*2.2. Solubility Studies*

To select the most effective drug solvent for liquisolid systems formulation, the GLY solubility in different non-volatile water-miscible solvents, namely Labrasol®, Transcutol®, Kolliphor®HS15, PEG 400, Kollisolv®, Solketal®, Kollisolv®PYR (2-pyrrolidone, 2-PYR), N,N-dimethylacetamide (DMA), benzyl benzoate and 1,3-butandiole, was evaluated. The minimum amount necessary to solubilize 5 mg GLY (drug therapeutic dose) was determined by adding progressive aliquots of each solvent to the exactly weighed drug amount, at room temperature. Only in the case of Kolliphor®HS15, solid at room temperature, it was necessary to heat to 40 ◦C for obtaining its fusion. The stability of GLY dissolved in the various solvents was checked by UV assay (UV/Vis 1601 Shimadzu, Tokyo, Japan) at 300 nm of its concentration immediately after the solution preparation, and then every 30 days for 6 months.

## *2.3. Characterization of the Mesoporous Silicas and Clays*

#### 2.3.1. Apparent and Tapped Density

Apparent density (DA) and tapped density (DT) were evaluated according to the USP method, using a PT-TD 300 instrument (Pharma Test, Hainburg, Germany) endowed with a standard 100 mL graduated cylinder. Carr's Index (CI) and Hausner Ratio (HR), indicative of the powder compressibility and flowability, were determined by the following equations:

$$\text{CL}(\%) = 100 \frac{\text{D}\_{\text{T}1250} - \text{D}\_{\text{A}}}{\text{D}\_{\text{T}1250}} ; \text{HR} = \text{DT}\_{1250} / \text{D}\_{\text{A}} \tag{1}$$

where DT1250 is the tapped density value obtained after 1250 taps of the cylinder.
