Luc Picton
Rouen University, Chimie, Faculty Member
Exopolysaccharide (EPS) from marine microalgae are promising sources of a new generation of drugs. However, lot of them remain to be discovered and tested. In this study, EPS produced by Porphyridium marinum and its oligomers prepared by... more
Exopolysaccharide (EPS) from marine microalgae are promising sources of a new generation of drugs. However, lot of them remain to be discovered and tested. In this study, EPS produced by Porphyridium marinum and its oligomers prepared by High Pressure Homogenizer have been tested for different biological activities, i.e., antibacterial, anti-fungal and antibiofilm activities on Candida albicans, as well as for their effects on the viability of murine breast cancer cells. Results have shown that all EPS samples present some biological activity. For antibacterial and antibiofilm activities, the native EPS exhibited a better efficiency with Minimum Inhibitory Concentration (MIC) from 62.5 µg/mL to 1000 µg/mL depending on the bacterial strain. For Candida albicans, the biofilm formation was reduced by about 90% by using only a 31.3 µg/mL concentration. Concerning breast cancer cells, lower molar masses fractions appeared to be more efficient, with a reduction of viability of up to 55%. ...
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La presence de contraintes exterieures severes rend necessaire l'utilisation d'amidons modifies voire reticules dans de nombreuses applications alimentaires ou non alimentaire. Ainsi les proprietes rheologiques et la stabilite... more
La presence de contraintes exterieures severes rend necessaire l'utilisation d'amidons modifies voire reticules dans de nombreuses applications alimentaires ou non alimentaire. Ainsi les proprietes rheologiques et la stabilite thermique de l'amidon de pomme de terre hydroxypropyle (DS = 0,5) s'averent tres moyennes. La reticulation chimique (epichlorohydrine) apparait etre une solution quant a l'amelioration de ces proprietes. Toutefois, nous avons montre que la resistance au traitement thermique etait fonction d'une part du degre de reticulation et d'autre part du mode de modification avant (HPR A) ou apres (HPR) gelatinisation du grain d'amidon natif. Ce resultat semble pouvoir s'expliquer par les differences de structures de ces echantillons reticules.
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The rheological properties of low molecular weight (LW) and high molecular weight (HW) hydrophobically modified hydroxyethylcellulose (HMHEC) have been studied in semi-dilute regime of concentration (C>C*) and compared with their... more
The rheological properties of low molecular weight (LW) and high molecular weight (HW) hydrophobically modified hydroxyethylcellulose (HMHEC) have been studied in semi-dilute regime of concentration (C>C*) and compared with their unmodified parent polymers (HEC). Flow behavior and viscoelastic properties of modified polymers as a function of salt (NaCl, KSCN), temperature (20–60°C) and shear rate (0.1–1000 s−1) are explained by the existence of hydrophobic interactions. These latter are reinforced in the presence of water structure makers (NaCl).
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Abstract Hyaluronic acid (HA) of different molar masses from 38 000 to 990 000 g mol−1 were used as terminating agents during the cationic ring-opening polymerisation of 2-methyl-2-oxazoline. HA was first converted into a... more
Abstract Hyaluronic acid (HA) of different molar masses from 38 000 to 990 000 g mol−1 were used as terminating agents during the cationic ring-opening polymerisation of 2-methyl-2-oxazoline. HA was first converted into a tetrabutylammonium salt to solubilize it in polar aprotic organic solvents where the termination was conducted by varying the excess of HA units to the growing poly(2-methyl-2-oxazoline) (PMeOx) chains (with various PMeOx degree of polymerisation). This led to HA derivatives with various PMeOx degrees of substitution from 4% up to 13% (determined by 1H NMR). HA-g-PMeOx copolymers were analysed by Size Exclusion Chromatography with on-line detectors (Multi-angle light scattering, Viscometer, Refractive index) in 0.1 mol L−1 LiNO3 to study their macromolecular characteristics in dilute medium. The reaction was applied to functionalize HA with thermo-responsive poly(2-isopropyl-2-oxazoline)-co-poly(2-n-butyl-2-oxazoline) moieties, resulting in materials displaying thermally dependent hydrogel properties in aqueous solutions which could be used for biomedical applications.
