Evolution of an In Vivo Bioreactor
Holt, Ginger E. et. al. Journal of Orthopedic Research. Vol. 23. 2005. 916-923.

Bone grafts are typically needed when fractures fail to mend, there is substantial bone loss after severe injury, necrosis due to avascularization, or for bone reconstruction post tumor removal (i.e. bone marrow cancer). These cases are usually treated with autogenous bone grafts. As with any implantation/transplantation, donor health (site of treatment), mechanical performance of the implant, vascularization, sterilization, and cost are critical considerations for successful treatment. To ameliorate or even alleviate these issues, the field of tissue engineering has lately been developing ideal bone graft substitutes.

There are three properties to characterize an ideal bone graft substitute: using 1) osteoconductive scaffolds, 2) osteoinductive proteins, that in turn maintain 3) osteogenic cells. Experimental implants were created using a combination of a coral exoskeleton scaffold, with and without bone morphogenic protein (BMP-2) and with or without a vascular pedicle. The bioreactors were harvested in rats. Via histology, actual bone formation (osteocytes, osteoblasts, and osteiod regions) and new vascularization only occurred in the presence of BMP-2 and a vascular pedicle (and the coral scaffold).

This paper was particularly interesting because bone formation can provide a model for the study cancer. It is believed that the same processes that occur in osteogenesis within a scaffold, cell differentiation and proliferation are very similar to that of tumor metastisis. Furthermore we talked about the use of controls and their importance in experimental design. Though seemingly having a minor effect, without the controls constructed in this experiment, key factors of bone formation could not be understood. And in turn tumor metastisis dynamics would have that much less potential for understanding.