Page 122 - IJB-7-2

Effect of Oil Content on the Printability of Coconut Cream
A B

C

Figure 2. Rheological characterization and printability of coconut cream ink (Ink A contains 25% water with 10% (w/w) oil, ink B contains
25% water with 12.5% (w/w) oil, and ink C contains 33% water wi 10% (w/w) oil. (A) Viscosity as a function of applied shear rate.
(B) Storage moduli (G’) and loss moduli (G’’) as a function of applied oscillatory shear stress. (C) Top and front views of printed cube.
(Scale bar: 5 mm).

modulus of 1670–49000 Pa were printable using a DIW Table 1. Rheological properties of coconut cream inks. All values
printer [1,2,22,23,43] . The addition of oil led to a decrease of were calculated as means (± standard deviations).
yield stress from 216 Pa to 160 Pa while the addition of Sample Yield Storage
water led to a decrease from 216 Pa to 53 Pa (Table 1). The stress (Pa) modulus (Pa)
decrease in yield stress implied that the particle network 25% water with 216 ± 35 a 2520 ± 122 a
within the ink was weakened. A sufficiently high value of 10% (w/w) oil (Ink A)
yield stress allowed to maintain the material in its shape 25% water with 160 ± 44 a 2750 ± 23 b
and position after being printed without lateral spreading. 12.5% (w/w) oil (Ink B)
The yield stress of Ink C did not meet the yield stress from 33% water with 53 ± 29 b 1320 ± 65 c
the previous work ; it was hence not deemed printable, 10% (w/w) oil (Ink C)
[23]
which was subsequently experimentally confirmed. a,b,c Means that do not share a superscripted letter are significantly different
The values of G’ were higher than the values of G” at p<0.05
in the linear viscoelastic region for all coconut cream inks
which indicated that the inks have solid-like behaviors. all Inks A, B, and C possessed solid-like behaviors which
They allow the deposited inks to self-support themselves would allow the printed materials to retain their shapes.
(Figure 2B). Ink C exhibited the lower G’ than Inks A
and B (Table 1); this difference suggested that the bond 4.3. 3D printability of coconut cream ink
strength within the ink matrix was the weakest and would A printable ink should display shear thinning behavior
not be able to hold its shape as much as the other two inks. and no spreading of ink that allows the printed material
The high values of G’ suggested strong intermolecular to retain its shape. We printed mesh structures (20 mm
bonds within the ink that permit to hold the structures of × 20 mm × 20 mm) with Inks A, B, and C to verify the
the printed inks. Both G’ and G” started to deviate from ability of the inks to self-sustain the printed structures with
linearity due to the deformation of the bonds within the fidelity (Figure 2C). In this design of the 3D model (i.e.,
ink, suggesting the flow of the ink. In this observation, mesh grid), the spreading of inks results in the reduction

118 International Journal of Bioprinting (2021)–Volume 7, Issue 2