During the past 10 years particle engineering in the pharmaceutical industry has become a topic of increasing
importance. Engineers and pharmacists need to understand and control a range of key unit manufacturing
operations such as milling, granulation, crystallisation, powder mixing and dry powder inhaled drugs which can be
very challenging. It has now become very clear that in many of these particle processing operations, the surface energy
of the starting, intermediate or final products is a key factor in understanding the processing operation and or
the final product performance. This review will consider the surface energy and surface energy heterogeneity of
crystalline solids, methods for the measurement of surface energy, effects of milling on powder surface energy, adhesion
and cohesion on powder mixtures, crystal habits and surface energy, surface energy and powder granulation
processes, performance of DPI systems and finally crystallisation conditions and surface energy. This review will
conclude that the importance of surface energy as a significant factor in understanding the performance of many particulate pharmaceutical
products and processes has now been clearly established. It is still nevertheless, work in progress both in terms of development of
methods and establishing the limits for when surface energy is the key variable of relevance.
Keywords: Surface energy, contact angle, inverse gas chromatography, pharmaceutical powders, surface properties, powder processing.
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