**6. Conclusions**

Chitosan, as a resourced natural molecule has been widely explored for biomedical applications. The prominent characteristics of chitosan such as non-toxic, biodegradable, antibiosis, and structural similarities to ECMs, make it a favorable candidate for a variety of tissue repair and 3D organ bioprinting applications. Especially, the structural similarities of chitosan with glycosaminoglycan are a favorable factor for tissue repair and organ 3D bioprinting. The 3D printed chitosan-containing porous sca ffolds and cell-laden constructs have particular usages in promoting skin regeneration, wound healing, bone rehabilitation, cartilage reconstruction, nerve repair, and liver restoration. The biochemical and physiological properties of the chitosan-containing "bioinks" can easily be adjusted by changing the chitosan molecules in the hydrogels. It is expected that further study of chitosan molecules and their association with other polymers will reveal greater prospects of this unique polymer in complex organ manufacturing and clinical applications.

**Author Contributions:** S.L. designed and wrote the main content; X.T., J.F., H.T., and Q.A. contributed some detailed techniques, X.W. conceived, allocated, and revised the manuscript.

**Funding:** The work was supported by grants from the National Natural Science Foundation of China (NSFC) (Nos. 81571832 & 81571919 & 31600793 & 81271665), the 2017 Discipline Promotion Project of China Medical University (CMU) (No. 3110117049), the Key Research & Development Project of Liaoning Province (No. 2018225082), and the 2018 Scientist Partners of China Medical University (CMU) and Shenyang Branch of Chinese Academy of Sciences (CAS) (No. HZHB2018013).

**Conflicts of Interest:** The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.
