Low-degree oxidized scleroglucan and its hydrogel

Evaluation of rheological properties and swelling behaviour of sonicated scleroglucan samples

Scleroglucan is a natural polysaccharide that has been proposed for various applications. However there is no investigation on its property variations when the molecular weight of this polymer is reduced. Scleroglucan was sonicated at two different polymer concentrations for different periods of time and the effect of sonication was investigated with respect to molecular weight variations and rheological properties. Molar mass, estimated by viscometric measurements, was drastically reduced already after a sonication for a few min. Sonicated samples were used for the preparation of gels in the presence of borate ions. The effect of borax on the new samples was investigated by recording the mechanical spectra and the flow curves. A comparison with the system prepared with the dialysed polymer was also carried out. The anisotropic elongation, observed with tablets of scleroglucan and borax, was remarkably reduced when the sonicated samples were used for the preparation of the gels.

Investigation on a new scleroglucan/borax hydrogel: structure and drug release

The aim of this work is to elucidate the structure of the new hydrogel prepared with scleroglucan (Sclg) and borax, suitable for drug delivery, applying theoretical approaches, and to explain its very peculiar swelling. The possible linkages with borate ions have been investigated and original parameters for the 4,6-gluco-borate moiety have been introduced. The structures relative to the Sclg chains in the presence of borax and the possible mutual arrangements among the triple helices are given. According to molecular dynamics simulations, the most probable assembly of the chains in the network is proposed, without and in the presence of three tested model drugs with different molecular dimensions: theophylline (TPH), Vitamin B12 (Vit. B12) and myoglobin (MGB). The hydrogel supramolecular structure, formed via chemical and physical linkages among the polysaccharidic chains, is built up taking into account the steric hindrance of the entrapped molecules. It is shown that molecular dynamics analysis can be a useful tool capable to shed some light on the anomalous swelling of the hydrogel, suitable for drug release, giving a new insight on the network structure and the release rate of the guest molecules.

A new polysaccharidic gel matrix for drug delivery: preparation and mechanical properties

A new type of hydrogel was prepared, under controlled conditions, by diffusion of Ca(II) ions into a solution of the carboxylated derivative of Scleroglucan (Sclerox). The obtained hydrogel was loaded with Theophylline (TPH) and Myoglobin (MGB), two model drugs of remarkably different steric hindrance, and also used, after freeze drying, for the preparation of tablets. Release studies were carried out on both the freshly prepared gel and on the tablets. As far as the gel systems experiments are concerned, the delivery profiles resulted to be deeply dependent on the molecular dimensions of the loaded molecules; TPH was easily released while the larger tested molecule (MGB) remained partially entrapped within the three-dimensional network. Furthermore, in the case of MGB, the release was dependent also on polymer concentration (c(p)): at the highest investigated c(p) value a corresponding lowest delivery of the guest molecule was observed. This effect of polymer concentration on the rate of delivery was studied applying three different mathematical approaches: the one that better fitted the experimental release profile allowed to support the explanation of the mechanism involved in the observed two-step delivery that has been related to the drug trapping inside the clusters of the gel network. The delivery profiles from the tablets showed how the release, in this case, could be related, essentially, to the molecular dimensions of the guest molecules, independently on the c(p) used to prepare the starting hydrogel. TPH was completely delivered in a few hours while the MGB was almost unable to diffuse out of the matrix and more than 80% resulted entrapped in the network for at least 24 h. The novel hydrogel, at different c(p), was also characterized by means of a texture analyzer to inspect its mechanical properties. According to the compression data, the hardness, the work of cohesion and the work of adhesion of the networks were estimated. Furthermore, by means of relaxation experiments, analysed applying the generalized Maxwell model, the gels can be classified as solid viscoelastic materials and the mechanical spectra indicated a predominance of the viscous behaviour, while the Young modulus, E0, as expected, was found to increase with polymer concentration.

Scleroglucan: a versatile polysaccharide for modified drug delivery

Scleroglucan is a natural polysaccharide, produced by fungi of the genus Sclerotium, that has been extensively studied for various commercial applications (secondary oil recovery, ceramic glazes, food, paints, etc.) and also shows several interesting pharmacological properties. This review focuses its attention on the use of scleroglucan, and some derivatives, in the field of pharmaceutics and in particular for the formulation of modified-release dosage forms. The reported investigations refer mainly to the following topics: natural scleroglucan suitable for the preparation of sustained release tablets and ocular formulations; oxidized and crosslinked scleroglucan used as a matrix for dosage forms sensitive to environmental conditions; co-crosslinked scleroglucan/gellan whose delivery rate can be affected by calcium ions. Furthermore, a novel hydrogel obtained with this polysaccharide and borate ions is described, and the particular structure of this hydrogel network has been interpreted in terms of conformational analysis and molecular dynamics. Profound attention is devoted to the mechanisms involved in drug release from the tested dosage forms that depend, according to the specific preparation, on swelling and/or diffusion. Experimental data are also discussed on the basis of a mathematical approach that allows a better understanding of the behavior of the tested polymeric materials.

Structural and rheological characterization of Scleroglucan/borax hydrogel for drug delivery

The polysaccharide Scleroglucan, one of the most rigid polymers found in nature, can form a chemical/physical gel, in the presence of borax. The obtained hydrogel was loaded with three different model molecules (Theophylline, Vitamin B12 and Myoglobin) and then, after freeze-drying, was used as a matrix for tablets. The release profiles of the substances from the dosage forms were evaluated; the matrix appeared capable to modulate the diffusion of the chosen molecules, and different diffusion rates were observed, according to the different radii of the tested molecules. Interestingly, in the dissolution medium the matrix undergoes an anisotropic swelling taking place only in the axial direction, while a negligible radial variation occurs. The water uptake of the matrix occurs according to a Fickian process. Samples at two different polymer concentrations (0.7 and 2.3%, w/v) were characterized in terms of rheological and mechanical parameters and the properties were interpreted in terms of the molecular structure obtained by conformational analysis. The flow curves acquired in the viscoelasticity interval, show the effect of the borate ion in improving the resistance of the gel in comparison to the polymer alone. The evaluation of the moduli indicates that the system is viscoelastic, with an appreciable liquid component that increases as the polymer concentration decreases. Also the cohesion of the gel is higher in comparison to the Scleroglucan and is strongly dependent on temperature. The combination of experimental and theoretical conformational analysis approaches, allowed us to propose a model for the structure of the macromolecular network and to give an explanation to the anomalous swelling that was observed. It came out that the polymer can built up a channel structure, mediated via borax ion interaction, that can accommodate guest molecules of different size.

Scleroglucan/borax: characterization of a novel hydrogel system suitable for drug delivery

A new hydrogel, with scleroglucan using borax as a crosslinker, has been prepared. The physical gel has been loaded with a model molecule (theophylline) and the release of the drug from the gel was evaluated. The same system was used to prepare tablets and the delivery of theophylline in different environmental conditions (HCl and SIF) was determined. A recent theoretical approach has been applied to the dissolution profiles obtained from the tablets and a satisfactory agreement has been found with the experimental data. Furthermore, the diffusion coefficient of the model molecule was evaluated according to a suitable strategy that was tested on two set of data obtained with different set-ups (permeation and diffusion experiments). A simplified mathematical approach allows to reduce the two-dimensional problem of the Fick's second law in a one-dimensional system leading to a much easier handling of the data without loosing the accuracy of the original problem in two dimensions. The characterization of the gel has been also carried out following the kinetics of swelling in terms of water uptake.