Page 287 - IJB-10-1

International Journal of Bioprinting Scaffolds manufacturing by fused deposition modeling

from Testing Machines Inc. (Delaware, USA) with a raster angles are compared to those produced by injection
resolution of 0.01 g/cm . molding in a previous work. In any case, regardless of
58
3 56
the manufacturing method, composites with the largest

Totalporosity 1 scafold (II) proportion of nHA (10%) consistently showed the lowest
material average values for the ultimate tensile strength and
Scaffolds were manually dried with paper for a short period elongation at break. Nonetheless, nHA also increased the
of time (less than 2 min) to remove the PBS from the surface stiffness of P(3HB-co-3HHx), as the tensile modulus of the
and weighed (W ) to obtain the amount of absorbed PBS composites with 10% of nHA was significantly higher than
w
(W ), according to Equation III. After this, samples were the rest of combinations for all the production processes. It
g
oven-dried (60°C for 48 h) to remove moisture and then can be inferred that the reinforcement effect produced by
weighed (W ), allowing the determination of weight loss the nanoparticles limits the mobility of the polymer chains
d
(W), according to Equation IV. In each extraction, the pH during tensile tests. 59
l
of PBS was measured. In the comparison of samples with the same proportion
W W of nHA, differences arise due to the high dependence of the
W% w 0 100 (III) additive manufacturing parameters employed in terms of
g
W
0 raster angle. Those with the raster aligned with the tensile
W W effort direction (0°) resulted in the best outputs in tensile
W% d W 0 100 (IV) strength and stiffness (tensile modulus), since a favorable
l
0
Surface morphology of the scaffolds (prior and after monoaxial orientation of P(3HB-co-3HHx) improves the
60
immersion in PBS) was assessed by means of field emission mechanical behavior. In agreement with this result, other
scanning electron microscopy (FE-SEM) in a Zeiss authors have reported that additive manufactured samples
Ultra 55 FESEM microscope from Oxford Instruments of PLA obtained the best tensile strength values for raster
61
(Abingdon, UK), operating at an accelerating voltage of angles between 0° and 20°. Under these conditions, stress
2 kV. Samples were coated with gold-palladium alloy in is transferred along the deposited lines. Bigger raster angles
an EMITECH model. SC7620 sputter coater was obtained imply transmission of mechanical stress at the interfaces
from Quorun Technologies Ltd. (East Sussex, UK). This of adjacent deposited lines, so the strength is limited by
62
test was conducted to measure the mineralization ability their adhesion. Nonetheless, for the elongation at break,
of the different composites manufactured following the the 45°/–45° disposition provided the best results. In this
procedure proposed by Monshi et al. 57 case, the lines deposited have certain ability to rotate,
allowing for a slightly greater deformation before rupture
Finally, the chemical analysis of the scaffold surface as described by Santo et al. All these effects show the
63
was analyzed by attenuated total reflectance-Fourier typical anisotropic behavior of an additive manufactured
transform infrared spectroscopy (ATR-FTIR). Bruker sample. 64
S.A. Vector 22 (Madrid, Spain) coupled with an ATR
measuring accessory from Pike Technologies (Madision, In injection molding, the packing pressure applied
WI, USA) was employed. Wavelengths between 4000 cm avoids pore generation, so the best mechanical properties
−1
65
−1
and 600 cm with a resolution of 4 cm were used for the are obtained. As an exception to this trend that appeared
−1
scan, and each spectrum was collected from an average of in this work, samples with a raster angle of 0° improved
10 measurements. the tensile strength attained by injection molding for all
of P(3HB-co-3HHx)/(HA) composites, regardless of
2.6. Statistical analysis the composition. Porosity formation is a well-known
Differences among the samples were evaluated at 95% limitation of 3D printing by the way that the polymer
66
confidence level (p ≤ 0.05) by analysis of variance lines are deposited next to each other. Pore formation
(ANOVA) following Tukey’s test. Open-source R software limits, in most cases, the mechanical behavior of the
(https://www.r-project.org) was employed for the analysis. 3D-printed samples. Lay et al. reported different polymers
like PLA, ABS, or nylon; the injection molding samples
3. Results achieved higher values in terms of tensile strength, tensile
modulus and elongation at break than the ones obtained
3.1. Mechanical properties of the P(3HB-co-3HHx)/ by additive manufacturing. The differences were linked
67
HA nanocomposites to the presence of voids in the 3D-printed samples. The
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The performance of the 3D-printed samples in tensile tests polymeric matrix employed herein is highly sensitive to the
is displayed in Figures 2, and Figure 3 shows the tensile test shear rates applied. In the injection molding process, it is
curves obtained. Tensile specimens printed with different necessary to completely fill the mold cavity before polymer

Volume 10 Issue 1 (2024) 279 https://doi.org/10.36922/ijb.0156