Biomaterial design principles to accelerate bone tissue engineering

Healing of bony defects is a unique challenge due to the complex mechanical properties, irregular shapes, and critical size of missing bone. Bone defects that require surgery are typically caused by significant missing portions of bone and the methods of repair involve surgical implantation of a biomaterial. The gold standard for this repair is the use of autografts, but these can lead to bone morbidity. Alternatives include allografts and xenografts; however, multiple challenges associated with their use motivate tissue engineering efforts. To date, a wide spectrum of efforts have explored the design of osteogenic or osseoinductive biomaterials such as polymers, metals, and ceramics. Increasingly, efforts have also explored alternative fabrication approaches to create patient-specific implants. These efforts include adaptation of generative design principles and 3D printing to create unique geometries, methods to incorporate exogenous cell sources, and the use of conventional and exotic growth factor patterning and release approaches to further improve biological response. Here, we discuss the mechanisms of bone repair, the current available technologies, biomaterial design criteria, 3D printing as a fabrication method, and the influence of cells and growth factors on bone repair.