic strengths were also investigated.

Chemical Phenomena↗

PubMed2000

Physicochemical behaviour of chitin gels.

Syneresis of chitin gels formed in the course of N-acetylation of chitosan in hydroalcoholic media has been studied. A critical cross-linking density related to a critical acetylation degree for which the gel undergoes weak syneresis and swells in water was shown (degree of acetylation (DA) 88%). Above this value, the weight loss during syneresis increases with DA. Conversely, syneresis decreases on increasing the polymer concentration, but disappears at a macroscopic level for a polymer concentration close to the critical concentration of entanglement in the initial solution. An increase in temperature favours the formation of hydrophobic interactions and new inter- and intramolecular hydrogen bondings. Due to the weak polyelectrolyte character of chitin, the weight of the gel depends on the pH and ionic strength of the media. Swelling-deswelling experiments show that the swelling of the gel is not fully reversible in relation with the formation of new cross-links during the depletion of the network. Our results reveals that the balance between segment-segment and segment-solvent interactions as well as the molecular mobility play the major role.

Acetylation↗

PubMed2000

Interactions between chitosan and glycosaminoglycans (chondroitin sulfate and hyaluronic acid): physicochemical and biological studies.

Chitosan is a polysaccharide well known for its numerous and interesting biological properties, indeed, it is a biocompatible, bioresorbable and bioactive biopolymer. It is therefore often introduced in the human body, where it happens to be in contact with glycosaminoglycans (GAG's), especially chondroitin sulfates and hyaluronic acid which play important part in living media. Thus it seems interesting to consider systems associating chitosan and GAG's. The aim of our work is to study the mechanism of formation of biomaterials constituted of chitosan and GAG's which could have interesting biological properties such as improving the wound-healing acceleration and the cellular assistance for skin and cartilage recovery. In the same time, it was interesting to try to understand what can happen when chitosan is introduced in a natural surrounding containing GAG's. In a first part, the complexes between chitosan and GAG's were characterised by various physicochemical techniques: pH-metry, conductometry and Infra-red spectrometry. They appeared to be polyelectrolyte complexes obtained by the formation of polyanion-polycation interactions held between ammonium functions of chitosan and carboxylate and/or sulfate groups of GAG's. The complexes formed are very strong and can, in some cases, even conduct to the deprotonation of carboxylic functions. In a second part we considered the biological properties of the complexes previously obtained. The hydrolysis activity in presence of specific enzymes was investigated. We also studied the cytocompatibility of chitosan alone and its complexes with the two considered GAG's toward two kinds of cells (chondrocytes and keratinocytes). At the end of the work, a short animal experimentation on rats was performed allowing the comparison between in vitro and in vivo results.

Animals↗

PubMed1999

Study of molybdate ion sorption on chitosan gel beads by different spectrometric analyses.

Molybdate ion uptake both by raw chitosan and by glutaraldehyde cross-linked chitosan beads was investigated. This study focused on the identification of sorption mechanisms by means of several analytical procedures such as infra-red and reflectance spectrophotometries and CP-MAS 13C NMR analyses. Although the amine functions of glucosamine residues remain the major sites of interaction with the metal species, other functional groups can also be involved. It is certainly the case with carbonyl functions provided by the glutaraldehyde structure in cross-linked sorbents. Due to the large size of the polynuclear hydrolysed molybdate species, the sorption may involve several monomer units, resulting in additional linkages between the polymer chains. This behaviour can be confirmed by the chemical shifts of the carbon atoms observed by CP-MAS 13C NMR on raw chitosan beads, showing that the carbon atoms supporting the amino sites are not the only atoms affected by molybdate ion sorption. Moreover, cross-linking promotes a partial reduction of molybdenum species in the presence of some unreacted aldehyde groups.

Adsorption↗

PubMed1999

Mode of action of chitin deacetylase from Mucor rouxii on N-acetylchitooligosaccharides.

