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Influence of electrohydrodynamic jetting parameters on the morphology of PCL scaffolds

compared. Stage performance was obtained from the and the fibre diameter increases with the solution feed
feedback images. To select the best stage performance, rate. Higher solution feed rate results in increased
the length of the stable region was compared, and the pressure from the pump acting on the Taylor cone,
longest one was chosen as the best. When the stage which leads to an increase in the volume of the solu-
reached a r elatively stable region, there still existed tion that comes out of the nozzle. Therefore, higher
some fluctuation, and any error below ±5% was de- solution feed rate always causes larger fibre diameter.
fined as sustainable error. Based on these criteria, a set In this experiment, solution concentration did not
of acceleration values with corresponding stable re- have significant influence on the fibre diameter. Both
gion length were found and listed in Table 1. In this 60% PCL and 70% PCL exhibited similar trends.
study, all of the experimental results were based on the However, there are other factors that were influ-
scaffold fabricated in the effective fabrication area. enced by varying solution concentration, such as elec-
trical conductivity, surface tension, viscosity, and sol-
Table 1. Stage motion characterization results vent evaporation rate. All of these factors determine
6tage speed $cceleration 6table reJion 'eceleration the amount of solution being stretched out from the
(mm/s) region (mm) (mm) region (mm) nozzle tip under high voltage, thus affecting fibre
50 1.7 36.3 1.9 formation. During the process initiation, the surface
100 3.6 32.8 3.6 tension of the solution should be overcome, and then
150 3.6 32.4 4.0 the EHD jets will be stretched. Less acetic acid means
200 4.3 31.2 4.5 fewer frees ions, and a decrease in electrical conduc-
250 6.1 27.6 6.3 tivity. Thus less solution volume was pulled out of the
300 9.1 21.2 9.7 nozzle under higher concentration. These multiple
factors work together to determine the fibre diameter,
and some of them are significantly affected by solu-
3. Results and Discussion tion concentration and feed rate.
3.1 Grid Scaffold Structure and Process Parameters (2) Effects of Stage Speed on Fibre Diameter
Stage speed has significant influence on the posi-
Effects of two process parameters on fibre diameter tioning of EHD jetted fibres. When this speed is much
were investigated: solution feed rate and motorized lower than the speed of jetting, linear, aligned micro-
stage speed. In addition, the nozzle-to-substrate dis- structures were achieved even when the motion stage
tance plays an important role in positioning and tuning movement was linear. Air turbulence or buckling of
the degree of solidification. If this distance was below solid fibres disturbs the linear deposition of fibres.
2.5 mm, the deposited fibres we always straight even When the two speeds are closer, the deposited fibres
at very slow stage speed values. If the nozzle-substrate were linear and aligned straight due to the mechanical
distance was between 2 mm and 5 mm, straight fibres drawing force. When the stage speed exceeds the jet-
can only be obtained when the stage speed was larger ting speed, fibre diameter can be tuned by varying the
than that of the jetting speed. stage speed.
(1)Effects of Solution Feed Rate on Fibre Diameter Table 2 shows the relationship between stage speed
Relationship between solution feed rate and fibre and fibre diameter. The range of the stage speed used
diameter has been investigated. Solution feed rate was were 100 mm/s to 300 mm/s at increments of 50 mm/s;
varied from 1.0 μL/min to 2.0 μL/min at increments of the supply voltage was 3.0 kV, nozzle-substrate dis-
0.5 μL/min. The other parameters were kept constant: tance was 3.0 mm, and the solution feed rate was
voltage of 3.0 kV, nozzle-to-substrate distance of 1.5 μL/min. Two different PCL concentrations, 60%
3 mm, stage speed of 200 mm/s, and temperature of and 70%, were used for this experiment.
20°C. Two concentrations of PCL solution were used: As shown in Figure 4, fibre diameter decreases
60% and 70%. For 60% PCL, the measured fibre di- with increased stage speed. Faster stage speed can
ameter varied from 18.9 μm to 36.0 μm. For the 70% effectively reduce the volume of dispensed solution on
PCL, the measured fibre diameter varied from 18.7 μm the substrate, and hence, by increasing the stage speed,
to 37.6 μm. In Figure 3, the variation of the solution thinner fibres can be fabricated. For 70% PCL solution,
feed rate vs the fiber diameter is shown. Solution feed when the stage speed was 100 mm/s, the average fibre
rate at 2.0 μL/min always could generate thicker fibres, diameter was around 32.8 μm, and when the stage
76 International Journal of Bioprinting (2017)–Volume 3, Issue 1