Use of the solubility parameter and surface energy concepts in the formulation of solid dosage forms

This review presents some theoretical notions on both the solubility parameter and surface energy concepts, including the different models and the power laws relating them as well as the methods of determination (experimental calculation). Subsequently, we describe the parameters derived from solubility parameters and surface energies (interfacial tension, spreading coefficient, interaction parameter, strength of interaction). The theoretical potential of these parameters is outlined along with practical uses published in the literature. The applications include all the major steps involved in the preparation of solid dosage forms, such as prediction of the organization of powder mixes during blending, estimation of binder efficiency in granulation, modification of the powder surface energy to change the tensile strength of tablets, and optimization of the interaction of plasticizers with coating polymers. Finally, a general approach taking particle size into account is proposed, and the consequences for blending (organization, colour and taste) and compactibility are outlined.