Influence of the Volatility of Solvent on the Reproducibility of Droplet Formation in Pharmaceutical Inkjet Printing

Abstract

Drop-on-demand (DOD) inkjet printing enables exact dispensing and positioning of single droplets in the picoliter range. In this study, we investigate the long-term reproducibility of droplet formation of piezoelectric inkjet printed drug solutions using solvents with different volatilities. We found inkjet printability of EtOH/ASA drug solutions is limited, as there is a rapid forming of drug deposits on the nozzle of the printhead because of fast solvent evaporation. Droplet formation of c = 100 g/L EtOH/ASA solution was affected after only a few seconds by little drug deposits, whereas for c = 10 g/L EtOH/ASA solution, a negative affection was observed only after t = 15 min, while prominent drug deposits form at the printhead tip. Due to the creeping effect, the crystallizing structures of ASA spread around the nozzle but do not clog it necessarily. When there is a negative affection, the droplet trajectory is affected the most, while the droplet volume and droplet velocity are influenced less. In contrast, no formation of drug deposits could be observed for highly concentrated, low volatile DMSO-based drug solution of c = 100 g/L even after a dispensing time of t = 30 min. Therefore, low volatile solvents are preferable to highly volatile solvents to ensure a reproducible droplet formation in long-term inkjet printing of highly concentrated drug solutions. Highly volatile solvents require relatively low drug concentrations and frequent printhead cleaning. The findings of this study are especially relevant when high droplet positioning precision is desired, e.g., drug loading of microreservoirs or drug-coating of microneedle devices.

Inkjet Printing Optimization: Toward Realization of High‐Resolution Printed Electronics

“…Rapid evaporation, especially for inks containing highly volatile solvent, during both non-operating and normal functioning period, can cause the accumulation of ink particulates on the nozzle wall and create partial or full blockage. [48][49][50] Nozzle clogging can adversely affect jetting formation, depending on the severity and nature of the clogging. Clogging changes nozzle flow patterns in various ways, such as reduced drop velocity, [51] inconsistent drop shape between nozzles, [52] drop trajectory, [53] and even worse, causes nozzle missing or damage.…”

“…The ink volatility can affect the printing performance in various ways, for example, nozzle clogging, droplet volume, and velocity as well as ink drying time on the substrate. [ 46–48 ] The ink should be formulated in such a way that the solvent or carrier liquid improves the surface tension and viscosity of the ink and also maintains the ink liquidity inside the nozzle.…”