Mechanistic Understanding of Microparticle Formation in Respiratory Applications
1University of Alberta, Department of Mechanical Engineering, Edmonton, Alberta, T6G 1H9, Canada
This contribution summarizes recent advances in the mechanistic understanding of particle formation processes that provides the basis for microparticle based products with respiratory applications. Key mechanisms are heat and mass transport on evaporating or condensing droplets, internal redistribution of components in droplets by diffusion, phase separation processes like nucleation and crystal growth, and particle plasticity, such as shell buckling or collapse of porosity. Since the parameter space governing these processes is much too large for empirical studies, systematic experimental and modelling studies need to be undertaken.
Because of the complexity of actual manufacturing processes, experimental studies of particle formation are best conducted on idealised model systems. Progress on a variety of such experimental models is presented, ranging from highly idealised systems, like single particle levitation and droplet chains, to more representative ones like monodisperse spray drying and well-instrumented process equipment in combination with process models.
Analytical and numerical models for particle formation in single solvent and co-solvent systems provide predictive parameters that can be used in the engineering of microparticles. Application examples are shown for glass stabilization in amorphous systems, surface modifications in partially crystalline systems, and encapsulation of nano-emulsions.