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

Abstract

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, modifications of the polymer with these functional groups are 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.

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Publication details

The article was received on 04 Sep 2017, accepted on 04 Dec 2017 and first published on 05 Dec 2017


Article type: Paper
DOI: 10.1039/C7TB02363D
Citation: J. Mater. Chem. B, 2017, Accepted Manuscript
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    Structural effects of phosphate groups on apatite formation in copolymer modified with Ca2+ in a simulated body fluid

    R. Hamai, H. Maeda, H. Sawai, Y. SHIROSAKI, T. Kasuga and T. Miyazaki, J. Mater. Chem. B, 2017, Accepted Manuscript , DOI: 10.1039/C7TB02363D

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