Biologization of allogeneic bone grafts with polyphosphate : a route to a biomimetic periosteum

Abstract

The physiological polyphosphate (polyP), released primarily from platelets after bone fractures, acts as a donor for metabolic energy and as a phosphate source for bone mineralization. In this study allogeneic, decellularized bone samples are biologized with a layer of inorganic polyP by submersion of human femur cortex slices into a solution of Na-polyP. Then polyP coat is modified by exposure to CaCl2, resulting in in situ formation of amorphous Ca-polyP microparticles (Ca-polyP-MP; diameter of ≈155 nm). Energy dispersive X-ray spectroscopy analysis of the Ca-polyP-MP coat reveals a Ca:P molar ratio of ≈0.78, while the nonmodified bone cortex is characterized by a Ca:P ratio of ≈1.52. An ionic shift promotes the strong binding of the polyP to the bone. While the polyP modification only insignificantly increases the hardness of the bone sample, without changing the elastic surface properties, the polyP-modified bone provides a very favorable substrate for SaOS-2 cells to attach and to mineralize. In the presence of medium/serum the polyP coat transforms to a functionally active coacervate. The cells, attached to the polyP coat, show a marked spreading behavior and became entrapped into the polyP-coacervate. The results suggest that regenerative-active polyP might be of potential use in healing of bone.