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Bjorn T Stokke - One of the best experts on this subject based on the ideXlab platform.
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Structural properties of polyC–Scleroglucan complexes
Biopolymers, 2005Co-Authors: Marit Sletmoen, Bjorn T StokkeAbstract:Successive changes of solvent conditions can be used to dissociate and reassociate the triple-helical structure of (1,3)-beta-D-glucans. Ultramicroscopic techniques have revealed a blend of circular and other structures following renaturation. When this solvent exchange process is carried out in the presence of certain polynucleotides, the process creates a novel macromolecular complex. Here, we use size exclusion chromatography (SEC) to study such (1,3)-beta-D-glucan-polynucleotide complexes. Online multi-angle laser-light scattering (MALLS) and refractive index (RI) detectors allowed determination of molecular weight and radius of gyration of the molecules. An ultraviolet (UV) detector allowed specific detection of the polynucleotide. The poly-cytidylic acid (poly C) shifted to coelution with the linear fraction of the Scleroglucan following the renaturation of poly C-Scleroglucan blends, indicating that poly C is incorporated in linear, but not in circular, structures of Scleroglucan. This conclusion was consistent with AFM topographs that revealed a decreased fraction of circular structures upon addition of poly C during the renaturation process. The combined information about radius of gyration (R(g)) and molecular weight (M(w)) allowed us to conclude that the poly C-Scleroglucan complexes are more dense and have a higher persistence length than linear Scleroglucan triple helixes. The experimentally determined mass per unit length was used as a basis for elucidating possible molecular arrangements within the poly C-Scleroglucan complex.
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structural properties of polyc Scleroglucan complexes
Biopolymers, 2005Co-Authors: Marit Sletmoen, Bjorn T StokkeAbstract:Successive changes of solvent conditions can be used to dissociate and reassociate the triple-helical structure of (1,3)-beta-D-glucans. Ultramicroscopic techniques have revealed a blend of circular and other structures following renaturation. When this solvent exchange process is carried out in the presence of certain polynucleotides, the process creates a novel macromolecular complex. Here, we use size exclusion chromatography (SEC) to study such (1,3)-beta-D-glucan-polynucleotide complexes. Online multi-angle laser-light scattering (MALLS) and refractive index (RI) detectors allowed determination of molecular weight and radius of gyration of the molecules. An ultraviolet (UV) detector allowed specific detection of the polynucleotide. The poly-cytidylic acid (poly C) shifted to coelution with the linear fraction of the Scleroglucan following the renaturation of poly C-Scleroglucan blends, indicating that poly C is incorporated in linear, but not in circular, structures of Scleroglucan. This conclusion was consistent with AFM topographs that revealed a decreased fraction of circular structures upon addition of poly C during the renaturation process. The combined information about radius of gyration (R(g)) and molecular weight (M(w)) allowed us to conclude that the poly C-Scleroglucan complexes are more dense and have a higher persistence length than linear Scleroglucan triple helixes. The experimentally determined mass per unit length was used as a basis for elucidating possible molecular arrangements within the poly C-Scleroglucan complex.
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Swelling, mechanical properties and effect of annealing of Scleroglucan gels
Carbohydrate Polymers, 2005Co-Authors: Einar Aasprong, Olav Smidsrød, Bjorn T StokkeAbstract:Abstract Scleroglucan gels were made by alkaline denaturation and subsequent renaturation of the Scleroglucan triple helix by in situ neutralization. Gels prepared from 4 to 5% Scleroglucan solutions were incubated in aqueous solutions and dependence of pH, temperature and ionic strength, I , were studied. (i) The Scleroglucan gels were observed to be stable for more than 600 days in solutions of NaCl or CaCl 2 ( I ∈0–3 M) or in solutions of pH∈1–12 ( I =0.1 M) at ambient temperatures. Gels incubated at pH 13 were found to dissolve within 1 day of storage. (ii) Under conditions, where a triple helical conformation of Scleroglucan prevails, isotropic swelling was observed. This was consistent with a weakly negatively charged network, and a charge density of 0.017 per tetramer repeating unit of the Scleroglucan was determined using counter-ion binding. (iii) Annealing in aqueous 0.1 M NaCl at 96 °C for 5 h yielded a marked increase in the failure strain and stress. Gels subsequently transferred to incubation at 21 °C maintained their acquired properties for more than 400 days. (iv) Large deformation data in uniaxial compression were adequately fitted by a model consisting of a linear and an exponential regime, with two material parameters, the Young's modulus ( E ) and a transition strain ( e t ) between the two regimes.
