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New hydrogels obtained by a crosslinking reaction between the polycarboxylated derivative of scleroglucan (sclerox) and 1, 6-hexanedibromide have been prepared and characterized. Different ratios between the alkane dihalide and sclerox yielded products with appreciably different properties. Water uptake by the hydrogel with a low degree of crosslinking was remarkably affected by ionic strength. The diffusion of a model molecule (theophylline) through the swelled crosslinked polymers was studied and the theoretical analysis leading to the calculation of permeability coefficients in different environmental conditions is reported. Tablets prepared with one of the new hydrogels behaved as swellable monolithic systems suitable for sustained drug release.

The formulation of a new controlled delivery system, based on a novel type of matrix obtained by the chemical reaction carried out in an aqueous medium on a mixed physical gel of gellan and scleroglucan, is described in this paper. The preparation yielded a new co-crosslinked polysaccharide (CCP) hydrogel, bearing carboxylic groups, that showed a sustained release behaviour that can be modulated by means of calcium ions. For the characterization of CCP, diffusion experiments through the swelled hydrogel were carried out in different environmental conditions and the release from tablets prepared with CCP and a model drug was evaluated. The addition of CaCl2 in the formulation of the dosage forms allowed a further marked reduction in delivery rate to be obtained; this effect is to be related to the free ionized carboxylic groups still present in the gellan moiety of CCP. The different behaviour of Ca+2 and Na+ ions is discussed.

The ability of gellan to form gels in the presence of calcium ions enabled us to prepare capsules by gelation of this polysaccharide around a core containing starch, calcium chloride and a model drug. Release from the dried capsules was studied in vitro by means of the rotating basket technique (USP) in different environmental conditions (distilled water, pH = 2.0, pH = 6.8) and the effects of the presence of increasing amounts of drug in the formulation were also investigated. The behaviour of the gellan capsules was compared with that of beads prepared with the same polysaccharide but containing different additives. Results obtained indicate that gellan is suitable for the formulation of sustained release capsules and that solvent uptake by the dried capsules is most likely the main factor capable of affecting the rate of delivery from the tested preparations.

Four carboxylated derivatives of scleroglucan have been obtained by oxidation, to different extents, of the glucopyranose side chains of the natural polysaccharide. The diffusion of model molecules through aqueous solutions of these new products was measured at various pH values. The reversible pH induced sol-gel transition of some of the polyelectrolyte solutions tested effects a remarkable variation in the diffusion rate of the permeating species; in this sense the most interesting polysaccharide appears to be the product with 70% oxidized glucopyranose moieties. The behaviour of scleroglucan and its derivatives has been compared with that of carboxymethylcellulose and the mechanism involved in drug permeation and release discussed. The possible application of one of the new products in controlled release formulations for oral use is also reported.

The diffusion of model molecules from water dispersions of ethylenevinyl-N,N-diethylglycinate copolymer microfibers has been studied in different conditions. The influence of pH on diffusion rate has been related to water association and swelling effects following structural transitions induced in the copolymer by the acidic medium, rather than to difference in binding of the diffusing species to the macromolecule.