This chapter briefly describes the biological processes of bone development and fracture repair, highlighting the current applications of stem cells and growth/differentiation factors involved in bone regeneration, and focuses on the principles of design and fabrication of scaffolds. Bone formation proceeds in two different ways: endochondral ossification, which is a complex, multistep process requiring the sequential formation and degradation of cartilaginous templates for the developing bones, and intramembranous ossification, which occurs through the direct differentiation of precursor cells into osteoblasts. Fracture repair involves multiple factors and the establishment of a specific morphogenetic field to drive the differentiation of precursor cells, and, in some ways, could be considered a recapitulation of bone development. Many growth/differentiation factors are used in bone tissue engineering. Among these, bone morphogenetic proteins (BMPs) have the unique ability to stimulate the differentiation of mesenchymal precursor cells to chondrocytes and osteoblasts, and induce formation of new bone at both ectopic and orthotopic sites. A simple method for bone regeneration is to supply growth factors such as BMPs to the site of defect for cell proliferation and differentiation in a controllable manner. Regional gene therapy offers another approach to delivery of growth/differentiation factors to the healing sites. Transfected cells express growth/differentiation factors for a sustained period. At any time during bone development or fracture healing, multiple growth/differentiation factors are functioning in a coordinated manner thus the combinations of bioactive factors might synergistically stimulate bone regeneration. 2011 Elsevier Inc. All rights reserved.
