Long-term clinical study and multiscale analysis of in vivo biodegradation mechanism of Mg alloy.

There has been a tremendous amount of research in the past decade to optimize the mechanical properties and degradation behavior of the biodegradable Mg alloy for orthopedic implant. Despite the feasibility of degrading implant, the lack of fundamental understanding about biocompatibility and underlying bone formation mechanism is currently limiting the use in clinical applications. Herein, we report the result of long-term clinical study and systematic investigation of bone formation mechanism of the biodegradable Mg-5wt%Ca-1wt%Zn alloy implant through simultaneous observation of changes in element composition and crystallinity within degrading interface at hierarchical levels.

Rapid in vitro corrosion induced by crack-like pathway in biodegradable Mg-10% Ca alloy.

The in vitro corrosion mechanism of the biodegradable cast Mg-10% Ca binary alloy in Hanks' solution was evaluated through transmission electron microscopy observations. The corrosion behavior depends strongly on the microstructural peculiarity of Mg₂Ca phase surrounding the island-like primary Mg phase and the fast corrosion induced by the interdiffusion of O and Ca via the Mg₂Ca phase of lamellar structure. At the corrosion front, we found that a nanosized crack-like pathway was formed along the interface between the Mg₂Ca phase and the primary Mg phase.

Biodegradability engineering of biodegradable Mg alloys: tailoring the electrochemical properties and microstructure of constituent phases.

Crystalline Mg-based alloys with a distinct reduction in hydrogen evolution were prepared through both electrochemical and microstructural engineering of the constituent phases. The addition of Zn to Mg-Ca alloy modified the corrosion potentials of two constituent phases (Mg + Mg2Ca), which prevented the formation of a galvanic circuit and achieved a comparable corrosion rate to high purity Mg. Furthermore, effective grain refinement induced by the extrusion allowed the achievement of much lower corrosion rate than high purity Mg.

Biocompatibility and strength retention of biodegradable Mg-Ca-Zn alloy bone implants.

The biocompatibility and strength retention of a Mg-Ca-Zn alloy were studied to evaluate its efficacy for osteosynthesis applications. Mg-Ca-Zn alloy and self-reinforced poly l-lactide (SR-PLLA) bone screws were implanted into New Zealand rabbits for radiography analysis, micro computed tomography analysis, histomorphometry, hematology, serum biochemistry, histopathology, and inductively coupled plasma mass spectrometry analysis. Bending and torsion tests were performed on intact specimens to find the initial mechanical strength of these Mg-Ca-Zn alloy bone screws.

In vivo corrosion mechanism by elemental interdiffusion of biodegradable Mg-Ca alloy.

We elucidated the in vivo corrosion mechanism of the biodegradable alloy Mg-10 wt % Ca in rat femoral condyle through transmission electron microscope observations assisted by focused ion beam technique. The alloy consists of a primary Mg phase and a three-dimensional lamellar network of Mg and Mg(2)Ca. We found that the Mg(2)Ca is rapidly corroded by interdiffusion of Ca and O, leading to a structural change from lamellar network to nanocrystalline MgO.

Load-bearing capacity and biological allowable limit of biodegradable metal based on degradation rate in vivo.

In this study, a newly developed Mg-Ca-Zn alloy for low degradation rate and surface erosion properties was evaluated. The compressive, tensile, and fatigue strength were measured before implantation. The degradation behavior was evaluated by analyzing the microstructure and local hardness of the explanted specimen.