Page 500 - IJB-10-2

International Journal of Bioprinting Mineralization of 3D-printed PHA scaffolds

3. Results and discussion PHA scaffold was 81.025° ± 2.25, whereas the contact
angle for the PHA–pDA and PHA–pDA–HA scaffolds was
3.1. Surface characterization of PHA biopolymer 0° within 1 min. Water droplets rapidly penetrated the
scaffold with pDA and HA surface when pDA was present. Thus, the hydrophilicity
PHA has been identified as a promising material for use of the surface increased sharply with the pDA coating.
in biopolymer scaffolds due to its biocompatibility and Surface wettability has a significant influence on the
biodegradability. PHA is also a promising biopolyester for interactions between the scaffold surface and the cells.
extrusion-based printing due to its comparatively low glass A hydrophilic surface provides for better adsorption of
transition temperature. 12 proteins (e.g., fibronectin) and growth factors compared
When using 3D bioprinting to fabricate scaffolds, it is with a hydrophobic surface. 17,18
essential to meet the required conditions such as structure, A compression test was conducted to measure the
mechanical properties, and osteoconductivity to fulfill the mechanical properties of PHA and functionalized PHA
role of a bone scaffold. In particular, it is crucial for the scaffolds (Figure 3b). Pressure was applied up to a stain
scaffold to possess a structure that precisely matches the of 0.6 mm/mm, and stress–strain graphs for all groups
bone defect, enabling the reconstruction of the original exhibited a similar trend.
bone shape and effectively responding to dynamic forces.
Precise printability with excellent spatial capabilities is Furthermore, the results also indicated that there was
required to ensure that the printed structures accurately not a significant difference in Young’s modulus (Figure
replicate virtual models. The printing state of the PHA was 3c). It was confirmed that the physical properties were not
verified by adjusting the pressure and printing speed, which greatly altered by the reactions of pDA and HA.
are the speeds of the print head. To identify conditions with 3.2. Physicochemical characterization of the PHA
strand sizes similar to the size of the nozzle, the strand sizes scaffold with pDA and HA
at pneumatic pressures of 60, 80, and 100 kPa, and printing The formation of pDA and HA on the PHA scaffold was
speed of 400, 500, and 600 mm/min were compared (Figure verified through examination of the physicochemical
2a). The dots in Figure 2a represent the strand sizes obtained characteristics (Figure 4). Before the growth of HA,
when printing PHA under various pressure and printing ATR-IR spectroscopy was conducted to confirm pDA
speed conditions. Additionally, the red-shaded region formation (Figure 4a). The broad absorption band at 3360
denotes an error margin of approximately 10%, determined cm corresponds to the stretching vibrations of catechol–
-1
based on a nozzle size of 400 μm. This region was considered OH in pDA. The peak at 1615 cm is associated with the
-1
indicative of suitable printability. A higher pressure and stretching vibration of the C=O bond, and the peak at 1500
a slower printing speed resulted in an increasing trend in cm indicates aromatic C=C stretching and N-H bending.
-1
strand size. As the printing speed increased and the pressure The presence of a pDA coating was confirmed on the
decreased, the strand tended to become thinner in size. At PHA–pDA and PHA–pDA–HA scaffolds. 19–21
the condition of 80 kPa and 500 mm/min, a strand size of
405.47 ± 3.98 μm was observed, which closely matched the After confirming pDA formation on the PHA scaffold,
nozzle size of 400 μm (Figure S2 in Supplementary File). HA formation was subsequently verified using XPS analysis
Therefore, all the scaffolds for subsequent experiments were (Figure 4b). The presence of an N1s peak was confirmed in
fabricated under these conditions. both the PHA–pDA and PHA–pDA–HA groups, but not in
22
the PHA group. Furthermore, the Ca2p peak was observed
The surface morphology of the printed PHA scaffold, only for the PHA–pDA–HA group (Figure 4c). These results
pDA-coated PHA scaffold, and pDA-HA-coated PHA indicate the formation of biominerals and pDA on the PHA
scaffold were evaluated. The results showed that the surface. It is widely recognized that pDA contains numerous
printed PHA scaffold had a smooth surface (Figure 2b). catecholamine groups that play a significant role in biomineral
The pDA-coated PHA scaffold surface was covered by formation. The catecholamine groups not involved in
agglomerates after 24 h. HA, in the form of a large plate, substrate adhesion are capable of binding with Ca ions.
2+
14
covered the surface of the biomineralized scaffold through The formation of HA was confirmed by XRD with
SBF treatment for 72 h. It is well known that pDA coating reference to the JCPDS 9-432 standard. 23,24 Peaks
facilitates rapid CaP nucleation due to the availability of corresponding to HA were detected only in the PHA–
free catechols not involved in substrate adhesion, which is pDA–HA group (Figure 4d). The peak of HA appeared to
important for CaP nucleation. 14–16
be relatively broad, indicating that the formed HA has low
These surface treatments led to differences in crystallinity and an irregular orientation, as confirmed in
wettability (Figure 3a). The water contact angle of the SEM images.
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Volume 10 Issue 2 (2024) 492 doi: 10.36922/ijb.1806