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Scleroglucan Gelation by in Situ Neutralization of the Alkaline Solution
Biomacromolecules, 2003Co-Authors: Einar Aasprong, Olav Smidsrød, Bjorn T StokkeAbstract:Scleroglucan gels were prepared by neutralization of aqueous alkaline solution of Scleroglucan by in situ release of acid. Transition of Scleroglucan chains in a disordered state to the triple-helical state result in cross-linking of the polysaccharide. The pH and the storage and loss moduli, G' and G' ', were determined as a function of time after initiating the pH reduction. Experiments were performed in the temperature range from 20 to 90 degrees C and in the polymer concentration range from C(p) = 10-200 mg/mL. The concentration dependence of the apparent plateau value of the storage modulus showed a lower critical concentration, C(p,0), in the range 12-15 mg/mL needed for gelation and a second power dependence of G' on concentration in the range 50-200 mg/mL. In situ pH reduction was achieved using formamide (methanoic acid) or ethyl acetate (ethyl ethanoate) which hydrolyze in alkaline solution, yielding carboxylic acids. The more rapid hydrolyses of ethyl acetate compared to formamide yielded a faster decrease of pH in solution and a more rapid increase of the storage modulus. The present gelation process of Scleroglucan based on the in situ reduction of pH has advantages in applications where external control of the conditions is difficult to achieve.
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Rheology of xanthan and Scleroglucan in synthetic seawater
Carbohydrate Polymers, 2003Co-Authors: Bjorn T Stokke, Arnljot Elgsaeter, E.Ø. Bjørnestad, T. LundAbstract:Abstract Rheological characterization of xanthan from three different sources and Scleroglucan from two different sources has been carried out using synthetic seawater as solvent. The measurements spanned temperatures from 20°C to 70°C, shear rates from 0·5 s−1 to 100 s−1 and polymer concentrations from 30 μg/ml to 1 mg/ml. The observed difference in effectiveness of increasing solution viscosity at low shear is quantitated in terms of the intrinsic viscosity [η]. Scleroglucan A was found to be the most effective with [η] = 14 000 ml/g and xanthan B the least effective with [η] = 5060 ml/g, both at T = 20°C. The temperature coefficients of the intrinsic viscosities, ∂ ln [η] ∂T , was found to lie in the range ∂ ln [η] ∂T = −(9–19) 10−3 K−1 for the xanthans and ∂ ln [η] ∂T = −1·9 10−3 K−1 for the Scleroglucans. These findings were interpreted in terms of a decrease in chain stiffness with temperature. Assuming a worm-like chain model the temperature coefficients of the persistence length q were ∂ ln q ∂T = −(9·4–21) 103 K−1 and −2·1 10−3 K−1 for xanthans and Scleroglucans, respectively. The viscosity at low shear rate in the semi-dilute concentration range is accounted for in terms of entanglement of overlapping chains. The lowering of viscosity in the semi-dilute concentration range associated with increasing shear rate is observed for smaller shear rates than in the dilute regime. Thus the decrease in entanglement starts at lower shear rate than orientational effects at the molecular level.
Rekha S. Singhal - One of the best experts on this subject based on the ideXlab platform.
