Human osteoblastic cell integrin expression, maturation and growth on tissue engineered matrices designed for skeletal regeneration

The main objective of this study was to examine the molecular interaction involved in human osteoblastic cells seeded on biodegradable tissue engineered matrices, polylactic-co-glycolic acid (PLAGA) and polylactic acid (PLA) polymers designed for skeletal regeneration. Initial examination revealed that human osteoblastic cells isolated from trabecular bone were successfully obtained and grown on polymeric matrices both at relatively short and long-term periods. Examination of cells at the molecular level revealed, human osteoblastic cells adhered through their known adhesion receptors, integrins, with a higher rate of expression being controlled by the matrices polymeric composition and surface properties. In addition, studies on the extracellular matrix molecules (ECM), in which the integrins adheres to, were confirmed to be produced by osteoblastic cells seeded on matrices at various rates as well. Studies on blocking integrin adhesion receptors, via antibodies specific to the subunits, and peptides (RGD and RGE), revealed that initial cellular adhesion is dependent on integrin binding to key components of collagen ([alpha]2[beta]1) and fibronectin ([alpha]5[beta]1) molecules, respectively. Long-term growth of these materials revealed that human osteoblastic cells were able to grow, maturate and produce a mineralized matrix from collagen and proteoglycan constituents. In addition, studies on optimizing the PLAGA matrix into a 3-Dimensional microsphered matrix to resemble bone revealed that human osteoblastic cells were able to fully attach, grow, maintain their phenotypic behavior as well as a cytoskeletal (actin) framework throughout the material. During, in vivo analysis of this matrix in 15 mm non-union defect model in New Zealand White rabbits, osseointegration at the bone/implant site, integrin receptor formation and healing of the defect were observed and enhanced through providing a scaffold fabricated into an osteoinductive, osteocondcutive or osteogenic material. Overall, we feel that these studies have provided the area of tissue engineering of bone a better understanding of the molecular events involved in osteoblast adhesion, especially to novel polymeric matrices that are becoming more applicable in the fields of science and medicine.