Measurement of interaction forces between individual powder particles using an atomic force microscope

The atomic force microscope (AFM) was used to investigate the interaction f orces between individual particles qualitatively as well as quantitatively. Lactose as a typical excipient for solid drugs was chosen as model substan ce. The interaction forces were determined between a single particle of cry stalline lactose and a tablet of lactose. Their surface topography was char acterized by AFM and scanning electron microscopy (SEM) in order to allow a quantitative assessment of the surface roughness and its influence on the measured forces. To analyze the representative surface segments, the minimu m and maximum surface roughness of the lactose tablet is determined in depe ndence of the segment size. The contact area between the tablet and the par ticle of lactose was quantified by the tip estimation of Villarrubia. Inter particle forces were measured with force volume scans, They allow the deter mination of the three-dimensional surface structure and, simultaneously, a defined number of force curves in regular distances is taken. (C) 2001 Else vier Science B.V. All rights reserved.