Page 285 - IJB-10-1

International Journal of Bioprinting Scaffolds manufacturing by fused deposition modeling

was manually premixed in zippered bags at nHA contents Table 2. Printing parameters for the tensile test specimens and
of 0.0, 2.5, 5.0, and 10.0 wt%. The premixture consisted the scaffolds
of 800 g of material, which were passed through a twin- Printing process parameter Tensile test specimens Scaffolds
screw extruder (Dupra S.L., Castalla, Spain) with an
average residence time of 2 min. The extruder is equipped Printing temperature (°C) 170 170
with four individual heating zones and two screws with a Bed temperature (°C) 65 65
diameter of 25 mm and a length-to-diameter (L/D) ratio Printing speed (mm/s) 30 30
of 24. All extrusions were performed with a screw speed Layer height (mm) 0.2 0.2
ranging from 20 to 25 rpm with a temperature profile of Infill (%) 100 70
140/145/150/155°C. This extruder was employed in order Raster angle (°) 0; 0/90 and 45/−45 0/90
to obtain a proper filler dispersion in the polymer matrix, Printing orientation Flat Flat
as the second extruder employed is a single-screw extruder
designed for filament fabrication only.
designed using FreeCAD software. To achieve the desired
The extruded materials were pelletized in an air- porosity, the gcode was set with a linear infill patter with the
knife unit and stored in hermetic plastic bags to prevent lines oriented at 0°/90° (with no walls and no top/bottom
moisture uptake. The resulting samples were labeled as layers) and a 70% infill density. The infill density was chosen
P(3HB-co-3HHx)/HA content. For instance, the sample in order to get connected pores but with a low porosity values
containing 5.0 wt% of nHA was codified as P(3HB-co- so that the mechanical properties were not greatly reduced. 52
3HHx)/5HA, while the neat matrix (0.0 wt% nHA) was
named as P(3HB-co-3HHx). On the one hand, tensile tests were used to characterize
the mechanical properties of the proposed formulations
2.3. Filament extrusion and 3D printing parameters obtained by means of additive manufacturing. For this
Once the nanocomposites were prepared and pelletized, a reason, an infill density of 100% was employed. Only the
single-screw extruder equipped with four heating zones, infill pattern was changed since it is the most relevant
Next 1.0 model from 3devo (Utrecht, The Netherlands), parameter in terms of mechanical properties in additive
was used to obtain the 3D printing filaments with the manufacturing. Other printing parameters like the layer
53
proper dimensions. The temperature profile from the inlet height were set to improve the final properties according
hopper to the nozzle was 150/155/160/150°C, with an to the information obtained in literature. On the other
54
extrusion speed of 5 rpm. The extruder uses a feedback hand, scaffolds were used to assess their degradation in
cascade controller to adjust the rotational speed of the a phosphate-buffered solution by means of immersion.
spool to target the desired filament diameter. The diameter Compression tests were also carried out with the scaffolds
was set at 2.85 mm, obtaining average diameters of 2.85 ± at a different immersion time.
0.03, 2.85 ± 0.05, 2.85 ± 0.04, and 2.84 ± 0.10 mm, for the
nanocomposites containing 0.0, 2.5, 5.0, and 10.0 wt% 2.4. Physical and mechanical characterization of
of nHA, respectively. Changes in the diameters and nanocomposites
deviation obtained for each material led to the differences For the tensile test, 3D-printed standardized tensile
in rheological behavior with the addition of the nHA. But test samples were employed following the ISO 527.
in any cases, the filaments obtained could be perfectly For the scaffold characterization, a compression test
employed for the manufacturing process. was performed following the ISO 604. To this effect, a
universal testing machine (under tensile or compression
3D printing was carried out using an Ultimaker 3 mode) ELIB 30 from S.A.E. Ibertest (Madrid, Spain) was
(Utrecht, The Netherlands) equipped with a 0.8-mm employed. In both cases, the machine was equipped with
nozzle. For the present work, two geometries were a 5-kN load cell and a crosshead speed of 5 mm/min was
considered: tensile test specimens (Figure 1a), according to selected according to the testing speeds proposed in the
ISO 527, and scaffolds of 12 × 12 × 25 mm (Figure 1b). The standard. Regarding the tensile test, three specimens of
3
printing parameters are given in Table 2. Figure 1 shows each material were tested for the raster angle proposed.
the geometry and raster angle of the printed materials, In contrast, three scaffolds were tested each week for the
both for tensile test specimens (Figure 1a) and scaffolds material considered; therefore, 15 scaffolds were printed
(Figure 1b).
for each material. For the result analysis, on the one hand,
Three replicates were printed for each raster angle the data recorded during tensile test were the maximum
condition in the case of tensile test specimens, while 15 tensile strength measured during the test (tensile strength),
scaffolds were printed. For the scaffold manufacture, a cube the maximum elongation of the sample achieved during
with the mentioned external dimensions of the device was the test (elongation at break), and the tensile modulus

Volume 10 Issue 1 (2024) 277 https://doi.org/10.36922/ijb.0156