In vivo degradation behavior of Ca-deficient hydroxyapatite coated Mg–Zn–Ca alloy for bone implant application
Graphical abstract
Highlights
▶ Using adult rabbits as animal models, we investigate the effect of Ca-def HA coating on the degradation behavior and bone response of the Mg–Zn–Ca alloy. ▶ In vivo degradation of the Ca-def HA coating and magnesium substrate occurs almost simultaneously, and in vivo valid life of this coating is about 8 weeks. ▶ The Ca-def HA coating has good osteoconductivity and is in favor of the formation of more new bone around the coated magnesium implants.
Introduction
Investigation of magnesium and its alloys in the field of biomaterials has increased considerably for the development of biodegradable bone implants because of their good biocompatibility and biodegradability [1], [2], [3], [4], [5], [6]. Compared with other metallic implant materials such as stainless steel and titanium alloy, Mg and its alloys have a moderate elastic modulus similar to that of natural bone and show favorable tensile and compressive strengths, which would effectively avoid stress-shielding effect [2]. Unfortunately, magnesium is highly susceptible to corrosion in physiological conditions such as human body fluid or blood plasma, which results in the loss of mechanical integrity and the production of hydrogen [1], [7]. So it is necessary to improve the corrosion resistance of Mg-based materials for bone implant application. Many researchers [8], [9], [10], [11], [12], [13] have pointed out that surface modification with an appropriate coating is an effective approach, which could improve the corrosion resistance and surface biocompatibility of Mg-based implants.
Owing to its resemblance to the major inorganic constituent of natural bone, hydroxyapatite (Ca10(PO4)6(OH)2, HA) is recognized as one of the most biocompatible materials and is widely used for bone replacement and regeneration. However, its mechanical strength is too poor to be used for load-bearing applications. For this reason, HA is often used as a bioactive coating on metallic substrates such as Ti alloys [14], [15], [16]. Recently, there are such reports about HA coating on biodegradable Mg-based materials [17], [18], [19]. Because of the substitution of Mg2+ ions, the prepared coating is often calcium-deficient HA (Ca-def HA, calcium and phosphorus with an atomic ratio ranging from 1.33 to 1.65). It is reported that Ca-def HA seems to be more soluble than stoichiometric HA and may induce precipitation of a new bonelike apatite after implantation [20], [21], [22], which just meets the requirements for biodegradable implants. However, up to now, there is insufficient data about the in vivo effect of the Ca-def HA coating on Mg alloy implant.
In this paper, using adult rabbits as animal models, the influence of a Ca-def HA coating on degradation behavior and bone response of Mg–Zn–Ca alloy was investigated during 24 weeks implantation.
Section snippets
Sample preparation
Since small amounts of zinc, calcium and magnesium are all essential for human body, as-cast Mg–Zn–Ca (Mg–2.0Zn–0.2Ca, in wt%) alloy of high purity, which was prepared in our laboratory, was used in this study. Cylinder-like samples with diameter of 3.5 mm and length 9.0 mm were used for in vivo implants. A Ca-def HA coating was prepared on Mg–Zn–Ca alloy by pulse electrodeposition process according to our previous study [18]. Electrolytes were prepared by mixing a solution of 0.042 mol/l Ca(NO3)2
Implant degradation behavior
Fig. 1 illustrates the typical micro-CT 2D reconstruction images of the rabbit femora containing Mg implants at 8, 12, 18 and 24 weeks postoperatively. Clearly, at 8 weeks, the surface morphology of the residual bare Mg implant exhibits obvious corrosion pits (as indicated by red arrows in Fig. 1a), while there is only slight corrosion with superficial pits for Ca-def HA coated specimen (as indicated by red arrows in Fig. 1e). With the increase of implantation time, corrosion of both samples
In vivo degradation mechanism of Ca-def HA coated Mg–Zn–Ca alloy
As a degradable orthopedic implant, the primary concern about Ca-def HA coated Mg alloy is the degradation behavior of the coating and the substrate. From the above micrographs of the residual Ca-P coating and the coated implants, it is found that the Ca-def HA coating on the surface of Mg alloy gradually degrades with the increase of implantation time, and the in vivo valid life of the coating is about 8 weeks which is longer than that of MF2 coating [11] while shorter than that of
Conclusion
In summary, the degradation of the Ca-def HA coating and magnesium alloy occurs almost simultaneously when implanted into rabbit femora, and the in vivo valid life of the Ca-def HA coating is about 8 weeks. Because of the effective protection of the Ca-def HA coating, the degradation rate of the coated magnesium alloy implant is greatly slower than that of the uncoated implant in the first 8 weeks implantation. This is to decrease the release rate of magnesium ions. The analysis results of the
Acknowledgements
Thanks for the financial supports of National Natural Science Foundation of China (No. 30870634). We are also grateful for the characterization supports of the Key Laboratory of Surface & Interface Science of Henan Province and the materials research center of Zhengzhou University.
References (35)
- et al.
Biomaterials
(2005) - et al.
Biomaterials
(2006) - et al.
Biomaterials
(2008) - et al.
Acta Biomater.
(2010) - et al.
Acta Biomater.
(2011) - et al.
Corros. Sci.
(2010) - et al.
Appl. Surf. Sci.
(2009) - et al.
Biomaterials
(2009) - et al.
Acta Biomater.
(2010) - et al.
Biomaterials
(2010)
Colloids Surf. B
Biomaterials
Biomaterials
Acta Biomater.
Acta Biomater.
Mater. Sci. Eng. C
Mater. Charact.
Cited by (115)
Effect of PLGA+MAO composite coating on the degradation of magnesium alloy in vivo and in vitro
2023, Materials Today CommunicationsA review on surface coating techniques on Mg based bio-degradable implants
2023, Materials Today: ProceedingsTailoring degradation of MgZn alloy films with bioinert amorphous carbon
2022, Journal of Alloys and CompoundsAccumulative extrusion bonding of Mg-Mn-Ca/FA+GNP hybrid biocomposite: On microstructure evaluation, mechanical and corrosion properties
2022, Materials Today CommunicationsApplication of sustainable polymers for reinforcing bio-corrosion protection of magnesium implants–a review
2022, Sustainable Chemistry and PharmacyA review of effective strides in amelioration of the biocompatibility of PEO coatings on Mg alloys
2022, Journal of Magnesium and Alloys