**Abbreviations**

increasing amounts of cellular damage resulting in increasing cell death via apoptosis [11] (and our unpublished observations) but only when the cells are placed in hypotonic solutions.

Microextrusion is an excellent 3D bioprinting method that can yield high cell viabilities (≥85%) similar to Inkjet printing using 28G nozzles of either 1/2″ or 1″ lengths for pressures up to 220 psi as long as the hydrogels or solutions are isotonic. Good viability of over 75% can also be achieved using 30G nozzles of 1″ or shorter lengths using 220 psi. Thus, cells can survive with good viability (~85%) under considerable pressure for short periods of time during the micro-

The author thanks Dr. Girish Kumar for help with flow cytometry, Randy Bidinger for making the apparatus that securely housed the pressure pump device, Dr. Stephen J. Merrill for help with statistical analysis, and Dr. Shelby Skoog for critically reviewing this manuscript.

The findings and conclusions in this paper have not been formally disseminated by the Food and Drug Administration and should not be construed to represent any agency determination or policy. The mention of commercial products, their sources, or their use in connection with material reported herein is not to be construed as either an actual or implied endorsement of

such products by the Department of Health and Human Services.

extrusion 3D bioprinting process if they are in isotonic hydrogels.

**5. Conclusions**

194 Tissue Regeneration

**Acknowledgements**

**Conflicts of interest**

**Source of funding**

Food and Drug Administration

No competing financial interests exist.

**Disclosure statement**

**Disclaimer statement**

None.

