Page 46 - IJB-3-2

A dual crosslinking strategy to tailor rheological properties of gelatin methacryloyl

Figure 3. Effect of the MTGase concentration on the gelling period of 10% GelMA solutions at incubation temperature (37 °C). The inset
photo shows representative images of transition from a liquid to a chemical gel of 10% GelMA treated with 3 U/mL MTGase at 37 °C.

Table 1. Gelling period of enzyme-catalysed MTGase-GelMA with various concentrations of MTGase at 37 °C with a fixed GelMA
concentration of 10% (w/v)
MTGase Concentration (U/mL) Gelling period (within 4 hours)
1 –
3 3–4 h
5 1–2 h

Figure 4. (a) The time-dependent viscosity of 10% GelMA solution incubated with different concentration of MTGase at 37 °C under the
shear rate of 100 s ; (b) the flow behaviour of 10% GelMA solution incubated with 3 U/mL MTGase at 37 °C
-1
material with shear thinning behaviour and a suitable °C. The rate of viscosity increment was higher with
viscosity will be favoured for 3D printing. Murphy et increasing MTGase concentration. At a concentration of
al. summarized that a range of viscosity (30 mPa∙s to 1 U/mL MTGase, the viscosity of 10% GelMA solution
6 × 10 mPa∙s) would be suitable for extrusion-based increased from 5.9 mPa∙s (0 h) to 12.1 mPa∙s (4 h), while
7
[5]
printing . The viscosity of 10% GelMA solution without there was a great change in viscosity for 10% GelMA
MTGase treatment was 5.9 mPa∙s (Figure 4a) under the containing 3 U/mL MTGase and 5 U/mL MTGase, from
-1
shear rate of 100 s (which was reported as the shear rate 8.4 mPa∙s (0 h) to 438.5 mPa∙s (4 h) and 13.6 mPa∙s (0
of materials experienced in the needle tip [37,38] ), which h) to 5776.1 mPa∙s (4 h), respectively. The addition of
was far below the aforementioned range of printing MTGase enzyme catalyses the covalent crosslinking
viscosity. Literature has shown that the viscosity of ge- action in gelatin, resulting in an increased molecular
latin solution increases after transglutaminase induced- weight and crosslinking degree [40] , and most likely
enzymatic crosslinking , so for the current study, it was
[39]
intended to alter the viscosity of 10% GelMA solution contributing to higher viscosity when added to GelMA.
with MTGase treatment, and thus the viscosities of 10% Though higher viscosity values can reach the threshold
GelMA solutions incubated with different concentrations value suitable for printing, the continued increment in
of MTGase at 37 °C were investigated under the shear viscosity (Figure 4a) may eventually lead to the clogging
rate of 100 s . Additionally, the flow behaviours of the of nozzle over time. Thus, a suitable incubation time
-1
solutions were studied within the range of shear rates should be optimized in the future. Notably, the solutions
-1
from 0.1 to 1000 s , as shown in Figure 4b. exhibited shear-thinning behaviour at certain incubation
Figure 4a shows that the addition of MTGase resulted times (Figure 4b), which would facilitate the printing
in a net increase in viscosity after incubation at 37 process.

134 International Journal of Bioprinting (2017)–Volume 3, Issue 2