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Abstract Polyelectrolyte complexes (PECs) of hyaluronic acid (HA) and diethylaminoethyl dextran (DEAE-D), promising for biomedical applications, have been investigated with respect to physicochemical properties, mainly in terms of... more
Abstract Polyelectrolyte complexes (PECs) of hyaluronic acid (HA) and diethylaminoethyl dextran (DEAE-D), promising for biomedical applications, have been investigated with respect to physicochemical properties, mainly in terms of particle size and relative hydrophobicity as well as storage stability. Influences of charge ratio, polymer concentration, molar masses of HA, ionic strength and mixing methods have been particularly investigated. The complexation between HA and DEAED generally resulted in colloidal particles having mean hydrodynamic diameter of 150–350 nm, with larger particle size observed at negative to positive charge ratio (n-/n+) further from the unity. Higher polymer concentration or higher molar mass of HA also led to higher particle size of the PECs, whereas the increasing ionic strength led to a non-monotonic evolution in particle size. The effects of mixing mode and mixing order on particle size were interdependent and depended also on n-/n+. PECs at n-/n+ ≤ 0.4 showed lack of stability, which seemed not to be sensitive to storage temperature but significantly improved at higher salt concentration or lower polymer concentration. The relative hydrophobicity of such PECs was also confirmed by the fluorescence spectra of pyrene incorporated in PEC particles. Such results gave a better insight to polysaccharides-based PECs, especially as a potential system to encapsulate hydrophobic active molecules for drug delivery purposes.
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Hyaluronic acid (HA) of different molar masses (respectively 38,000, 140,000 and 1,200,000 g.mol−1) have been functionalized with a commercial poly(etheramine), Jeffamine® M2005, in order to devise physical thermo-responsive hydrogels.... more
Hyaluronic acid (HA) of different molar masses (respectively 38,000, 140,000 and 1,200,000 g.mol−1) have been functionalized with a commercial poly(etheramine), Jeffamine® M2005, in order to devise physical thermo-responsive hydrogels. Two routes have been studied, involving the use of either water for the first one or of N,N′-Dimethylformamide (DMF), a polar aprotic solvent, for the second one. In the case of the water route, the reaction was performed using a mixture of N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide (EDC) and N-hydroxysuccinimide (NHS) as coupling reagents. The reaction was optimized while making sure no free M2005 remained in the final material, leading to M2005 grafting degrees of about 4%, which enabled the formation of hydrogels by increasing the temperature. In the case of the organic solvent route, propylphosphonic anhydride T3P® was used as a coupling reagent in DMF, resulting in a M2005 grafting degree of around 8% with better thermo-responsive properties ...
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Several thermo-sensitive polyelectrolyte complexes were prepared by ionic self-association between an anionic polysaccharide (alginate) and a monocationic copolymer (polyether amine, Jeffamine®-M2005) with a... more
Several thermo-sensitive polyelectrolyte complexes were prepared by ionic self-association between an anionic polysaccharide (alginate) and a monocationic copolymer (polyether amine, Jeffamine®-M2005) with a 'Low Critical Solubility Temperature' (LCST). We show that electro-association must be established below the aggregation temperature of the free Jeffamine®, after which the organization of the system is controlled by the thermo-association of Jeffamine® that was previously electro-associated with the alginate. Evidence for this comes primarily from the rheology in the semi-dilute region. Electro- and thermo-associative behaviours are optimal at a pH corresponding to maximum ionization of both compounds (around pH 7). High ionic strength could prevent the electro-association. The reversibility of the transition is possible only at temperatures lower than the LCST of Jeffamine®. Similar behaviour has been obtained with carboxymethyl cellulose (CMC), which suggests that this behaviour can be observed using a range of anionic polyelectrolytes. In contrast, no specific properties have been found for pullulan, which is a neutral polysaccharide.
