Page 185 - IJB-9-3

International Journal of Bioprinting Chitin/gelatin/PVA scaffolds

For short-term biocompatibility, results were in particular, the α-form has an antiparallel arrangement .
[46]
relativized to the controls. In the case of mortality, CTR- As can be seen in XRD patterns (Figure 1D), chitin showed
was considered having 100% of mortality and CTR+ a high level of crystallinity, with XRD peaks observed at 9°,
having 0%; they were considered inversely in the assay of 19°, 21°, and 23°, characteristic of α-chitin . Sharp peaks
[27]
metabolic activity. around 9° and 19° are (0 2 0) and (1 1 0) diffraction planes
of the orthorhombic crystal structure . Additionally, a
[6]
3. Results and discussion number of XRD peaks are attributed to some impurities
3.1. Chitin extraction yield and characterization found in chitin from insects, as also shown by other
[34]
Since insects have a large protein content, deproteinization authors . These results are similar to those reported
[39]
must be carried out and the temperature, NaOH for chitin extracted from other insects . Regarding
concentration, and reaction time used in this process crystallinity, the CrI value found was 86%, in accordance
[34]
influence the extraction yield . In this work, the extraction with literature . It should be noted that the nature of
[32]
yield achieved was 25.52%. Other Diptera species, such as the organism from which the chitin is extracted and the
Hermetia illucens, have also shown values around 20%– conditions used in the process can affect the crystallinity
[47]
25% . Considering that the extraction yield of chitin values .
[33]
from insects is similar to that obtained from crustacean 13 C NMR analysis was performed to confirm that
shell waste, insects can be considered an alternative chitin chitin powder extracted from fruit fly pupae showed
source . the typical α-chitin C NMR spectrum. As shown in
[34]
13
Figure 1E, C NMR spectrum contains eight well-defined
13
Chitin presents in three crystalline forms, known as α,
β, and γ, with α-chitin being the most abundant form [35,36] . peaks ranging from 20 to 190 ppm, corresponding to
C1-C6, CH and C=O carbons. Specifically, the signals
The α- and β-forms can be differentiated by FTIR analysis. associated to C1-C6 were clustered in the 50–110 ppm
3
The spectrum of the α-form has two bands at 1650 and region: C1 (103.73ppm), C2 (54.80 ppm), C3 (73.11 ppm),
1620 cm -1[37] , while the β-form has only one band at C4 (83.08 ppm), C5 (75.24 ppm), and C6 (60.62 ppm).
1630 cm -1[38] . As can be seen in Figure 1A, the amide I band Meanwhile, methyl and carbonyl carbons showed peaks at
was divided into two peaks, which appear at about 1650 23 ppm and 173 ppm, respectively .
[48]
(shoulder) and 1622 cm ; therefore, α-chitin was obtained
-1
in this work. α-chitin is usually found in the cuticles of Additionally, elemental analysis was performed to
[39]
insects . Other characteristic bands of chitin are amide II calculate the DA of chitin. The nitrogen content of chitin
-1
(1550 cm ) and amide III (1309 cm ) . Moreover, a major found was 4.5%, a significant indicator of its purity . In
[49]
-1 [40]
peak around 3425 cm is due to O-H and two sharper chitin samples with high percentages of nitrogen, protein
-1
-1
peaks at 3255 and 3107 cm are attributed to N-H [41,42] . residues can be present . The DA value for chitin was
[50]
-1
The peak around 1010 cm is associated to C-O stretching. calculated as 99%, so it can be concluded that the extraction
These characteristic bands indicate the high purity of chitin process allowed obtaining chitin with high purity.
isolated from fruit fly pupae . 3.2. Rheological properties of 3DP and ES inks
[40]
In order to analyze thermal events occurred in chitin First of all, rheological analysis was carried out to determine
extracted from fruit fly pupae, DSC analysis was performed the temperature range for 3D printing. As can be observed
and results are shown in Figure 1B. As can be observed, in Figure 2A and C, viscosity values decreased when shear
chitin showed an endothermic peak around 75°C, ascribed rate increased, indicating that 3DP and ES inks showed
to the evaporation of entrapped water . shear thinning behavior, a favorable performance for both
[43]
Additionally, derivative thermo-gravimetry (DTG) 3D printing and electrospinning techniques. Regarding
was carried out and curves are shown in Figure 1C. The Gʹ and G˝ moduli (Figure 2B and D), these values did not
first mass loss step was found around 57°C, related to change a lot at different frequencies for 3DP inks, while
the evaporation of water. The second mass loss step was they showed a noticeable increase for ES inks at high
observed around 385°C, attributed to the decomposition frequencies. 3DP inks showed higher storage modulus (Gʹ)
of the polysaccharide structure . It is worth highlighting than loss modulus (G˝) and, thus, tan δ < 1, while ES inks
[44]
that chitin was degraded before reaching the fusion showed the opposite tendency during the entire frequency
temperature, a typical behavior of polysaccharides . sweep. Therefore, it can be said that 3DP inks had solid-like
[45]
As mentioned in the above, there are three crystalline behavior, while ES inks had liquid-like behavior [51,52] . The
forms of chitin, known as α, β, and γ, with α-chitin being two moduli joined at high frequency values for both inks.
the most abundant and stable form. These chitin forms have Regarding the effect of temperature on viscosity
different chain arrangements in the crystalline region and, (Table 2), zero shear viscosity values were reduced by half
Volume 9 Issue 3 (2023) 177 https://doi.org/10.18063/ijb.701