title: Amorphous polyphosphate-hydroxyapatite: A morphogenetically active substrate for bone-related SaOS-2 cells in vitro.
abstract: 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 (<10wt.%, referred to the CaP deposits) results in an increased size of the HA crystals. Surprisingly, at higher polyP concentrations (>10wt.%) the formation of crystalline HA is prevented and amorphous polyP/HA hybrid particles with a size of ≈50nm are formed, most likely consisting of polyP molecules linked via Ca(2+) 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.
  
  
  CONCLUSIONS
  Hydroxyapatite (HA) is a naturally occurring mineral of vertebrate bone. Natural HA, a bio-ceramic material which is crystalline to different scale, has been used as a biomaterial to fabricate scaffolds for in situ bone regeneration and other tissue engineering purposes. In contrast to natural HA, synthetic apatite is much less effective. In general, while HA is bioactive, its interaction and biocompatibility with existing bone tissue is low. These properties have been attributed to a minimal degradability in the physiological environment. In the present study we introduce a new Ca-phosphate (CaP) fabrication technology, starting from calcium chloride and dibasic ammonium phosphate with the HA characteristic Ca/P molar ratio of 10:6 and report that after addition >10% (by weight) of polyphosphate (polyP) amorphous CaP/HA samples were obtained. Those samples elicits strong morphogenetic activity let us to conclude that polyP/HA-based material might be beneficial for application as bone substitute implant.
authors.affiliation: ERC Advanced Investigator Grant Research Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University, Duesbergweg 6, D-55128 Mainz, Germany. Electronic address: wmueller@uni-mainz.de.
authors.forename: Werner E G
authors.initials: WEG
authors.lastname: Müller
authors.affiliation: ERC Advanced Investigator Grant Research Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University, Duesbergweg 6, D-55128 Mainz, Germany.
authors.forename: Emad
authors.initials: E
authors.lastname: Tolba
authors.affiliation: ERC Advanced Investigator Grant Research Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University, Duesbergweg 6, D-55128 Mainz, Germany.
authors.forename: Heinz C
authors.initials: HC
authors.lastname: Schröder
authors.affiliation: Department of Physical Chemistry of Polymers, Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany.
authors.forename: Rafael
authors.initials: R
authors.lastname: Muñoz-Espí
authors.affiliation: NanotecMARIN GmbH, Duesbergweg 6, D-55128 Mainz, Germany.
authors.forename: Bärbel
authors.initials: B
authors.lastname: Diehl-Seifert
authors.affiliation: ERC Advanced Investigator Grant Research Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University, Duesbergweg 6, D-55128 Mainz, Germany. Electronic address: wang013@uni-mainz.de.
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Wang
mesh_terms: D000469:Alkaline Phosphatase / Q000737:chemistry; D001672:Biocompatible Materials / Q000737:chemistry; D002113:Calcification, Physiologic / Q000187:drug effects; D002118:Calcium / Q000737:chemistry*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D024042:Collagen Type I / Q000737:chemistry; D017886:Durapatite / Q000737:chemistry*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D006882:Hydroxyapatites / Q000737:chemistry; D007477:Ions; D059630:Mesenchymal Stem Cells / Q000166:cytology; D008854:Microscopy, Electron; D046529:Microscopy, Electron, Transmission; D008863:Microspheres; D010006:Osteoblasts / Q000166:cytology*; D010012:Osteogenesis; D011108:Polymers / Q000737:chemistry; D011122:Polyphosphates / Q000737:chemistry*; D012964:Sodium / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D023822:Tissue Engineering / Q000379:methods; D054457:Tissue Scaffolds / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D001672:Biocompatible Materials; D024042:Collagen Type I; D006882:Hydroxyapatites; D007477:Ions; D011108:Polymers; D011122:Polyphosphates; D017886:Durapatite; D012964:Sodium; D000469:Alkaline Phosphatase; D002118:Calcium
keywords: Alkaline phosphatase; Collagen type I; Hydroxyapatite; Microparticles; Morphogenetic activity; Polyphosphate