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Research Interests: Materials Engineering, Materials Science, Fluorescence Spectroscopy, Mass Spectrometry, Nanomaterials, and 15 moreGold nanoparticle, Differential scanning calorimetry, Optical Properties, Bioconjugate Chemistry, Inflammatory disease, Infrared, Green Nanotechnology, Non Linear Optics, American Chemical Society, Elsevier, National Institute of Health, nuclear factor kappa B, Catalytic oxidation, Mixing Process, and Human serum albumin
ABSTRACT Polysaccharides have attractive advantages for using in the field of pharmaceutics. In most cases, they are non toxic, biocompatible and plentiful. The presence of hydroxyl groups (always) and carboxylic acid groups (sometimes)... more
ABSTRACT Polysaccharides have attractive advantages for using in the field of pharmaceutics. In most cases, they are non toxic, biocompatible and plentiful. The presence of hydroxyl groups (always) and carboxylic acid groups (sometimes) permits crosslinking of the chains and obtaining hydrogels. These hydrogels present interesting swelling and mechanical properties. They have the capacity to entrap active compounds such as drugs and release them through modifications of the solvation conditions vias pH or ionic strength changes. This review deals with polysaccharide hydrogels obtained by the formation of covalent bounds between polymeric chains. We have focused our attention on systems with an anionic character. These charges are due to the presence of acidic functions on the polysaccharide backbone or are brought by the crosslinking agent. The anionic character dependents on the ionic strength and pH. We discuss the synthesis of these hy-drogels. After a short presentation of a few polysaccharides, we describe the different crosslinking agents and their action mode. Applications in drug delivery are discussed along.
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Summary New xanthan hydrogels were synthesized at 90 C in water acid media using adipic acid dihydrazide (ADH) as crosslinking agent, in the presence of 1-ethyl-3[3-dimethyl amino] propyl carbodiimide hydrochloride (EDCI) as reagent. In... more
Summary New xanthan hydrogels were synthesized at 90 C in water acid media using adipic acid dihydrazide (ADH) as crosslinking agent, in the presence of 1-ethyl-3[3-dimethyl amino] propyl carbodiimide hydrochloride (EDCI) as reagent. In these conditions, xanthan chains are in a predominantly helical conformation and through rheological measurements the influence of the temperature over the helix-coil transition was assessed. Xanthan hydrogels
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Polysaccharides were isolated from nopals mucilage pulp and peel of Opuntia Ficus Indica (OFI) and Opuntia litoralis (OL) by aqueous extraction and purified by ultrafiltration. Studying the glycosyl residue composition, these... more
Polysaccharides were isolated from nopals mucilage pulp and peel of Opuntia Ficus Indica (OFI) and Opuntia litoralis (OL) by aqueous extraction and purified by ultrafiltration. Studying the glycosyl residue composition, these polysaccharides were assumed to be rhamnogalacturonan I (RG-I). The macromolecular features of these compounds have been characterized by SEC/MALLS and by low shear viscosimetry. In the present work, we have undertaken a comparative study about different polysaccharides resulting from OFI and OL growing in different area. This comparison is to see the influence of the geographical area in which these two plants push on the mechanism of retention of water by the different polysaccharides extract. The polysaccharides resulting from the nopal peels of the two plants are highly methylated (>70%), thus they are much more hydrophobic especially for peels of OFI growing in the desert area than those resulting from pulps. Consequently, they probably prevent the evaporation of water in nopals by increasing their water retention capacity. Prickly pear nopals of OFI and OL contain a significant amount of water (>80%), carbohydrates (75% compared to the soluble matter), proteins (8% compared to the soluble matter) and salt (17% compared to the soluble matter). Thus, they represent an important source of water and alimentation especially in the arid and semi-arid areas.
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Research Interests: Materials Engineering, Chemical Engineering, Chemistry, Organic Chemistry, Pergamon, and 14 morePh, Surface Tension, Functional Type, Chemical Reaction, Food Sciences, Total Nitrogen, Laser Light Scattering, Quaternary Ammonium Compounds, Zeta Potential, Aqueous Solution, Physicochemical Properties, Polyelectrolyte, Carbohydrate Polymers, and degree of substitution
Page 1. SLAP 2010 Revista Iberoamericana de Polímeros Diciembre de 2010 Leal et al. Interacción carbohidrato-proteína SLAP 2010 495 Rev. Iberoam. Polím., 11(7), 485-504 (2010) ESTUDIO DE LA INTERACCIÓN CARBOHIDRATO-PROTEÍNA EN LA ...
