Mineralized Collagen: Adaptation of the Mineral Content to Control BMP-2 Delivery

To achieve bone regeneration in critical size defects, filling of the defect either with autologous bone or with a biodegradable bone substitute material possessing osteoconductivity and osteoinductivity is required. Biomimetically mineralized collagen is a nanocomposite material that closely resembles the natural bone matrix in composition and structure and has proven potential for filling bone defects. Since the mineral phase hydroxyapatite can bind proteins, the aim of the present study was to explore this biomaterial as a delivery system for the osteoinductive factor bone morphogenetic protein-2 (BMP-2) and to investigate the dependence of BMP-2 release on the mineral content. Three-dimensional scaffolds with varying mineral content were prepared by blending biomimetically mineralized collagen and non-mineralized collagen suspensions, followed by freeze-drying and chemical crosslinking. While the average pore size decreased, the stiffness of the scaffolds increased with increasing mineral content; all scaffold variants exhibited a fundamentally elastic behavior. After loading, the release of BMP-2 was investigated over 28 days. A significant influence of the mineral content on the release kinetics of BMP-2 was observed-the higher the mineral content, the stronger the retention of BMP-2 in the scaffolds. In contrast, the release of the vascular growth factor-A (VEGF-A), which was examined for comparison, was hardly influenced by the mineral content, indicating a low retention of VEGF-A by binding to the mineral phase. In summary, adjustment of the mineral content opens up the possibility of controlling the release of BMP-2 in a customized manner, but this is not transferable to VEGF-A.