Page 130 - IJB-6-4

Preheating of gelatin improves its printability with transglutaminase
increase in gel weight after 24 h and equilibrated 4 Materials and methods
to a ~20% increase in gel weight until 96 h. The
overall swelling could be attributed to a high 4.1 Preparation of the inks and hydrogels
concentration of gelatin (20%) in the hydrogel. Freshly prepared gelatin (FG) was defined as
Interestingly, FG exhibited smaller changes in gelatin (Porcine skin, Bloom 300, type A) (Sigma-
gel weights than PG regardless of swelling or Aldrich, USA) that had not undergone preheating.
shrinking. This observation could be attributed Briefly, FG stock was prepared by dissolving
to the rigidity of the gelatin network. Extended and mixing 12 g of gelatin powder with 18 g of
heating may cause the polypeptide chains of PG distilled water in a water bath at 40 – 50°C with
to be partially hydrolyzed. The resulting network stirring until a clear yellow solution was obtained.
in PG gel is more pliable than that in FG and may Subsequently, the FG stock was kept at 4°C
permit physical changes in the structure of the until further use. PG was prepared by placing
gel network. The flexibility of the gel network in an FG stock in a heat oven at 65°C for 7 days.
PG allowed for an increased degree of shrinking Both gelatins were mixed with a 5% w/w TG
or swelling in 1 × PBS, depending on the (Moo Gloo TI TG) (Modernist Pantry, USA) to
concentration of gelatin within the composition. achieve their desired final concentrations before
Overall, the preheating of gelatin altered the the experiments. To produce hydrogels, the final
properties to shrink or swell when placed in mixture was placed in the incubator at 37°C for
aqueous environments. The consideration of 24 h to complete the crosslinking of gelatin by
volume changes is essential when intending to TG. The inks were prepared by mixing the gelatin
create precise structures of gelatin by 3D printing. stock solution that was pre-warmed to 40°C with
For the ink of PG10 that offered adequate printing TG. The mixture was subsequently stirred for
duration, we shall account for the shrinkage if the 30 s before transferring into a metal syringe for
printed model is used in aqueous environments. printing. The addition of TG to gelatin initiated

3 Conclusions the gelation. The temperature of the ink was
maintained in the syringe at 40°C throughout the
In this paper, we explored the effect of preheating printing.
of gelatin to improve the duration of printable 4.2 DIW 3D printer and printability
time in DIW 3D printing. Our study suggested characterization
that preheating gelatin for 7 days extended the
duration of the acceptable printability 10 times FG and PG inks were printed using a DIW 3D
longer than freshly prepared gelatin of the same printer using a commercial 3D printing robot
concentration (10% w/w), and 4 times longer than and a dispenser (SHOTmini 200 Sx and IMAGE
freshly prepared gelatin with similar stiffness MASTER 350 PC Smart, Musashi Engineering
(10 kPa). The preheating of the gelatin altered the Inc., Japan). The dispenser was equipped with
shrinking and swelling behaviors of the resulting a single metal syringe (to maintain constant
hydrogels over 4 days in 1 × PBS, which provides printing temperature) and a precise pressure
an important consideration when the printed controller (ML-5000XII and ML-808GX,
models are used in aqueous environments such as Musashi Engineering Inc., Japan). MuCAD V
cell culture media. We believe the preheating of software (Musashi Engineering Inc., Japan) was
gelatin shall serve as a facile route to enhance the used to generate the design of the grid. Printing
usability of gelatin in extrusion-based processes. was performed with a metal nozzle head with a
Gelatin inks are increasingly used in DIW 3D diameter of 200 μm under the dispending pressure
printing to fabricate single-layered structures and ranging from 0.001 MPa to 0.7 MPa and the
multi-layered complex 3D structures that require a writing speed of 16 mm/s. The print speed was
long duration of time for printing. maintained at 16 mm/s to ensure the uniformity of

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