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Huijun Li, Sijun Liu and Lin Li

Figure 2. (a) Dependence of tan δ on CaCl 2 content for 2 wt.% alginate solution at different angular frequencies in rad/s as indicated
in the inset, and (b) relationship of the Cg with alginate concentration.

(a) (b) 10 3 1 2 3
10 2 10 2

Viscosity (Pa.s) 10 1 0 Alg2 Viscosity (Pa⋅s) 10 1 Alg2

10
Alg4
Alg4
Alg6
10
-1
Alg8
Alg8 10 0 Alg6
Alg10 Alg10
10 -2 10 -1
1 10 100 0 20 40 60 80 100 120
Shear rate (1/s) Time (s)
Figure 3. (a) Viscosity as a function of shear rate at room temperature, and (b) effect of various alginate concentrations on the recov-
ery behavior of alginate hydrogels at a fixed CaCl 2 content of 25 mM/L.
concentration on viscosity is significant. The viscosity test, we should know the appropriate value of shear
increases with increasing alginate concentration and rate. As discussed in the Section 2.2, the shear rate can
decreases with shear rate. This is the most common be calculated using Equation (12). Firstly, rheological
behavior of a non-Newtonian fluid [27] . Specially, the measurements were performed on hydrogel samples
influence of shear rate on viscosity for the 2 wt.% algi- using a rheometer. Based on the power-law model as
nate solution is more significant than that for the 10 wt.% described in Equation (4) and experimental data, the
alginate solution. This viscosity will affect the amount constants m and n for each sample can be obtained
of hydrogel extruded from the printing nozzle and the through curve fitting. The details of the samples and
printing quality. the values of m and n are given in Table 1. The vis-
An ideal printable hydrogel should be highly thixo- cosity of 2 wt.% alginate hydrogel is too low, so that
tropic, which means that viscosity of the hydrogel the printed scaffold could collapse quickly. Thus, this
become low quickly when applying a shear force but sample is not appropriate for 3D printing. For the other
the viscosity recovers quickly after the shear force is concentrations of hydrogels (see Table 1), the maxi-
removed. It is also important to know how the cros- mum shear rate in the nozzle for each sample is aro-
–1
slinks of the hydrogel can recover before the next und 100 s at the printing speed of 0.009 mm/s used
layer starts to be printed. Thixotropic properties and in this study, where the diameter of the syringe and
recovery times were investigated by applying a steady the nozzle are 3.88 mm and 0.25 mm, respectively.
shear rate. Thus, before conducting the rheological Thus, we will examine the thixotropic properties
of each
International Journal of Bioprinting (2016)–Volume 2, Issue 2 59