Multiscale 3D Bioprinting by Nozzle-Free Acoustic Droplet Ejection

Bioprinting allows the manufacture of complex cell-laden hydrogel constructs that can mature into tissue replacements in subsequent cell culture processes. The nozzles used in currently available bioprinters limit the print resolution and at dimensions below 100 µm clogging is expected. Most critically, the reduction of nozzle diameter also increases shear stress during printing. At critical shear stress, mechanical damage to printed cells triggers cell death. To overcome these limitations, a novel 3D bioprinting method based on the principle of acoustic droplet ejection (ADE) is introduced here. The absence of a nozzle in this method minimizes critical shear stress. A numerical simulation reveals that maximum shear stress during the ADE process is 2.7 times lower than with a Ø150 µm microvalve nozzle. Printing of cell clusters contained in droplets at the millimeter length scale, as well as in droplets the size of a single cell, is feasible. The precise 3D build-up of cell-laden structures is demonstrated and evidence is provided that there are no negative effects on stem cell morphology, proliferation, or differentiation capacities. This multiscale acoustic bioprinting technique thus holds promise for cell-preserving creation of complex and individualized cell-laden 3D hydrogel structures.