Tuning pharmaceutically active zein-based formulations for additive manufacturing

Zein, a biopolymer from corn, was plasticized by glycerol and an Active Pharmaceutical Ingredient-Ionic Liquid (API-IL) for its melt processing at 130 degrees C. In order to enhance the rheological properties of the formulation for 3D printing, the ratio of glycerol to API-IL was adjusted while maintaining a consistent addition of 20% plasticizer. A 50/50 ratio allowed obtaining an initial melt viscosity suitable for extrusion-based processes, at approximately 1 kPa.s at a shear rate of 10 s-1, with a shear thinning behavior. This viscosity remained stable during a processing window of about 6 min, before zein proteins start to aggregate, leading to an apparent gelation phenomenon for long residence times. The processability of this formulation containing API-IL for the printing of tablets for potential therapeutic applications was confirmed by tests on a 3D printer. Nonetheless, in comparison to a reference formulation containing only glycerol, the printing accuracy experienced a decrease. This was ascribed to slower viscous sintering kinetics in presence of API-IL, evidenced by monitoring fusion-bonding during dynamic X-ray tomography trials carried out at Synchrotron SOLEIL.