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RESEARCH ARTICLE

Controlling Droplet Impact Velocity and Droplet

Volume: Key Factors to Achieving High Cell Viability

in Sub-Nanoliter Droplet-based Bioprinting

Wei Long Ng *, Xi Huang , Viktor Shkolnikov , Guo Liang Goh , Ratima Suntornnond ,
3
1
1
2
1
Wai Yee Yeong *
1,3
1 HP-NTU Digital Manufacturing Corporate Lab, 65 Nanyang Avenue, Singapore 637460, Singapore
2 HP Inc., 1501 Page Mill Road, Palo Alto, CA 94304, United States
3 Singapore Centre for 3D Printing (SC3DP), School of Mechanical and Aerospace Engineering, Nanyang Technological
University (NTU), 50 Nanyang Avenue, Singapore 639798, Singapore
Abstract: Three-dimensional (3D) bioprinting systems serve as advanced manufacturing platform for the precise deposition
of cells and biomaterials at pre-defined positions. Among the various bioprinting techniques, the drop-on-demand jetting
approach facilitates deposition of pico/nanoliter droplets of cells and materials for study of cell-cell and cell-matrix interactions.
Despite advances in the bioprinting systems, there is a poor understanding of how the viability of primary human cells within
sub-nanoliter droplets is affected during the printing process. In this work, a thermal inkjet system is utilized to dispense
sub-nanoliter cell-laden droplets, and two key factors – droplet impact velocity and droplet volume – are identified to have
significant effect on the viability and proliferation of printed cells. An increase in the cell concentration results in slower
impact velocity, which leads to higher viability of the printed cells and improves the printing outcome by mitigating droplet
splashing. Furthermore, a minimum droplet volume of 20 nL per spot helps to mitigate evaporation-induced cell damage and
maintain high viability of the printed cells within a printing duration of 2 min. Hence, controlling the droplet impact velocity
and droplet volume in sub-nanoliter bioprinting is critical for viability and proliferation of printed human primary cells.
Keywords: 3D Bioprinting; 3D Printing; Biofabrication; Drop-on-demand printing; Sub-nanoliter cell printing

*Correspondence to: Wei Long Ng, HP-NTU Digital Manufacturing Corporate Lab, 65 Nanyang Avenue, Singapore 637460, Singapore;
ng.wl@ntu.edu.sg; Wai Yee Yeong, Singapore Centre for 3D Printing (SC3DP), School of Mechanical and Aerospace Engineering, Nanyang
Technological University (NTU), 50 Nanyang Avenue, Singapore 639798, Singapore; wyyeong@ntu.edu.sg
Received: July 28, 2021; Accepted: September 16, 2021; Published Online: October 28, 2021

(This article belongs to the Special Section: 3D Printing and Bioprinting for the Future of Healthcare)
Citation: Ng WL, Huang X, Shkolnikov V, et al., 2022, Controlling Droplet Impact Velocity and Droplet Volume: Key Factors to Achieving
High Cell Viability in Sub-Nanoliter Droplet-based Bioprinting. Int J Bioprint, 8(1):424. http:// doi.org/10.18063/ijb.v8i1.424

1. Introduction cells and plays important role in regulating cell-cell and
cell-biomaterial interactions [5-8] , and the 3D bioprinting
The advances in three-dimensional (3D) bioprinting techniques facilitates the fabrication of complex micro-
techniques enable the fabrication of highly-complex 3D
patient-specific tissue-engineered constructs; the highly- architecture that closely resembles the ECM components
automated manufacturing platform facilitates the precise within the 3D bioprinted constructs [9-14] . The 3D
patterning of living cells and biomaterials in a layer-by- bioprinting techniques can be categorized into 3 distinct
layer approach to control the spatial arrangement of these processes: material jetting [15-20] , material extrusion [21-26] ,
functional components within the complex 3D tissue- and vat polymerization [27-29] . Although the extrusion-based
engineered constructs [1-4] . The extracellular matrix (ECM) bioprinting approach is a commonly used technique for
provides a suitable microenvironment for the living fabrication of 3D complex tissue constructs due to its wide

© 2021 Author(s). This is an Open Access article distributed under the terms of the Creative Commons Attribution License, permitting distribution and
reproduction in any medium, provided the original work is properly cited.
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