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comparison of artificial neural network ann and response surface methodology rsm in fermentation media optimization case study of fermentative production of Scleroglucan
Biochemical Engineering Journal, 2008Co-Authors: Kiran M. Desai, Parag S. Saudagar, S S Lele, Shrikant A. Survase, Rekha S. SinghalAbstract:Abstract Response surface methodology (RSM) is the most preferred method for fermentation media optimization so far. In last two decades, artificial neural network-genetic algorithm (ANN-GA) has come up as one of the most efficient method for empirical modeling and optimization, especially for non-linear systems. This paper presents the comparative studies between ANN-GA and RSM in fermentation media optimization. Fermentative production of biopolymer Scleroglucan has been chosen as case study. The yield of Scleroglucan was modeled and optimized as a function of four independent variables (media components) using ANN-GA and RSM. The optimized media produced 16.22 ± 0.44 g/l Scleroglucan as compared to 7.8 ± 0.54 g/l with unoptimized medium. Two methodologies were compared for their modeling, sensitivity analysis and optimization abilities. The predictive and generalization ability of both ANN and RSM were compared using separate dataset of 17 experiments from earlier published work. The average % error for ANN and RSM models were 6.5 and 20 and the CC was 0.89 and 0.99, respectively, indicating the superiority of ANN in capturing the non-linear behavior of the system. The sensitivity analysis performed by both methods has given comparative results. The prediction error in optimum yield by hybrid ANN-GA and RSM were 2% and 8%, respectively.
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Use of complex media for the production of Scleroglucan by Sclerotium rolfsii MTCC 2156
Bioresource Technology, 2006Co-Authors: Shrikant A. Survase, Parag S. Saudagar, Rekha S. SinghalAbstract:Submerged fermentation was carried out for the production of Scleroglucan by Sclerotium rolfsii MTCC 2156 using complex media, such as coconut water, sugarcane molasses and sugarcane juice at 28 ± 2 °C and 180 rpm for 72 h. Sugarcane juice gave maximum Scleroglucan production of 23.87 g/l as compared to 12.58 and 18.45 g/l with coconut water and sugarcane molasses, respectively. Utilization of these substrates would be ecologically sound and economically advantageous.
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Enhanced production of Scleroglucan by Sclerotium rolfsii MTCC 2156 by use of metabolic precursors
Bioresource Technology, 2006Co-Authors: Shrikant A. Survase, Parag S. Saudagar, Rekha S. SinghalAbstract:The aim of this work was to study the effect of addition of different amino acids and sugar nucleotides as metabolic precursors on the production of Scleroglucan. A maximum yield of 20.00 g/l and 22.32 g/l was obtained with optimized media supplemented with L-lysine (1.1 mM) and uridine mono-phosphate (UMP), respectively as compared to 16.52 g/l Scleroglucan achieved with the control in the absence of metabolic precursors.
Julia Inés Fariña - One of the best experts on this subject based on the ideXlab platform.
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Microbial production of Scleroglucan and downstream processing.
Frontiers in Microbiology, 2015Co-Authors: Natalia A. Castillo, Alejandra Leonor Valdez, Julia Inés FariñaAbstract:Synthetic petroleum-based polymers and natural plant polymers have the disadvantage of restricted sources, in addition to the non-biodegradability of the former ones. In contrast, eco-sustainable microbial polysaccharides, of low-cost and standardized production, represent an alternative to address this situation. With a strong global market, they attracted worldwide attention because of their novel and unique physico-chemical properties as well as varied industrial applications, and many of them are promptly becoming economically competitive. Scleroglucan, a beta-1,3-beta-1,6-glucan secreted by Sclerotium fungi, exhibits high potential for commercialization and may show different branching frequency, side-chain length and/or molecular weight depending on the producing strain or culture conditions. Water-solubility, viscosifying ability and wide stability over temperature, pH and salinity make Scleroglucan useful for different biotechnological (enhanced oil recovery, food additives, drug delivery, cosmetic and pharmaceutical products, biocompatible materials, etc.), and biomedical (immunoceutical, antitumor, etc.) applications. It can be copiously produced at bioreactor scale under standardized conditions, where a high EPS concentration normally governs the process optimization. Operative and nutritional conditions, as well as the incidence of Scleroglucan downstream processing will be discussed in this chapter. The relevance of using standardized inocula from selected strains and experiences concerning the intricate Scleroglucan scaling-up will be also herein outlined.
