Extracorporeal shock wave-induced proliferation of periosteal cells.

The cambium cells of the periosteum are an important cell source for select tissue engineering/regenerative medicine applications due to their osteogenic and chondrogenic potential. However, the cambium layer is only 2-5 cells thick, which complicates its harvest, and the low cell number limits its suitability for certain applications. Extracorporeal shock waves (ESWs) have been reported to cause periosteal osteogenesis following cambium layer thickening. This study quantified the proliferation of cambium cells in the femur and tibia of adult rats following ESW treatment at two different energy flux densities. Four days after application of ESWs, there was a significant (3- to 6-fold) increase in cambium layer thickness and cell number. Proliferation was seen with an energy flux density as low as 0.15 mJ/mm(2). The tibial cambium cells were more proliferative than those of the femur, with the cells closest to the ESW source proliferating the most. Within the thickened periosteum, α-smooth muscle actin and von Willebrand Factor expression were upregulated, suggesting a vascular role in ESW osteogenesis. Bone formation was seen within the stimulated periosteum at day 4. We propose that non-invasive ESWs can be used to rapidly stimulate cambium cell proliferation, providing a larger cell population for use as a progenitor cell source for tissue engineering applications, than can normally be provided by periosteum.