Non-invasive shock wave stimulated periosteum for bone tissue engineering

Abstract

The cambium cells of the periosteum, which are known osteoprogenitor cells, have limited suitability for clinical applications of bone tissue engineering due to their low cell number (2-5 cells thick). Extracorporeal shock waves (ESWs) have been reported to cause thickening of the cambium layer and subsequent periosteal osteogenesis. This work proposes that ESW-therapy can be used as a non-invasive, inexpensive, and rapid method for stimulating cambium cell proliferation, and investigates the use of these cells for orthotopic bone growth. The response of periosteal cells to ESWs was evaluated using two different energy densities applied to either the intact femur or tibia of the rat. Just four days after application of ESWs, there was a significant 3- to 6-fold increase in cambium cell number and thickness. The most effective treatment of those tested was high dose ESW applied to the tibia. Immunohistochemical staining of the proliferated cells demonstrated osteoblasts and bone formation (osteocalcin stain); it also demonstrated extensive vonWillebrand factor expression, which reveals the vascular contribution to the proliferating cambium layer. In a rabbit model, ESW-thickened cambium layer cells were overlaid in situ on a porous calcium phosphate scaffold. At two weeks post-surgery, there was a significant increase in all outcome variables for the ESW-treated group when compared with controls: a 4-fold increase in osteoprogenitor tissue in the scaffold upper half, a 10- fold increase in osteoprogenitor tissue above the scaffold, and a 2-fold increase in callus size. The results successfully demonstrated the efficacy of ESW-stimulated periosteum for bone tissue engineering.