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Effects of thermal, alkaline and ultrasonic treatments on Scleroglucan stability and flow behavior
Carbohydrate Polymers, 2013Co-Authors: Silvana Carolina Viñarta, Osvaldo Delgado, Lucía I. C. De Figueroa, Julia Inés FariñaAbstract:Abstract Aqueous solutions (0.2%, w/v) of Scleroglucans from Sclerotium rolfsii ATCC 201126 from different cultivation time or purification protocol (EPS I, EPS II, EPSi) as well as a commercial Scleroglucan (LSCL) exhibited different sensitivity against thermal (65, 95 and 150 °C), ultrasonic (1, 5 and 10 min; 20% amplitude) or alkaline (0.01–0.2 N NaOH) treatments. Scleroglucan triple helix usually showed signs of denaturation at 150 °C or with 0.2 NaOH with a pronounced decrease in apparent viscosity and loss of pseudoplastic behavior. Differences in sensitivity could be noted depending on the Scleroglucan sample, which may be likely related to polysaccharide conformational features, and these latter to production and/or downstream processing conditions. Transmission electron microscopy showed Scleroglucan topologies in accordance with thermal and alkaline denaturation. Size exclusion chromatography of control Scleroglucans revealed elution profiles compatible with macromolecular aggregates which tended to diminish or disappear as thermal, alkali or sonication treatments progressed. Scleroglucan granule dissolution process took ∼8–14 s, according to DIC-light microscopy, and showed to be facilitated by addition of NaOH.
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Scleroglucan compatibility with thickeners, alcohols and polyalcohols and downstream processing implications.
Carbohydrate Polymers, 2012Co-Authors: Silvana Carolina Viñarta, Lucía I. C. De Figueroa, Mariana M. Yossen, Jorge Ruben Vega, Julia Inés FariñaAbstract:Abstract Thickening capacity and compatibility of Scleroglucan with commercial thickeners (corn starch, gum arabic, carboxymethylcellulose, gelatin, xanthan and pectin), glycols (ethylene glycol and polyethylene glycol), alcohols (methanol, ethanol, 1-propanol and isopropanol) and polyalcohols (sorbitol, xylitol and mannitol) was explored. Exopolysaccharides (EPSs) from Sclerotium rolfsii ATCC 201126 and a commercial Scleroglucan were compared. Compatibility and synergism were evaluated taking into account rheology, pH and sensory properties of different thickener/Scleroglucan mixtures in comparison with pure solutions. S. rolfsii ATCC 201126 EPSs induced or increased pseudoplastic behaviour with a better performance than commercial Scleroglucan, showing compatibility and synergy particularly with corn starch, xanthan, pectin and carboxymethylcellulose. Compatibility and a slight synergistic behaviour were also observed with 30% (w/v) ethylene glycol whereas mixtures with polyethylene glycol (PEG) precipitated. Scleroglucan was compatible with polyalcohols, whilst lower alcohols led to Scleroglucan precipitation at 20% (v/v) and above. PEG-based Scleroglucan downstream processing was compared to the usual alcohol precipitation. Downstream processed EPSi (with isopropanol) and EPS-p (with PEG) were evaluated on their yield, purity, rheological properties and visual aspect pointing to alcohol downstream processing as the best methodology, whilst PEG recovery would be unsuitable. The highest purified EPSi attained a recovery yield of ∼23%, similar to ethanol purification, with a high degree of purity (88%, w/w vs . EPS-p, 8%, w/w) and exhibited optimal rheological properties, water solubility and appearance. With a narrower molecular weight distribution ( M w , 2.66 × 10 6 g/mol) and a radius of gyration ( R w , 245 nm) slightly lower than ethanol-purified EPSs, isopropanol downstream processing showed to be a proper methodology for obtaining a refined-grade Scleroglucan.
