In vitro stability of SBA-15 under physiological conditions

The numerous applications of mesoporous silicas are highly dependent on the stability of these matrices. Consequently, it is convenient to carry out stability studies of these materials under the conditions in which they are going to be employed. Thus, when targeting these matrices for biomedical purposes, in vitro stability tests of mesoporous silica matrices are necessary. In this manuscript, the amount of silica lixiviated from SBA-15 matrices and their stability in aqueous solutions mimicking physiological fluids at 37 °C have been investigated. The selected aqueous media, which exhibit different ionic composition and presence of proteins, have been: saline solution, a simulated body fluid and completed Dubecco’s modified Eagle medium. These are aqueous solutions widely employed as release media in drug delivery, bioactivity and cell culture assays. The obtained results indicate that SBA-15 degrades in all tested media and that there is a partial loss of the mesostructure after 60 days of assay. With the aim of decreasing the silica lixiviation rate, SBA-15 has been organically modified by using different organic functions: alkyl chains (methyl and octyl) and aminopropyl groups. In vitro stability tests of functionalized samples reveal that the amount of SiO2 is reduced compared to unmodified SBA-15 due to the organic coverage that act as a protection barrier for the nucleophilic attack of water to the siloxane (Si–O–Si) groups of the silica framework that leads to the preservation of the mesostructure arrangement. These preliminary tests indicate that organic functionalization of mesoporous silica is a good strategy to decrease SiO2 lixiviation.