Stereolithographic 3D printing: Formulation design based on percolation thresholds

Abstract

Stereolitograpy (SLA) is an optical photosolidification technology, which can be used to produce 3D printed dosage forms. In the present work, the model drug 4-Aminosalicylic was combined with the photopolymer poly(ethylene glycol) diacrylate (PEGDA), the plasticizer poly(ethylene glycol) (PEG) and the photoinitiator diphenyl(2,4,6- trimethylbenzoyl) phosphine oxide (DPPO) to form a printable resin. The design of a commercial SLA printer was modified to enable printing of different light-curing mixtures in the same tank. This optimisation allowed to evaluate up to 18 different resins by printing in parallel, thus reducing time and costs. Resulting 3D printed drug delivery systems were analyzed with respect to mechanical parameters and drug dissolution rate. The principles of percolation theory were applied, for the first time, to provide a mechanistic insight into the impact of varying PEGDA-PEG ratios. It could be demonstrated that a critical point is reached at 18 %v/v of PEGDA, representing the minimum amount needed in the resins to produce solid objects. This critical point was related to the site percolation threshold of PEGDA. Additional critical points were identified related to the percolation thresholds of PEGDA and PEG in the formulation. We conclude that percolation theory is a valuable concept to obtain mechanistic insights into 3D printed systems manufactured by SLA and to define the Design Space of these innovative dosage forms.