Page 228 - IJB-10-5

International Journal of Bioprinting Effect of ingredient flow speed

2.5. Measurement of filament width and actual where the power law index (n) and flow consistency
printing speed index (K) are displayed as the function of non-Newtonian
Measurements of the length and line width of the printed viscosity (v). The power law index (n) indicates the flow
straight line were performed thrice using ImageJ software behavior. A shear-thinning fluid would have n < 1. A
(National Institutes of Health, USA). Premium Rush smaller n indicates stronger shear thinning capability of
(Adobe Inc., USA) was used to locate the two frames when the fluid. Fluids with small n and K form ideal food inks as
extrusion occurred, and the time taken for each print these fluids can be ejected out of the extruder with ease. 50,51
was measured. The actual printing speed was acquired by Equation (I) was subsequently linearized into log form to
dividing the average length of the printed straight line by determine the value of the power law and flow consistency
the average time taken for each print. index (Figure 1B and Equation [II]).

3. Results log v = log K + (n – 1) log γ II
·
3.1. Rheological characterization of MP food ink
To understand the rheological behavior of the MP food Through curve fitting, the power law index and flow
inks, viscosity experiments were conducted. The rheology consistency index are determined to be 0.347 and 131.5,
results are depicted in Figure 1A, where it can be observed respectively. These values could be useful for designing
that the viscosity of the MP food inks decreased at a any mathematical model.
high shear rate and increased at a low shear rate. The
ability to exhibit shear thinning behavior meant that 3.2. 3D printing using dot extrusion
MP inks are pseudoplastic materials, which is essential
for food extrusion printing 44,45 as the food has to behave 3.2.1. Effect of nozzle geometry on food extrusion
like a liquid to be extruded and a solid to form stable The nozzle is a crucial part of 3D printing as the materials
self-supporting structures. 46 would be extruded through this small orifice. In 3DFP,
the nozzle diameter is essential to get a robust model.
The data from the rheological study were then fitted According to existing 3DFP experiments, a high-
45
to a viscosity model. According to researchers in the resolution 3D model would require a small-sized nozzle
3DFP field, 40,47 the power law model is a better fit for MP diameter. However, utilizing a smaller-sized nozzle would
food inks as compared to other models. Furthermore, increase the printing time of the 3D models as compared
48
the power law model is best suited for shear-thinning to using a larger-sized nozzle. Therefore, the nozzle size
fluids and chosen due to the best fit of R = 0.9991. The was examined to understand its effect on food extrusion.
49
2
relationship between kinematic viscosity (v) and shear rate With a digital microscope, it was observed that the exterior
·
(γ) was analyzed using Equation (I): design of the different-sized nozzles was tapered. Even
though the nozzles were tapered internally, the nozzles
v = Kγ I differed in terms of the geometry at the orifice. From
· n-1
Figure 2A, the digital microscope revealed a flat, thin wall

Figure 1. Rheological characterization of mashed potato (MP) food ink: (A) viscosity of the MP ink versus shear rate curve, and (B) linearized viscosity
versus shear rate curve in logarithm form for curve fitting.

Volume 10 Issue 5 (2024) 220 doi: 10.36922/ijb.2787