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Hang Liu, Sanjairaj Vijayavenkataraman, Dandan Wang, et al.

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Table 2. Optical microscope images of scaffold pattern under varied stage speed (FR=1.5 μL/min, D=3 mm, V=3 kV, and T=20 C).
Scale bar 400 µm
Stage speed (mm/s)

100 150 200 250 300

Scaffold pattern
60% PCL

Fiber diameter (μm) 37.8 30.7 29.5 25.0 23.2

Scaffold pattern
70% PCL

Fiber diameter (μm) 32.8 30.0 23.7 20.7 19.3

3.2 Coiled Structure and Influencing Factors
Coiled structure has more surface area than the normal
mesh structure and hence provides more area for the
cells to attach and grow. It is also expected to pro-
vide better pore interconnectivity and hence increased
cell-cell interaction. Coiled structure scaffold is based
on the control of the unstable bulking/whipping beha-
viour observed during EHD-jetting process, in which
the unstable jet fiber can be positioned on the sub-

strate by the combined control of process parameters.
Figure 3. Relationship between feed rate and fibre diameter This section discusses the effects of PCL properties,
(V=3 kV, D=3 mm, SS=200 mm/s, and T=20°C). stage speed, solution feed rate, and solution concen-
tration on the formation of a coiled structure.
(1) Effects of PCL chemical property on EHD-jet-
ting Process
In EHD-jetting process, the pendent drop of poly-
mer solution under electric field is influenced by many
forces: columbic, electric, viscoelastic, surface tension,
air drag and gravitational force. Among them, electric,
viscoelastic and surface tension are the three main
forces working on the EHD jetting process, and the
last two forces are closely relevant to the viscosity of
solution.

PCL shows high solubility in many polar solvents,
Figure 4. Relationship between feed rate and fibre diameter such as tetrahydrofuran and acetic acid [26] . As a hy-
(FR=1.5 μL/min, D=3 mm, V=3 kV and T=20°C). drophobic, semi-crystalline polymer, the crystallinity
of PCL tends to decrease with increasing molecular
speed was increased to 300 mm/s, the average fibre weight (MW). The good solubility of PCL, its low
diameter decreased to 19.3 μm. melting point (59–64 °C) and exceptional blend-com-

International Journal of Bioprinting (2017)–Volume 3, Issue 1 77