In samples b and a slow delivery is observed up to 7h with a 45wt% of the loaded drug released, and then a stationary stage was reached. This behavior is probably due to the presence of extraframe Al in this material, forming a strong interaction with the carboxylic groups of ibuprofen. It has been reported that carboxylic acids adsorbed in aluminum oxide surfaces [18–20] and in dealuminated FAU [7] are in the form of carboxylate species and the drug was present as ibuprofenate coordinately bonded to extraframework Al species. Therefore, the adsorption of the drug on the surface is stronger for materials with high Al content, Inhibitors,research,lifescience,medical leading to a slower delivery in
the media, as it has been observed for zeolite sample b (higher Al content). For sample c (lower Al content) due to its hydrophobic character, the drug molecule probably diffuses into the zeolite channels and van der Waals interactions become see more important to retain the ibuprofen molecules; this could explain the slower drug delivery Inhibitors,research,lifescience,medical rate Inhibitors,research,lifescience,medical observed in this sample during the first 24h (Figure 9). Figure 8 TGA IBU loading of the different materials studied. Figure 9 Cumulative release rates of ibuprofen in simulated body fluid. Table 3 Loading degree of ibuprofen determined by UV and TGA for the different micro- and mesoporous materials. In the mesoporous
materials the drug adsorption of both materials was slightly different. The SBApH0 showed a loading degree of
21.33%, Inhibitors,research,lifescience,medical and 25.77% for SBApH4.5; these values were determined by UV-Vis spectrophotometry, in good agreement with the values reported in the literature for these materials [8, 18] and very similar to the amount adsorbed by the zeolite materials (Table 3). In order to understand the differences in drug adsorption between both mesoporous materials, the amount of ibuprofen adsorbed per gram of material was calculated (Table 3). The values obtained at maximum loading were 10.7mg/g for SBApH0 Inhibitors,research,lifescience,medical and 12.9mg/g for SBApH4.5. The larger reduction in superficial area and pore volume observed, after drug loading, can be attributed to IBU adsorption mainly on the micropores of these materials. The IBU release in vitro process (in Sodium butyrate SBF) is presented in Figure 9 and Table 3, showing a very similar delivery pattern for SBA materials. They show a fast drug release in the initial periods, and after only 1h a stationary stage is reached, but only releasing 58% of the loaded drug, even after long periods. The ibuprofen molecular size (1.3 × 0.6nm2) is small compared to the mesopores size of both SBA materials. The free spaces available, in these open cylindrical pores, do not present any diffusion impediment, favoring drug transport from the pores to the solution.