Wettability of pharmaceutical solids: its measurement and influence on wet granulation

The wettability of several pharmaceutical powders was assessed by the contact angle method, and the values for surface energies, as well as their dispersive and polar components, were determined. This method was found to work well for hydrophobic powders. The dispersive surface energies determined from the contact angle were consistent with those measured by inverse gas chromatography. The data also showed that the contact angle approach was difficult to apply to hydrophilic powders due to drop penetration. The surface energy data obtained by the contact angle method were applied to the selection of the granulating solvent for a wet granulation process. The prediction of granulating solvent performance based on solvent–drug spreading coefficients was in good agreement with the characteristics of the resulting granules, in terms of density, porosity and friability.