Page 559 - IJB-10-6

International Journal of Bioprinting Internally-crosslinked ADA/Alg/Gel bioinks

bioprinting of AHCFs-and H9C2/laden hydrogels was to the asymmetric and symmetric stretching vibrations of
investigated, and cell viability after printing was studied. carboxylate salt groups (-C=(O)O-) of Alg. In the ADA
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ATR-FTIR spectrum, additional bands with very low
3.1. ADA production and characterization intensity were detected at 2850 and 1740 cm associated
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Alginate dialdehyde (ADA) was prepared via oxidation of respectively with the C-H and C=O vibrations in aldehyde
Alg using sodium metaperiodate, achieving a production groups suggesting successful ADA production. 41
yield of 70 ± 5%. Oxidation reaction causes the cleavage of
a carbon–carbon bond and the formation of two aldehyde To further assess aldehyde group formation, C CP-
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groups. 49,50 Following previous literature reports, 41,50 MAS NMR spectroscopy was performed on Alg and ADA
a theoretical oxidation degree of 25% was targeted by lyophilized samples (Figure 1B). Both Alg and ADA spectra
controlling the stoichiometric addition of NaIO . ADA displayed peaks associated with the carbon atoms present
4
oxidation degree was measured by both indirect and direct in mannuronate (M1: 99.5 ppm; M2, M3: 71.6 ppm; M4,
methods. The indirect method was used as a preliminary M5: 76.4 ppm; M6: 172.6 ppm) and guluronate (G1: 102.2
assessment of the oxidation degree by measuring the ppm; G2: 65.5; G3, G5: 68.4 ppm; G4: 82.8 ppm; G6: 172.6
amount of unreacted sodium metaperiodate. 41,51 As 99% ppm). The spectra of ADA exhibited an additional peak
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sodium metaperiodate was consumed in the reaction, at 92.2 ppm, attributed to hemiacetalic groups originating
the theoretical oxidation degree was calculated to be 23 ± from aldehydic groups. Moreover, the resonance of both
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1%. Conversely, the direct method is based on the direct M-6 and G-6 at 176.2 ppm, attributed to carboxylate groups,
quantification of aldehyde groups in ADA using the TNBS were not altered, proving that sodium metaperiodate
assay. This method yielded an oxidation degree of 25 ± 4% can convert diols to aldehydes without affecting the
(mol aldehyde group/mol polymer). carboxylate groups. Deconvolution of the C CP-MAS-
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The initial chemical characterization of ADA and Alg NMR (Figure S1A and B, Supporting Information) spectra
was analyzed using ATR-FTIR (Figure 1A). ATR-FITR of Alg and ADA allow to determine the M/G ratio in both
spectra of Alg and ADA displayed the typical absorption polymers; 1.2 ± 0.3 for Alg and 1.5 ± 0.5 for ADA. ADA
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bands of the Alg structure: 1318 cm due to C-O displayed a slight reduction of G groups compared to Alg,
stretching; 1126 cm indicating C-C stretching; 1021 cm though no significant differences were detected in the M/G
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attributed to C-O-C stretching; 1590 and 1414 cm due ratio between the two materials. Literature studies have
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Figure 1. Characterization of ADA and Alg (A) Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra of alginate (Alg; black) and
lyophilized Alg dialdehyde (ADA; red). The inset figures represent magnifications of the spectra areas at 2840–2860 cm (left) and 1650–1800 cm (right).
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(B) C cross polarization under magic angle spinning nuclear magnetic resonance (CP-MAS NMR) spectra of Alg (black) and lyophilized ADA (red). G
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and M represents guluronate and mannuronate groups, respectively.
Volume 10 Issue 6 (2024) 551 doi: 10.36922/ijb.4014