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

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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, 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.

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

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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, 2018, Advance Article
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    Structural effects of phosphate groups on apatite formation in a 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, 2018, Advance Article , DOI: 10.1039/C7TB02363D

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