Fluid dynamics of the droplet impact processes in cell printing

Cell printing, in which cell-laden droplets are delivered to target positions using inkjets or other devices, is an emerging technique in tissue engineering. Despite significant progress, the survival rate of cells delivered to these positions is often inadequate for targeted applications. Here, we developed a simple model for cell printing based on multiphase fluid-structure interactions. Using this model, we reconstructed the droplet and cell dynamics during the droplet impact process in cell printing. Based on extensive simulations, we developed a general picture of the droplet impact process by dividing it into four stages: the inertia stage, the interfacial flow stage, the elastic response stage, and the viscous flow stage. We provided a simple estimation of the duration of each stage and the magnitude of stress within the cell during each stage. From that estimation, we determined that surface tension is essential for controlling the deformation and stress inside cell under low-to-moderate droplet impact velocities relevant to inkjet-based cell printing. Based on extensive parametric studies, strategies for controlling the stress and deformation of cells during cell printing are examined and their practical implementations are discussed.