Bioactivity, cytocompatibility and effect of cells on degradation behavior of Mg–2Zn–2Gd alloy

Magnesium (Mg) alloys are the most promising candidates to be next-generation biomaterials due to their ability to degrade biologically in the physiological environment. The authors elucidate here the structure–process–property relationship of a Mg–2Zn–2Gd alloy with enhanced mechanical behavior for retaining mechanical integrity during degradation. Furthermore, the authors studied the effect of the presence of cells (seeding density: 10 000 cells/cm²) on the degradation behavior. As-cast Mg–2Zn–2Gd alloy was subjected to heat treatment and multiaxial forging cycles, to produce different grain sizes. Microstructural and phase characterizations were carried out by using scanning electron microscopy and X-ray diffraction (XRD), respectively. Mechanical behavior as a function of grain size was studied through tensile tests. XRD and Fourier transform infrared analysis were carried out to test the bioactivity of the samples after immersion in simulated body fluid, to confirm the coating phases and degradation product. The samples coated with apatite using the biomimetic approach were used in degradation studies. Changes in pH were monitored at regular intervals. The study showed that the degradation rate was enhanced in the presence of cells due to the metabolic activities of the cells, which reduced the formation of a salt layer, resulting in increased charge transfer from the substrate to solution, which also led to a greater drop in pH in the presence of cells. The study also revealed that ultrafine-grained samples showed controlled degradation and enhanced cellular attachment, viability and higher fibronectin expressions in comparison with their coarse-grained counterparts.