Page 290 - IJB-8-4

3D Printed Dressings for Burn Wound Treatment
mechanical properties of this sample is not measurable The FTIR spectrum of gelatin has the characteristic
due to the lack of crosslinks. absorption bands at 1659 cm (amide I, C–O, and C–N
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stretching), 1547 cm and 1243 cm (amide II and
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3.3. Chemical structure III, C–H stretching vibration, and N–H bending), and
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Notably, the hydrogel-based bioinks provide good 601 cm (Amide IV, C–N), respectively [45-47] .
permeability to oxygen and nutrients. FTIR spectroscopy In the spectra of the alginate-gelatin complex in
was conducted to evaluate the interactions between the G6-A2, G4-A4, and G2-A6 samples, the stretching peak
alginate and gelatin within the hydrogel blend. The IR assigned with carboxylate groups of alginate slightly
spectra of the gelatin-alginate complex are shown in shifted to the left, which is due to the overlapping
Figure 7 in accordance with their structure, as shown in peaks of amide I and amide II peaks and the dominant
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Figure 1 and Figure 8A-B. Alginate and gelatin have absorption of water O-H scissors (1634 cm ) in this
overlapping carboxylate groups and hydroxyl groups in area. The formation of intermolecular hydrogen bonds
different intensities associated with 3200 – 3500 cm between different functional groups in gelatin and
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characteristic peaks. The amide bonds increase as the alginate makes a favorable entanglement for enhanced
gelatin concentration increases, while at the same time, rheological, shear thinning, and mechanical behavior
the carboxylate groups decrease as the concentration of at certain ratios of gelatin: alginate. However, after
alginate decreases, which is compensated by the rising crosslinking the 3D-printed dressings, the formation of
gelatin content. Specifically, the spectrum of sodium covalent cross-links between calcium ions and guluronic
alginate displayed the characteristic absorption bands acid blocks in alginate results in lower permeability and
[25]
of its polysaccharide structure at 1318 cm (C–O higher mechanical stiffness .
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stretching), 1126 cm (C–C stretching), and 1021 cm 3.4. Degradation rate and hydrating activity
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(C–O–C stretching). The absorption bands around 1620
and 1416 cm are assigned to asymmetric and symmetric Figures 9A and B depict the swelling and degradation
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stretching peaks of the carboxylate groups in alginate [42-44] . profile of the 3D-printed dressings after immersing in
PBS at 32°C. All samples showed swelling (i.e., water
absorption) in the early 24 h, while G6-A2 dressings
showed significantly higher swelling capacity than the
other 3D-printed dressings. The higher swelling capacity
of this sample is due to the higher water permeability of
the gelatin chains, which is clearly associated with the
low molecular weight and weak chemical bonds in the
gelatin structure. After cross-linking, stronger chemical
bonds will form within the alginate chains by exchanging
the sodium ions with calcium ions. It is associated
with a lower permeability to water molecules and, thus
Figure 7. Fourier-transform infrared spectroscopy spectra of lower swelling in the alginate chain. Based on the same
hydrogel samples. The characteristic IR bands associated with rationale, the degradation rate of the samples with higher
gelatin, sodium alginate, and water are shown by red arrows, blue gelatin content is significantly faster than the alginate
arrows, and light blue boxes, respectively. chain. This is particularly important when investigating

A B

Figure 8. (A) Sodium alginate has linear chains composed of mannuronic acid and guluronic acid with carboxylate groups and hydroxyl
groups. During cross-linking calcium ions replace the sodium ions in the guluronic acid monomers, resulting in intermolecular bonds
between calcium ions and alginate chains that forms a linear and packed egg-box structure. (B) Gelatin is a bioactive derivative of collagen
composed of amide groups with relatively high free volume and low viscosity.

282 International Journal of Bioprinting (2022)–Volume 8, Issue 4