Structural effects of phosphate groups on apatite formation in a copolymer modified with Ca2+ in a simulated body fluid

Ryo Hamai, Hirotaka Maeda, Hikaru Sawai, Yuki Shirosaki, Toshihiro Kasuga, Toshiki Miyazaki

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4 Citations (Scopus)


Organic-inorganic composites are novel bone substitutes that can ameliorate the mismatch of Young's moduli between natural bone and implanted ceramics. Phosphate groups contribute to the formation of apatite in a simulated body fluid (SBF) and the adhesion of osteoblast-like cells. Therefore, modification of a polymer with these functional groups is expected to enhance the ability of the organic-inorganic composite to bond with bone. Two phosphate groups have been used, phosphonic acid (-C-PO3H2) and phosphoric acid (-O-PO3H2). However, the effects of structural differences between these phosphate groups have not been clarified. In this study, the apatite formation of copolymers modified with Ca2+ and either -C-PO3H2 or -O-PO3H2 was examined. The mechanism of apatite formation is discussed based on analytical and computational approaches. The copolymers containing -O-PO3H2, but not those containing -C-PO3H2, formed apatite in the SBF, although both released similar amounts of Ca2+ into the SBF. Adsorption of HPO42- from -O-PO3H2 in the SBF following Ca2+ adsorption was confirmed by zeta-potential measurement and X-ray photoelectron spectroscopy. The measurement of the complex formation constant revealed that the -O-PO32-⋯Ca2+ complex was thermodynamically unstable enough to convert into CaHPO4, which was not the case with -C-PO32-⋯Ca2+. The formation of CaHPO4-based clusters was found to be a key factor for apatite nucleation. In conclusion, this study revealed that modification with -O-PO3H2 was more effective for enhancing apatite formation compared with -C-PO3H2.

Original languageEnglish
Pages (from-to)174-182
Number of pages9
JournalJournal of Materials Chemistry B
Issue number1
Publication statusPublished - 2017
Externally publishedYes

ASJC Scopus subject areas

  • Chemistry(all)
  • Biomedical Engineering
  • Materials Science(all)


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