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Investigation on the film-forming properties of lab fermenter scale produced Scleroglucans from Sclerotium rolfsii ATCC 201126
Carbohydrate Polymers, 2011Co-Authors: Nora J Francois, Silvana Carolina Viñarta, Julia Inés Fariña, Marta E DaraioAbstract:The film-forming capacity of the biopolymer Scleroglucan produced on the lab fermenter scale by Sclerotium rolfsii ATCC 201126 was studied. The effect of a freeze–thawing process on the physical properties of Scleroglucan films was investigated with hydrogels of three different Scleroglucan samples. Films were made from 1% (w/w) Scleroglucan hydrogels using 2% (w/w) glycerol as plasticizer by applying two different protocols: (1) a room-temperature drying method and, (2) a freeze–thawing cyclic process (prior to the application of room-temperature drying). The obtained materials were characterized by physical studies including swelling, water vapor transmission, and environmental scanning electron microscopy. Based on the results obtained, when eight freezing–thawing cycles were applied during Scleroglucan film preparation, a reinforcement of the structure was achieved pointing to an increase in the number of crosslinking points by H-bonding. All exopolysaccharides produced by S. rolfsii ATCC 201126 at lab fermenter scale showed a general promising behavior for the preparation of reinforced films, opening new perspectives for their potential use in either controlled release systems or the formulation of additive-complemented films for specific applications.
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sclerotium rolfsii Scleroglucan the promising behavior of a natural polysaccharide as a drug delivery vehicle suspension stabilizer and emulsifier
International Journal of Biological Macromolecules, 2007Co-Authors: Silvana Carolina Viñarta, Lucía I. C. De Figueroa, Nora J Francois, Marta E Daraio, Julia Inés FariñaAbstract:Abstract Gel matrices of Scleroglucans from Sclerotium rolfsii ATCC 201126 (EPS I and EPS II, from 48-h and 72-h fermentations, respectively) were evaluated on their release kinetics of theophylline (Th). Equivalent polymer (2%, w/w) and Th (0.2%, w/w) concentrations showed almost coincident drug release patterns, independently of polymer molecular weight or the microstructural properties of gel matrices. Dynamic rheological studies of Scleroglucan hydrogel structures (storage, G ′, and loss, G ″, moduli) indicated a solid-like behavior. Differences on pore size dimensions (EPS I = 20 μm and EPS II = 7 μm) were in accordance to the differences in G ′ (EPS I = 113 Pa and EPS II = 161 Pa), a fact likely related to variations in the cross-linking density of polymer networks. Compared to already known biopolymers, EPS I and EPS II at 0.5 g/L showed a good dispersing ability against particulate suspensions of activated charcoal, bentonite, CaCO 3 , celite and quartz powder. Emulsifying ability of both EPSs at 2 g/L was high ( E = 56–60%) when tested with kerosene, moderate (∼30%) with hexadecane, and negligible in the presence of olive oil-in-water emulsions.
Olivier Lafforgue - One of the best experts on this subject based on the ideXlab platform.
