Strategies and mechanisms to improve the printability of pharmaceutical polymers Eudragit® EPO and Soluplus®

The poor printability of most pharmaceutical polymers greatly restricts the application of the fused deposition modeling (FDM) technique in the field of personalized pharmaceutical preparations. General strategies to improve printability and provide practical guidelines for the optimization of formulations are lacking. Moreover, the mechanism associated with the smooth printing process of modified printing materials needs to be investigated. In this study, three different strategies were used to improve the FDM printability of typical brittle polymers with poor printability. The relationship among additives, material properties, and printability was explored. The finite element method was used to simulate the radial stress-strain behavior of the filament, while computational fluid dynamics was used to simulate the axial melt flow field in the printing head. It was found that the addition of an inert filler (i.e., talc), a drug with high melting points (i.e., diclofenac sodium), and a polymer with high strength (i.e., plasticized ethylcellulose) effectively improved the printability of plasticized Eudragit® EPO and Soluplus®. In addition, regulating the mechanical properties of filaments improved printability, and it was deduced that printable filaments should have neither very low stiffness nor very low flexibility. The suitable melt viscosity or shear-thinning property of the printing material facilitated smooth extrusion without filament breakage or nozzle blockage. The results of this study also showed that simulation could assist in understanding the stress-strain behavior of filaments and the flow field of melts during FDM printing.