Figure 1. Overview of the experimental method and parameter definition.

A two-phase spray nozzle is used to generate the spray, and placed at a distance h from the surface. The cell-containing liquid (with viscosity μ) is delivered to the nozzle using a syringe pump (not shown). Air at controlled pressure P is applied to the nozzle gas inlet. The impact substrate is moved under the spray (indicated by horizontal arrows) using a linear motor, ensuring clean and homogeneous impact. Generally, a clean glass substrate is used, but gelatin-water mixtures (with gelatin weight fractions C_g) are used to assess the influence of the surface stiffness. (b) Cross-section of the nozzle, illustrating the air and liquid flows, and the coordinate system used. Figures (c) and (d) illustrate key variables describing the cell-containing droplets in air (c) and during impact (d).