How to preserve cell viability by selecting the right printing nozzle?

Published : 09/15/2020 20:07:09

The stress profile experienced by the cells in bioinks while printing plays a significant role in the cell viability by the impact on the cells’ physical and biological properties. Inside the cartridge (or syringe) cells in extrusion based bioprinting systems experience a predominantly hydrostatic force induced by the pressure to move the formulated ink through the barrel. However, inside the nozzle (or tip) shear forces prevail.

From the hydrostatic pressures experienced by the bioinks inside the cartridge, a great stress is applied on the biomaterial and cells when the formulation travels through a narrow channel and enters the nozzle tip. A rational choice of the nozzle can help alleviating the shearing effect onto cells.

Shape 

The format of the nozzle represents a relevant factor towards cell viability because it contributes to the shear stress experienced by the bioink. The literature demostrates that lower printing pressure is required when conical nozzles are used. Straight nozzles, however, are associated with high shear stresses (Lee et al., 2019). The choice of the nozzle geometry should take into consideration minimizing the time that cell-based formulation would flow through a narrow channel and preventing the shearing effect onto cells. In this case, tapered geometries are preferred over straight cylindrical nozzles.

various tips

Dimension

The gauge number represents the opening diameter of the nozzle (or tip). The higher the gauge, the smaller the diameter. Example: Gauge 27 (internal diameter = 0.20 mm) and Gauge 18 (internal diameter = 0.84 mm). The choice of the gauge relies on the balance between printing resolution and cell survival.

Cidonio et al. (2019) demonstrated that high shape fidelity and cell survival can be achieved upon extrusion with medium size nozzle apertures (250 - 800 microns). The use of large nozzle diameters (> 800 microns) compromises the resolution of printing, however, it promotes high post-printing cell survival because of the low shear imposed on the printed cells. Conversely, a nozzle with a small aperture can enable printing of highly precise structures but leads to elevated stress on printed cells while printing (Cidonio et al., 2019).

References

Cidonio, G., Glinka, M., Dawson, J. I., & Oreffo, R. O. C. (2019). The cell in the ink: Improving biofabrication by printing stem cells for skeletal regenerative medicine. Biomaterials, 209, 10–24. https://doi.org/https://doi.org/10.1016/j.biomaterials.2019.04.009

Lee, J. M., Ng, W. L., & Yeong, W. Y. (2019). Resolution and shape in bioprinting: Strategizing towards complex tissue and organ printing. Applied Physics Reviews, 6(1), 11307. https://doi.org/10.1063/1.5053909

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