Year: 2007
Type: dissertation
Abstract: The healing of large bone defects remains a major challenge in orthopedic and cranio-facial surgery. Existing treatments use autologous or allogenic bone grafts but may cause donor site pain and infection or host versus graft disease. Distraction osteogenesis provides a surgical alternative but requires long healing times. A promising and innovative approach aiming at a better solution for the healing of large bone defects is bone tissue engineering. Indeed, healing of such lesions can be achieved by seeding cells in an appropriate carrier, followed by implantation of the construct into the defect. In this PhD work we have explored the use of periosteum derived cells in bone tissue engineering. Cells isolated from human and rabbit periosteum (respectively HPDCs and RPDCs) were brought in culture and their in vitro and in vivo osteogenic characteristics were tested. In vitro, growth analysis indicated that RPDCs expanded faster and were smaller than HPDCs under the same conditions. BMP6 but not osteogenic medium induced osteogenic differentiation of HPDCs and RPDCs in vitro, but at different rates. In contrast to HPDCs, RPDCs failed to make ectopic bone in a hydroxyapatite/tri-calciumphosphate/collagen type I (Collagraft™) carrier after implantation in nude mice. Moreover, seeding and implantation of autologous RPDCs in a Collagraft™ and Vitoss™ (β-tricalcium) carrier did not enhance orthotopic bone formation under a titanium cup which was placed on the skull of White New Zealand rabbits. These findings may jeopardize the rabbit as a preclinical model and prompted us to further investigate the mechanisms of action of ectopic bone formation by HPDCs. Cell tracking experiments revealed that the ectopic bone formed by HPDCs was a chimeric tissue consisting of engrafted HPDCs and mouse cells. Hence, the mode of action comprises recruitment of host cells and proliferation and osteogenic differentiation of both donor and host cells. Furthermore, we have shown that endogenous BMP signaling of the HPDCs plays a central role in this cascade of biological events. However, BMP signaling alone did not explain the discrepancy observed between protein versus cell based induced bone formation. Implanting Collagraft™ coated with BMP6 protein resulted in endochondral bone formation whereas Collagraft™ containing HPDCs displayed intramembranous ossification. Thus the secretion of BMP signals seems not to explain cell based bone formation. Some preliminary data (β-catenin immunohistochemistry) and work from others suggest that Wnt signaling may be involved in this process. In addition, we have noticed that HPDCs produce limited amounts of bone tissue in scaffolds as compared to the amount of bone formed by the periosteum during fracture healing or distraction osteogenesis. This may partially be explained by the lack of mechanical load in the ectopic assay, whereas stretch and pressure occur during fracture healing and distraction osteogenesis. To provide a dynamic mechanical environment to HPDCs, we have developed and validated a bioreactor which can apply both Hydrostatic Pressure and Stretch (HyPaS) on cells. This unique feature of HyPaS makes it possible to answer the question if hydrostatic pressure and stretch differentially regulate genes involved in the osteochondral differentiation of HPDCs. Our first experiments showed that HPDCs can respond on stretch and on hydrostatic pressure. HyPaS will be used to study the interplay of BMP/Wnt signaling and mechanical load in the context of osteochondral differentiation. Understanding the molecular basis of mechanical and biochemical signaling in every stage of de novo bone formation i.e. cell recruitment, proliferation, differentiation, tissue formation, integration and remodeling, may lead to the design of better tissue engineering solutions restoring the ‘bio-mechanical’ function of the newly formed bone in the defect.
Source: Lirias
Author: Jeroen Eyckmans
Language: English
Subfield: Biomedical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2522884483