Understanding deposition dynamics of inkjet-printed bi-solvent biopolymer droplets

Inkjet printing of biopolymer droplets is gaining popularity due to its potential applications in creating cellular scaffolds for regenerative medicine. Due to the instantaneous change in viscosity and surface tension of an evaporating biopolymer ink, solvent evaporation and polymer deposition dynamics of biopolymer drops are complex and not well understood. Using high-speed interferometry, we directly observe in real time the instantaneous drop shape of inkjet-printed pico-liter gelatin carboxyl drops containing glycerol and water. It is observed that, for gelatin drops with surfactants, gelatin moves to the pinned contact line at an early stage driven by a strong outward flow causing the drop shape to change from a spherical cap to a volcano shape during evaporation, while a spherical cap is maintained for the case without surfactants. The final deposition of bi-solvent biopolymers is found to highly depend on the composition of the bi-solvent. The decrease in the high-volatility solvent results in the transition of the final deposition from a ring-like to a dome-like profile. Experimental results are also compared against numerical simulations from the literature.