Rheological and thermal stability of novel weak gels based on sulfonated polyacrylamide/scleroglucan/chromium triacetate

The present study deals with weak gels based on sulfonated polyacrylamide (SPA)/scleroglucan (SC)/Cr³⁺ with an exceptional thermal stability in electrolyte media. The rheological results showed that on increasing the SC concentration the shear viscosity and storage modulus of the SPA/SC/Cr³⁺ system were increased and the dependence of the storage modulus on frequency became weaker. The yield stress of the SPA/SC/Cr³⁺ system was higher than that of the corresponding SPA/SC system. The thermochemical stability increased with increasing relaxation time. The SPA/SC/Cr³⁺ semi‐interpenetrating network exhibited the lowest viscosity loss in electrolyte media; therefore this system may be a potential candidate for enhanced oil recovery applications. © 2016 Society of Chemical Industry     

Rheological and drug‐release behaviour of a scleroglucan gel matrix at different drug loadings

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. The rheological and kinetic properties of a 2 % w/w scleroglucan gel matrix loaded with 0, 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 applying a semi‐empirical power law. The influence of scleroglucan molar weight on kinetic and rheological 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. Copyright © 2005 Society of Chemical Industry     

Preparation and characterization of scleroglucan drug delivery films: The effect of freeze‐thaw cycling

This study examined the effect of the freeze‐thaw process on the physical properties of films prepared from scleroglucan (Scl) hydrogels, suitable for drug delivery applications. Films made from Scl, using glycerol as plasticizer, were prepared from hydrogels by two procedures: a room temperature drying (RTD) method and a freeze‐thaw cyclic process, before the application of RTD, which results in a reinforced physically cross‐linked network. Films were characterized by studies of water vapor transmission (WVT), swelling, tensile tests, ESEM microscopy, FTIR, and drug release measurements. These determinations showed significant differences between films obtained by both treatments. The films prepared through freeze‐thaw cycles showed an important increase of the tensile strength with respect to those corresponding to films only air dried and a decreasing swelling degree in direct relationship to the number of freeze‐thaw cycles. A model drug, Theophylline, was included in these biocompatible films for in vitro drug release measurements, using a flat Franz cell. The physical differences observed between Scl films prepared with both methods can be explained proposing that the number of crosslinking points by hydrogen bonding increase when increasing the number of freezing and thawing cycles used for film preparation. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Composites of polymeric gels and magnetic nanoparticles: Preparation and drug release behavior

The article is concerned with the preparation of polymer–iron oxide nanocomposites and the study as drug‐delivery matrices under the influence of applied magnetic field. Biocompatible materials were prepared by incorporating an aqueous ferrofluid in poly(vinyl alcohol) and scleroglucan (SCL) hydrogels, loaded with theophylline as model drug for release studies. The in vitro release profile was obtained using a flat Franz cell and the kinetic parameters were derived applying a semiempirical power law. A magnetic characterization of nanoparticles contained in the ferrofluid was performed by obtaining the magnetization curve. For both systems, the observed drug release profiles decreased when a uniform external magnetic field is applied suggesting they can be used as environmental responsive matrices for biomedical applications. Dynamic rheological measurements show that a higher storage modulus and a more compact structure are obtained by incorporating the ferrofluid into the hydrogels. These rheological results and environmental electron scanning microscopy micrographs point to an understanding of release behavior once the magnetic field is applied. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

A Comparison Between Two Biopolymers Used in Drillings Muds

Abstract

The study of biopolymers is increasing considerably in the oil industry because they possess desirable properties such as environmental friendliness. Xanthan gum and scleroglucan are biopolymers used to reduce mud toxicity. These biopolymers are exopolysaccharides added to aid in control of fluid loss to the formation and to increase the viscosity of the drilling mud. In this article, we suggest evaluating the properties of biopolymers used in drilling mud. We constituted a fluid model compliant with the American Petroleum Institute's standards, where the composition differs by the nature of biopolymer. Biopolymer properties were investigated by using two main analytical methods: X-ray diffraction (XRD) and rheology. The substances used in this study are considered to cause little or no risk to the environment. This article describes the characterization of these polymers and the effect of additives such as clay and weighting material on drilling muds.     

APPARENT NON-FICKIAN RELEASE FROM A SCLEROGLUCAN GEL MATRIX

Hydrogels, and particularly biopolymeric hydrogels, have recently received tremendous interest as controlled release systems for their peculiar features such as high biocompatibility, biodegradability, bioadhesivity, chemical and thermal resistance and good mechanical properties. Among biopolymers, the exocellular microbial polysaccharide scleroglucan appears to be particularly well suited for the formulation of monolithic hydrogel matrices for controlled drug release. In this work we studied the macroscopic factors influencing the kinetics of a model drug release (theophylline) from a scleroglucan hydrogel matrix (2%w/w) and modeled the relevant experimental results. The evidences for the release experiments indicate that the kinetics of the processes follow an apparently non-Fickian behavior under different active drug concentration, temperature and stirring speed. However, by considering the peculiar nature of the hydrogel matrix and the geometrical features of the experimental setup in the formulation of the appropriate initial and boundary conditions, data can be satisfactorily modeled with the classical Fick's law.     

Physicochemical factors affecting the formation of the biological response modifier scleroglucan

The use of phosphate as the limiting nutrient for scleroglucan formation by Sclerotium glucanicum led to stimulation of glucan formation. Final exopolysaccharide concentrations achieved in phosphate-limited (18·9 kg m^?3) cultures were much higher than in the usual nitrogen-limited fermentations (11·4 kg m^?3). The mechanism by which phosphate limitation engendered glucan formation may be largely non-specific, involving a generalised diversion of the carbon source away from biomass formation and towards glucan synthesis. The effect of stirrer speed was examined in a fermenter fitted with a 6-bladed Rushton turbine impeller of 0·5 vessel diameter. It was noted that biomass and scleroglucan formation showed different optima. This may have been due to the markedly different oxygen requirements of the two processes.     

齐整小核菌SCL2010产小核菌多糖培养基优化的研究

采用单因素和正交试验对小核菌多糖高产菌株齐整小核菌（Sclerotium rolfsii）SCL2010的培养基成分进行了深入地筛选与优化。结果表明,最佳培养基配方为葡萄糖45.0 g/L,玉米浆1.5 g/L,NaNO3 2.0 g/L,K2HPO4·3H2O 2.0 g/L,柠檬酸0.7 g/L,MgSO4·7H2O 1.5 g/L,KCl 2.0 g/L。在此优化条件下,小核菌多糖的产量为31.81 g/L,碳源转化率为70.69%。采用发酵罐进行小试放大试验,小核菌多糖的产量达到31.86 g/L,碳源转化率为70.80%,发酵液表观黏度达到4 500 mPa·s,并将发酵时间缩短至60 h左右,具有显著效果。