Evaluation of the flowability of surface-modified preparations by the measurement of the inter-particle adhesive force

In our previous study, we succeeded in manufacturing rapidly disintegrating tablets by a simple method of direct compression of a mixture of surface-modified ibuprofen using a high-speed agitating granulator. In direct compression, the flowability of the mixture of powdery ingredients is a very important qualitative factor such as for the consistency of the tabletting process and the uniformity of the drug contents. We evaluated the flowability of the surface-modified powders according to the angle of repose in the previous study. However, the angle of repose represents a characteristic of a powder as a mass of particles, and does not enable accurate evaluation of characteristics of individual particles. Also, as the flowability of powder is affected by the adhesive-agglomerative property of particles, the adhesive-agglomerative property is expected to affect the measured value of the angle of repose. In this study, we measured inter-particle adhesion force of surface-modified ibuprofen particles under various conditions, using a newly developed apparatus for the measurement of adhesion force among microparticles. Since the measurement of inter-particle adhesion force was found to enable not only more accurate and quantitative evaluation of the flowability than the measurement of the angle of repose but also an evaluation of the uniformity of surface modification, which was impossible according to the angle of repose, a new method was established for evaluating the flowability of surface-modified particles.