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BackgroundMost studies on biodegradable magnesium implants published recently use magnesium-calcium-alloys or magnesium-aluminum-rare earth-alloys.However, since rare earths are a mixture of elements and their toxicity is unclear, a reduced content of rare earths is favorable. The present study assesses the in vivo biocompatibility of two new magnesium alloys which have a reduced content (ZEK100) or contain no rare earths at all (AX30).Methods24 rabbits were randomized into 4 groups (AX30 or ZEK100, 3 or 6 months, respectively) and cylindrical pins were inserted in their tibiae. To assess the biodegradation μCT scans and histological examinations were performed.ResultsThe μCT scans showed that until month three ZEK100 degrades faster than AX30, but this difference is leveled out after 6 months. Histology revealed that both materials induce adverse host reactions and high numbers of osteoclasts in the recipient bone. The mineral apposition rates of both materials groups were high.ConclusionsBoth alloys display favorable degradation characteristics, but they induce adverse host reactions, namely an osteoclast-driven resorption of bone and a subsequent periosteal formation of new bone. Therefore, the biocompatibility of ZEK100 and AX30 is questionable and further studies, which should focus on the interactions on cellular level, are needed.

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.

Research on magnesium based degradable implant materials has finally obtained success in orthopaedics. Based on the previous good results with LAE442 magnesium alloy, the new LANd442 alloy was developed. In doing this, the single element neodymium replaces the rare earth compound. The primary objective of this study is to assess the biocompatibility of the new alloy in the rabbit model. During a 26 week period, the animals were investigated using clinical, radiological and in vivo µ‐CT techniques. Following euthanasia, histological, fluorescent microscopy and ex vivo µ‐CT investigations were done. Clinically, additional bone formed at the implant's location and accumulation of small amounts of subcutaneous gas can be observed. Radiological investigations show brightening of the medullary cavity and thickening in the region of the diaphysis. The µ‐computed tomographies reveal a reduction in the bone density from 1226.31 to 1192.95 mg HA/ccm together with increases in bone porosity from 4.55 to 6.6% and bone volume from 1.51 to 2.06 mm3 · slice−1. By means of fluorochrome sequential marking, the determined MARs lie between day 93 and 120 at 3.58 µm · d−1 and between day 120 and 179 at 2.25 µm · d−1. Elevated remodelling processes in the bone are histologically confirmed due to the periosteal and endosteal growths and an increased appearance of osteoclasts. Owing to the established considerable bone remodelling processes following intramedullary implantation, LANd442 appears to be a less suitable degradable implant material for cortical bone applications.

With 9 figures and 4 tables Summary This study’s aim was to determine the optimal scan parameters for imaging the middle and inner ear of the cat with micro‐computertomography (μCT). Besides, the study set out to assess whether adequate image quality can be obtained to use μCT in diagnostics and research on cat ears. For optimisation, μCT imaging of two cat skull preparations was performed using 36 different scanning protocols. The μCT‐scans were evaluated by four experienced experts with regard to the image quality and detail detectability. By compiling a ranking of the results, the best possible scan parameters could be determined. From a third cat’s skull, a μCT‐scan, using these optimised scan parameters, and a comparative clinical CT‐scan were acquired. Afterwards, histological specimens of the ears were produced which were compared to the μCT‐images. The comparison shows that the osseous structures are depicted in detail. Although soft tissues cannot be differentiated, the osseous structures serve as valuable spatial orientation of relevant nerves and muscles. Clinical CT can depict many anatomical structures which can also be seen on μCT‐images, but these appear a lot less sharp and also less detailed than with μCT.