Characterization, Dissolution, and Solubility of Zn-Substituted Hydroxylapatites [(ZnxCa1−x)5(PO4)3OH] at 25°C

Xin Zhao,Zongqiang Zhu,Ju Lin,Yanpeng Liang,Yinian Zhu,Yanlong Niu

doi:10.1155/2017/4619159

Xin Zhao, Zongqiang Zhu + Show 4 more

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https://doi.org/10.1155/2017/4619159

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Abstract

A series of Zn-substituted hydroxylapatites [(ZnxCa1−x)5(PO4)3OH, Zn-Ca-HA] with the Zn/(Zn + Ca) molar ratio (XZn) of 0~0.16 was prepared and characterized, and then the dissolution of the synthesized solids in aqueous solution was investigated by batch experiment. The results indicated that the aqueous zinc, calcium, and phosphate concentrations greatly depended on the Zn/(Zn + Ca) molar ratio of the Zn-Ca-HA solids (XZn). For the Zn-Ca-HA dissolution at 25°C with an initial pH of 2.00, the final solution pH increased, while the final solution calcium and phosphate concentrations decreased with the increasing XZn. The final solution zinc concentrations increased with the increasing XZn when XZn≤0.08 and decreased with the increasing XZn when XZn = 0.08~0.16. The mean Ksp values for (ZnxCa1−x)5(PO4)3OH at 25°C decreased from 10−57.75 to 10−58.59 with the increasing XZn from 0.00 to 0.08 and then increased from 10–58.59 to 10–56.63 with the increasing XZn from 0.08 to 0.16. This tendency was consistent with the dependency of the lattice parameter a on XZn. The corresponding free energies of formation (ΔGfo) increased lineally from −6310.45 kJ/mol to −5979.39 kJ/mol with the increasing XZn from 0.00 to 0.16.

Highlights

Phosphate apatites form an enormous mineral group due to their huge isomorphic capacity [1, 2], which play an important role in many research areas such as biomaterials and environmental science [3,4,5,6,7].As the main inorganic constituent of bone and dental enamel of vertebrates, calcium hydroxylapatite (HA) has been broadly used in osteoinductive coatings, bone replacement and repair, dental orthopaedics, and so forth [3, 6, 8,9,10,11]
An aqueous solution with [P] = 0.12 mol/L was first prepared by dissolving NH4H2PO4 into ultrapure water, and a series of the mixed aqueous solutions with [Zn + Ca] =
The moles of Zn(CH3COO)2⋅2H2O and Ca(CH3COO)2⋅H2O were varied in each preparation to get the mixed aqueous solutions with different [Zn]/[Zn + Ca] molar ratios of 0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, 0.16, 0.18, and 0.20. 250 mL of the Zn2+ and Ca2+ mixture solution was added to 250 mL

Summary

Introduction

Phosphate apatites form an enormous mineral group due to their huge isomorphic capacity [1, 2], which play an important role in many research areas such as biomaterials and environmental science [3,4,5,6,7].As the main inorganic constituent of bone and dental enamel of vertebrates, calcium hydroxylapatite (HA) has been broadly used in osteoinductive coatings, bone replacement and repair, dental orthopaedics, and so forth [3, 6, 8,9,10,11]. The substitution of trace ions in hydroxylapatite can affect its lattice parameters a and c, crystallinity, and morphology, and its dissolution mechanism and other physicochemical properties [10,11,12]. Zinc is one of the most important essential trace elements for the growth of humans and its incorporation in Ca-hydroxylapatite can significantly improve the bioactivity of Ca-hydroxylapatite [8,9,10]. The slow release of zinc substituted in an implant Ca-hydroxylapatite material can promote bone metabolism and growth around the implant. The zinc-substituted hydroxylapatite can be a novel biomaterial for bone tissue engineering [10, 13]

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