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Huijun Li, Sijun Liu and Lin Li

Figure 4. The images of printed hydrogel scaffolds with various alginate concentrations. (a) 2 wt.%; (b) 4 wt.%; (c) 6 wt.%; (d) 8
wt.%; (e) 10 wt.% alginate hydrogels at a fixed CaCl 2 content of 25 mM/L; (f) the effect of various alginate concentrations on fila-
ment width.

easy to collapse compared to the hydrogel with a low show the shear-thinning properties. GO can increase
alginate concentration. Thus, a smaller width implies a the viscosity of hydrogels, whilst viscosity increases
better printing quality of the scaffold. with increasing content of GO. On the other hand, it is
We also observed the time dependence of the pri- shown that the hydrogels with various GO contents
nted structures from time 0 to 20 minutes. Figure 5 also reveal the thixotropic properties (Figure 6(b)).
shows the images of printed hydrogel scaffolds at dif- Figure 7(a) shows the effect of GO on the mor-
ferent ageing times and the relationship between width phologies of the printed scaffolds with 10 wt.% algi-
and ageing time for 2 wt.% alginate hydrogels added nate hydrogels. The higher concentration of GO pro-
with a fixed CaCl 2 content of 25 mM/L. It is obvious duced a structure with a thinner width. GO is essen-
that the shape of the scaffolds changed with time as tially an atomic sheet with a large number of func-
the hydrogel was soft and easy to collapse. On the tional groups (e.g., hydroxyl, epoxide, and carbonyl
other hand, the filament width broadens with ageing groups) bound on the surface. After adding GO into
time. The effect of ageing time on the filament width the alginate solution, the functional groups from GO
for other alginate hydrogels are similar to those ob- such as (-OH, and -COOH) will interact with the gr-
served in Figure 5 (data not shown). oups (-OH) from calcium alginate. Thus, a large am-
ount of hydrogen bonds formed between the GO and
3.4 Effect of GO on 3D Printability of Alginate alginate may significantly improve the rheological
Hydrogels
properties of the composite hydrogels.
Alginate composite hydrogels filled with various GO Furthermore, the traditional process of 3D printing
contents were used as a printing material in this sec- is to print a scaffold layer-by-layer and there is no
tion to study on how GO could improve the 3D prin- pause between the two layers. However, printing of a
tability of alginate hydrogels. The printed scaffold dis- scaffold continuously on one layer after another with-
cussed in this section has 50 layers. From Figure 6(a), out any pause seems unreasonable for an extrusion
it is observed that the hydrogels filled with GO also based printer, because the viscosity of the extruded

International Journal of Bioprinting (2016)–Volume 2, Issue 2 61