**10. Regenerative cell therapy**

Although the autograft is accepted as the gold standard for the treatment of bone defects, some drawbacks of autogenous bone grafts such as limited graft accessibility, prolonged operation time and donor site morbidity as well as high costs, continue to drive the quest for development of alternative methods for bone regeneration and repair. Three new strategies are recently undergoing investigation:

**Stem cell therapy**; the transplantation of cultured osteogenic cells from host tissues like bone marrow.

**Protein therapy**; the application of osteoinductive growth factors in various reconstruction techniques.

**Gene therapy**; the transduction of genes encoding cytokines with osteogenic capacity into cells at the repair sites.

Bone engineering techniques consist of three main components: cell, growth factor, and carrier. Osteogenic cells are responsible for the generation of new bone. Without existing cells with osteogenic potential no new bone would be produced and no defect would be reconstructed. The proteins with osteoinductive potential known as growth factors are the second factor needed for reconstruction of defects. These growth factors are responsible for enhancement of new bone formation by affecting the cells which play a role in bone healing. The application of cultured cells or growth factors without any scaffold is almost impossible. Choosing the right scaffold for delivery of the cells and growth factors and acting as mesh for new bone formation is a significant issue in bone engineering.
