Investigation of the extent of surface coating via mechanofusion with varying additive levels and the influences on bulk powder flow properties

• Published in: International journal of pharmaceutics Vol. 413; no. 1; pp. 36 - 43
• Main Authors: Zhou, Qi (Tony), Qu, Li, Gengenbach, Thomas, Denman, John A., Larson, Ian, Stewart, Peter J., Morton, David A.V.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15-07-2011; Elsevier
• Subjects: Biological and medical sciences; chemical composition; Coated Materials, Biocompatible - chemistry; coatings; cohesion; Drug Compounding; Drug Delivery Systems; Excipients - chemistry; Fine cohesive lactose powder; General pharmacology; lactose; Lactose - chemistry; magnesium; Magnesium stearate; Mechanical dry coating; Mechanofusion; Medical sciences; Microscopy, Electron, Scanning - methods; Particle Size; Pharmaceutical technology. Pharmaceutical industry; Pharmacology. Drug treatments; Photoelectron Spectroscopy - methods; Powder flow properties; Powders - chemistry; scanning electron microscopy; Spectrometry, Mass, Secondary Ion - methods; stearic acid; Stearic Acids - chemistry; Surface analysis; Surface Properties; surface roughness; X-ray photoelectron spectroscopy; Fine cohesive lactose powder; Magnesium stearate; Mechanical dry coating; Surface analysis; Powder flow properties; Mechanofusion; Coating material; Pharmaceutical technology; Stearate; Inorganic element; Additive; Lactose; Coating; Magnesium; Fine powder
• ISSN: 0378-5173; 1873-3476
• DOI: 10.1016/j.ijpharm.2011.04.014

The objective of this study was to investigate if the coating extent created by a mechanofusion process corresponded with observed changes in bulk powder properties. A fine lactose powder (approximate median diameter 20
μm) was dry coated with magnesium stearate using from 0.1 to 5% (w/w) content. An ultra-thin coating layer of magnesium stearate was anticipated, but previous attempts to determine such thin layers on these fine particles have had limited success, with poor resolution. In this study, the surface coating was examined using the state-of-the-art XPS and ToF-SIMS systems. The powder flow was characterized by Carr index and shear cell testing. XPS was successfully applied to demonstrate variations in surface coverage, as a function of additive levels, and indicated near complete coating coverage at additive levels of 1% (w/w) and above. ToF-SIMS results supported such coating coverage assessment, and indicated coating uniformly across the fine particle surfaces. The flow metrics employed could then be related to the coating coverage metrics. The mechanofusion process also modified the apparent surface roughness observed by SEM and BET. It was suggested that the changes in the surface chemical composition exerted a more evident and direct impact on the powder cohesion and flow characteristics than the changes in the surface morphological properties after the mechanofusion in this study.