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Research Interests: Materials Engineering, Chemical Engineering, Chemistry, Organic Chemistry, Pergamon, and 14 morePh, Surface Tension, Functional Type, Chemical Reaction, Food Sciences, Total Nitrogen, Laser Light Scattering, Quaternary Ammonium Compounds, Zeta Potential, Aqueous Solution, Physicochemical Properties, Polyelectrolyte, Carbohydrate Polymers, and degree of substitution
ABSTRACT New water soluble and amphiphilic PCL-grafted-alginates with two different molar masses of PCL (530 and 1250 g mol−1) and molar hydrophobe contents from 3.5 to 15% have been prepared by new aqueous micellar grafting technique.... more
ABSTRACT New water soluble and amphiphilic PCL-grafted-alginates with two different molar masses of PCL (530 and 1250 g mol−1) and molar hydrophobe contents from 3.5 to 15% have been prepared by new aqueous micellar grafting technique. Physico-chemical behaviour in aqueous solution (pure water and NaCl 0.1 M) has been studied by means of viscosity measurements and on-line Flow field flow fractionation/Multi-angle laser light scattering/Quasi-elastic light scattering/Differential refractive index analyses. Expected associative behaviour has been evidenced in pure water whatever the length of the PCL chains. In salt media, the associative behaviour strongly depends on the length of PCL chains. For PCL chains of 530 g mol−1, intramolecular hydrophobic interactions are predominant, even in semi-dilute regime. This non-classical behaviour for an associative polyelectrolyte opens the way to the conception of amphiphilic matrices with hydrophobic clusters for controlled release applications.
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New amphiphilic polysaccharides based on alginate-grafted-Poly (ε-caprolactone) or alg-g-PCL bearing two kinds of PCL chains with different molar masses (1250 and 530gmol−1) with various amounts from 3% to 15% were prepared. Rheological... more
New amphiphilic polysaccharides based on alginate-grafted-Poly (ε-caprolactone) or alg-g-PCL bearing two kinds of PCL chains with different molar masses (1250 and 530gmol−1) with various amounts from 3% to 15% were prepared. Rheological properties in aqueous solutions of such systems have been investigated as a function of polymer concentration, added salt and temperature in semi-dilute regime. Strong hydrophobic intermolecular associations were clearly demonstrated in pure water whatever the PCL chain length and extend of modification. Increasing polymer concentration, grafting rate and/or PCL chains length can lead to a structured liquid behaviour. Rheological properties of the most organized system have been found independent to the temperature (until 60°C). In salt media, a strong dependence of hydrophobic interactions to the length of PCL chains was observed. For MPCL=1250g.mol−1 the screening of charges promotes the establishment of intermolecular interactions and leads to a strong physical gel for the highest grafting rates. For MPCL=530gmol−1, ionic strength leads to a decrease of rheological properties when increasing grafting rate. This result may indicate an increase of hydrophobic clusters even in the entangled regime. This unusual behaviour opens the ways for the preparation of suitable hydrogels for drug release.
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... 8 describes the release from systems where there is a change in surface area and ... Muhammad K, Hussin F, Ghazali YC, Kennedy JF (2000) Effect of pH on phosphorylation ... Le Cerf D, Picton L (2003) Stiffness xanthan hydrogels:... more
... 8 describes the release from systems where there is a change in surface area and ... Muhammad K, Hussin F, Ghazali YC, Kennedy JF (2000) Effect of pH on phosphorylation ... Le Cerf D, Picton L (2003) Stiffness xanthan hydrogels: synthesis, swelling characteristics and controlled ...
