The use of bioactive molecules is a promising approach to enhance the bone healing properties of biomaterials. The aim of this study was to define the role of bone sialoprotein (BSP) immobilized in collagen type I in various settings. In vitro studies with human primary osteoblasts in mono- or in co-culture with endothelial cells demonstrated a slightly increased gene expression of osteogenic markers as well as an increased proliferation rate in osteoblasts after application of BSP immobilized in collagen type I. Two critical size bone defect models were used to analyze bone regeneration. BSP incorporated in collagen type I increased bone regeneration only marginally at one concentration in a calvarial defect model. To induce the mechanical stability, three-dimensional printing was used to produce a stable porous cylinder of polylactide. The cylinder was filled with collagen type I and immobilized BSP and implanted into a femoral defect of critical size in rats. This hybrid material was able to significantly induce bone regeneration. Our study clearly shows the osteogenic effect of BSP when combined with collagen type I as carrier and thereby offers various approaches and options for its use as bioactive molecule in bone substitute materials
