Advances in 3D/4D printing of bone scaffolds and their shape/properties adaptability

Artificial bone transplantation has become a hot topic in the field of bone defect treatment and repair research, where bone scaffold is the core factor. The scaffold that provides a temporary microenvironment for the regeneration of bone tissue needs to endow it with similar structural and functional characteristics to natural bone, namely shape/properties adaptability. The "shape" mainly refers to the fact that the scaffold must have a personalized shape and an internal interconnected porous structure, while the "properties" mainly refers to basic functions such as bone formation and additional functions such as antibacterial function. This paper first introduced different 3D printing technologies on how to endow bone scaffold with "shape" characteristics, emphasizing the selection of appropriate printing technologies based on existing raw materials such as polymers, metals or ceramics. Considering that natural bone was a complex system composed of organic and inorganic materials that was intricately interwoven, bioceramic/biopolymer composite bone scaffold was introduced to meet the basic functions with two challenges of interface bonding and degradation regulation being discussed. Subsequently, the antibacterial functionalization strategies of bone scaffold were introduced, with emphasis on the biocompatibility and controllable responsiveness of different methods. Then the application of 4D printed bone scaffold was also discussed, and the safety and other characteristics of different stimulation methods were briefly analyzed. Finally, an prospect of the research needs for the expansion of artificial bone scaffold application was provided.