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Development and characterisation of a photocurable alginate bioink for 3D bioprinting
higher than the loss modulus. After the strain critical alginate structures based on functionalized alginate
value, the loss modulus becomes more significant due prepared during 24 h of reaction time swelled up to
to the break of the cross-linked network. In the case of 155%, while alginate structures based on functionalized
alginate methacrylate samples obtained after 24 h of alginate prepared during 8 h of reaction time swelled up
reaction time, Gʹ-24h modulus is always higher than to 190%. Moreover, it is also possible to observe that the
Gʹ-8h of alginate methacrylate samples obtained after 8 level of functionalization of the pre-polymerized alginate
h of reaction time. This is due to the high-crosslinking not only determines the internal morphology of the cross-
density of the alginate methacrylate samples obtained linked structures but also the degradation process as
after 24 h of reaction time. shown in Figure 19b and d.
3.5 Internal Morphology of Alginate Hydrogels 4. Conclusion

The internal structure of cross-linked alginate This paper describes the synthesis and characterization of
methacrylate is presented in Figure 16. SEM images alginate systems for UV-based bioprinting applications.
were obtained for samples containing 2% w/v of alginate The alginate was successfully functionalized in the
prepared during 8 and 24 h of reaction time and 1 w% presence of methacrylate to introduce the necessary
of a photoinitiator. Results show that the reaction time number of unsaturation allowing its crosslinking on
influences the hydrogel morphology, with high reaction photopolymerization. Two different functionalization
times being associated with structures presenting both reaction times were considered and photocurable systems
small pore size and number of pores. In addition, results containing different photoinitiator concentrations
seem to indicate that long reaction times generate prepared. From the results, it is possible to conclude that
structures with more closed pores. high functionalization reaction times originates cross-
linked structures with less porosity, smaller pores and
3.6 Mechanical Characterization a larger number of closed pores, less swelling, higher
The mechanical performance of cross-linked alginate degradation properties, and higher mechanical stiffness.
structures is presented in Figures 17 and 18. As observed, By increasing photoinitiator concentration, it was possible
high compression moduli was obtained for cross- to observe an increase of mechanical properties and
linked disks produced with high functionalization times gelation time. Moreover, for high values of photoinitiator
(13.16 kPa for 24 h of reaction time and 2.63 kPa for 8 h of concentration, the reaction tends to reach verification.
reaction time) and 0.5% w/v photoinitiator concentration.
These results can be explained by the high crosslinking Acknowledgment
density that characterizes the structures obtained from Mr. H.H. Mishbak wishes to acknowledge the support of
alginate samples functionalized during long reaction the Government of Iraq for supporting his PhD through a
times and the corresponding internal morphology grant provided by the Higher Committee for Development
characterized by small size and a low number of pores. It Education Iraq. We would like to thank our colleagues
is also possible to observe that the mechanical properties from School of Materials, and the School of Mechanical,
increase by increasing the photoinitiator concentration. Aerospace, and Civil Engineering, The University of
For samples containing 1.5% w/v of photoinitiator, Manchester who provided insight and expertise with the
compression moduli was obtained (75.4 kPa for 24 h of mechanical compression test and rheological test that
reaction time and 7.23 kPa for 8 h of reaction time). greatly assisted the research.

3.7 Swelling and Degradation Kinetics References
The swelling and degradation behavior of cross-linked 1. Pereira R, Bártolo PJF, 2015, 3D Bioprinting of
alginate hydrogel disks are presented in Figure 19 (a,b,c
and d). Results show that samples absorb both DMEM Photocrosslinkable Hydrogel Constructs. Appl Polym Sci,
and diH O until reaching a state of equilibrium. This 132(48):132A4. DOI 10.1002/app.42458.
2
state is accomplished when the osmotic pressure from 2. Zhou D, Yoshihiro I, 2014, Visible Light-curable Polymers
the swelling and the elasticity of the hydrogel network for Biomedical Applications. Sci China Chem, 57(4):510-21.
is equal. It is also possible to observe that cross-linked DOI 10.1007/s11426-014-5069-z.
samples prepared with alginate methacrylate obtained 3. Pereira RF, Sousa A, Barrias CC, et al., 2018, A Single-
after 24 h of functionalization present low swelling ratio,
which shows that the degree of crosslinking controls the component Hydrogel Bioink for Bioprinting of Bioengineered
swelling properties of the hydrogel. In all samples, the 3D Constructs for Dermal Tissue Engineering. Mater Horiz,
equilibrium status was reached on day 3. Cross-linked 5(6):1100-11. DOI 10.1039/c8mh00525g.

24 International Journal of Bioprinting (2019)–Volume 5, Issue 2