In Vitro Biodegradation of Resorbable Magnesium Alloys Promising for Implant Development.

The aim of the investigation was to study the biodegradation characteristics and rate of magnesium alloys in vitro. MATERIALS AND METHODS: We studied the biodegradation of magnesium alloys Mg-Zn-Ca and WE43 (Mg-Y-Nd-Zr) in homogenized (initial) condition and after strengthening by mechanical processing using equal channel angular pressing (ECAP). The samples were incubated in a model system based on reference fetal calf serum (FCS) in the static and dynamic modes. The morphology of alloy surfaces was analyzed using light microscopy and computed tomography. Biodegradation was assessed by calculating weight loss within a certain incubation period. Cell adhesion and colonization stimulation were quantified in terms of a cell index (CI) using an analyzer xCELLigence RTCA Systems (ACEA Biosciences, Inc., USA) during the incubation of HEK 293 cells on WE43 specimens. RESULTS: Strengthening of magnesium alloys Mg-Zn-Ca and WE43 using ECAP and, consequently, the changed structure resulted in the biodegradation acceleration as high as eightfold. Among the specimens incubated in FCS in different modes, those incubated in liquid flow exhibited the biodegradation rate twice as high as that of the specimens tested under static conditions. The biodegradation process was accompanied by local corrosion, although the degradation was primarily concentrated along the specimen margins stimulating cell adhesion and colonization. Such nature of degradation, as a rule, does not lead to anisotropy of the strength characteristics, that is important for medical materials. Superficial degradation of the alloys with no X-ray density changes in the bulk of the specimens was confirmed by computed tomography. CONCLUSION: The study of the biodegradation rate and further characteristics of magnesium alloys Mg-Zn-Ca and WE43 showed that the materials in both structural conditions are suitable for implants and can be used in bone implants and surgical fasteners.

Interaction of Magnesium-Based Materials with Human Blood Cells and Culture of Human Diploid Cells In Vitro.

We studied morphofunctional properties of human blood cells and diploid culture cells exposed to different types of magnesium materials: pure magnesium (Mg), magnesium-yttrium-neodymium-zirconium alloy (Mg-Y-Nd-Zr) and magnesium-zinc-calcium alloy (Mg-Zn-Ca). The materials were incubated with donor blood and mesenchymal multipotent stromal cells over 3 days. The studied materials did not induce massive lysis of human erythrocytes and leukocytes in vitro, but gradually impaired their structural integrity. In all cases, spontaneous platelet aggregation was observed in 6 h. In the presence of pure Mg and Mg-Zn-Ca alloy, this was accompanied by a decrease in the number of platelets with granules. In 24 h, substantial platelet degranulation occurred in all cases and in 72 h, the platelets did not contain granules. In parallel, the formation of large aggregates (60 µ) was observed. In the culture of stromal cells, all Mg-based materials reduced structural integrity of cells in 24 h, but did not significantly inhibit cell proliferation. Structural integrity of stromal cells partially recovered by day 3 in culture. The studied materials (Mg, Mg-Y-Nd-Zr, and Mg-Zn-Ca) seemed to be low-toxic for human cells during short-term contact, but could stimulate platelet aggregation and spontaneous degranulation and reduced the viability of diploid cells in vitro.