Enhanced bone morphogenetic protein-2 performance on hydroxyapatite ceramic surfaces

The immobilization of biomolecules on biomaterial surfaces allows for the control of their localization and retention. In numerous studies, proteins have been simply adsorbed to enhance the biological performance of various materials in vivo. We investigated the potential of surface modification techniques on hydroxyapatite (HA) ceramic discs in an in vitro approach. A novel method for protein immobilization was evaluated using the aminobisphosphonates pamidronate and alendronate, which are strong Ca chelating agents, and was compared with the established silanization technique. Lysozyme and bone morphogenetic protein-2 (BMP-2) were used to assess the suitability of the two surface modification methods with regard to the enzymatic activity of lysozyme and to the capacity of BMP-2 to stimulate the osteoblastic differentiation of C2C12 mouse myoblasts. After immobilization, a 2.5-fold increase in enzymatic activity of lysozyme was observed compared with the control. The alkaline phosphatase activity per cell stimulated by immobilized BMP-2 was 2.5-fold higher [9 x 10(-6) I.U.] than the growth factor on unmodified surfaces [2-4 x 10(-6) I.U.]. With regard to the increase in protein activity, both procedures lead to equivalent results. Thus, the bisphosphonate-based surface modification represents a safe and easy alternative for the attachment of proteins to HA surfaces.