3D Bioprinting: Surviving under Pressure

Because 3D bioprinting using microextrusion was reported to yield cells with low viability (~40%) after pneumatic pressure (40 psi) printing through stainless steel nozzles, or blunt-end needles, with about 150 μm diameters (28 and 30G), we set out to improve the viability by coating the interior of the nozzles with silicone. For these studies, H9 human lymphoma cells were used to simulate human stem cells in suspension, and cell viability was measured using propidium iodide dye exclusion and flow cytometry. We tried to improve the viability by coating the inside of the 28 and 30G nozzles (1′′ length) with silicone to protect the cell membranes from being damaged by the imperfections in the stainless steel nozzle. However, we discovered silicone coating had little effect on viability because imperfections in the nozzle were not the problem. Instead, the cells being placed in hypotonic 3% (w/v) alginate prepared in water prior to printing caused significant cell death (~25%) and considerably more (≥50%) after simulated printing under pressure. By preparing the alginate in isotonic solutions of either phosphate buffered saline or complete culture media, we could use pressures over five times (>220 psi) what most printing procedures use and obtain ~80% viability.