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Gao and Zhou

A B C

D E F

G H I

Figure 7. (A) Multilayered ordered complex structure of polyurethane. (B) Close-up view of (c) (adapted from Ahmad et al.[1]). (C) Spiral-in
circle two-dimensional (2D) pattern fabricated by electrohydrodynamic (EHD) jet printing of melted polycaprolactone (PCL). (D) 3D scaffold
structures fabricated by EHD jet plotting of melted PCL. (E) Scanning electron microscope (SEM) images of the hierarchical 3D scaffold
structures (adapted from Wei and Dong [44] ) and (G) Surface topography of PCL structure built by EHD printing method (adapted from Cai et
al. [46] ). (H) 3D scaffold fabricated by a normal EHD-printing without cushioning bath in SEM micrographs. (I) The highly roughened surface
morphology of the EHD-plotted 2D scaffold on the PEO solution bath (adapted from Ahn et al. [47] ).

jets. In addition, a nozzle-ring electrode is proposed to 4(5): 174-183.
improve the performance of EHD printing in 3D printing 3. Park S E, Kim S, Lee D, et al., 2013, Fabrication of silver
applications. nanowire transparent electrodes using electrohydrodynamic

Acknowledgments spray deposition for flexible organic solar cells. J Mater Chem
A, 1(45): 14286–14293. https://doi.org/10.1039/c3ta13204h.
This work was partially supported by the [NSF] under 4. Yogi O, Kawakami T, Yamauchi M, et al., 2001, On–demand
Grant [number 1437798]; and [NSF] under Grant droplet spotter for preparing pico-to femtoliter droplets on
[Number 1538318]. The authors would like to thank surfaces. Anal Chem, 73: 1896–1902. https://doi.org/10.1021/
Dr. Richard Forbes who provided important suggestions ac0012039.
on revision, and we appreciated his support and help.
5. Chen C H, Saville D A, Aksay I A, 2006, Scaling laws for pulsed
References electrohydrodynamic drop formation. Appl Phys Lett, 89(12):
1241031–1241033. https://doi.org/10.1063/1.2356891.
1. Ramos A, Chen C H, 2011, Electrohydrodynamic stability. In: 6. Poon H F, 2002, Electrohydrodynamic Printing. PhD Thesis.
Electrokinetics and Electrohydrodynamics in Microsystems. 7. Khan A, Rahman K, Kim D, et al., 2012, Direct printing
Springer, Verlag Wien, 177-220. http://doi.org/10.1039/ of copper conductive micro–tracks by multi–nozzle
b906909g. electrohydrodynamic inkjet printing process. J Mater
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