Verifying the cytotoxicity of a biodegradable zinc alloy with nanodiamond sensors.

Metals are widely utilized as implant materials for bone fixtures as well as stents. Biodegradable versions of these implants are highly desirable since patients do not have to undergo a second surgery for the materials to be removed. Attractive options for such materials are zinc silver alloys since they also offer the benefit of being antibacterial. However, it is important to investigate the effect of the degradation products of such alloys on the surrounding cells, taking into account silver cytotoxicity. Here we investigated zinc alloyed with 1 % of silver (Zn1Ag) and how differently concentrated extracts (1 %-100 %) of this material impact human umbilical vein endothelial cells (HUVECs). More specifically, we focused on free radical generation and oxidative stress as well as the impact on cell viability. To determine free radical production we used diamond-based quantum sensing as well as conventional fluorescent assays. The viability was assessed by observing cell morphology and the metabolic activity via the MTT assay. We found that 1 % and 10 % extracts are well tolerated by the cells. However, at higher extract concentrations we observed severe impact on cell viability and oxidative stress. We were also able to show that quantum sensing was able to detect significant free radical generation even at the lowest tested concentrations.

Enhancing the Mechanical Properties of Biodegradable Mg Alloys Processed by Warm HPT and Thermal Treatments.

In this study, several biodegradable Mg alloys (Mg5Zn, Mg5Zn0.3Ca, Mg5Zn0.15Ca, and Mg5Zn0.15Ca0.15Zr, numbers in wt%) were investigated after thermomechanical processing via high-pressure torsion (HPT) at elevated temperature as well as after additional heat treatments. Indirect and direct analyses of microstructure revealed that the significant strength increases arise not only from dislocations and precipitates but also from vacancy agglomerates. By contrast with former low-temperature processing routes applied by the authors, a significant ductility was obtained because of temperature-induced dynamic recovery. The low initial values of Young's modulus were not significantly affected by warm HPT-processing. nor by heat treatments afterwards. Also, corrosion resistance did not change or even increase during those treatments. Altogether, the study reveals a viable processing route for the optimization of Mg alloys to provide enhanced mechanical properties while leaving the corrosion properties unaffected, suggesting it for the use as biodegradable implant material.

Mechanical properties, structural and texture evolution of biocompatible Ti-45Nb alloy processed by severe plastic deformation.

Biocompatible ß Ti-45Nb (wt%) alloys were subjected to different methods of severe plastic deformation (SPD) in order to increase the mechanical strength without increasing the low Young׳s modulus thus avoiding the stress shielding effect. The mechanical properties, microstructural changes and texture evolution were investigated, by means of tensile, microhardness and nanoindentation tests, as well as TEM and XRD. Significant increases of hardness and ultimate tensile strength up to a factor 1.6 and 2, respectively, could be achieved depending on the SPD method applied (hydrostatic extrusion - HE, high pressure torsion - HPT, and rolling and folding - R&F), while maintaining the considerable ductility. Due to the high content of ß-stabilizing Nb, the initial lattice structure turned out to be stable upon all of the SPD methods applied. This explains why with all SPD methods the apparent Young׳s modulus measured by nanoindentation did not exceed that of the non-processed material. For its variations below that level, they could be quantitatively related to changes in the SPD-induced texture, by means of calculations of the Young׳s modulus on basis of the texture data which were carefully measured for all different SPD techniques and strains. This is especially true for the significant decrease of Young׳s modulus for increasing R&F processing which is thus identified as a texture effect. Considering the mechanical biocompatibility (percentage of hardness over Young׳s modulus), a value of 3-4% is achieved with all the SPD routes applied which recommends them for enhancing ß Ti-alloys for biomedical applications.