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

Structural and rheological characterization of Scleroglucan/borax hydrogel for drug delivery
September 2003
Received 4 October 2002; revised 25 March 2003; accepted 10 April 2003. ; Available online 9 July 2003.
Tommasina Coviello, , a, Gina Coluzzia, Antonio Palleschib, Mario Grassic, Eleonora Santuccia and Franco Alhaiquea
International Journal of Biological Macromolecules
Volume 32, Issues 3-5
ScienceDirect
a Department of Chemistry and Technology of Biologically Active Compounds, Faculty of Pharmacy, University of Rome "La Sapienza", P.le Aldo Moro 5, 00185, Rome, Italy
b Department of Sciences and Chemical Technologies, University of Rome "Tor Vergata", Via della Ricerca Scientifica, 00133, Rome, Italy
c Department of Chemical Engineering, Environment and Raw Materials, University of Trieste, P.za Europa 1, 34127, Trieste, Italy
Abstract
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.
Author Keywords: Scleroglucan; Hydrogel characterization; Controlled release
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