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In a previous study, we presented the development of a series of functionalized carboxymethylpullulan (CMP) grafted with aminoguaiacol (derivative of guaiacol with known antibacterial and antioxidant activities) leading to CMP-G... more
In a previous study, we presented the development of a series of functionalized carboxymethylpullulan (CMP) grafted with aminoguaiacol (derivative of guaiacol with known antibacterial and antioxidant activities) leading to CMP-G derivatives with various degrees of substitution [DS(Ga)] from 0.16 to 0.58. Our results have shown the efficiency of the grafting both with the evidence of antioxidant and antibacterial activities (Staphylococcus aureus) of the CMP-G derivatives. Nevertheless, an important result has shown surprisingly that such biological activity was not clearly improved with the DS(Ga) unlike the antioxidant activity. These results were probably correlated with a peculiar associative behavior of the derivative (i.e. amphiphilic character) due to the grafted hydrophobic guaiacol groups leading to preferential intramolecular association which was particularly important in the more concentrated regime (polysoap behavior). To complete this study, we propose here two strategi...
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Flintiella sanguinaria is a red unicellular microalgae belonging to Porphyridiophyceae with a high potential as an exopolysaccharide producer. A new culture medium was developed by a stoichiometry approach based on elemental analysis of... more
Flintiella sanguinaria is a red unicellular microalgae belonging to Porphyridiophyceae with a high potential as an exopolysaccharide producer. A new culture medium was developed by a stoichiometry approach based on elemental analysis of microalgae, and culture conditions were improved after measurements of photosynthetic activity as a function of irradiance, temperature and pH. These optimal conditions were thus validated in a photobioreactor for the production of biomass and exopolysaccharide (EPS). After extraction and purification of the EPS, it was characterised by HPAEC-PAD, HPLC and FT-IR as a methylated and acetylated galactoxylan including a significant amount of rhamnose and glucuronic acid in its structure. Macromolecular conformation in dilute solution of native, deproteinised and desubstituted EPS from F. sanguinaria revealed that this polysaccharide had a strong associative behaviour in which hydrophobic interactions or hydrogen bonding but also proteins were implicated.
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Novel chemical stimulus-responsive multilayer assemblies have been elaborated through the layer-by-layer deposition of oppositely charged polysaccharides on either flat or spherical surfaces. Concentration-dependent glucose responsiveness... more
Novel chemical stimulus-responsive multilayer assemblies have been elaborated through the layer-by-layer deposition of oppositely charged polysaccharides on either flat or spherical surfaces. Concentration-dependent glucose responsiveness was obtained through chemical modification of alginate, selected as polyanion, with phenylboronic acid moieties. QCM measurements showed that the alginate derivate still self-assembles though electrostatically-driven interactions with chitosan at pH 4, and that the polysaccharides multilayer assemblies, as obtained after crosslinking, exhibit improved stability versus pH (in the range 4-9) as well as swelling ability in the presence of glucose-containing solution. Glutaraldehyde-mediated crosslinking was achieved through reaction with free primary amines of chitosan. This approach was further extended to the preparation of smart capsules using CaCO microparticles as dissolvable core templates. Success of the LbL deposition process, stability (pH ra...
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Antioxidant and cytocompatible chemically modified polysaccharides and their hydrogels were obtained by a biomimetic approach. For this purpose, carboxymethylpullulan grafted with ferulic acid (CMP-FA) was firstly synthesized with... more
Antioxidant and cytocompatible chemically modified polysaccharides and their hydrogels were obtained by a biomimetic approach. For this purpose, carboxymethylpullulan grafted with ferulic acid (CMP-FA) was firstly synthesized with different substitution degrees (DS). Their hydrogels were secondly obtained by enzymatic cross-linking with laccase. Hydrogel swelling has been found dependent on both DS and media ionic strength. The CMP-FA antioxidant properties were evaluated by the DPPH method and ABTS assays. The DPPH radical scavenging effect was high for CMP-FA solutions (80% after 30 min) and lower for the corresponding hydrogels (70% after 7 h). The antibacterial properties of ferulic acid and CMP-FA derivatives were tested against Staphylococcus aureus but the minimal inhibitory concentration of CMP-FA was not reached in the range of concentrations studied. Finally the CMP-FA derivatives showed no cytotoxicity towards mouse fibroblast cells.
