Amorphous polyphosphate-hydroxyapatite: A morphogenetically active substrate for bone-related SaOS-2 cells in vitro

摘要

There is increasing evidence that inorganic calcium-polyphosphates (polyp) are involved in human bone hydroxyapatite (HA) formation. Here we investigated the morphology of the particles, containing calcium phosphate (Cap) with different concentrations of various Na-polyP concentrations, as well as their effects in cell culture. We used both SaOS-2 cells and human mesenchymal stem cells. The polymeric phosphate readily binds calcium ions under formation of insoluble precipitates. We found that addition of low concentrations of polyP (<10 wt.%, referred to the CaP deposits) results in an increased size of the HA crystals. Surprisingly, at higher polyp concentrations (>10 wt.%) the formation of crystalline HA is prevented and amorphous polyP/HA hybrid particles with a size of a similar to 50 nm are formed, most likely consisting of polyp molecules linked via Ca2+ bridges to the surface of the CaP deposits. Further studies revealed that the polyp-Cap particles cause a strong upregulation of the expression of the genes encoding for two marker proteins of bone formation, collagen type I and alkaline phosphatase. Based on their morphogenetic activity the amorphous polyp-Cap particles offer a promising material for the development of bone implants, formed from physiological inorganic precursors/polymers.