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.

Dynamic Recrystallization and Its Effect on Superior Plasticity of Cold-Rolled Bioabsorbable Zinc-Copper Alloys.

High plasticity of bioabsorbable stents, either cardiac or ureteral, is of great importance in terms of implants' fabrication and positioning. Zn-Cu constitutes a promising group of materials in terms of feasible deformation since the superplastic effect has been observed in them, yet its origin remains poorly understood. Therefore, it is crucial to inspect the microstructural evolution of processed material to gain an insight into the mechanisms leading to such an extraordinary property. Within the present study, cold-rolled Zn-Cu alloys, i.e., Zn with addition of 1 wt.% and 5 wt.% of Cu, have been extensively investigated using scanning electron microscopy as well as transmission electron microscopy, so as to find out the possible explanation of superior plasticity of the Zn-Cu alloys. It has been stated that the continuous dynamic recrystallization has a tremendous impact on superior plasticity reported for Zn-1Cu alloy processed by rolling to 90% of reduction rate. The effect might be supported by static recrystallization, provoking grain growth and thereby yielding non-homogeneous microstructures. Such heterogeneous microstructure enables better formability since it increases the mean free path for dislocation movement.

Texture-Governed Cell Response to Severely Deformed Titanium.

The phenomenon of superior biological behavior observed in titanium processed by an unconventional severe plastic deformation method, that is, hydrostatic extrusion, has been described within the present study. In doing so, specimens varying significantly in the crystallographic orientation of grains, yet exhibiting comparable grain refinement, were meticulously investigated. The aim was to find the clear origin of enhanced biocompatibility of titanium-based materials, having microstructures scaled down to the submicron range. Texture, microstructure, and surface characteristics, that is, wettability, roughness, and chemical composition, were examined as well as protein adsorption tests and cell response studies were carried out. It has been concluded that, irrespective of surface properties and mean grain size, the (101̅0) crystallographic plane favors endothelial cell attachment on the surface of the severely deformed titanium. Interestingly, an enhanced albumin, fibronectin, and serum adsorption as well as clearly directional growth of the cells with preferentially oriented cell nuclei have been observed on the surfaces having (0001) planes exposed predominantly. Overall, the biological response of titanium fabricated by severe plastic deformation techniques is derived from the synergistic effect of surface irregularities, being the effect of refined microstructures, surface chemistry, and crystallographic orientation of grains rather than grain refinement itself.