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Natural proteins have been extensively studied as matrices for tissue engineering, due to their excellent biocompatibility and biological properties associated with increasing cell proliferation. By generating complex materials, cell and... more
Natural proteins have been extensively studied as matrices for tissue engineering, due to their excellent biocompatibility and biological properties associated with increasing cell proliferation. By generating complex materials, cell and tissue functions can be tailored to obtain a specific direction, according to the medical needs. The aim of this paper was to obtain scaffolds based on collagen, hyaluronan and sericin, with morphology and physical-chemical properties adequate for controlled drug delivery systems. In this aim various tests were performed: in vitro swelling and degradation studies, Fourier Transform Infrared spectroscopy (FT-IR), Scanning Electronic Microscopy (SEM) and thermogravimetric analysis. Loading and releasing of ibuprofen is also discussed. The results indicate that scaffolds based on collagen, hyaluronan and sericin have a porous structure, strength and stability adequate for skin tissue engineering. The obtained scaffolds swell, degrade and have controlle...
Research Interests: Engineering, Materials Science, Technology, Tissue Engineering, Scanning Electron Microscopy, and 12 moreScanning Transmission Electron Microscopy, Medicine, Porosity, Collagen, Drug Delivery Systems, CHEMICAL SCIENCES, Hyaluronic Acid, Fourier transform infrared spectroscopy, Biocompatible Materials, Nanoscience and nanotechnology, Sericins, and Tissue Scaffolds
Aminoguaiacol, the aminated derivative of guaiacol, a natural phenolic compound, was chemically grafted onto a polysaccharide (carboxymethylpullulan, CMP) in the presence of the activator agent... more
Aminoguaiacol, the aminated derivative of guaiacol, a natural phenolic compound, was chemically grafted onto a polysaccharide (carboxymethylpullulan, CMP) in the presence of the activator agent 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide hydrochloride (EDCI). The grafted polysaccharides were characterized by FTIR and 1H NMR spectroscopy to confirm and quantify the grafting. All polysaccharide derivatives (grafting rates of aminoguaiacol between 16% and 58%) were soluble in water. Their physicochemical properties were studied in a dilute regime and a semidilute regime by light scattering, fluorescence, and rheology, showing associative properties with peculiar polysoap behavior. The antibacterial activities of the synthesized products against Staphyloccocus aureus were assessed using a counting method. The antioxidant activities of the derivatives were also highlighted using the α,α-diphenyl-β-picrylhydrazyl (DPPH) method. Finally, the cytotoxicity of the derivatives was studied with fibroblast cells and they showed a very good cytocompatibility. Such polymers could be used to replace chemical preservatives in food and cosmetic aqueous formulations.
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The elaboration of chemically crosslinked hydrogels based on collagen (C), hyaluronanic acid (HA) and sericin (S) with different polymer ratios was investigated by in-situ rheology. This reaction was performed via amide or ester bond... more
The elaboration of chemically crosslinked hydrogels based on collagen (C), hyaluronanic acid (HA) and sericin (S) with different polymer ratios was investigated by in-situ rheology. This reaction was performed via amide or ester bond reaction activated by carbodiimide, in pure water. Prior to molecule crosslinking, the rheological behaviour of the biopolymers (alone or in mixture) was characterized in a semi-dilute concentration regime. Both flow and dynamic measurements showed that uncrosslinked collagen alone appears to be rather elastic with yield stress properties, whereas uncrosslinked HA alone appears to be rather shear thinning and viscoelastic in agreement with entangled polymer behaviour. Sericin exhibited Newtonian low viscosity behaviour according to its very low molar mass. Before crosslinking, HA exhibited viscoelastic behaviour at concentrations above the critical entangled concentration (C*) in the mixtures, thus HA shows promise as a matrix for future crosslinked networks, whereas sericin did not significantly modify the rheology. During the reaction, followed by rheology, the kinetics were slower for pure HA systems compared with the mixtures (i.e., with added collagen and/or to a lesser extent sericin). At the same time, the final network of hydrogels (i.e., the elastic modulus) was more structured in the mixture based systems. This result is explained by ester bonds (the only possibility for pure HA systems), which are less favourable and reactive than amide bonds (possible with sericin and collagen). The presence of collagen in the HA matrix reinforced the hydrogel network. SEM studies confirmed the structure of the hydrogels, and in vitro degradability was globally consistent with the effect of the selected enzyme according to the hydrogel composition. All the elaborated hydrogels were non-cytotoxic in vitro.
