Page 73 - IJB-1-1

Mohammad Vaezi and Shoufeng Yang

followed by cooling to room temperature, thus miti- evaluate presence of air bubbles within the
gating thermal stress and cracking. biocomposites after moulding. CT scanning of the
• Dynamic Loading: Mould was heated up to 400℃ composites was performed with a 225 kV X-ray
and maintained for 20 minutes. Load was applied for source and Tungsten target and peak voltage was set
5 seconds before heating was stopped, then the mould to 120 kV with no pre-filtration. In order to achieve
was left to cool under pressure, until the temperature sufficient flux, 93 µA current was used (11.16 W).
fell below 143℃, at which the sample was removed. Throughout the 360 degrees rotation, 3142 projections
A series of HA scaffolds with a range of filament were taken, with an average of 8 frames per projection
and pore sizes were 3D printed, and subsequently to improve the signal to noise ratio. Exposure time of
overmoulded using dynamic loading to investigate the each projection was 177 ms with a gain of 30 dB. To
effects of filament/pore size on PEEK infiltration reduce the effect of ring artefacts, shuttling was
depth into the HA scaffold. The effect of dwelling applied with a maximum displacement of 15 pixels.
time at the target temperature on the formation of Projection data was reconstructed using Nikon’s
PEEK HA composites was also explored. Through CTPro and CTAgent reconstruction software, which
experimentation of the effect of load application dur- uses a filtered back projection algorithm. VG Studio
ing load and dwelling time, it was possible to optimize Max 2.1 image processing application was used to
infiltration of molten PEEK through the HA pores standardize the volume (average volume of 220.14
3
without causing degradation of the polymer. Table 1 mm ) analysed from each sample.
shows the details of the samples and the condition of 3. Results
the experiments. Samples were cut using diamond
cutter (Mecatome T210, Presi, France). Infiltration HA scaffolds with a range of filament and pore sizes
depth was measured with the use of the optical micro- were printed using the bespoke developed 3D printer.
scopy (Olympus BH2-UMA, Japan). Scan- Through control of the printing parameters such as
ning electron microscope (SEM) (JEOL JSM-6500F, solvent content, paste deposition speed, and layer
Oxford Instruments, UK) was used for analysis of the thickness, the microstructure of the scaffolds could be
samples. Static loading was also used to produce determined. HA filaments were delivered with high
another set of PEEK/HA composites with a range of precision, with diameters down to 50 µm, achieved
HA scaffold filament and pore sizes as shown in Table with the use of customized nozzle with a small die
2. Computed tomography (CT) (Custom 225 kV land length. The printed scaffolds were highly uniform,
Nikon/Metris HMX ST) with a resolution of 9 µm per with a consistent and repeatable production process.
pixel (or 9 × 9 × 9 µm voxel) was performed to (i) Figures 3(A) and 3(B) depict SEM images of a sin-
determine HA percentage volume in the composite; (ii) tered 3D printed HA scaffold, and a magnified
investigate fractures in the HA network; and (iii) image of a fractured region (the red rectangle),

Table 1. Specifications of the samples overmoulded under different conditions
Designed scaffold Moulding Loading Dwelling time Moulding temper- Heating rate
HA scaffold size
filament/pore size (µm) pressure (MPa) type (min) ature (℃) (℃/min)
10×10×3 mm 250/200 0.39 static 20 400 20
10×10×3 mm 400/400 0.39 dynamic 20 400 20
10×10×3 mm 400/500 0.39 dynamic 4, 12, 16, 20 400 20
10×10×3 mm 400/550 0.39 dynamic 20 400 20
10×10×3 mm 400/670 0.39 dynamic 20 400 20
20×18×3.7 mm 910/1200 0.39 dynamic 20 400 20

Table 2. Details of the PEEK/HA samples prepared for CT analysis; pressure 0.39 MPa, static loading, moulding temperature 400℃,
dwelling time: 20 min, heating rate 20℃/min
Designed scaffold
filament/pore size (µm) 250/200 250/400 400/250 400/400 400/550 400/700
Qt. 2 2 1 1 1 5

International Journal of Bioprinting (2015)–Volume 1, Issue 1 69