Page 82 - IJB-9-5

International Journal of Bioprinting Biocompatible BSA-GMA and TPP of 3D hydrogels with free radical type I photoinitiator

is higher than the rate of oxygen diffusion into the exposed and microstructure by TPP, which also demonstrates the
volume, independent of the exposure time and the laser two-bond opening of vinyl on GMA during two-photon
writing speed at the lower laser writing speed . Thus, crosslinking. The =CH bending vibration, C=C stretching
[58]
2
only the data at high scanning speeds were chosen for the vibration, and C=O stretching vibration of GMA in Raman
fitting. For the higher scanning speeds (V ≥ 50 μm s ), spectroscopy were reported as 1425, 1644, and 1732 cm ,
-1
-1
s
respectively [60,61] . Before the polymerization, BSA-GMA
P ∝ C × V S 1/N (III) has Raman peaks of 1410 cm as an in-plane deformation
-1
th
-1
where N is the non-linear exponent of the photoinitiator vibration of =CH on GMA, 1643 cm as a C=C double bond
2
and C is a constant related to the fabrication performance stretching with the C=O peak of amide I of BSA forming
-1
of the photoresist. We investigated the relationship between a double peak, and 1720 cm as a C=O vibration peak on
the laser threshold power and the scanning speed using the GMA chain. After TPP, most of the Raman peaks were
the R D photoresist as an example. The N value obtained still preserved. However, the Raman intensity of some
35
40
from Figure 2C is 2.3, which is close to the two-photon peaks decreased or disappeared. The Raman intensity at
-1
absorption coefficient. The TPP mechanisms of BSA and 1409 cm (the deformation of =CH in the face) decreased
2
-1
BSA-GMA were studied by FT-IR micro-spectroscopy and after TPP, and the disappearance of the peak at 1643 cm
Raman, respectively. Figure 2D shows the FT-IR spectra changed from a double peak to a single peak. These results
of the BSA+RB precursor solution and the microstructure suggest that the C=C bond in BSA-GMA was depleted. The
-1
by TPP. The broad absorption peak at 3311 cm is the intensity of the C=O peak at 1720 cm was also weakened,
-1
characteristic peak of BSA with significantly decreasing which was thought to be the disappearance of the C=C
peak intensity after polymerization, which is the stretching double bond leading to the loss of the conjugated system.
vibration of the amino (single bond -NH ) group and the The analyses of UV-Vis absorption spectra, FT-IR micro-
2
hydroxyl (O-H) group. Amide I, amide II, and amide III spectroscopy, and Raman spectra demonstrate that the
show peaks at 1660, 1540, and 1249 cm , respectively. The BSA-GMA precursor solution with LAP as photoinitiator
-1
intensity of the peak of amide II decreased and that of under the femtosecond laser at a wavelength of 780 nm is
amide III increased. Moreover, strong C-O-C peaks have a TPP process, and the site of polymerization is the vinyl
been observed at 831 and 1081 cm , which are thought to group on the GMA chain without consuming other amino
-1
be the oxidation of some phenolic hydroxyl groups on BSA acid residues.
tyrosine residues by the excited state of RB and coupling
with other amino acid residues to form C-O-C bonds. The 3.3 TPP properties of BSA-GMA hydrogels
decrease in the intensity of the amino acid peak and the The hydrogel precursor solution contains the BSA-GMA
appearance of the C-O-C peak suggests that the TPP in as the monomer and the LAP as the photoinitiator.
the BSA+RB system consumes a large number of amino Many parameters could affect the quality of BSA-GMA
acid residues. These amino acid residues are essential for hydrogels, including laser power as well as the degree of
cell attachment to protein scaffolds, so the depletion of methacrylation and the concentration of BSA-GMA. To
primary amino groups and carboxylate groups can affect fabricate highly precise and stable protein microstructures
the biocompatibility of the scaffold [38,59] . under appropriate conditions, the TPP properties of BSA-
In contrast, TPP of BSA-GMA using a radical I type GMA precursor solutions with different concentrations and
photoinitiator occurs only on the GMA chain and does not different degrees of methacrylation were first investigated.
consume amino acid groups. Figure 2E shows the FT-IR The fabrication performance of the BSA-GMA hydrogel
micro-spectroscopy spectra of GMA, BSA-GMA precursor systems was evaluated by laser threshold power, fabrication
solution, and the microstructure by TPP. The broad resolution, and 3D fabrication capability.
absorption peak exhibited at 3417 cm is the characteristic To determine the laser threshold power and the line
-1
peak of BSA, which is the stretching vibration of N-H width of different BSA-GMA hydrogels, the relationship
and O-H bonds. Amide I, amide II, and amide III show between line width and laser scanning power was
peaks at 1656, 1542, and 1245 cm , respectively. Most of investigated at a constant scanning speed of 10 μm s .
-1
-1
the FT-IR micro-spectroscopy peaks were retained after When the scanning speed was set as a constant, the higher
the TPP, and the characteristic peak wagging C=CH of the starting efficiency of the photoinitiator, the lower
2
GMA was at 942 cm , which was significantly weakened the polymerization threshold. Figure 3 shows the TPP
-1
after polymerization. This result indicates that the C=C properties of the R D , R D , R D , R D , and R D
15
40
40
35
30
52
20
52
40
52
bond in BSA-GMA is initiated by a radical type I initiator hydrogel systems, and the TPP laser threshold powers of
under a femtosecond laser to achieve TPP. Figure 2F shows 13.6, 12.3, 18.0, 13.3, and 5.6 mW, respectively. When the
the Raman spectral analysis of GMA, R D precursor, power is below the threshold, the obtained hydrogel line
40 52
Volume 9 Issue 5 (2023) 74 https://doi.org/10.18063/ijb.752