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Rheological properties of synthetic mucus for airway clearance
Journal of Biomedical Materials Research Part A, 2018Co-Authors: Olivier Lafforgue, Isabelle Seyssiecq, Sébastien Poncet, Julien FavierAbstract:In this work, a complete rheological characterization of bronchial mucus simulants based on the composition proposed by Zahm et al. [1] is presented. Dynamic Small Amplitude Oscillatory Shear (SAOS) experiments, Steady State (SS) flow measurements and three Intervals Thixotropy Tests (3ITT), are carried out to investigate the global rheological complexities of simulants (viscoelasticity, viscoplasticity, shear-thinning and thixotropy) as a function of Scleroglucan concentrations (0.5 to 2wt%) and under temperatures of 20 and 37 °C. SAOS measurements show that the limit of the linear viscoelastic range as well as the elasticity both increase with increasing sclerogucan concentrations. Depending on the sollicitation frequency, the 0.5wt% gel response is either liquid-like or solid-like, whereas more concentrated gels show a solid-like response over the whole frequency range. The temperature dependence of gels response is negligible in the 20-37°C range. The Herschel-Bulkley (HB) model is chosen to fit the SS flow curve of simulants. The evolution of HB parameters versus polymer concentration show that both shear-thinning and viscoplasticity increase with increasing concentrations. 3ITTs allow calculation of recovery thixotropic times after shearings at 100s-1 or 1.6s-1. Empiric correlations are proposed to quantify the effect of polymer concentration on rheological parameters of mucus simulants.
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Thermo-physical properties of synthetic mucus for the study of airway clearance
Journal of Biomedical Materials Research Part A, 2017Co-Authors: Olivier Lafforgue, Isabelle Seyssiecq, Sébastien Poncet, Julien Favier, N. Bouguerra, S. ElkounAbstract:In this article, dynamic viscosity, surface tension, density, heat capacity and thermal conductivity, of a bronchial mucus simulant proposed by Zahm et al., Eur Respir J 1991; 4: 311–315 were experiementally determined. This simulant is mainly composed of a galactomannan gum and a Scleroglucan. It was shown that thermophysical properties of synthetic mucus are dependant of Scleroglucan concentrations. More importantly and for some Scleroglucan concentrations, the syntetic mucus, exhibits, somehow, comparable thermophysical properties to real bronchial mucus. An insight on the microstructure of this simulant is proposed and the different properties enounced previously have been measured for various Scleroglucan concentrations and over a certain range of operating temperatures. This synthetic mucus is found to mimic well the rheological behavior and the surface tension of real mucus for different pathologies. Density and thermal properties have been measured for the first time.
Marta E Daraio - One of the best experts on this subject based on the ideXlab platform.
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MULTIFRACTAL ANALYSIS OF Scleroglucan HYDROGELS FOR DRUG DELIVERY
Fractals, 2011Co-Authors: Nora J Francois, M. Piacquadio Losada, Marta E DaraioAbstract:The non-homogeneity and complexity of micro network distribution of hydrogel matrices prepared with two Scleroglucan biopolymers obtained with different fermentation times were analyzed using environmental scanning electron microscopy (ESEM) and dynamic rheology. ESEM images were processed with the tools of multifractal theory using the box-counting method in order to obtain the gels multifractal spectra. Dynamic rheological measurements indicate that both polymeric networks correspond to physical gels that exhibit a solid like behavior. These results suggest the existence of a relationship between the fermentation time used in the polymer production, the degree of self-similarity and the rigidity of the Scleroglucan gel structure.
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Investigation on the film-forming properties of lab fermenter scale produced Scleroglucans from Sclerotium rolfsii ATCC 201126
Carbohydrate Polymers, 2011Co-Authors: Nora J Francois, Silvana Carolina Viñarta, Julia Inés Fariña, Marta E DaraioAbstract:The film-forming capacity of the biopolymer Scleroglucan produced on the lab fermenter scale by Sclerotium rolfsii ATCC 201126 was studied. The effect of a freeze–thawing process on the physical properties of Scleroglucan films was investigated with hydrogels of three different Scleroglucan samples. Films were made from 1% (w/w) Scleroglucan hydrogels using 2% (w/w) glycerol as plasticizer by applying two different protocols: (1) a room-temperature drying method and, (2) a freeze–thawing cyclic process (prior to the application of room-temperature drying). The obtained materials were characterized by physical studies including swelling, water vapor transmission, and environmental scanning electron microscopy. Based on the results obtained, when eight freezing–thawing cycles were applied during Scleroglucan film preparation, a reinforcement of the structure was achieved pointing to an increase in the number of crosslinking points by H-bonding. All exopolysaccharides produced by S. rolfsii ATCC 201126 at lab fermenter scale showed a general promising behavior for the preparation of reinforced films, opening new perspectives for their potential use in either controlled release systems or the formulation of additive-complemented films for specific applications.
