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Miaomiao Zhou, et. al.

3.3 The Effect of Different Crosslinking MTGase could catalyse the bond formation in GelMA.
Methods on Viscoelastic Properties of Hydrogels The viscosity of GelMA solution could be increased by
increasing the enzyme concentration and incubation time,
While sufficient viscosity is required for printability and the solutions exhibited shear-thinning behaviour.
during printing, further gelation is necessary for handling Subsequently, fast photo-crosslinking of GelMA aided in
and maintaining the final constructed shape. Thus, fre- maintaining its structural integrity. Such dual crosslinked
quency sweep test was performed to investigate the hydrogels could achieve higher mechanical stability.
effects of single (either enzymatic or photo-crosslinking) Thus, MTGase treatment on GelMA could be a practical
or dual (both enzymatic and photo-) crosslinking on method to facilitate the application of GelMA in 3D
viscoelastic properties. The enzymatic crosslinked printing.
hy dro gels formed during incubation with MTGase. Conflict of Interest
Subsequently, enzymatic crosslinked hydrogels were
photocured on exposure to UV light to support long-term No conflict of interest was reported by the authors.
stability of GelMA constructs. Such dual crosslinked
hydrogels exhibited enhanced viscoelastic properties Acknowledgment
when compared with single crosslinked samples, as The authors gratefully acknowledge the National
evident from Figure 5; the enzymatic crosslinked Research Foundation (NRF) Competitive Research
hydrogel had the lowest G’ when compared to photo- Programme (NRF-CRP10-2012-07) for the financial
and dual-crosslinked hydrogels, with the latter exhibiting support.
the largest G’ values. Figure 6 shows structural integrity,
in increasing order, during the handling of the constructs References
with the type of crosslinking (single or dual). 1. Abouna G M, 2008, Organ shortage crisis: Problems and

4. Conclusion possible solutions. Transplantation Proceedings, vol.40(1):
In this study, an enzymatic crosslinking method was 34–38.
introduced to GelMA system to improve its rheological http://dx.doi.org/10.1016/j.transproceed.2007.11.067
properties for 3D printing application. It was found that 2. Ikada Y, 2006, Tissue engineering: Fundamentals and

Figure 5. Viscoelastic properties of different crosslinked hydrogels. Enzymatic crosslinking hydrogel was formed by incubating 10%
GelMA with 3 U/mL MTGase for 12 h. Photo crosslinking hydrogel was formed by curing 10% GelMA at 1.5 mW/cm for 5 min. Dual
2
crosslinking hydrogel was formed by enzymatic crosslinking and then by photo crosslinking.

Figure 6. Handling of (a) enzymatic, (b) photo- and (c) dual crosslinked hydrogels

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