Page 549 - IJB-10-3

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

hydroxyl group and intermolecular/intramolecular the aldehyde and hydroxyl groups of PVA do not always
hydrogen bonding; 2940 and 2908 cm attributed to the consume both sides of the aldehyde. Thus, the free sides
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stretching vibration of C–H from alkyl groups (methyl and of the aldehyde are available for new bonding of one of
methylene); 1750 cm assigned to the stretching vibration the amino groups from lysine. This approach is further
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in the acetate group; 1420 and 1385 cm attributed to the supported by the reaction conditions, specifically the basic
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bending vibration of C–H from alkyl groups; 1230 cm pH, which restricts esterification between the hydroxyl
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specific to the structural backbone; and 1090 cm assigned group from PVA and the carboxyl group from lysine (an
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to C–O–C and C–O stretching vibrations (crystallinity). alternative pathway).
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GA spectrum analysis suggests chemical interactions that
occur during crosslinking: peak at 3381 cm attributed to 3.3. X-ray diffraction analysis
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the intermolecular hydrogen bonding due to water presence XRD was conducted to reveal the direct relationship
(GA in aqueous solution); peaks at 2978, 2970, and 2760 between the thermal treatment and crystallinity degree of
cm attributed to the stretching vibration of C–H from PVA filament and 3D-printed channels. The correlation
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alkyl groups; peak at 1720 cm assigned to the stretching between thermal treatment and PVA crystallinity
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vibration in carbonyl group; and the peak at 1640 cm influenced the corresponding crosslinking behavior.
assigned to the hydrogen bonding of GA interaction with Figure 5 (left side) displays the crystallinity of the PVA
water molecules. Considering GA in aqueous solution, the filament following thermal treatment. The filament without
hydrogen bonding contribution is high enough to appear thermal treatment (Filament 0D) presented an important
in the hydroxyl region (3381 cm ) and carbonyl region; peak at 2θ 19.6° specific for the monoclinic crystal with an
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however, the stretching vibration of C=C bond due to aldol orthorhombic lattice (1 0 1 plane). In the case of PVA with
condensation between two GA molecules is not excluded; a high crystallinity degree, the crystal was strong enough
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peaks in the region 1465–1380 cm are attributed to the to exhibit two peaks for 1 0 1 and 2 0 0 planes. According
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bending vibration of C–H from alkyl groups. The C–C to the literature, the second peak may appear before or
bond and structural peaks in the region 1111–900 cm after the main peak. The two peaks can merge into one
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58–60
are also present. The spectra of the crosslinked channels if the crystal is not sufficiently strong, as in this case.
were directly related to the previously presented peaks. The This main peak appears because of the intermolecular
main peaks that reveal chemical crosslinking are further interactions between PVA chain segments in the main
described. The structural peak at 970 cm from GA is direction of the intermolecular hydrogen bonding. The
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present in all crosslinked samples (shifted toward lower peak intensity is correlated with the number of PVA
values); a new peak in the region 1143–1111 cm (specific chains packed together. The increased intensity indicates a
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for each crosslinked sample) may be attributed to acetal larger crystallite size. A secondary broad peak appeared
and semi-acetal bridges due to crosslinking; a peak at at 2θ 46° due to the semi-crystalline arrangement of PVA
chains. Filaments treated for 1 day (Filament 1D) and 3
1465 cm is present in all crosslinked samples; the peak at days (Filament 3D) revealed a new peak at 2θ 12.6°, which
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3375 cm has a decreased intensity due to hydroxyl group corresponded to a strong PVA crystal. This result suggests
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consumption (specific for each crosslinked sample); a peak a direct correlation between crystallinity and thermal
at 2970 cm is present in almost all crosslinked samples treatment. Furthermore, the Debye–Scherrer equation was
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(shifted toward higher values). Sample 3D-3H displayed used to better observe the influence of thermal treatment
only a shoulder of this peak without any shifting. Samples on crystallinity by estimating the crystallite size. Table 2
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0D-3H and 0D-24H revealed a peak decrease at 3375 displays the estimated crystallite size, the relative number
cm while samples 3D-3H and 3D-24H revealed a lower of layers in the crystallite, and the full width at half
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decrease. This result suggests that the hydroxyl group was maximum (FWHM). The results reported an increase in
consumed in a higher percentage of the samples without crystallite size with thermal treatment time in the case of
any thermal treatment.
the filament. The relative number of the crystalline layers
The biofunctionalization of PVA grafts with lysine was increased for the peak 2θ 46°, suggesting that less-ordered
examined using FTIR-ATR. The results are depicted in domains started to arrange due to hydrogen bonding.
Figure 4B. The FTIR spectrum of the lysine-functionalized FWHM values revealed that the peaks tended to be
PVA graft revealed a new peak at 1640 cm , which can be sharper because of the more ordered crystalline state. For
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attributed to the stretching vibration in C=N bonds. This 3D-printed PVA channels (Figure 5, right side; Table 1),
type of bonding is possible by the reaction of the carbonyl the investigation demonstrated the same correlation as in
group of aldehydes with an amino group from lysine. the case of the PVA filament. Thermal treatment favored
Therefore, lysine was linked to PVA through GA. This chain-ordering behavior, resulting in higher crystallinity.
reaction is possible because the acetal bridges provided by PVA behavior is similar to that of other polymers that

Volume 10 Issue 3 (2024) 541 doi: 10.36922/ijb.2193