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Correlation between gel structural properties and drug release pattern in Scleroglucan matrices.
Drug Delivery, 2008Co-Authors: Marta E Daraio, Nora J Francois, Delia L. BernikAbstract:The drug delivery behavior of Scleroglucan hydrogels was correlated with the structural features found by means of steady-state fluorescence studies. Theophylline at 0.4% in weight was used as the model drug and its release was measured using a Franz cell device. The results were fitted with a semi-empirical power law equation, finding significant differences between the 0.5% and higher than 0.8% Scleroglucan concentrations (w/w). Four molecular fluorescent probes were used to test microenvironmental properties of the gel cavities, which will play a key role on the release of the pharmaceutical drugs. The results found by the fluorescence analysis are in good agreement with the ones obtained by release kinetics.
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sclerotium rolfsii Scleroglucan the promising behavior of a natural polysaccharide as a drug delivery vehicle suspension stabilizer and emulsifier
International Journal of Biological Macromolecules, 2007Co-Authors: Silvana Carolina Viñarta, Lucía I. C. De Figueroa, Nora J Francois, Marta E Daraio, Julia Inés FariñaAbstract:Abstract Gel matrices of Scleroglucans from Sclerotium rolfsii ATCC 201126 (EPS I and EPS II, from 48-h and 72-h fermentations, respectively) were evaluated on their release kinetics of theophylline (Th). Equivalent polymer (2%, w/w) and Th (0.2%, w/w) concentrations showed almost coincident drug release patterns, independently of polymer molecular weight or the microstructural properties of gel matrices. Dynamic rheological studies of Scleroglucan hydrogel structures (storage, G ′, and loss, G ″, moduli) indicated a solid-like behavior. Differences on pore size dimensions (EPS I = 20 μm and EPS II = 7 μm) were in accordance to the differences in G ′ (EPS I = 113 Pa and EPS II = 161 Pa), a fact likely related to variations in the cross-linking density of polymer networks. Compared to already known biopolymers, EPS I and EPS II at 0.5 g/L showed a good dispersing ability against particulate suspensions of activated charcoal, bentonite, CaCO 3 , celite and quartz powder. Emulsifying ability of both EPSs at 2 g/L was high ( E = 56–60%) when tested with kerosene, moderate (∼30%) with hexadecane, and negligible in the presence of olive oil-in-water emulsions.
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rheological and drug release behaviour of a Scleroglucan gel matrix at different drug loadings
Polymer International, 2005Co-Authors: Nora J Francois, Ana M Rojas, Marta E DaraioAbstract:The aim of this study was to investigate the drug-loading effects on release and mechanical properties of a Scleroglucan gel, with the intention of considering them in delivery systems formulations. Therheologicalandkineticpropertiesofa2 %w/wScleroglucan gel matrixloadedwith0,0.02,0.04,0.06,0.2 and 0.4 % w/w of theophylline (Th, used as a model drug) were investigated. Rheological measurements were performed in a controlled-stress rotational-shear rheometer under isothermal conditions. For theophylline release from the gel a flat Franz cell was used and the kinetic parameters were derived applyingasemi-empiricalpowerlaw. TheinfluenceofScleroglucanmolar weightonkineticandrheological behaviour was also studied. Results suggest two possible effects of drug loading on the gel network: in the 0.04-0.06 % w/w Th range a plasticizing effect and in the 0.2-0.4 % w/w Th range a rigidization effect. In the first range mentioned, the changes in the gel structural properties tested by means of rheological measurements are coincident with changes in drug-release kinetics. 2005 Society of Chemical Industry
