In vitro corrosion resistance and cytocompatibility of Mg66Zn28Ca6 amorphous alloy materials coated with a double-layered nHA and PCL/nHA coating

https://doi.org/10.1016/j.colsurfb.2020.111251Get rights and content

Highlights

  • The Mg66Zn28Ca6 amorphous alloy rods can be prepared by a copper die spray-casting process with diameter of 2 mm

  • The thickness of a double-layered coating was about 328 mm.

  • The porosity of the nHA/PCL coating can be controlled in the range of 0.5–4 μm.

  • The sample that were coated with intermediate HA layer and outer PCL/2%nHA composite coating has exhibited outstanding cytocompatibility.

  • The composite material will be completely degraded within a certain time.

Abstract

In this study, the double-layered nHA and PCL/nHA coatings were prepared on the substrate of Mg66Zn28Ca6 amorphous alloy. The phase composition and morphological were analyzed by Scanning electron microscopy, Energy dispersive spectrometry and X-ray diffraction. The electrochemical properties of these samples were measured on electrochemical workstation. The degradation rate was evaluated by measuring the pH value and weight loss. Experiment results show that the outer composite PCL/nHA coating is a porous structure, where the porosity and pore size could be easily controlled by adding nHA. The combined properties of double-layered nHA and PCL/nHA coating can control the degradation of the Mg66Zn28Ca6 amorphous alloy in the scheduled time. Moreover,the cell co-culture and cell adhesion tests show that the double-layered nHA and PCL/2%nHA coating possesses the best cytocompatibility with cell organization. The above experiments have demonstrated that the Mg66Zn28Ca6 amorphous alloy which was coated with PCL/nHA composite coating have good mechanical properties, good corrosion resistance and perfect cytocompatibility. It can be used as a potential novel biomaterial for bone tissue engineering.

Introduction

Metallic materials play a considerable role as biomaterials, it can repair or replace the bone tissue that has been fractured or damaged. Metallic materials with high tensile properties and excellent fracture toughness are more suitable for load-bearing applications compared to polymeric or ceramics materials [[1], [2], [3], [4]]. However, the limitation of metallic materials is the possibility of releasing toxic ions that could destroy the ion balance, damage human tissue, cause inflammation and reduce cytocompatibility during the rehabilitation process [5]. Normally, the metallic implant materials will not be degraded in the body for a long time, hence a second surgery is necessary to take it out.

Due to their outstanding properties, magnesium alloys are widely used in automobile and aerospace industries, as well as in clinical practice [[6], [7], [8], [9]]. Magnesium alloy received much more attention in recent years. Particularly, the magnesium alloys are known for their degradability and cytocompatibility. The Mg66Zn28Ca6 amorphous alloy can act as potential novel biomaterial for bone tissue engineering, in comparison with conventionalmaterials, such as stainless steels, ceramics, titanium alloys and others. Firstly, the Mg66Zn28Ca6 amorphous alloy could be degraded in body fluids forming non-toxic oxide which are excreted in urine. This means there is no need for a second surgery to take it out, and it extremely relieves the financial pressure and mental pain of patient. Secondly, the density, elastic modulus and yield strength of the magnesium alloys are closer to natural bones. Thirdly, these alloys are harmless to human body, which are essential characteristic for creature metabolism and naturally found in bone tissue. As mentioned earlier, the degradation products of Mg, Zn, Ca are non-toxic, and the creature body fluid containing enough Mg2+, Zn2+, Ca2+, which could promote bone growth and adjust neuromuscular activity [10,11]. However, considerable work is needed to control the degradation rate and improve cytocompatibility of magnesium alloys before they can be used as a potential novel biomaterial for bone tissue engineering [[12], [13], [14], [15], [16], [17]].

Previous studies have shown that nano-hydroxyapatite coating can be formed on the substrate of the Mg66Zn28Ca6 amorphous alloyby using a hydrothermal pre-treatment [18]. Nevertheless, the degradation rate and biological activity of the HA coating still cannot meet the requirements of the experiment. Polycaprolactone/nHA composite coated on the surface of HA is expected to further increase its corrosion resistance and cytocompatibility [19].

In this paper, the Mg66Zn28Ca6 amorphousalloy was fabricated by firstly adding zinc and calcium elements. Normally, zinc oxide has good antibacterial function and calcium will promote the growth of the bone tissue. Subsequently, the Mg66Zn28Ca6 amorphous alloy samples were coated with an intermediate HA layer by hydrothermal pre-treatment and an outer PCL/nHA composite layer by a dip-coating process.In order to verify the sample’s corrosion resistance, the degradation experiment and electrochemical tests were performed in simulated body fluids. Further, the cell adhesion and co-culture experiment were performed to qualitatively analyze the sample’s cytocompatibility.

Section snippets

Preparation of Mg-base amorphous alloy

99.9% industrial magnesium ingot, Mg-Ca master alloy and zinc grain were used to prepare Mg66Zn28Ca6 amorphous alloy rods with diameter of 2 mm, by a copper die spray-casting process under the protection of high purity argon. Subsequently, the Mg66Zn28Ca6 amorphous alloy samples were polished with SiC papers successively up to 2000 grit, ultrasonically cleaned in ethanol for 15 min, and dried in the air.

Hydrothermal pre-treatment

The Mg66Zn28Ca6 amorphous alloy rods were cut into small samples 15

mm each in length.

Mechanical properties analysis

The compressive performance of these samples were tested by a tensile-compression testing machine. Fig. 1(a) is the stress-strain curve, Fig. 1(b) is a statistical chart of compressive strength. It can be seen that The compressive strength of uncoated sample is the worst, as the thickness of the coating is increasing, the compressive strength of the sample is increasing. As shown in Fig. 1(b), The compressive strength of samples are distributed between 80.7–93.9 MPa, and the compressive

Conclusions

In this paper, the double-layered nHA and PCL/nHA composite coatings were successfully coated onto the substrate of Mg66Zn28Ca6 amorphous alloy The thickness of a double-layered coating was about 328 μm. Micropores with 0.5∼3.7 μm diameter size were produced in the PCL/nHA composite coating by varying the HA nanoparticle content.

The above experimental results show that the corrosion resistance and cytocompatibility of the samples were significantly improved by the uniform PCL/nHA composite

Credit author statement

I have made substantial contributions to the conception or design of the work, or the acquisition, analysis, or interpretation of date for the work.

I have drafted the work or revised it critically for important intellectual content.

I have approved the final version to be published.

I agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

All authors are contribute to

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

The authors gratefully acknowledge the financial supports from the National Natural Science Foundation of China (No. 51665036).

References (31)

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