In this paper, the role of mesoporous silica (MS) particle size in the stabilization of amorphous simvastatin (SVT) is revealed. For inhibiting recrystallization of the supercooled drug, the two MS materials (Syloid® XDP 3050 and Syloid® 244 FP) were employed. The crystallization tendency of SVT alone and in mixture with the MS materials was investigated by Differential Scanning Calorimetry (DSC) and Broadband Dielectric Spectroscopy (BDS). Neither confinement of the SVT molecules inside the MS pores nor molecular interactions between functional groups of the SVT molecules and the surface of the stabilizing excipient could explain the observed stabilization effect. The stabilization effect might be correlated with diffusion length of the SVT molecules in the MS materials that depended on the particle size. Moreover, MS materials possessing different particle sizes could offer free spaces with different sizes, which might influence crystal growth of SVT. All of these factors must be considered when mesoporous materials are used for stabilizing pharmaceutical glasses.

Faculty of Science and Technology Institute of Physics University of Silesia SMCEBI 75 Pułku Piechoty 1a 41 500 Chorzów Poland

Faculty of Science and Technology Institute of Physics University of Silesia SMCEBI 75 Pułku Piechoty 1a 41 500 Chorzów Poland International Center for Materials Nanoarchitectonics National Institute for Materials Science Tsukuba Ibaraki 305 0044 Japan

International Center for Materials Nanoarchitectonics National Institute for Materials Science Tsukuba Ibaraki 305 0044 Japan

International Center for Materials Nanoarchitectonics National Institute for Materials Science Tsukuba Ibaraki 305 0044 Japan Department of Physical Chemistry Faculty of Chemical Technology University of Pardubice Studentská 573 532 10 Pardubice Czech Republic

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