2.4.2. Rheological properties of carrageenan-based bioink
The rheological properties of various concentrations of carrageenan and
carrageenan composite hydrogel were measured using a rheometer (HR-2, TA
Instruments, USA) with a 100-mm round plate at a constant temperature of
37°C. All rheological experiments were performed in triplicate. To
assess the rheological properties for optimising the printing
parameters, the shear rate sweep test and frequency sweep test were
performed. For various shear-thinning materials including
carrageenan-based hydrogels, the power-law model has been widely used to
analyse the viscoelastic properties. The power-law index (n) and zero
viscosity (η0) were calculated from the shear
rate-viscosity curve of the shear rate sweep test in this study. The
printing parameters such as the pressure and printing speed were
calculated from the power-law index equation, as described below:
η=η 0 γ n−1
where, η is the shear viscosity, γ is the shear rate, and
η0 is the viscosity at the reference shear rate called
the zero viscosity (Morrison, 2001; Malkin and Isayev, 2017). The
viscosity (η) of the composite hydrogels was assessed using the shear
rate sweep test under the shear rate range of 0.1–500
s-1. The frequency sweep test was performed in the
angular frequency of 0.1–500 rad/s at a strain in the linear
viscoelastic region, where the test was performed without destroying the
structure of the sample to assess the storage modulus (G’) and the loss
modulus (G”).