Fabrication and evaluation of Zn containing fluoridated hydroxyapatite layer with Zn release ability

doi:10.1016/j.actbio.2007.08.013

Acta Biomaterialia

Volume 4, Issue 2, March 2008, Pages 441-446

https://doi.org/10.1016/j.actbio.2007.08.013 Get rights and content

Abstract

A biphasic layer with a Zn-containing β-tricalcium phosphate (ZnTCP) phase and a fluoridated hydroxyapatite (FHA) phase on titanium alloy substrate was prepared by the sol–gel technique. Scanning electron microscopy and energy-dispersive X-ray analysis results showed the ZnTCP/FHA layer to have a heterogeneous surface with microscaled gibbous structures originating from ZnTCP particle agglomeration. This layer had a slow and sustained Zn release behavior. The scratch test result of the ZnTCP/FHA layer was 489 ± 4 mN, indicating good interface bonding between the layer and substrate. The ZnTCP/FHA layer supported cell growth, and showed a statistically significant increase in cell viability in comparison with another biphasic layer (TCP/FHA) without Zn. This work demonstrates that the present biphasic ZnTCP/FHA layer has the potential to play a significant role in enhancing bone growth when used as the outermost part of bioactive coatings on metallic implants.

Introduction

Titanium implants with hydroxyapatite (HA) coatings have been widely used in orthopedic surgery as bone substitutes because of the combination of good biocompatibility and good mechanical properties [1], [2], [3], [4]. However, there are still concerns about their use, such as the in vivo resorption of HA coatings over time, which could deteriorate bone bonding at the interface. Additionally, the debris that peels off from the coating may activate osteoclasts, leading to osteolysis [5], [6]. In order to improve the long-term chemical and mechanical stability of the coated implants, fluoridated hydroxyapatite (FHA) coatings have attracted considerable attention, with FHA being proven to have lower resorption than HA but comparable bioactivity [7], [8], [9], [10], [11], [12]. However, FHA coatings have not been demonstrated to show early osteointegration.

The incorporation of trace elements into Ca–P biomaterials has proven to be an effective way to simulate cell viability [13], [14]. Zn has been shown to be capable of increasing osteoblast proliferation, biomineralization and bone formation [15], [16]. However, the pharmacological performance of zinc ions is dependent on the release behavior. Generally, the initial burst release of ions in the body may induce adverse reactions. Yamamoto evaluated the cytotoxicity of zinc salts using the colony formation method, and found that the 50% inhibitive concentration of zinc for MC3T3-E1 cells cultured in α-modified Eagle’s medium + 10% fetal bovine serum (FBS) was about 5.85 mg l^–1 [17]. Thus, the release process should be controlled, and a slow and sustained rate is required during bone tissue regeneration.

In our previous work, we prepared a biphasic β-tricalcium phosphate (TCP)/FHA layer with heterogeneous structure and chemistry [18], in which the TCP phase is biodegradable and can serve as a good carrier for zinc [14]. Here, we propose a bilayer strategy (as shown in Fig. 1) to create an early osteointegration ability for FHA coatings. The bottom layer is FHA, which provides the bioactivity and long-term stability of the coating, and the top layer is designed as a biphasic layer that consists of ZnTCP and FHA. In the top ZnTCP/FHA layer, ZnTCP biodegradation causes the simultaneously release of Zn, which leads to a coating with Zn ion release ability. In this work, a ZnTCP/FHA biphasic layer was prepared by the sol–gel technique, the microstructure of the layer was characterized and the layer was evaluated for cell culture behavior.

Section snippets

Synthesis of ZnTCP powders

Ca(NO₃)₂ · 4H₂O (AR) and poly(ethylene glycol) (AR) were dissolved in deionized water. After 0.5 M Zn(NO₃)₂ · 4H₂O (AR) was mixed in at a molar percentage of 9% (Zn/(Zn + Ca)), the mixed solution was vigorously stirred in a beaker placed in an ice-water bath. NH₄H₂PO₄ (AR) solution was added dropwise to produce a gelatinous precipitate, and ammonia solution was added simultaneously to maintain the pH at 10.5. The system was allowed to age for a further half an hour before vacuum filtration. The

Layer characterizations

We have previously shown that the layer obtained from the colloidal solution is composed of two phases: FHA and TCP [18]. The surface morphology of the biphasic layer is shown in Fig. 2. Both the ZnTCP/FHA and the TCP/FHA layers on Ti6Al4V substrate exhibit a heterogeneous surface with microscale roughness. The rough morphology formation is attributed to the ZnTCP or TCP particle agglomeration on the surface by the surface tension drive force during the transformation of the liquid layer into a

Conclusion

A novel ZnTCP/FHA layer with a microscale structure and Zn release ability on a titanium substrate was prepared using the sol–gel method. The biphasic ZnTCP/FHA layer has a heterogeneous surface and a well bonded interface. The results showed that the degradation of ZnTCP could release Zn ions in a slow and sustained manner for up to 10 days. In addition, the ZnTCP/FHA layer showed a statistically significant increase in cell viability in comparison with a control TCP/FHA layer without Zn. If

Acknowledgements

This work was supported by the Research Fund of the Doctoral Program of Higher Education of China (20050335040), the research fund of Science and Technology Department of Zhejiang province of China (2006C24009), and the Agency for Science Technology and Research of Singapore (A ∗ Star project 032 101 0005).

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Fabrication and evaluation of Zn containing fluoridated hydroxyapatite layer with Zn release ability

Abstract

Introduction

Section snippets

Synthesis of ZnTCP powders

Layer characterizations

Conclusion

Acknowledgements

Biomaterials

Biomaterials

Biomaterials

Biomaterials

Biomaterials

Biomaterials

Acta Biomater

Biomaterials

Biomaterials

Bone

Thin Solid Films

Biomaterials

Surf Coat Technol