Influence of the grain size on the in vivo degradation behaviour of the magnesium alloy LAE442

Abstract

The aim of this study was to investigate the differences in the in vivo degradation behaviour of magnesium implants with various grain sizes and damaged surfaces. For this purpose, three different LAE442 magnesium implants were produced: cast, single and double extruded implants, in order to obtain different grain sizes. Furthermore, defects were positioned on the surfaces of some of the single extruded implants. The initial stability was determined. Four pins of each implant material were implanted into rabbits' tibiae and regularly clinically, radiologically and m-computed tomographically investigated over a period of 27 weeks. Following explantation, investigations were carried out using stereo and scanning electron microscopy including energy-dispersive X-ray analyses. Weight and strength changes were measured. The double extruded implants possessing the finest grains exhibited the highest initial stability (179.18 N). These implants demonstrated the lowest in vivo corrosion rates (0.0134 mm/year) and the least radiologically visible changes. The highest corrosion rate was computed for the implants possessing damaged surfaces. Radiologically discernible bone changes occurred at almost the same time as implant changes for all groups. Based on these results, the aim should be to produce fine-grained magnesium-based alloys for resorbable implants and to avoid any surface damage.

In vivo evaluation of a magnesium-based degradable intramedullary nailing system in a sheep model

“…Also Ullmann et al [86] found no significant changes in LANd442 implant volume but a significant decrease in density after 26 weeks. Additionally, they reported a significant decrease in maximum force as corrosion magnesium usually undergoes if exposed to chloride ions in nonoxidizing solutions [87] and was observed by several authors examining different magnesium-based alloys in vivo [44] or in vitro [88]. However, others did not observe signs of pitting on the surface of LAE442 pins after in vivo degradation [83,84].…”

“…Histological examinations of liver, kidney and spleen after implantation of different magnesium-based alloys (AZ31, MgZn) also did not give any hint on systemic toxicity [29,32]. In previous investigations, the magnesium-based LAE442 alloy has already proven its favorable properties in rabbits such as a comparatively slow and uniform degradation, a good biocompatibility and a high initial stability [43][44][45][46][47]. However, only little is known about the local (bone) and systemic (internal organs) effects caused by the implantation of large amounts of biodegradable implant material in long bones.…”

In vivo study of magnesium plate and screw degradation and bone fracture healing

“…One way to achieve this could be through grain refinement, as has 369 been previously demonstrated with Mg alloy LAE442 [28]. as improved passive film formation due to increased activity of 378 reduced grain size area, and consequently, better adhesion due to 379 increased grain boundary density [29].…”

In vitro and in vivo studies on as-extruded Mg- 5.25wt.%Zn-0.6wt.%Ca alloy as biodegradable metal

“…After the surgical trauma, the oxygen tension and local pH would be reduced and re- sulted in fast corrosion. Furthermore, Ulmann et al [43] found defects on the surface of intramedullary implantations of LAE442 alloys and the defects led to the faster initial corrosion than the intact implants. In the present study, the implants were tapped in the narrow predrilled bone tunnel, which could have scratched the implant's surface and caused fast initial corrosion [44].…”