Page 552 - IJB-10-3

International Journal of Bioprinting Engineered 3D-printed PVA vascular grafts

Figure 7. Swelling measurements. Abbreviations: D: duration of thermal treatment (in days); h: duration of crosslinking (in hours).

treatment lasting 1 or 3 days, the removal of water 3.5. Swelling degree
molecules occurred, thereby doubling the favorability Swelling analysis is an important aspect of assessing the
of the crystallization process. Both the mobility of chain crosslinking process of the PVA channels. Crosslinked
segments and the removal of water molecules influence channels obtained under various conditions (0D-3h/0D-
this crystallization process. 24h, 1D-3h/1D-24h, and 3D-3h/3D-24h) were used
The initial cooling run exhibited a broad exothermic for the swelling investigation. Small pieces were cut and
peak characteristic of melt cooling within the range of immersed in PBS at pH 7.4 and 37℃. Figure 7 displays
105–108°C, indicating the occurrence of crystallization. the swelling behavior of various PVA grafts. The swelling
The second heating run was influenced by the first cooling equilibrium was reached after 300 min for all samples.
event. The hysteresis peak disappeared, and the T values Samples subjected to thermal treatment (1 and 3 days) and
g
were approximately 60℃ for all samples. The second with 3 h of crosslinking had the highest swelling values,
cooling run revealed melt crystallization only for the probably because of the decrease in network density
sample Filament 3D, as there were remaining chains where (Figure 7, 1D-3h/3D-3h). The increase in crosslinking time
ordering was favored. to 24 h drastically reduced the swelling values, owing to the
increase in network density (Figure 7, 1D-24h/3D-24h).
The thermal treatment temperature is of utmost
importance because a temperature similar to or above T For samples without any thermal treatment, the swelling
g
promotes chain segment mobility. This rationale guided the degree was low for both 3 and 24 h of crosslinking because
decision to optimize the thermal treatment at 50°C. During of the high network density. However, there was a small
3D printing, PVA crystallites melted, and the highly ordered difference between 3 and 24 h of crosslinking (Figure 7,
domains gained during the initial thermal treatment were 0D-3h/0D-24h). Thermal treatment positively influenced
lost. This indicates that the thermal treatment of the PVA the crystallinity degree. Higher PVA crystallinity resulted
filament would not have any additional influence on the in decreased swelling and dissolution capacity during
3D-printed channels. Consequently, the crystallinity of the crosslinking process. Specifically, higher crystallinity
the 3D-printed channels can only be controlled through negatively affected the crosslinking process, leading to a
thermal treatment. This explains the absence of crosslinked lower network density. It was noted that samples 1D-3h
channels from a heat-treated filament. The DSC results and 3D-3h exhibited lower network densities. However,
are consistent with the XRD data, indicating that thermal extending the crosslinking time to 24 h allowed sufficient
treatment favors chain crystallization. time for the PVA channels to swell with GA, thereby

Volume 10 Issue 3 (2024) 544 doi: 10.36922/ijb.2193