Page 80 - IJB-9-5

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

Figure 1. BSA-GMA as pre-hydrogel as well as FT-IR spectra and H-NMR spectra of unsubstituted BSA and BSA-GMA with different degrees of
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methacrylation. (A) Modification of BSA with GMA. BSA is covalently immobilized with GMA, which is a donor of the vinyl double bond as a two-photon
crosslinking site. (B) BSA powder was dissolved in PBS at pH 7.4, and GMA was added dropwise to this solution after half an hour and reacted at room
temperature for 5 days. It was dialyzed in distilled water for 3 days to remove the salt and then freeze-dried. A precursor solution was prepared by adding LAP
to the BSA-GMA solution. (C) FT-IR spectra of GMA, unsubstituted BSA, and BSA-GMA with different degrees of methylation. In FT-IR spectra, amide I
(1639 cm ), amide II (1512 cm ), and amide III (1234 cm ) in BSA were found, as well as spectra related to GMA, such as at 951 and 1165 cm ,
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-CH wagging stretching of methacrylate vinyl. (D) H-NMR spectra of unsubstituted BSA and BSA-GMA with different degrees of methylation. The
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modification of lysine residues in BSA was confirmed with increasing GMA, with a gradual decrease in lysine signal at δ = 2.9 ppm, an increase in
methacrylate vinyl signal at δ = 6.2–5.9 and 5.8–5.5 ppm, and an increase in methyl signal at δ = 1.8 ppm.
can increase the reaction with amino groups, and two GMA peaks in FT-IR (Figure 1C). BSA-GMA powders were
molecules can react with one free amino group. GMA can named according to the molar ratio of lysine and GMA
also increase the amount of vinyl methacrylate by reacting in the reaction. The variations of the BSA-GMA peaks
with the hydroxyl and carboxyl groups in BSA through an were determined by comparing the peaks of pure BSA and
esterification mechanism, thus maximizing the crosslink GMA. The spectra of pure BSA and all Lys: GMA samples
density of BSA-GMA hydrogels . To optimize the ratio of showed protein-related amide I, II, and III peaks at 1658,
[53]
BSA-GMA hydrogels, BSA-GMA was fabricated by adding 1539, and 1246 cm , respectively. The IR spectra of GMA
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GMA with lysine group ratios of 1:1, 1:1.5, and 1:2 into showed strong -CH swing and stretching vibrations of
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the BSA solution, respectively (Figure 1B). A series of BSA- vinyl at 1168 and 945 cm . The changes detected in the
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GMA powders were synthesized by the methacrylation BSA-GMA specimens compared to the BSA were at 1168
reaction, followed by dialysis and freeze-drying. LAP has and 945 cm , representing the -CH wagging stretching
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good water solubility, good biocompatibility, and a two- of vinyl in GMA. These peaks increase gradually with
photon absorption (TPA) of 0.16 GM at 800 nm, which is the increase of the GMA ratios. To further quantify
promising for TPP initiator [54,55] . Therefore, we chose LAP the degree of methacrylation of BSA-GMA under each
as the type I initiator for this study. condition, it was characterized H-NMR spectroscopy
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(Figure 1D). Specifically, the characteristic resonances of
The modification of GMA on BSA was confirmed by methacrylic acid vinyl groups (δ = 6.1 and 5.7 ppm) and
the identification of GMA-related peaks and BSA-related GMA methyl (δ = 1.8 ppm) appeared after the addition of
Volume 9 Issue 5 (2023) 72 https://doi.org/10.18063/ijb.752