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International Journal of Bioprinting Extrusion-based biomaterial inks

7. Conclusions
Extrusion-based bioprinting is the most widely used
bioprinting technology to fabricate bionic tissue or organ
constructs by combining biomaterial inks and living cells
for drug screening, tissue engineering, and regenerative
medicine. This paper reviews the properties of extrusion-
based biomaterial inks and details various biomaterial inks
classified by their functions, and presents the modifications
that could achieve the balance between biocompatibility,
mechanical properties, and printability. We also elaborate
the challenges and prospects of extrudable biomaterial
inks and introduce selected strategies based on different
extrusion strategies, especially multi-materials and
Figure 8. Future development of extrudable biomaterial inks. multiple-nozzle extrusion-based bioprinting. This
systematical review also provides some guidance on
The ECM could vary among species, organs, and even selecting appropriate extrusion-based biomaterial inks
individuals. The homogeneous biomaterial inks cannot and certainly contributes to new ideas and inspiration for
reflect the specificity of tissue and organ ECM, and owing bioprinting in vitro tissue models. We also firmly believe
to the insufficient interaction between cells and ECM, the that the currently existing challenges of extrusion-based
biological function of cells could be affected. In order to biomaterial inks can be addressed following the rapid
simulate the function and even pathological state of tissues development of technology in the near future.
and organs to the greatest extent, dECM should be selected
as organ-specific biomaterial inks to build personalized Acknowledgments
constructs for realize the specific biological function of None.
bioprinted tissues. Another strategy for organ-specific
ink is conjugation of biomaterial inks and specific growth Funding
factor or bioactive molecules for maximum simulation of
specific physiological microenvironment. F.Y. Zheng acknowledges support by the Beijing Nova
Program (Z201100006820038), National Natural Science
The biological soft tissues, other than bone tissues, Foundation of China (NSFC) Grants (No.82172110,
require strength and elasticity for regular tissue function, No.32001015, No.21635001), Beijing Nova Program
such as stretching and contracting, and their geometric Cross Cooperation Project (Z211100002121015), and the
structure should be restored after the external force of Fundamental Research Funds for the Central Universities
tension and compression is removed. Extrusion-based (YWF-21--BJ-J-1036, YWF-20-BJ-J-1035). L.Z. Wang
biomaterial ink shows viscoelasticity and thixotropy acknowledges support by NSFC Grants (No.11822201)
during printing. However, fully crosslinked hydrogels and Beijing Municipal Natural Science Foundation
after printing have greater rigidity with lower elasticity, (No.7212205). Y.B. Fan acknowledges support by the
and are brittle under mechanical action. In order to NSFC Grants (No. U20A20390, No.11827803)
simulate the high elasticity of biological soft tissues,
polymers with intrinsic elasticity and resilience can be Conflict of interest
applied to assist biomaterial inks for printing elastic
constructs [184] . The authors declare that they have no known competing
financial interests or personal relationships that could have
Bioprinted tissue constructs have macroscopic pore
structures, thus culture media could diffuse into filaments, appeared to influence the work reported in this paper.
providing mass transfer for cells embedded in filaments. Author contributions
However, interconnections between cells are blocked by
the gel matrix due to the lack of microporous structure. Conceptualization: Xiaorui Li, Fuyin Zheng
The microporous structure can provide large surface area Data curation: Xiaorui Li, Hui Liu, Xuezheng Geng, Yubing
for cell adhesion and promote vascularization of tissue Leng
constructs. Therefore, the preferred strategy is bioprinting Funding acquisition: Fuyin Zheng, Lizhen Wang, Yubo Fan
constructs with microporous structure or adding rapidly Project administration: Fuyin Zheng, Lizhen Wang, Yubo
degraded materials into biomaterial inks. Fan

Volume 9 Issue 2 (2023) 17 https://doi.org/10.18063/ijb.v9i2.649