Biomedical Engineering Reference
In-Depth Information
Line scanning in Fig.17 proved that large amount of Ca and P was found around the
magnesium implant. In the present study, the histological analyses revealed that this
magnesium-containing calcium phosphate degradation layer could promote or accelerate
the new bone formation.
Fig. 17. Tissue response of the Mg-Zn-Ca alloy implantation at 1, 2 and 3 months (a) Mg-
4.0Zn-0.2Ca 1 month, (b) Mg-4.0Zn-0.2Ca 2 month, (c) Mg-4.0Zn-0.2Ca 3 month, (d) cortical
bone.
In-vivo degradation was a very complex process, so it was difficult to accurately assess the
degradation rate of an implant material. F. Witte et al [35] found that the corrosion of a
magnesium rod in the medullar cavity was not homogeneous in all cross-sections by used
micro-computed tomography. In our study, the cross-section area of the residual implant
was calculated to describe the degradation rate of the Mg implant. Due to the
inhomogeneous corrosion of a magnesium rod in the medullary cavity, the calculated
degradation rate based on the images was similar to the real in-vivo degradation rate of
magnesium implants.
In-vivo degradation, compare with other metal implants, is an ultimate merit of magnesium
alloy. After implantation in the rabbit, Mg-4.0Zn-0.2Ca alloy would be reacted with body
fluid on the surface and get dissolved in the surrounding body fluid. At first, the released
Mg 2+ , Zn 2+ and Ca 2+ could be absorbed by the surrounding tissues and excreted through the
gastrointestinal route and the kidney. However, with the increasing time of implantation,
more Mg 2+ , Zn 2+ and Ca 2+ ions are dissolved into the solution, the local pH near the surface
of the Mg implants could be >10[36]. As a result, an insoluble magnesium-containing
calcium phosphate would be precipitated from the body fluid on the surface of the
magnesium implant and tightly attached to the matrix, which retarded degradation. In
addition, the corrosion layer on the Mg-4.0Zn-0.2Ca alloy contained Mg, Ca and P, which
could promote osteoinductivity and osteoconductivity, predicting good biocompatibility of
magnesium. Therefore, it is proposed that the Mg 2+ , Zn 2+ and Ca 2+ released during
degradation should be safe.
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