Pneumatic conveying inkjet bioprinting for the processing of living cells

Inkjet printing techniques are often used for bioprinting purposes because of their excellent printing characteristics, such as high cell viability and low apoptotic rate, contactlessmodus operandi, commercial availability, and low cost. However, they face some disadvantages, such as the use of bioinks of low viscosity, cell damage due to shear stress caused by drop ejection and jetting velocity, as well as a narrow range of available bioinks that still challenge the inkjet printing technology. New technological solutions are required to overcome these obstacles. Pneumatic conveying printing, a new type of inkjet-based printing technique, was applied for the bioprinting of both acellular and cellular fibrin-hydrogel droplets. Drops of a bioink containing 6 × 10⁶HEK293H cells ml^-1were supplied from a sterile nozzle connected to a syringe pump and deposited on a gas stream on a fibrinogen-coated glass slide, here referred to as biopaper. Fibrinogen film is the substrate of the polymerization reaction with thrombin and Ca²⁺present in the bioink. The pneumatic conveying printing technique operates on a mechanism by which drop ejection and deposition in a stream of gas occurs. The percentage of unprinted and printed dead HEK293H cells was 5 ± 2% and 7 ± 4%, respectively. Thus, compared to normal handling, pneumatic conveying printing causes only little damage to the cells. The velocity of the drop approaching the biopaper surface is below 0.2 m s^-1and does not cause any damage to the cells. The cell viability of printed cells was 93%, being an excellent value for inkjet printing technology. The HEK293H cells exhibited approximately a 24 h lag time of proliferation that was preceded by intense migration and aggregation. Control experiments proved that the cell migration and lag time were associated with the chemical nature of the fibrin hydrogel and not with cell stress.