A biodegradable Zinc-copper alloy (Zn-4wt.%Cu) with enhanced mechanical properties has been developed for potential use as craniomaxillofacial osteosynthesis implant material. In this study, three cell lines, namely L929 mouse fibroblasts, the human osteosarcoma cell line Saos-2, and a cell line of human immortalized cranial periosteal cells (TAg), were used to investigate cytotoxic effects of the Zn-4Cu alloy towards the respective cells in vitro.
An extract test was performed to evaluate cytotoxicity for both as-cast and as-rolled Zn-4Cu alloy, Ti-6Al-4V was used as negative control. Samples were extracted in the respective cell culture media without serum with a surface/volume ratio of 1.25 cm2/mL for 24 h. Metallic ion concentration and pH value of the extracts were determined. Cell morphology and attachment were qualitatively evaluated by live/dead staining. Inhibition of metabolic activity and cell proliferation were quantitatively assessed by CCK-8 assay and BrdU assay, respectively.
L929, Saos-2 and TAg cells exposed to the extracts showed a spindle-shaped attachment pattern, and cell morphologies were similar to the respective counterparts on the titanium controls. For as-cast and as-rolled Zn-4Cu alloys, the mean relative metabolic activities of all cells were always exceeding 70% of the controls, without statistically significant differences between both groups (p > 0.05). For Saos-2 and TAg cells, the as-rolled Zn-4Cu alloy even induced a statistically significant increase in cell proliferation compared to the negative control (p < 0.05).
The as-rolled Zn-4Cu alloy exhibited no obvious toxic effect towards L929, TAg and Saos-2 cells, probably due to the determined low Zn ion concentration in the extracts, which is well under cellular tolerance limits. Moreover, cell proliferation rates of TAg and Saos-2 were shown to be activated by specific Zn ion concentrations in the as-rolled Zn-4Cu alloy extracts. Nevertheless, further studies should analyze the in vivo biocompatibility of as-rolled Zn-4Cu alloys.