Spheroid construction strategies and application in 3D bioprinting

Tissue engineering has been striving toward designing and producing natural and functional human tissues. Cells are the fundamental building blocks of tissues. Compared with traditional two-dimensional cultured cells, cell spheres are three-dimensional (3D) structures that can naturally form complex cell–cell and cell–matrix interactions. This structure is close to the natural environment of cells in living organisms. In addition to being used in disease modeling and drug screening, spheroids have significant potential in tissue regeneration. The 3D bioprinting is an advanced biofabrication technique. It accurately deposits bioinks into predesigned 3D shapes to create complex tissue structures. Although 3D bioprinting is efficient, the time required for cells to develop into complex tissue structures can be lengthy. The 3D bioprinting of spheroids significantly reduces the time required for their development into large tissues/organs during later cultivation stages by printing them with high cell density. Combining spheroid fabrication and bioprinting technology should provide a new solution to many problems in regenerative medicine. This paper systematically elaborates and analyzes the spheroid fabrication methods and 3D bioprinting strategies by introducing spheroids as building blocks. Finally, we present the primary challenges faced by spheroid fabrication and 3D bioprinting with future requirements and some recommendations.