Effects of Osteoblast and Chondrocyte Co-culture on Chondrogenic and Osteoblasticphenotypes in Vitro

INTRODUCTION: Osteoarthritis is the predominant form of arthritis, with 21 million Americans suffering from this degenerative condition.[1] Articular cartilage has an inherently poor repair potential, thus clinical intervention is needed. A recent area of interest is the formation of osteochondral grafts[2-4] and the design of interfaces to facilitate integration of bone with cartilage. The osteochondral interface is believed to be critical in graft integration and long term functionality in vivo. Focusing on the interface, our long term goal is to develop osteochondral grafts by co-culturing osteoblasts and chondrocytes on constructs with optimized cellular and structural properties. It is not known how the interface between bone and cartilage is developed, and how it is remodeled during cartilage repair. Since osteoblast-chondrocyte interactions are not well understood, a simple and reliable in vitro culturing model is needed to identify optimal coculturing parameters which can later be applied to complex scaffolds. A significant challenge in osteoblast-chondrocyte co-culture is that, unlike osteoblasts, chondrocytes dedifferentiate in monolayer cultures. We propose a sequential culturing protocol whereby chondrocytes are initially seeded in high density micromass cultures, after which osteoblasts are allowed to directly adhere to the micromasses. The objective of this study is to evaluate the effects of co-culturing on the growth and phenotypic expression of osteoblasts and chondrocytes. It is hypothesized that osteoblasts and chondrocytes can be co-cultured together and individual phenotypes will be maintained during co-culture.