Use of fractal dimensions in the study of excipients: application to the characterization of modified lactoses

Abstract

In this paper, the morphological and surface characteristics of lactose and coated lactose particles are investigated, continuing with the use of SEM descriptors and fractal dimensions to characterize powder particles. The coating materials were different acrylic polymers of the Eudragit ® type. The size parameters of lactose and coated lactoses indicated that the particle forms deviated from irregular or acicular forms. Shape factor data of coated substances obtained demonstrated that these particles presented regular contours. This fact signifies that lactose particles without coating treatment present irregular profiles with patent edges implying poor flow properties. The aspect ratio values of coated lactoses were close to unity and smaller than that showed by lactose. It is concluded that the polymer particles are placed on the irregularities of lactose particles, smoothing the roughness of the excipient surface. The fractal dimensions calculated from the slope of Richardson plots were 1.11 for lactose and 1.04, 1.05 and 1.08 for coated lactoses. These results are consistent with the shape parameters and flow properties. Some interesting relationships between SEM descriptors and a number of rheological properties have been found.