Rheological insights into 3D printing of drug products: Drug nanocrystal-poloxamer gels for semisolid extrusion

[Display omitted] •Particle size reduction into nanoscale improved solubility properties of model poorly soluble API Indomethacin.•Rheometer aids in the development and quality control of semisolid extrusion 3D printing inks containing nanocrystals.•Rheological behavior suggested that polymer/water ratio and nanocrystal load were critical material attributes.•A strong correlation between the printing ink viscosity and printing pressure was established. The importance of ink rheology to the outcome of 3D printing is well recognized. However, rheological properties of printing inks containing drug nanocrystals have not been widely investigated. Therefore, the objective of this study was to establish a correlation between the composition of nanocrystal printing ink, the ink rheology, and the entire printing process. Indomethacin was used as a model poorly soluble drug to produce nanosuspensions with improved solubility properties through particle size reduction. The nanosuspensions were further developed into semisolid extrusion 3D printing inks with varying nanocrystal and poloxamer 407 concentrations. Nanocrystals were found to affect the rheological properties of the printing inks both by being less self-supporting and having higher yielding resistances. During printing, nozzle blockages occurred. Nevertheless, all inks were found to be printable. Finally, the rheological properties of the inks were successfully correlated with various printing and product properties. Overall, these experiments shed new light on the rheological properties of printing inks containing nanocrystals.