Exploring the 3D printing binder jetting process for pharmaceutical applications

Traditional mass production of pharmaceuticals is beginning to move towards patiebnt-specific pharmaceutical dosage solutions. Three-dimensional printing (3DP) is attracting increased interest as a potential manufacturing method for personalised medications. In 2015, the first 3D printed tablet Spritam received approval for the treatment of epilepsy. However, the materials available for 3D printing via binder-jetting are currently very limited. Commercial powders consist largely of either calcium sulfates or calcium carbonates. There is a need to understand the types of pharmaceutical excipient powders that can be used in binder-jetting printers. To do this, a framework to assess and screen the essential powder flow and wetting properties is needed.
To understand the powder flow characteristics, a Freeman FT4 Powder Rheometer was used to compare two different commercial binder-jetting powders with several common pharmaceutical excipients. Measured parameters included powder stability, flow rate sensitivity and powder compressibility. Many pharmaceutical powders were far more compressible than the standard industrial 3D printing powders. Over compression of the powder could have negative effects on the prior printed layer and the overall print resolution. To understand binder-powder interactions, drop penetration time studies were performed. The time taken for a binder drop to penetrate commercial samples of powder was found to be between 4-8 minutes. In comparison, a common cellulose pharmaceutical excipient had a drop penetration time of about 0.05 seconds. The commercial binder-jetting process rolls and spreads new layers quickly after printing. The reason why the drop penetration time differs so much in currently being investigated.