Effect of Heat Treatment on In Vitro Cytotoxicity of Ti-Nb-Zr Gum Metal Alloy

Abstract

Strain-induced deformations and phase evolutions are two hidden factors that may influence cytocompatibility of Gum Metal alloys during processing for relevant implant applications. In the present research, changes in cell viability of a new Gum Metal Ti-Nb-Zr alloy in its cold-rolled state and after heat treatments (at 700, 850, and 900 degrees C) were investigated by a comprehensive study of microstructural phases and their role in deformation mechanisms as well as mechanical properties. In its cold-rolled state, the alloy showed a lamellar microstructure along with stress-induced alpha '' martensite and omega phases, as confirmed by optical microscopy (OM) and X-ray diffractometry (XRD) analysis. The instability in the beta phase led to a strain-induced martensitic (SIM) transformation from beta to alpha '/alpha '' phases, causing lower viability of MG-63 cells compared with commercially pure titanium. MG-63 cell viability was significantly higher (p < 0.0001) in the alloy heat-treated at 900 degrees C compared with those heat-treated at 700 and 850 degrees C. This can be directly attributed to the increased portion of the stable and dominant beta phase. The stabilized beta phase greatly improved the alloy's cellular response by reducing harmful phase interactions and maintaining mechanical compatibility with bone (admissible strain of 1.3). Importantly, heat treatment at high temperatures (between 850 and 900 degrees C) effectively converted the stress-induced alpha '' and omega phases back into a stable beta phase matrix as the dominant phase.