Production and bio-corrosion resistance of porous magnesium with hydroxyapatite coating for biomedical applications

doi:10.1016/j.matlet.2013.06.096

Materials Letters

Volume 108, 1 October 2013, Pages 122-124

https://doi.org/10.1016/j.matlet.2013.06.096 Get rights and content

Highlights

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Porous Mg was produced by spark plasma sintering using NaCl as sacrificial spacer.
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Porous Mg was coated with a dense HA layer by treatment in an aqueous solution.
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HA-coated Mg showed significantly enhanced corrosion resistance, while preserving ductile behavior.

Abstract

Biodegradable porous magnesium (Mg) with hydroxyapatite (HA) coating suitable for biomedical applications was fabricated. A blend of Mg and NaCl particles was sintered by spark plasma sintering (SPS), and then the NaCl was dissolved to obtain a porous structure. Different levels of porosity (50%, 60% and 70%) were achieved by adjusting the volume fraction of NaCl, while preserving high pore interconnectivity with a large pore size of~240 μm. In addition, a dense HA coating layer comprised of needle-shaped HA crystals was formed on the surface of the porous Mg by treatment in an aqueous solution. Both bare and HA-coated porous Mg specimens with a porosity of 60% exhibited ductile behavior under compressive loading and similar levels of ultimate compressive strength (~15 MPa). However, HA coating significantly enhanced the corrosion resistance of porous Mg.

Introduction

Magnesium (Mg) has promising properties as a biomaterial, as it can degrade in physiological environment and promote bone growth, while its mechanical strength is much better than that of biodegradable polymers [1], [2], [3], [4], [5], [6], [7]. In addition, the elastic modulus of Mg is close to that of the bone, so that stress shielding effects are less pronounced than conventional metal implants.

Porous Mg has added benefits for biomedical applications, such as bone ingrowth and the transport of body fluids through pores for better healing [1], [4], [5], [6], [7], [8]. Among various manufacturing methods for the production of porous metals, the space holder method is a particularly useful one owing to its simplicity [1], [5], [6], [7], [8]. As a sintering technique, spark plasma sintering (SPS) is expected to fully densify Mg compacts, since sparks generated during SPS can destroy thin oxide films formed on metal particles [9], [10] that act as barriers to diffusion [11], [12]. Porous Mg with pore structure conductive for biomedical applications can be produced using sodium chloride (NaCl) powder as a sacrificial spacer in conjunction with densification by SPS technique, followed by removal of NaCl particles [7], [13]. However, special care should be taken to design a schedule for SPS, in order to fully densify Mg walls because of a high content of non-conductive NaCl.

One serious limitation in the use of porous Mg in medical implants is its excessively high corrosion rate. Not only does this fast bio-corrosion behavior deteriorate the mechanical strength of Mg implants, but it also leads to hydrogen gas evolution, which hinders cell attachment [1], [2], [3], [14], [15]. To inhibit corrosion of porous Mg, post-treatment is required, which may include surface treatment, alloying [1], [2], [3], [14], [15], or grain refinement [16]. Specifically, for the use of Mg in bone implants, hydroxyapatite (HA) coating can provide both excellent corrosion resistance and good biocompatibility [2], [14], [15].

In this study, we produced porous Mg implants with an HA coating layer and evaluated their potential applications in bone implants. A porous Mg implant was obtained by removing NaCl particles from a Mg/NaCl compact which had been densified via the SPS technique. Subsequently, the surface of the porous Mg was coated with an HA layer by treatment in an aqueous solution. The porous structure and morphology of the HA coating layer, as well as mechanical properties and bio-corrosion behavior of the HA-coated porous Mg were evaluated.

Section snippets

Materials and method

Mg powder (−100+200 mesh, Alfa Aesar, USA) and NaCl powder (+80 mesh, Sigma Aldrich, USA) were mixed with a small amount of ethanol as a binder. To fabricate porous Mg with different levels of porosity (50%, 60% and 70%), the volume fraction of NaCl powder was varied. The mixed powders were put inside a carbon die and pressed with a load of 20 MPa inside an SPS chamber. The sintering temperature was 585 °C. A holding time of 2 h and heating rate of 100 °C/min were employed during sintering. After

Results and discussion

Porous Mg samples were produced by removing NaCl particles from Mg/NaCl compacts which had been densified via the SPS technique. In particular, SPS was carried out at 585 °C for a relatively long dwelling time of 2 h, which was determined by preliminary compressive strength test results. The compressive strength of the porous Mg increased remarkably from ~8 MPa to ~17 MPa with increasing dwelling time from 5 min to 120 min. This finding suggests that the densification behavior of the Mg/NaCl compacts

Conclusions

Porous magnesium was fabricated by the spark plasma sintering of Mg powder blended with NaCl powder, which served as a sacrificial space holder. The porous Mg obtained after the dissolution of the NaCl particles possessed good mechanical properties and a pore structure that qualifies the materials for applications in biomedical implants. The bio-corrosion of porous Mg was significantly inhibited by HA coating. This demonstrates that HA-coated porous Mg produced in the way presented here is a

Acknowledgments

This research was supported by the International Collaborative R&D Program(No. 2010-BS-101007-001) funded by the Ministry of Knowledge & Economy, Republic of Korea and Korea Healthcare technology R&D Project (No. A121035) funded by Ministry for Health, Welfare & Family Affairs, Republic of Korea.

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Production and bio-corrosion resistance of porous magnesium with hydroxyapatite coating for biomedical applications

Highlights

Abstract

Introduction

Section snippets

Materials and method

Results and discussion

Conclusions

Acknowledgments

Biomaterials

Mater Lett

Mater Sci Eng C

Biomaterials

J Alloy Compd

Mater Sci Eng A

Electrochim Acta

Appl Surf Sci