Fig. 4: Drop-impact printing of biological solutions and biopolymers.

a Microscopic images of a single droplet patterned using cell (RBC)-laden PBS solution of different concentrations, scale bar: 50 µm. The cells are contained in an isolated droplet of volume 26 nL patterned using mesh type #0.009. b The number of cells per droplet for varying cell concentrations was examined for mesh types #0.009 and #0.0045. The single-cell printing was further demonstrated using drop-impact technique. c Single cells (MDA-MB-231) of average size ~17 µm were trapped in a 0.268-nL single drop. The drops were collected on an oil-coated glass slide. The concentration of cell solution was kept at 50 × 10⁴ cells per mm³ (scale bar: 50 µm). d Illustration showing printed DMEM droplet arrays using drop- impact printing technique. (1) Shows printed DMEM droplets on a hydrophobic Teflon surface. (2) Shows the arrays of MDA-MB-231 cells containing droplets after cell solution swipe, and a magnified image of a printed droplet containing cells (scale bar: 500 µm). Beside this, the technique’s ability was explored by using biopolymeric viscoelastic liquid (0.0125 g per mL polyacrylic acid mixed in water) for 3D printing applications. e The large patterned microposts of 875 µm diameter and 2 µm height were printed on APTES-coated glass slides and the corresponding scanning electron microscopy (SEM) image (scale bar: 400 µm).