Abstract:
Mg-based biodegradable materials, used for medical applications, have been extensively
studied in the past decades. The in vitro cytocompatibility study showed that the proliferation and viability (as assessed by quantitative MTT-assay—3-(4,5-dimethyltiazol-2-yl)-2,5-diphenyl tetrazolium
bromide) were not negatively affected with time by the addition of Mn as an alloying element. In
this sense, it should be put forward that the studied alloys don’t have a cytotoxic effect according to
the standard ISO 10993-5, i.e., the level of the cells’ viability (cultured with the studied experimental
alloys) attained both after 1 day and 5 days was over 82% (i.e., 82, 43–89, 65%). Furthermore, the
fibroblastic cells showed variable morphology (evidenced by fluorescence microscopy) related to
the alloy sample’s proximity (i.e., related to the variation on the Ca, Mg, and Mn ionic concentration as a result of alloy degradation). It should be mentioned that the cells presented a polygonal
morphology with large cytoplasmic processes in the vicinity of the alloy’s samples, and a bipolar
morphology in the remote region of the wells. Moreover, the in vitro results seem to indicate that
only 0.5% Mn is sufficient to improve the chemical stability, and thus the cytocompatibility; from
this point of view, it could provide some flexibility in choosing the right alloy for a specific medical
application, depending on the specific parameters of each alloy, such as its mechanical properties
and corrosion resistance. In order to assess the in vivo compatibility of each concentration of alloy,
the pieces were implanted in four rats, in two distinct body regions, i.e., the lumbar and thigh. The
body’s reaction was followed over time, 60 days, both by general clinical examinations considering
macroscopic changes, and by laboratory examinations, which revealed macroscopic and microscopic
changes using X-rays, CT(Computed Tomography), histology exams and SEM (Scanning Electron
Microscopy). In both anatomical regions, for each of the tested alloys, deformations were observed,
i.e., a local reaction of different intensities, starting the day after surgery. The release of hydrogen
gas that forms during Mg alloy degradation occurred immediately after implantation in all five of
the groups examined, which did not affect the normal functionality of the tissues surrounding the
implants. Imaging examinations (radiological and CT) revealed the presence of the alloy and the
volume of hydrogen gas in the lumbar and femoral region in varying amounts. The biodegradable
alloys in the Mg-Ca-Mn system have great potential to be used in orthopedic applications.
