Optimization of bone engineering by means of growth factors in a three-dimensional matrix

The direction and acceleration of differentiation by administering growth factors is one of the ways of optimizing bone engineering. The present study considered the influence of the growth factors factor XIII, TGF-beta 1, and b-FGF on the proliferation and osteogenic differentiation of porcine periosteal cells in a three-dimensional carrier matrix (bead), consisting of a fibrin-alginate-hydroxyapatite composite. F XIII, TGF-beta 1, and b-FGF were added to the culture medium of monolayer culture and fibrin beads in different concentrations. The monolayer culture was assessed on the basis of cell counts, while DNA, osteocalcin, osteonectin, and collagen content and alkaline phosphatase activity were determined, and microscopic and immunohistologic evaluations were performed for the beads. In the monolayer, the addition of b-FGF led to a significantly shorter time up to the confluence of the cells. In the bead, cell proliferation was accelerated by b-FGF and TGF-beta 1. With regard to alkaline phosphatase activity, factor XIII led to significantly higher values, while b-FGF and TGF-beta 1 resulted in lower activities. Osteocalcin content was significantly increased by the application of b-FGF. For the osteonectin content the addition of growth factors did not produce any changes. The application of TGF-beta 1 during the monolayer culture significantly increased the primary collagen content of the beads. The administration of different growth factors opens up new ways of optimizing cell growth in vitro and of directing the osteogenic differentiation of periosteal cells, without one universally applicable factor having been demonstrated. It will be the task of further studies to analyze the interaction of individual factors and the chronologic dependency of the action, on the way to in vitro bone generation.