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International Journal of Bioprinting 3D-printed diabetic diet

whereas the three inks based on Material-2 exhibited microstructure of food inks reinforced with XG, plays
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more distinct variations (Figure 2D). The elastic modulus a significant role in forming a gel-like matrix. This dense
(G’) reflected the ability of the material to store energy and irregular structural network enhances the mechanical
against shear deformation, while the viscous modulus (G’’) strength of starch-containing gels, providing them with
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characterized its liquid-like behavior, which resulted in the necessary mechanical stability. In contrast, Ink-M1-3,
energy loss under shear stress. The point at which the G’ which did not contain any food hydrocolloids (i.e., XG),
and G” curves intersected indicated the yield stress of the displayed numerous micropores of varying sizes in its
food ink. The pairwise comparison of the food inks based microstructure, and a high degree of porosity destabilizes
on Material-1 showed no significant difference in yield the 3D-printed product, leading to deformation and
stress except for the comparison between Ink-M1-2 and diminished precision. Unlike the densely packed pores
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Ink-M1-3 (Figure 2E). However, all three food inks based formed by starch which enhances the mechanical strength
on Material-2 exhibited significantly different yield stress of the food material, the pores in Ink-M1-3 are randomly
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when compared pairwise (Figure 2F). These observations positioned and loosely packed, bearing a resemblance to
were consistent with the viscoelastic behaviors displayed a piece of wood damaged by worms. The presence of this
by these inks in Figure 2A–D. type of micropores results in weak support, negatively

To evaluate the extrusion and self-supporting capabilities impacting the printability of the ink. Ink-M1-2 contains a
of the food inks, a thixotropy recovery experiment was small amount of XG, resulting in the formation of a feeble
conducted. It was observed that all inks exhibited a gradual gel system with a more compact structure.
decrease in viscosity at low shear rates, which aligned with The microstructure of the three inks based on Material-2
the observed shear-thinning behavior in the flow ramp exhibited typical granular structures of milk powder
study (Figure 1G and H). Once the peak shear rate was (Figure 3B). As the water content of Ink-M2-2, Ink-M2-1,
reached, the apparent viscosity of the food inks drastically and Ink-M2-3 gradually decreased, the microstructure
dropped, thereby facilitating smooth printing by enabling of the food ink became progressively more compact,
effortless flow of food inks from the nozzle. Following the with ink-M2-1 exhibiting a highest degree of porosity
printing process, the inks demonstrated rapid recovery of and ink-M2-3 showing almost no discernible pores.
their apparent viscosity, indicating their ability to maintain Notably, Ink-M2-2 displayed a prominent presence of
the structural integrity of the printed objects. The recovery stomata, primarily in the form of lamellar and filamentous
rates for ink-M1-1, ink-M1-2, and ink-M1-3 were 58.02%, structures. This presence of stomata was likely attributed
38.59%, and 81.33%, respectively. For ink-M2-1, ink-M2-2, to the gelation of starch when the water content became
and ink-M2-3, the recovery rates were 40.42%, 52.21%, sufficiently high.
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and 30.77%.
The texture profiles of all six inks are presented in
Interestingly, it was noticed that inks with similar Table 2. The normalized values are presented in Figure
viscoelastic behavior did not necessarily exhibit the 4A, and the original values are presented in Figure S1
same level of printability, and vice versa. Take Ink-M1-1 in Supplementary File. The addition of XG to Material-1
and Ink-M1-2 for instance, the two food inks shared resulted in a significant increase in hardness, a key
comparable apparent viscosity and shear modulus values parameter reflecting the potential irritation to the oral
at a given shear rate. However, their printability differed mucosa. In the case of the food inks based on Material-2,
significantly, as depicted in Figure 1. On the other hand, hardness increased as the moisture content decreased.
Ink-M2-1 and Ink-M2-2 displayed similar printability, Specifically, a 15% difference in moisture content led to
despite notable differences in apparent viscosity and an approximately 7.3-fold difference in hardness, while
yield stress.
a 5% difference led to approximately 2.1-fold difference
3.2. Microstructure in hardness. Cohesiveness, which indicated the energy
In addition to the rheology, the microstructure of food inks or the number of chewing times required to break down
plays an important role in their printability. Maintaining the food until it became palatable and swallowable, and
the stability of microstructural interactions over a wide gumminess, which referred to the energy needed to chew a
frequency range is believed to lead to improved printability. semi-solid food until it was swallowable, followed the same
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The scanning electron micrographs of all six food inks trend as hardness. The chewiness of the three inks based
are depicted in Figure 3A and B. A pronounced fibrous on Material-1 was similar, while the chewiness of the three
network was observed in Ink-M1-1 (Figure 3A), which inks based on Material-2 increased with decreasing water
had the highest XG content among the three inks based on content. Adhesiveness and springiness did not show any
Material-1. The fibrous network, which is a characteristic significant difference.

Volume 10 Issue 2 (2024) 302 doi: 10.36922/ijb.1862