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

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 micro-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.

The effects of handling and storage on magnesium based implants--first results.

The present work aimed to investigate the influence of acetone and formalin as well as the duration and type of storage on magnesium based implants by means of microscopic, µ-computed tomographic, scanning electron microscopic, EDX and metallographic investigations. In contrast to storing in acetone, storage in formalin led to an increase in surface to volume ratio, and a decrease of the volume and the density. The various types of storage exerted no differing effects on the implants but with increasing storage duration, a spreading of oxygen rich areas on the surface, increased precipitations and a decrease in grain size could be observed.

In Vivo Degradation Behavior of the Magnesium Alloy LANd442 in Rabbit Tibiae.

In former studies the magnesium alloy LAE442 showed promising in vivo degradation behavior and biocompatibility. However, reproducibility might be enhanced by replacement of the rare earth composition metal "E" by only a single rare earth element. Therefore, it was the aim of this study to examine whether the substitution of "E" by neodymium ("Nd") had an influence on the in vivo degradation rate. LANd442 implants were inserted into rabbit tibiae and rabbits were euthanized after 4, 8, 13 and 26 weeks postoperatively. In vivo µCT was performed to evaluate the in vivo implant degradation behaviour by calculation of implant volume, density true 3-D thickness and corrosion rates. Additionally, weight loss, type of corrosion and mechanical stability were appraised by SEM/EDS-analysis and three-point bending tests. Implant volume, density and true 3-D thickness decreased over time, whereas the variance of the maximum diameters within an implant as well as the corrosion rate and weight loss increased. SEM examination revealed mainly pitting corrosion after 26 weeks. The maximum bending forces decreased over time. In comparison to LAE442, the new alloy showed a slower, but more uneven degradation behavior and less mechanical stability. To summarize, LANd442 appeared suitable for low weight bearing bones but is inferior to LAE442 regarding its degradation morphology and strength.