Page 126 - IJB-6-4

Preheating of gelatin improves its printability with transglutaminase
A B

C D

E F

Figure 1. Flow diagrams of hydrogels made of different concentrations of FG and PG cross-linked with
TG (5% w/w). (A) FG5. (B) FG7.5. (C) FG10. (D) FG20. (E) PG10. (F) PG20.

of under-gelation was the longest for PG10, which inconsistent square grids with multiple broken
lasted at least 15 min (Figure 2B). The duration interconnected filaments at 10 min, and the ink was
of proper-gelation was 5 min for FG7.5 and 20 hardly extruded at 15 min (Figure 2A). However,
min for PG10, respectively, while it was 2 min for perfect squares may not be achieved even during
FG10 (Figure 2B). Over-gelation was observed for proper gelation for every smaller square grid
FG7.5 and PG10 as the printed ink was clumpy and within the printed lattice. The discontinuity in the
yielded the grids with irregular edges (Figure 2A). printed filament was due to a mismatch between the
Over-gelation was also identified by a fractured gelation state of the ink and the extrusion pressure.
grid morphology and disconnected filaments such The ink became gradually gel-like in the nozzle
as FG10 after 10 min. The gelation occurred most with time due to crosslinking by TG. The increase
rapidly for FG10 among the three inks, where over- in gelation required a corresponding increase in
gelation manifested in a clogging nozzle and the extrusion pressure to extrude the gel-like ink onto
filament barely extruded at the highest extrusion the substrate. However, as a single pressure was
pressure (0.7 MPa). This clogging resulted in the used to print the ink at every time point, small break

122 International Journal of Bioprinting (2020)–Volume 6, Issue 4