Degradation Behavior, Transport Mechanism and Osteogenic Activity of Mg–Zn–RE Alloy Membranes in Critical-Sized Rat Calvarial Defects

Abstract

In this study, a specific Mg–Zn–RE alloy membrane with 6 wt.% zinc and 2.7 wt.% rare earth elements (Y, Gd, La and Ce) was prepared to investigate implant degradation, transport mechanism and guide bone regeneration in vivo. The Mg-membrane microstructure and precipitates were characterized by the scanning electron microscopy (SEM) and the transmission electron microscopy (TEM). The Mg-membrane degradation process and effect on osteogenesis were investigated in a critical-sized rat calvarial defect model via micro-CT examination and hard tissue slicing after 2-, 5- and 8-week implants. Then, the distribution of elements in organs after 1-, 2- and 4-weeks implantation was examined to explore their transportation routes. Results showed that two types of precipitates had formed in the Mg–membrane after a 10-h heat treatment at 175 °C: γ-phase MgZn precipitation with dissolved La, Ce and Gd, and W-phase Mg3(Y, Gd)2Zn3 precipitation rich in Y and Gd. In the degradation process of the Mg-membrane, the Mg matrix degraded first, and the rare earth-rich precipitation particles were transferred to a more stable phosphate compound. The element release rate was dependent on the precipitate type and composition. Rare earth elements may be transported mainly through the lymph system. The defects were repaired rapidly by the membranes. The Mg-membrane used in the present study showed excellent biocompatibility and enhanced bone formation in the vicinity of the implants.

Feasibility and Efficacy of a Degradable Magnesium‐Alloy GBR Membrane for Bone Augmentation in a Distal Bone‐Defect Model in Beagle Dogs

“…The new bone was more porous in the group MG than that in the group BG, and the trabecular separation decreased gradually in the group MG ( Figure 5 ). These observations were consistent with those of our previous study [ 21 ], indicating that many isolated bone islands were formed initially and then fused gradually in the group MG. Qiao et al reported that administration of an appropriate amount of Mg 2+ in the early stage of inflammation could stimulate macrophages to secrete a series of cytokines that aided bone regeneration specifically [ 33 ]. However, only the correct duration of administration and the appropriate local concentration of Mg 2+ could help Mg 2+ exert its biological properties [ 33 – 35 ].…”

“…They found that the Mg-alloy membrane did not lead to higher bone regeneration than that in blank sites [ 16 ]. However, our previous study using a bone-defect model in the rat skull indicated that Mg-Zn-REE membranes could promote bone healing significantly [ 21 ]. The main reason for the controversy stated above is that the geometry of the material, anticorrosion treatment, and implant position in the body affect the degradation of Mg-alloys and local concentration of Mg 2+ [ 36 ].…”

“…Previously, we implanted Mg-alloy into the skull-bone defects of rats and analyzed the metabolism of this material in various organs (brain, heart, liver, spleen, lungs, kidneys, adrenal glands, submandibular lymph nodes). The content of all material-related elements was within the safe range, but REEs metabolized slowly and accumulated in submandibular lymph nodes [ 21 ]. However, a long-term study to ascertain the effect on the lymph nodes was not done.…”

“…The content of rare-earth elements (REEs) in Mg-Zn-Y-Nd alloy is only one-third of that of magnesium electron WE43 (a Mg-alloy used commonly in medicine), which indicates that it has greater biological safety [ 20 ]. In addition, we have used Mg-alloy GBR membranes to repair skull defects in rats and demonstrated its good biocompatibility and osteogenic effect [ 21 ].…”

Research status of biodegradable metals designed for oral and maxillofacial applications: A review

“…Zhao et al. Developed Mg–Zn–RE(Y, Gd, La and Ce) alloy membranes (diameter 5 mm, thickness 110 μm) with excellent biocompatibility and peomoted bone formation in critical-sized rat calvarial fefects [ 109 ]. Gao et al.…”