Mechanical Properties, Biodegradation, and Biocompatibility of Ultrafine Grained Magnesium Alloy WE43

Abstract

In this work, the effect of an ultrafine-grained (UFG) structure obtained by multiaxial deformation (MAD) on the mechanical properties, fatigue strength, biodegradation, and biocompatibility in vivo of the magnesium alloy WE43 was studied. The grain refinement down to 0.93 ± 0.29 µm and the formation of Mg41Nd5 phase particles with an average size of 0.34 ± 0.21 µm were shown to raise the ultimate tensile strength to 300 MPa. Besides, MAD improved the ductility of the alloy, boosting the total elongation from 9% to 17.2%. An additional positive effect of MAD was an increase in the fatigue strength of the alloy from 90 to 165 MPa. The formation of the UFG structure also reduced the biodegradation rate of the alloy under both in vitro and in vivo conditions. The relative mass loss after six weeks of experiment was 83% and 19% in vitro and 46% and 7% in vivo for the initial and the deformed alloy, respectively. Accumulation of hydrogen and the formation of necrotic masses were observed after implantation of alloy specimens in both conditions. Despite these detrimental phenomena, the desired replacement of the implant and the surrounding cavity with new connective tissue was observed in the areas of implantation.

WE43 and WE43-T5 Mg alloys screws tested in-vitro cellular adhesion and differentiation assay and in-vivo histomorphologic analysis in an ovine model

“…The two alloys were tested in vivo in an ovine model in two different conditions: subperiosteal, to simulate the condition of a plate, and intraosseous, to recreate the condition of an endosteal implant (screw); Both studies showed increased strength of WE43-T5 compared to as-cast (∼470±17.1 MPa vs ∼385±10.4 MPa respectively) and greater degradation rate of WE43 that of WE43-T5. In agreement with other studies that tested WE43 Mg alloys, 2,11,13,24–27 we found great biocompatibility of both the as-cast and WE43-T5 alloys however, conversely to the reported literature, minimal formation of hydrogen pockets was observed in the peri-implant region for any of the alloys evaluated, independent of time in vivo . One limitation of both studies was the implant design, represented by cylindrical rods (10 mm in diameter by 5 mm height), placed subperiosteally or embedded in osteotomy sites without fixation.…”

Effect of multi‐axial hot forging process on mechanical, and corrosion resistance behavior of Mg‐3Zn alloy for temporary orthopedic implants

“…In another effort, ultrafine grain structure was achieved by MAD of WE43 Mg alloy, and its effect on the mechanical, degradation, and biocompatibility was evaluated. 35 The average grain size of the initial alloy (∼64.9 ± 3 μm) reduced to the 0.93-0.29 μm after MAD. Reduction in the grain size of the alloy enhanced the degradation resistance.…”

Nanotomographic evaluation of precipitate structure evolution in a Mg–Zn–Zr alloy during plastic deformation

“…The structural properties of Mg can be very efficiently controlled through alloying and thermo-mechanical treatment aimed at solid-solution, precipitate and strain hardening 2 . The ability to tailor the degradation rate remains pivotal to facilitate widespread applicability of Mg and its alloys in medical applications, as an exceedingly fast degradation can lead to unacceptable results, such as impairment of cell adhesion by ensuing hydrogen evolution, thus hindering bone growth and implant stability 6 , 7 , as well as increased cell apoptosis 8 .…”

“…to unacceptable results, such as impairment of cell adhesion by ensuing hydrogen evolution, thus hindering bone growth and implant stability 6,7 , as well as increased cell apoptosis 8 .…”

“…This is especially the case when a radical variation of microstructure occurs during complex metal processing employed to improve the mechanical characteristics of Mg alloys. In addition to changes in the grain size and texture, severe plastic deformation associated with such processing may also bring about significant transformations in the population of intermetallic particles 8 . Traditional techniques of microstructure characterisation, such as scanning and transmission electron microscopy, provide insights into the local microstructure and, being surface-sensitive or limited to specimen thicknesses of the order of 100 nm, respectively, they may be insufficient to reveal fine detail of the intermetallic particle evolution over larger spatial scales.…”