Drop-on-Demand Dispensing of Pharmaceutical Suspensions: Correlation of Material Attributes and Operating Conditions to Process Performance

The ability to produce drops on demand is critical to microdosing applications, such as dispensing inks, polymers, and other biological fluids. In the pharmaceutical industry microdosing can be used to reliably fill capsules with multiple materials at strictly controlled ratios, under full closed loop control. Additionally the emergent trend of personalized dosing for therapies in hospitals could lead to personalized microbatch manufacturing based on drop on demand microdosing. While the satisfactory operation of microdosing equipment options for different liquids is usually confined to a narrow region of the system parameter space, there is still a significant lack of understanding of the underlying correlations between material attributes, processing parameters and properties of the dispensed droplets.

In this work, a piezo-electric dispensing device, a solenoid valve, and a positive displacement micropump have been chosen as typical micro-dispensing device. The process design space has been mapped for materials with varied properties (viscosity, surface tension, etc.). Process parameters considered include dwell voltage and rising time among others. To better investigate the underlying physical phenomena governing the performance of the system, a mechanistic model was developed. Specific focus was placed on the resolution of the flow directly before and after the nozzle orifice. The results of this study could provide a substantial contribution to the ability to a priori assess the operating parameters required to reliably dispense drops on demand for different materials.