**8. Future direction and conclusion**

Bone regeneration is a very complex process that includes various factors, cells, and biomolecules. In large bone defects, the body does not have the ability to heal these injuries by itself. As a result, it needs external interventions. Although extensive methods, including surgical methods and physical methods using different materials, are used to treat bone injuries today, these methods face limitations. The spread of bone diseases with the increase in the elderly population leads researchers to create alternative treatment methods for bone healing. Recently, 3D bio-printing has been proposed for the treatment of large bone injuries, and extensive research has been done in this field in the last few years. This study shows the potential of 3D bio-printing strategies in the creation of different scaffolds for large bone tissue defect regeneration. The use of printed scaffolds containing cells with the ability to imitate natural tissue has opened a window of hope for creating new bone substitutes. Innovation in the use of these methods, such as in-situ printing, pre-vascularization, or the use of multi-matrix scaffolds for the combined treatment of bone and cartilage increases the capability of these structures. There is still a need to investigate and create new scaffolds in this field, which can increase the therapeutic potential of these scaffolds in the future. It seems that 3D bio-printing can provide effective treatment methods for repairing large bone tissues in the near future.

*Recent Advances, Challenges and Future Opportunities for the Use of 3D Bioprinting in Large… DOI: http://dx.doi.org/10.5772/intechopen.111495*
