RESUMO
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 microm and EPS II=7 microm) 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 2g/L was high (E=56-60%) when tested with kerosene, moderate ( approximately 30%) with hexadecane, and negligible in the presence of olive oil-in-water emulsions.
Assuntos
Agaricales/química , Sistemas de Liberação de Medicamentos , Glucanos/química , Hidrogéis/química , Teofilina/química , Agaricales/crescimento & desenvolvimento , Emulsões , CinéticaRESUMO
The structure of scleroglucan gel matrices was characterized by dynamic rheological studies. The results were compared with the release kinetics of theophylline in analogous samples using a Franz diffusion cell, fitting the drug release data with a semi-empirical power law. Dynamic rheology gave information about the viscous and elastic components (loss and storage moduli, respectively) of the gel which could influence the drug-release profiles. Scleroglucan gels showed two structural transitions within the gel regime that coincided with changes in the release pattern. It was found that the introduction of 0.4% (w/w) of theophylline decreased the loss and storage moduli in the 2% (w/w) scleroglucan gels by 50%. The influence of the same wt.% theophylline in other gels was strongly dependent on the gel concentration. These results demonstrated the value of rheological studies to detect matrix structural changes produced by the inclusion of drugs which may modify the drug-release profile.
Assuntos
Géis/química , Glucanos/química , Química Farmacêutica , Portadores de Fármacos , Composição de Medicamentos , Géis/administração & dosagem , Glucanos/administração & dosagem , Cinética , Estrutura Molecular , Reologia , Teofilina/administração & dosagem , Teofilina/química , Fatores de Tempo , Vasodilatadores/administração & dosagem , Vasodilatadores/químicaRESUMO
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.