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Hui Wang, Sanjairaj Vijayavenkataraman, Yang Wu, et al.

(90% w/v), the effect of solution feed rate is much

less pronounced compared to the low concentration
solutions. To put it in other words, for the same range
of feed rate variation (4−20 μL/min), the variation
range of fibre diameter is larger in low concentration
solutions (50 μm to as large as 200 μm), whereas the
fibre diameter range is considerably lesser in high
concentration solution (100 μm to 140 μm only).
This is attributed to the reason that the viscoelastic
force due to the higher solution concentration is so

Figure 5. Effect of stage speed on fibre diameter. dominant that the effect of increased feed rate be-
comes very less.
or no fibre being attached onto the substrate. On top of
that, the effect of stage speed on fibre diameter was
found to be different at various solution concentrations.
With increase in concentration the fibre diameter is
larger, at the same stage speed . As seen from Figure 5,
at a particular stage speed, the fibre diameter of 70%
w/v solution is much higher than that of 50% w/v so-
lution. On an average, the difference is more than 40%,
which is predominantly due to the increase in the vis-
coelastic force, with increase in the concentration.
The effect was more pronounced at lower speeds and
the differences were narrowed down slowly as the Figure 6. Effect of solution feed rate on fibre diameter.

stage speed increases, which apparently prove the same
fact.
3.3 Effect of Supply Voltage on Fibre Diameter
3.2 Effect of Solution Feed Rate on Fibre Diameter
Supply voltage is a very important parameter in the
The feed rate at which the solution was delivered by E-jetting process, not only for the integrity of the fibre
the syringe pump to the nozzle and onto the substrate structure but also a safety concern. Too high values
plays a significant role in determining the final fibre may result in sparking, eventually leading to greater
diameter. Figure 6 shows the relationship between the safety risks. It is important to know the effect of supply
solution feed rate and fibre diameter. The solution feed voltage on fibre diameter so as to not exceed a certain
rate was varied from 4 to 20 μL/min, while the other value for safety reasons. The relationship between the
parameters were kept constant (D = 2.5 mm, V = 3 kV supply voltage and the fibre diameter is shown in Fig-
and S = 150 mm/s). The study was conducted in three ure 7. Voltage is varied from 2 kV to 3.5 kV, in small
different solution concentrations (60%, 70% and 90%) steps, with all other parameters constant (D = 2.5 mm,
(w/v). The fibre diameter increased with increase in Fd = 10μL/min, S = 150 mm/s) and at three different
solution feed rate, as expected. At the same stage solution concentrations (60% w/v, 70% w/v and 80%
speed and voltage, when the feed rate is increased, w/v). Voltage values below 2 kV resulted in disconti-
the amount of solution that is e-jetted out of the noz- nuous jet formations because of the inability of the
zle per unit of time will also increase, thereby re- electric field force to overcome the surface tension and
sulting in deposition of an increased volume of solu- viscoelastic force of the solution. The relationship is
tion on the substrate and hence, the fibre diameter not well established and the trend is not regular. How-
also increases. Also, at the same feed rate, solutions ever, two regions could be identified. In the first region,
with higher concentration resulted in greater fibre at lower voltages, a small change in voltage resulted in
diameter than the solution with lower concentration, a major change in the fibre diameter, For instance, at a
which is due to the dominant viscoelastic force as solution concentration of 60% w/v, when the voltage is
discussed in the previous section. One important ob- increased from 2 to 2.4 kV, the diameter increased
servation to make is that at very high concentration from 20 to 100 μm and at solution concentration of 70%
International Journal of Bioprinting (2016)–Volume 2, Issue 1 67