Marta E. Daraio

Dynamic rheological measurements and drug release kinetics in swollen scleroglucan matrices

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.

Aggregation and Photophysics of Rose Bengal in Alumina-Coated Colloidal Suspensions

The absorption and emission properties of Rose Bengal (RB) have been studied in colloidal suspensions of positively charged alumina-coated silica nanoparticles (Sil). Experimental spectra can be rationalized by the existence of an equilibrium between aqueous monomers and only one adsorbed species. However, a simple partition or a Langmuir-type adsorption-aggregation equilibrium do not explain the observed results. No evidence regarding the existence of adsorbed monomers is found even at low surface coverage. Aggregation stops at the dimer level, though, at high enough dye concentrations, the surface coverage is almost complete. Comparative experiments performed on negatively charged silica nanoparticles show that monomers are the only species present in this case. Fluorescence experiments on Sil indicate that dimers are fluorescent. Laser excitation of adsorbed dye leads to the formation of RB radical cations, while the dye triplet state is not observed.

Correlation Between Gel Structural Properties and Drug Release Pattern in Scleroglucan Matrices

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.

MULTIFRACTAL ANALYSIS OF SCLEROGLUCAN HYDROGELS FOR DRUG DELIVERY

The non-homogeneity and complexity of micro network distribution of hydrogel matrices prepared with two scleroglucan biopolymers obtained with different fermentation times were analyzed using environmental scanning electron microscopy (ESEM) and dynamic rheology. ESEM images were processed with the tools of multifractal theory using the box-counting method in order to obtain the gels multifractal spectra. Dynamic rheological measurements indicate that both polymeric networks correspond to physical gels that exhibit a solid like behavior. These results suggest the existence of a relationship between the fermentation time used in the polymer production, the degree of self-similarity and the rigidity of the scleroglucan gel structure.