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Aqueous solution properties of amphiphilic P(AA-co-tBA)-b-PPO-b- P(AA-co-tBA) copolymers having various tBA contents are presented in this article. These copolymers show pH-sensitive behavior depending on tBA/AA ratio. Hydrophobic... more
Aqueous solution properties of amphiphilic P(AA-co-tBA)-b-PPO-b- P(AA-co-tBA) copolymers having various tBA contents are presented in this article. These copolymers show pH-sensitive behavior depending on tBA/AA ratio. Hydrophobic interactions between tBA units leading to pH-dependent macroscopic aggregates were evidenced by turbidimetry. The aggregation behavior of the PPO middle block was concealed in presence of tBA units. The formation of water-soluble aggregated objects was characterized by Asymmetrical Flow Field Flow Fractionation (AsF4). By increasing tBA/AA ratio, we observed an increase of aggregates size as well as a reduction of the critical concentration aggregation. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1944–1949
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L'hydroxyethylcellulose hydrophobiquement modifiee (HMHEC) est un polymere associatif industriel obtenu par greffage d'une tres faible quantite de chaines hexadecyle sur le polymere precurseur (HEC). En solution aqueuse,... more
L'hydroxyethylcellulose hydrophobiquement modifiee (HMHEC) est un polymere associatif industriel obtenu par greffage d'une tres faible quantite de chaines hexadecyle sur le polymere precurseur (HEC). En solution aqueuse, l'association des groupes hydrophobes confere au polymere modifie des proprietes qui different profondement de celles des precurseurs. En regime dilue, le caractere associatif conduit a la formation d'agregats intermoleculaires et/ou d'interactions intramoleculaires. Au-dela d'une concentration critique, qui delimite le debut du regime semi-dilue, les associations deviennent essentiellement intermoleculaires et les proprietes epaississantes augmentent considerablement. Les solutions plus concentrees presentent alors une structure enchevetree tridimensionnelle enrichie de zones de jonctions hydrophobes fluctuantes, responsables de l'apparition d'un caractere viscoelastique. Les associations hydrophobes, de faible energie, sont facilement detruites sous l'influence d'une contrainte de cisaillement et on observe un caractere rheofluidifiant. Le temps necessaire a la reformation reversible des associations se traduit par un phenomene de thixotropie. Les associations hydrophobes sont induites par la structure de l'eau. L'amelioration de l'organisation des molecules d'eau favorise les mecanismes d'associations. Ainsi, les sels lyotropes (NaCl) renforcent les associations hydrophobes, tandis que les sels chaotropes (KSCN) les affaiblissent. La presence d'ethanol entraine la rupture des associations par une meilleure solvatation des groupements apolaires. D'autre part, la temperature semble favoriser l'etablissement des associations en accord avec leur caractere endothermique.
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Pullulan derivative was synthesized by coupling carboxymethylpullulan (degree of substitution DS0in=0.7) and dimethylaminopropylamine (DMAPA), activated by a hydrosoluble carbodiimide N′-(3-dimethylaminopropyl)-N-ethylcarbodiimide... more
Pullulan derivative was synthesized by coupling carboxymethylpullulan (degree of substitution DS0in=0.7) and dimethylaminopropylamine (DMAPA), activated by a hydrosoluble carbodiimide N′-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride (EDAC). FTIR and 13C and 1H NMR spectroscopic analyses have evidenced that the polysaccharide has been successfully modified. 1H NMR, nitrogen analysis, and conductimetric measurements allow determination of the degree of substitution in both carboxylic acid and amine functions.