The mode of action of chitin deacetylase from the fungus Mucor rouxii on N-acetylchitooligosaccharides with a degree of polymerization 1-7 has been elucidated. Identification of the sequence of chitin oligomers following enzymatic deacetylation was verified by the alternative use of two specific exo-glycosidases in conjunction with HPLC. The results were further verified by 1H-NMR spectroscopy. It was observed that the length of the oligomer is important for enzyme action. The enzyme cannot effectively deacetylate chitin oligomers with a degree of polymerization lower than three. Tetra-N-acetylchitotetraose and penta-N-acetylchitopentaose are fully deacetylated by the enzyme, while in the case of tri-N-acetylchitotriose, hexa-N-acetylchitohexaose and hepta-N-acetylchitoheptaose the reducing-end residue always remains intact. Furthermore, the enzyme initially removes an acetyl group from the nonreducing-end residue of all chitin oligomers with a degree of polymerization higher than 2, and further catalyses the hydrolysis of the following acetamido groups in a processive fashion. The results are in agreement with the mode of action that the same enzyme exhibits on partially deacetylated water soluble chitosan polymers.

Amidohydrolases↗

PubMed1998

Interaction between chitosan and uranyl ions. Part 2. Mechanism of interaction.

In this part of the study--understanding the mechanism of interaction between chitosan and uranyl ions, we confirmed the restrictive role of polymer crystallinity on uranyl sorption capacity. The saturation of the polymer by uranyl ions showed that approximately 1 mol of uranyl ions was sorbed for 2 mol of amino groups contained in the amorphous domain. This result can be related to the intrinsic properties of chitosan. Desorption experiments are in favour of strong interaction, in fact, no desorption was observed whatever the experimental conditions. Spectroscopic characterization was performed on complexes in solution and in the solid state. U.V.-visible spectrophotometric experiments showed that a unique type of complex was formed. FT-IR spectroscopy allowed us to observe the appearance of a new band at 1525 cm of amide II type and led us to conclude the formation of a unique complex by the coordination with chitosan amino groups.

Chitin↗

PubMed1998

Formation of a ternary complex between chitosan and ion pairs of strontium carbonate.

This work deals essentially with the study of the interactions between chitosan and an alkaline-earth metal: 85Sr. We showed that addition of carbonate ions is necessary to observe this interaction, but only for pH values over 11. The use of an appropriate calculation software allowed us to determine the nature of the strontium ionic species present in solution. In order to understand the mechanism of interaction, the influence of various parameters on the complexation was studied. Thus, the interaction was maximum for a CO3(2-) concentration close to 10(-2) mol/l, the lowest ionic strength, the most expanded physical form (lyophilisate) and the lowest degree of acetylation of the polymer. We conclude to the formation of a ternary complex between the ion pair Sr2+ CO3(2-) and the amino groups of chitosan. We also showed the presence of interactions between chitosan and carbonate ions which hinder further interactions with strontium ions.

Acetylation↗

PubMed1998

Interactions between chitosan and alpha emitters: 238Pu and 241Am.

This paper deals with the first study published on the interactions between chitosan and two radioactive elements (alpha emitters): 238Pu and 241Am. The authors determined the optimal experimental conditions for each of them (pH, ionic strength (FI), carbonate concentration) and attempted to explain the mechanism of interaction. The study of the nature and the percentage of the metallic ionic species present in solution as a function of the experimental conditions was carried out by means of the TOT software for 241Am. The authors showed a good fixation of 238Pu and 241Am on chitosan for pH's between 11-12, with the best results for 241Am. Nevertheless, an increase of the FI or the addition of a complexant of these alpha emitters induced a decrease of the interactions with chitosan.

Alpha Particles↗

PubMed1998

Chitosan-chondroitin sulfate and chitosan-hyaluronate polyelectrolyte complexes: biological properties.

In this work, we compare some biological properties of a highly deacetylated chitosan to those obtained with the materials made from its polyelectrolyte complexes with various GAG's such as chondroitin-sulfates and hyaluronic acid. The hydrolysis of the complexes by means of the specific hydrolytic enzymes is studied. Cell-adhesion and cell-proliferation on these materials is compared to that obtained with a pure chitosan material. Finally, a series of in vivo experiments is performed to test the wound-healing properties of this kind of complexes. All the results agree to show that chitosan has a protective effect against GAG's hydrolysis by their specific enzymes but only at pH's different from the optimal pH of the enzyme considered. In addition, they also agree to confirm that a pure chitosan material gives the best results in connection with cell-attachment and cell-proliferation or wound healing. Nevertheless, whatever the case, no adverse effect was observed with the polyelectrolyte complexes GAG's-chitosan.

