Dropwise Additive Manufacturing using Particulate Suspensions: Feasible Operating Space and Throughput Rates

In dropwise additive manufacturing, particularly in pharmaceutical application, process performance depends critically on stable formation of individual drops of reproducible volume and with a desired trajectory, as determined by the interaction of fluid properties and processing conditions (Basaran, et al., 2013). Current additive manufacturing techniques employ solvent-or melt-based printing inks, with which colloidal particles have been used (Hirshfield, et al., 2014, Icten, et al., 2015, Wang, et al., 2012). However, work with non-Brownian suspensions with particle concentrations relevant to practical application has yet to appear in the literature. Such suspensions involve particle sizes in the 10-200 micron range (Denn, et al., 2014) that are readily produced by conventional crystallization and milling operations. This focuses on elucidating the effects of particle size and aspect ratio distribution as well as particle concentration in suspensions which are used in a dropwise additive manufacturing process for production of pharmaceutical dosage forms. Results with drops produced from non-Brownian particle suspensions consisting of active pharmaceutical ingredient crystals and Newtonian carrier fluids indicate that such suspensions offer substantial advantages in mass-based production rate in comparison to solvent-or melt-based printing formulations. Based on the range of dimensionless parameters accessed in this work, a feasible operating space is developed for drop-on-demand drop formation with non-Brownian suspensions. Process monitoring capabilities sufficient to confirm that the resulting dosages meet quality metrics are also discussed.