title: Fabrication of amorphous strontium polyphosphate microparticles that induce mineralization of bone cells in vitro and in vivo.
abstract: Here we describe the fabrication process of amorphous strontium-polyphosphate microparticles ("Sr-a-polyP-MP"). The effects of these particles on growth and gene expression were investigated with SaOS-2 cells as well as with human mesenchymal stem cells (MSC) and compared with those particles prepared of amorphous calcium-polyphosphate ("Ca-a-polyP-MP") and of strontium salt. The results revealed a markedly higher stimulation of growth of MSC by "Sr-a-polyP-MP" compared to "Ca-a-polyP-MP" and a significant increase in mineralization of SaOS-2 cells, as well as an enhanced upregulation of the expression of the genes encoding for alkaline phosphatase and the bone morphogenetic protein 2 (BMP-2), likewise performed with SaOS-2 cells. On the other hand, "Sr-a-polyP-MP" only slightly changes the expression of the osteocyte-specific sclerostin, a negative regulator of the canonical Wnt signaling pathway and an inhibitor of bone cell differentiation as well as of mineralization in SaOS-2 cells. In contrast, "Ca-a-polyP-MP" strongly increased the steady-state expression of the SOST (sclerostin) gene. In animal studies poly(d,l-lactide-co-glycolide (PLGA) microspheres, containing polyP particles, were implanted into critical-size calvarial defects in rats. The results show that the amorphous Sr-polyP-containing microspheres caused an increased healing/mineralization of the bone defect even after short implantation periods of 8-12weeks, if compared to the β-tri-calcium phosphate control as well as to Ca-polyP. It is proposed that "Sr-a-polyP-MP" might elicit suitable properties to be applied as a regeneratively active implant material for bone repair.
  
  
  
  In this manuscript, we fabricated amorphous strontium-polyphosphate microparticles ("Sr-a-polyP-MP") and studied their effects on bone mineral formation in vitro as well as in vivo. In vitro, those particles substantially increased the expression of the genes encoding for alkaline phosphatase, the bone morphogenetic protein 2 and the mineralization. In vivo, the "Sr-a-polyP-MP" packed into PLGA microspheres and implanted into critical-size calvarial defects in rats resulted in a speeded up of the healing/mineralization of the bone defect. Those properties qualify Sr-a-polyP as a suitable biomaterial for bone regenerative implants.
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: Institute of Functional and Clinical Anatomy, University Medical Center of the Johannes Gutenberg University, Johann Joachim Becher Weg 13, D-55099 Mainz, Germany.
authors.forename: Maximilian
authors.initials: M
authors.lastname: Ackermann
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: Meik
authors.initials: M
authors.lastname: Neufurth
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: Shunfeng
authors.initials: S
authors.lastname: Wang
authors.affiliation: Key Laboratory of Advanced Materials of Ministry of Education of China, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China.
authors.forename: Qingling
authors.initials: Q
authors.lastname: Feng
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: 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: D000818:Animals; D000943:Antigens, Differentiation / Q000096:biosynthesis; D002113:Calcification, Physiologic / Q000187:drug effects*; D045744:Cell Line, Tumor; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D059630:Mesenchymal Stem Cells / Q000378:metabolism*; D008863:Microspheres; D010011:Osteocytes / Q000378:metabolism*; D011122:Polyphosphates / Q000737:chemistry / Q000494:pharmacology; D051381:Rats; D013324:Strontium / Q000737:chemistry / Q000494:pharmacology; D060449:Wnt Signaling Pathway / Q000187:drug effects
chemical_list: D000943:Antigens, Differentiation; D011122:Polyphosphates; D013324:Strontium
keywords: Alkaline phosphatase; BMP2; Bone; Bone repair; Critical size defect; Human mesenchymal stem cells; Microparticles; Polyphosphate; SaOS-2 cells; Sclerostin; Strontium