Bone tissue engineering by cell and matrix transplantation
Bancroft, Gregory Nelson
Mikos, Antonios G.
Doctor of Philosophy
There is a current significant clinical need for bone replacement. Although some therapies and bone substitutes are in current use, their disadvantages provide a strong motivation for new approaches. The field of tissue engineering seeks to mitigate this problem by the concerted application of strategies involving cells, scaffolding, and growth factors. One such approach is a cell-based bone tissue engineering paradigm which involves obtaining an osteoblast precursor population from a patient, expanding this cell population, and seeding it on a biomaterial scaffold before implanting the created tissue engineering construct back into the patient. One variable in this approach is the method of culturing the seeded scaffold prior to implantation. There are several commercially available bioreactors. They were investigated in this work. Although one of the bioreactors, the spinner flask, showed an enhancement in the growth and differentiation of the stromal osteoblasts cultured on the scaffold, the cell growth was limited to a superficial crusting on the surface of the scaffolds. To overcome these apparent internal diffusion limitations, a flow perfusion culture system was developed. In this research, such a system was found to not only allow for true three-dimensional culture with elaboration of cellular and matrix elements throughout a scaffold, but also allow for the potent mechanical stimulation of the cultured cells with fluid shear forces. These studies indicate that flow perfusion culture enhances marrow stromal osteoblast and dramatically increases mineralized matrix production when compared to static culture. This effect was found to be dependent on perfusing flow rate with higher rates leading to higher mineralization. The in vivo performance of these cell/scaffold constructs were evaluated in a rat critical size cranial defect model with constructs cultured for 1, 4, and 8 days in both static and flow perfusion culture. The best results were obtained with constructs cultured for 1 day in the flow perfusion system highlighting the importance of transplanting a osteoprogenitor population capable of migration, proliferation, and differentiation to a critical size cranial defect. The results also suggested that in vitro-generated matrix can contribute to in vivo bone healing.
Cell biology; Biomedical engineering