A relationship between surface free energy and polarity data and some physical properties of spheroids

Abstract

Spherical particles have been produced by extrusion and spheronisation of a wet mass of lactose, microcrystalline cellulose and indomethacin (as a model drug), and of mixtures of microcrystalline cellulose, barium sulphate and glyceryl monostearate (to test the general applicability of the surface energy predictions). The surface energies of the powders were estimated from contact angle measurements. The work of cohesion of each powder, and the work of adhesion between pairs of powders were assessed, as were spreading coefficients of the powders over each other. It was found that the spheres produced without indomethacin (lactose and microcrystalline cellulose only) required a significantly higher force to cause crushing, and were also of higher density than any of the four batches which contained different levels of indomethacin. The batches with added indomethacin had similar physical properties irrespective of indomethacin loading. Spheroids containing glyceryl monostearate and barium sulphate had much higher porosities and lower crushing strengths than the indomethacin based formulations. These differences are explained in terms of much lower works of adhesion and cohesion for barium sulphate and glyceryl monostearate than were obtained for the other materials. The differences in the properties of the spheroids have been explained in terms of interfacial phenomena, and in particular the relative works of adhesion between the solids.