Polyphosphate: A Morphogenetically Active Implant Material Serving as Metabolic Fuel for Bone Regeneration

The initial mineralization centers during human bone formation onto osteoblasts are composed of CaCO3. Those bioseeds are enzymatically formed via carbonic anhydrase(s) in close association with the cell surface of the osteoblasts. Subsequently, the bicarbonate/carbonate anions are exchanged non‐enzymatically by inorganic phosphate [Pi]. One source for the supply of Pi is polyphosphate [polyP] which is a physiological polymer, formed in the osteoblasts as well as in the platelets. The energy‐rich acid anhydride bonds within the polyP chain are cleaved by phosphatase(s); during this reaction free‐energy might be released that could be re‐used, as metabolic fuel, for the maintenance of the steady‐state concentrations of the substrates/products during mineralization. Finally it is outlined that polyP, as a morphogenetically active scaffold, is even suitable for 3D cell printing. Polyphosphate (polyP) is a natural inorganic polymer that is synthesized in cells in close vicinity of bone tissue. This polymer is biocompatible and bioresorbable. The characteristic features of polyP are the physiological origin and the huge conserved reservoir of metabolic energy. Since Ca‐polyP is built of phosphate and Ca2+, it can be fabricated to bone scaffolds.