In magnesium alloys, the components used modify the alloy properties. For magnesium implants in contact with bone, rare earths alloys are commonly examined. These were shown to have a higher corrosion resistance than other alloys and a high mechanical strength, but their exact composition is hard to predict. Therefore a reduction of their content could be favorable. The alloys ZEK100 and AX30 have a reduced content or contain no rare earths at all. The aim of the study was to investigate their in vivo degradation and to assess the suitability of the in vivo µCT for the examination of their corrosion. Implants were inserted in rabbit tibiae. Clinical examinations, X-rays and in vivo µCT scans were done regularly. Afterwards implants were analyzed with REM, electron dispersive X-ray (EDX), weighing and mechanical testing. The in vivo µCT is of great advantage, because it allows a quantification of the corrosion rate and qualitative 3D assessment of the corrosion morphology. The location of the implant has a remarkable effect on the corrosion rate. Due to its mechanical characteristics and its corrosion behavior, ZEK100 was judged to be suitable, while AX30, which displays favorable degradation behavior, has too little mechanical strength for applications in weight bearing bones.

Aim of the present study was to establish methods for the evaluation of biocompatibility and degradation behaviour of coated magnesium sponges in cancellous bone. So bioglass coated sponges of the magnesium alloy AX30 were implanted into the femurs of rabbits for an observation period of 6, 12 and 24 weeks, respectively. In the follow up clinical and radiographical examinations and in vivo l-computed tomographies (XtremeCT) were taken regularly. After euthanasia ex vivo l-computed tomographies (lCT80) and histological examinations were executed. As result the greater trochanter proved to be a suitable implantation site and all coated magnesium sponges were tolerated well. The radiographs showed no development of gas or severe bone alterations. The XtremeCT depicted the proceeding degradation and accumulations of gas, but turned out to be not as meaningful in exact determination of bone and sponge changes. Better results regarding the degradation state of the sponges were provided by the lCT80 at the end of the test. After all implantation periods different sized implant residues and newly formed bone around the implant were found. The histological examinations resulted in new bone formation and a mild, decreasing inflammation. The bone-implant-interface could not be evaluated at all localisations, since the remaining implants partly coiled up during microtome sectioning. In conclusion the chosen methods are suitable for usage in further studies. But supplement of the cutting and grinding method according to Donath is required to examine the bone-implant-compound.Keywords: sponge / bioglass coating / in vivo / magnesium alloy / resorbable / Ziel dieser Studie war die Methodenetablierung zur Untersuchung von Biokompatibilität und Degradationsverhalten von Magnesiumschwämmen mit Beschichtung in spongiösem Knochen. Es wurden bioglasbeschichtete Schwämme der Magnesiumlegierung AX30 für 6, 12 oder 24 Wochen in Kaninchenfemora implantiert. Es folgten regelmäßige klinische und radiologische Untersuchungen, in vivo (XtremeCT) und ex vivo (lCT80) l-Computertomographien und histologische Untersuchungen. Der Trochanter major erwies sich als geeigneter Implantationsort und die beschichteten Magnesiumschwämme als gut verträglich. Die Röntgenaufnahmen zeigten weder Gasentwicklung noch gravierende Knochenveränderungen. Das XtremeCT stellte Degradationsfortschritte und Gas dar, stellte sich aber als wenig aussagekräftig bezüglich der exakten Bestimmung der Umbauvorgänge von Implantat und Knochen heraus. Bessere Ergebnisse bezüglich des Degradationsfortschritts der Schwämme lieferte hingegen das lCT80 am Versuchsende. Nach allen Implantationszeiten wurden unterschiedlich große Schwammresiduen und neu gebildeter Knochen nachgewiesen. Die histologischen Untersuchungen ergaben neben der Knochenneubildung milde, abnehmende Entzündungsreaktionen. Die Knochen-Implantat-Grenzflächen konnten nicht an allen Lokalisationen untersucht werden, da sich das Implantatmaterial während des Schneidevorgangs am Mikrotom z. T. herauslöste. Insgesamt ...

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Current research focuses on magnesium based alloys in the course of searching a resorbable osteosynthetic material which provides sufficient mechanical properties besides a good biocompatibility. Previous studies reported on a favorable biocompatibility of the alloys LAE442 and MgCa0.8. The present study compared the degradation process of cylindrical LAE442 and MgCa0.8 implants after 12 months implantation duration. Therefore, 10 extruded implants (2.5 x 25 mm, cross sectional area 4.9 mm²) of both alloys were implanted into the medullary cavity of both tibiae of rabbits for 12 months. After euthanization, the right bone-implant-compound was scanned in a µ-computed tomograph (µCT80, ScancoMedical) and nine uniformly distributed cross-sections of each implant were used to determine the residual implants´ cross sectional area (Software AxioVisionRelease 4.5, Zeiss). Left implants were taken out of the bone carefully. After weighing, a three-point bending test was carried out. LAE442 implants degraded obviously slower and more homogeneously than MgCa0.8. The mean residual cross sectional area of LAE442 implants was 4.7 ± 0.07 mm². MgCa0.8 showed an area of only 2.18 ± 1.03 mm². In contrast, the loss in volume of LAE442 pins was more obvious. They lost 64 % of their initial weight. The volume of MgCa0.8 reduced clearly to 54.4 % which corresponds to the cross sectional area results. Three point bending tests revealed that LAE442 showed a loss in strength of 71.2 % while MgCa0.8 lost 85.6 % of its initial strength. All results indicated that LAE442 implants degraded slowly, probably due to the formation of a very obvious degradation layer. Degradation of MgCa0.8 implants was far advanced.

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