Zero-length crosslinked hydrogels have been synthesized by covalent linking of three natural polymers (collagen, hyaluronic acid and sericin), in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide. The... more
Zero-length crosslinked hydrogels have been synthesized by covalent linking of three natural polymers (collagen, hyaluronic acid and sericin), in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide. The hydrogels have been investigated by FT-IR spectroscopy, microcalorimetry, in vitro swelling, enzymatic degradation, and in vitro cell viability studies. The obtained crosslinked hydrogels showed a macroporous structure, high swelling degree and in vitro enzymatic resistance compared to uncrosslinked collagen. The in vitro cell viability studies performed on normal human dermal fibroblasts assessed the sericin proliferation properties indicating a potential use of the hydrogels based on collagen, hyaluronic acid and sericin in skin tissue engineering.
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In Venezuela, the genus Terminalia (Combretaceae), is represented by thirteen (13) species. Terminalia catappa exudes an amber-colored gum, soluble in water. Relatively few studies exist concerning the gum of this species. The objective... more
In Venezuela, the genus Terminalia (Combretaceae), is represented by thirteen (13) species. Terminalia catappa exudes an amber-colored gum, soluble in water. Relatively few studies exist concerning the gum of this species. The objective of this work is to determine the physicochemical parameters of the gum of T. catappa and to compare these parameters to those published for other gum exudates of Combretaceae. The physicochemical parameters were determined by the classic methodology for carbohydrates, size exclusion chromatography SEC-MALLS and IR spectroscopy. In general, the gum of T. catappa showed parameters comparable to those reported for the species of the same genus and, in general, of the sub-tribe Terminaliinae. It also exhibits characteristics analogous to those exudates from Combretum spp. (sub-tribe Combretinae). Greater differences were observed with the gum of Laguncularia racemosa, belonging to a superior taxonomic category (Tribe Laguncularieae). The physicochemical ...
Carboxymethylpullulan (CMP) has been modified in a two-step grafting reaction of ferulic acid (FA). Acid adipic dihydrazyde (ADH) was first reacted with FA activated with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC).... more
Carboxymethylpullulan (CMP) has been modified in a two-step grafting reaction of ferulic acid (FA). Acid adipic dihydrazyde (ADH) was first reacted with FA activated with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC). Then the product of this first reaction was reacted with CMP (activated with EDC). Grafted polysaccharides structure was confirmed by FTIR and (1)H NMR spectroscopy. Analyses by size-exclusion chromatography (SEC) coupling on-line with a multi-angle light scattering detector (MALS), a viscometer and a differential refractive index detector (DRI) (SEC/MALS/DRI/Visco) showed that associations between FA moieties occurred due to hydrophobic interactions. The grafting rates of FA were determined by the Folin-Ciocalteu method and were found between 1.0% and 11.2% (mol/mol anhydroglucose unit). The CMP-FA were then enzymatically cross-linked with laccase from Pleurotus ostreatus. The crosslinking reactions were followed by rheological measurements, demonstrating the influence of laccase concentration on kinetics. Elastic modulus and swelling rates of hydrogels depends on FA content only for low values.
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Polysaccharides have attractive advantages for using in the field of pharmaceutics. In most cases, they are non toxic, biocompatible and plentiful. The presence of hydroxyl groups (always) and carboxylic acid groups (sometimes) permits... more
Polysaccharides have attractive advantages for using in the field of pharmaceutics. In most cases, they are non toxic, biocompatible and plentiful. The presence of hydroxyl groups (always) and carboxylic acid groups (sometimes) permits crosslinking of the chains and obtaining hydrogels. These hydrogels present interesting swelling and mechanical properties. They have the capacity to entrap active compounds such as drugs and release them through modifications of the solvation conditions vias pH or ionic strength changes. This review deals with polysaccharide hydrogels obtained by the formation of covalent bounds between polymeric chains. We have focused our attention on systems with an anionic character. These charges are due to the presence of acidic functions on the polysaccharide backbone or are brought by the crosslinking agent. The anionic character dependents on the ionic strength and pH. We discuss the synthesis of these hy-drogels. After a short presentation of a few polysacc...