4.2. Rheological properties of carrageenan composite hydrogel
The rheological study was performed for composite hydrogel with alginate
concentrations of 0.5%, 1.0%, and 1.5%, and with MCNT concentrations
of 0.01%, 0.03%, 0.05%, and 1.5%, respectively. A rheological study
was performed to evaluate the effects on the viscoelastic properties and
the printability of carrageenan composite hydrogel. As shown in Figure
3, all the samples demonstrated shear-thinning properties, which
indicated that bioinks with low viscosity avoid blocking nozzle during
printing and cell vitality during cell-laden printing. Shear thinning of
composite hydrogel was caused by the destruction of ion cross-linking
and rearrangement of the molecular chain by shearing. Moreover, high
initial viscosity makes the hydrogel undergo high shear forces during
the printing process, which affects the ultimate printability and
vitality of the cells. Therefore, we introduced alginate and MCNTs; the
initial viscosity of the carrageenan composite hydrogel was decreased
with increasing concentrations of alginate and MCNTs, while the
shear-thinning properties remained unchanged. The result demonstrated
that the introduction of alginate and MCNTs can improve printability and
vitality of cells as well as the cytocompatibility
of kc-based bioink.
As shown in Figure 4, the initial modulus of kc and composite hydrogel
with sa increased slightly. However, the modulus of the composite
hydrogel with MCNT and sa increased obviously with the shear frequency.
Lower initial modulus endows better survival of cells in the
microenvironment. High modulus in a high frequency of hydrogel could
avoid the structure disruption and supports the cell well integrity.
The storage modulus (G’) of kc was higher than the loss modulus (G”)
,gel point(G’= G”) was not observed in a range of the test. On the
other hand, the gel point was observed in kc-sa and kc-sa-c in the range
of measured frequency, which was within the range of shear frequency of
the printing nozzle. The results cumulatively implied that kc composite
hydrogel was liquid during the process of printing, which ensures that
the cells loaded underwent one lower shear force.