Animals↗

PubMed1998

Comparison of the ability of partially N-acetylated chitosans and chitooligosaccharides to elicit resistance reactions in wheat leaves

Chitin, a linear polysaccharide composed of (1-->4)-linked 2-acetamido-2-deoxy-beta-D-glucopyranose (GlcNAc) residues, and chitosan, the fully or partially N-acetylated, water-soluble derivative of chitin composed of (1-->4)-linked GlcNAc and 2-amino-2-deoxy-beta-D-glucopyranose (GlcN), have been proposed as elicitors of defense reactions in higher plants. We tested and compared the ability of purified (1-->4)-linked oligomers of GlcNAc (tetramer to decamer) and of GlcN (pentamer and heptamer) and partially N-acetylated chitosans with degrees of acetylation (DA) of 1%, 15%, 35%, 49%, and 60% and average degrees of polymerization between 540 and 1100 to elicit phenylalanine ammonia-lyase (PAL) and peroxidase (POD) activities, lignin deposition, and microscopically and macroscopically visible necroses when injected into the intercellular spaces of healthy, nonwounded wheat (Triticum aestivum L.) leaves. Purified oligomers of (1-->4)-linked GlcN were not active as elicitors, whereas purified oligomers of (1-->4)-linked GlcNAc with a degree of polymerization >/= 7 strongly elicited POD activities but not PAL activities. Partially N-acetylated, polymeric chitosans elicited both PAL and POD activities, and maximum elicitation was observed with chitosans of intermediate DAs. All chitosans but not the chitin oligomers induced the deposition of lignin, the appearance of necrotic cells exhibiting yellow autofluorescence under ultraviolet light, and macroscopically visible necroses; those with intermediate DAs were most active. These results suggest that different mechanisms are involved in the elicitation of POD activities by GlcNAc oligomers, and of PAL and POD activities by partially N-acetylated chitosan polymers and that both enzymes have to be activated for lignin biosynthesis and ensuing necrosis to occur.

Journal Article↗

PubMed1997

Capillary electrophoresis of glycosaminoglycan-derived disaccharides: application to stability studies of glycosaminoglycan chitosan complexes.

Capillary zone electrophoresis (CZE) was used to separate the disaccharides produced by chondroitinase digestion of chondroitin sulfates. The main disaccharides formed upon depolymerization have identical charge and mass. Baseline resolution of these two compounds was achieved by selecting appropriate concentration and pH of a borate buffer. Validation of the method showed a good linearity of the response and a very satisfactory reproducibility of migration times with a relative standard deviation (RSD) of less than 0.4%. The reproducibility of peak areas was improved by using an internal standardization. The addition of cinnamic acid (internal standard) to the incubation medium allowed us to perform kinetic measurements of the depolymerization while keeping a baseline resolution of the two main disaccharides analyzed during the complete digestion course even when their concentration in the incubation medium increased. Application of this method to the comparison of the rate of hydrolysis of chondroitin sulfate and of a complex associating chondroitin sulfate with chitosan showed clearly that, at the physiological pH, chitosan protected the chondroitin sulfate from depolymerization. This phenomenon was more pronounced as the pH of the incubation medium was far from the optimum pH activity of the chondroitinase.

Chitin↗

PubMed1997

Interaction between chitosan and uranyl ions. Part 1. Role of physicochemical parameters.

This work is devoted to the comprehension of the sorption mechanism of uranyl ions on chitosan particle dispersions. The uranyl concentration measurements were obtained by inductively coupled plasma atomic emission spectrometry (ICP-AES) and we considered the role of various physicochemical parameters (pH; nature and concentration of added salts; degree of acetylation, DA). The use of appropriate calculation software allowed us to determine the chemical nature of uranyl species in solution in relation to these different parameters. The optimal pH of fixation has been found to be within 6.5-7.5 and can be related to the necessity of having both deprotonated amino groups and no carbonate ions, which are a strong complexant of uranyl ions, thus inhibiting their interaction with chitosan. The decrease of metal uptake with an increase of DA and the lack of influence of ionic strength, confirm the results obtained with pH and allowed us to suppose the formation of a complex with chitosan amino groups rather than interactions of an electrostatic nature.

Acetylation↗