Infuence of Microstructure in Drug Release Behavior of Silica Nanocapsules

Meso- and nanoporous structures are adequate matrices for controlled drug delivery systems, due to their large surface areas and to their bioactive and biocompatibility properties. Mesoporous materials of type SBA-15, synthesized under different pH conditions, and zeolite beta were studied in order to compare the different intrinsic morphological characteristics as pore size, pore connectivity, and pore geometry on the drug loading and release process. These materials were characterized by X-ray diffraction, nitrogen adsorption, scanning and transmission electron microscopy, and calorimetric measurements. Ibuprofen (IBU) was chosen as a model drug for the formulation of controlled-release dosage forms; it was impregnated into these two types of materials by a soaking procedure during different periods. Drug loading and release studies were followed by UV-Vis spectrophotometry. All nano- and mesostructured materials showed a similar loading behavior. It was found that the pore size and Al content strongly influenced the release process. These results suggest that the framework structure and architecture affect the drug adsorption and release properties of these materials. Both materials offer a good potential for a controlled delivery system of ibuprofen. 1. Introduction The design of materials for controlled drug delivery has been growing in the last years, due to their importance in the pharmaceutical and health industry. Mesoporous and microporous materials are potentially interesting systems for this purpose due to their high surface area, pore size, structure stability [1, 2], and their characteristics of bioactivity in bone generating implants [3] and biocompatibility [4]. The pore architecture and particle size of the matrix could affect the release profile of the hosted molecules [5–7]. Qu et al. [6] reported that drug loading was directly correlated to surface area, pore geometry, and pore volume in a series of mesoporous materials. Andersson et al. [8] showed that 1D or 3D interconnected pore structures have a strong influence in the release kinetics of the drug. The design strategy for different pore and particle sizes in mesoporous can be approached in different ways, by changing the supramolecular surfactant structure-directing agent or by changing the synthesis conditions. The pH of the synthesis gel strongly affects the hydrolysis-condensation rate of tetraethylorthosilicate (TEOS) and therefore will affect the material geometry modifying the pore architecture, wall thickness and particle size, and the terminal groups located at the walls