Mesenchymal stem cells and bioceramics: strategies to regenerate the skeleton.

Bone is formed by cells called osteoblasts, which arise from mesenchymal stem cells (MSCs). The cells are known to exist in thin tissues surrounding bone (periosteum) and bone marrow, but the population is extremely small. The number of marrow-derived MSCs can be expanded using tissue culture techniques. These culture-expanded MSCs have the in vitro capacity to differentiate into osteoblasts. Importantly, the cultured osteoblasts can form extracellular matrix in culture. This matrix consists of fine crystals of hydroxyapatite comparable to natural bone mineral, as evidenced by X-ray diffraction and Fourier-transform infrared spectroscopy. It is possible to fabricate the osteoblasts/ bone matrix on the surface of bioceramics. Thus in vitro cultured bone can show further bone-forming capability after in vivo implantation. We have begun studying this tissue-engineering approach in patients with skeletal problems. This paper describes this and other approaches using MSCs to regenerate skeletal tissue.