The perspective of combining application-specific mechanical properties with degradability and osteinductive properties, enhance the prospects of magnesium and its alloys as biodegradable implants.
Actual challenges of magnesium biodegradable materials lay on the need of reaching the required mechanical properties with a desired biocompatibility, and an accurate prediction of in vivo resorption process. The difficulty of in vivo degradation prediction has to address the complex environment of the implantation site. Currently immersion tests take into account the complex chemical composition and the restricted physical conditions of the physiological fluids and surrounding tissues. Apart from that, the amount and rate exchange of the physiological fluid can have a strong influence on the stability of the potentially protective degradation layer.
Mg2Ag T4 heat treated and extruded disks (10 mm x 2 mm) were tested in vitro for 30 days under sterile cell culture conditions in different volumes (1, 5, 10 ml/cm2) of MEM-α supplemented with 10 % FBS and 1 % penicillin-streptomycin. The medium was changed every 2 – 3 days, and at the same time the osmolality and the pH were evaluated. Mass loss, degradation roughness, and degradation layer morphology and composition were evaluated at 2, 7, 15, 21, 30 days of immersion.
The degradation rate showed a limit in the V/A ratio below which the degradation behaviour is significantly decreased. Despite this, the degradation morphology shows a general degradation process for all conditions applied. Differences in the degradation layer morphology and composition for the different conditions, lead to correlate the degradation behaviour with the degradation layer developed on the surface. Different V/A ratios seem to generate differences in the saturation levels, modify the buffer capacity and provide different quantity of calcium, phosphorous and carbonate influencing the degree of precipitation.