Fabrication of composite microcapsules by drop-on-demand inkjet: Effect of precursor composition on the process limits

The feasibility of using drop-on-demand inkjet technology for the fabrication of calcium alginate hydrogel microcapsules containing dispersed sub-micron solid particles (TiO₂ photocatalyst) was demonstrated. The influence of the printed solution viscosity on the micro-droplet size has been investigated and a study of the effect of solids fraction in the suspension on its printability was carried out. It was found that solutions with viscosities of up to 28 mPa s and solids content of up to 7.8 vol% can be reproducibly printed, resulting in droplets ranging from 45 to 105 μm depending on the inkjet operating conditions. In order to ensure stable and reproducible droplet formation, a pressure difference ranging from −200 to −1800 Pa had to be maintained in the nozzle. A uniform distribution of dispersed solids in the resulting microcapsules was achieved by adjusting pH and viscosity. The relationship between the printhead operating pressure, the fluid viscosity, the solids loading and the final size of the obtained microcapsules was established, allowing rapid prototyping of artificial cell-like structures with internal solid inclusions by the inkjet method.