Polyphosphate as a Bioactive and Biodegradable Implant Material: Induction of Bone Regeneration in Rats

Inorganic polyphosphate (polyP) is a naturally occurring polymer that is bioresorbable and anabolically active on bone forming cells in vitro. In order to demonstrate if polyP also shows morphogenetic activity in vivo, animal studies are performed applying the rat calvarial defect model. Poly(D,L-lactide-co-glycolide) (PLGA) microspheres with a narrow size distribution (approximate to 820 mu m) are prepared, containing either encapsulated polyP or beta-tricalcium phosphate (beta-TCP), used as a reference material. Discs are prepared from the microspheres and inserted into 10mm large defects created in the calvaria of rats. Both the formation of COL-I and the expression of ALP is upregulated, as well as the extent of mineralization within and around the polyP implant. Our data demonstrate that amorphous and resorbable inorganic polyP is also morphogenetically active in vivo.