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The Influence of Printing Parameters and Cell Density on Bioink Printing Outcomes.

  • Gillispie, Gregory J1
  • Han, Albert1, 2, 3
  • Uzun-Per, Meryem4
  • Fisher, John5
  • Mikos, Antonios G2, 3
  • Niazi, Muhammad Khalid Khan4
  • Yoo, James J1
  • Lee, Sang Jin1
  • Atala, Anthony1
  • 1 Wake Forest Institute for Regenerative Medicine, Wake Forest School of Medicine, Winston-Salem, North Carolina, USA.
  • 2 Department of Bioengineering, Rice University, Houston, Texas, USA.
  • 3 Department of Chemical and Biomolecular Engineering, Rice University, Houston, Texas, USA.
  • 4 Center for Biomedical Informatics, Wake Forest School of Medicine, Winston-Salem, North Carolina, USA.
  • 5 Fischell Department of Bioengineering, University of Maryland, College Park, Maryland, USA.
Published Article
Tissue Engineering Part A
Mary Ann Liebert
Publication Date
Oct 14, 2020
DOI: 10.1089/ten.TEA.2020.0210
PMID: 32928068


Bioink printability persists as a limiting factor toward many bioprinting applications. Printing parameter selection is largely user-dependent, and the effect of cell density on printability has not been thoroughly investigated. Recently, methods have been developed to give greater insight into printing outcomes. This study aims to further advance those methods and apply them to study the effect of printing parameters (feedrate and flowrate) and cell density on printability. Two printed structures, a crosshatch and five-layer tube, were established as printing standards and utilized to determine the printing outcomes. Acellular bioinks were printed using a testing matrix of feedrates of 37.5, 75, 150, 300, and 600 mm/min and flowrates of 21, 42, 84, 168, and 336 mm3/min. Structures were also printed with cell densities of 5, 10, 20, and 40 × 106 cell/mL at 150 mm/min and 84 mm3/min. Only speed ratios (defined as flowrate divided by feedrate) from 0.07 to 2.24 mm2 were suitable for analysis. Increasing speed ratio dramatically increased the height, width, and wall thickness of tubular structures, but did not influence radial accuracy. For crosshatch structures, the area of pores and the frequency of broken filaments were decreased without impacting pore shape (Pr). Within speed ratios, feedrate and flowrate had negligible, inconsistent effects. Cell density did not affect any printing outcomes despite slight rheological changes. Printing outcomes were dominated by the speed ratio, with feedrate, flowrate, and cell density having little impact on printing outcomes when controlling for speed ratio within the ranges tested. The relevance of these results to other bioinks and printing conditions requires continued investigation by the bioprinting community, as well as highlight speed ratio as a key variable to report and suggest that rheology is a more sensitive measure than printing outcomes. Impact statement Cell-based 3D bioprinting strategies have a great promise to bioengineer clinically relevant tissue constructs. A better understanding of the underlying mechanisms that affect the printability of cell-laden hydrogel bioinks is mandatory. This study investigated the effects of printing parameters and cell density on the printing outcomes, which could provide a significant impact on further bioink development and bioprinting applications.

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