Effects of Co-culture on Ligament Fibroblast and Osteoblast Growth and Differentiation

INTRODUCTION The anterior cruciate ligament (ACL) connects the femur to the tibia, and functions as a joint stabilizer. ACL tears and ruptures are the most common knee ligament injuries, and affect over 250,000 people per year in the United States alone[1]. Current ACL reconstruction procedures cannot fully restore function without associated side effects such as donor site morbidity, muscle atrophy, tendonitis, and arthritis. Although semitendonous autografts are superior to other clinical alternatives, they often fail at the insertion site between the graft and the bone tunnel [6]. Thus, the degree of graft integration with osseous tissue is a critical factor governing its clinical success. The long term objective of our research program is to design functional interfaces which can facilitate the integration of bone with soft tissues. The natural insertion site between ACL and bone is divided into four zones: ligament, non-mineralized and mineralized cartilage, and bone [4-6]. It is not well understood how this interface is formed and how cell-cell interactions may regulate its maintenance and repair. In order to examine the formation of such an interface in vitro , and eventually replicate it on a tissue-engineered scaffold, we have elected to first focus on establishing reliable co-culture systems of osteoblasts and ligament fibroblasts. The objective of this study is to develop an in vitro osteoblast-fibroblast co-culture model, and to examine the morphology, growth and phenotypic response of each cell type during co-culture. It is hypothesized that osteoblasts and ACL fibroblasts will maintain their phenotype during co-culture.