In vitro degradation characteristics and cell viability of Mg-6Zn-0.6Si-xSn alloy

Permanent biomedical implants crafted from titanium, cobalt, and stainless steel alloys often necessitate secondary surgeries due to their non-biodegradable nature. Magnesium (Mg) and its alloys have emerged as promising alternatives for temporary implants, offering advantages like low density, high strength-to-weight ratio, and biodegradability, closely matching the mechanical properties of human bone. Previous studies have indicated that alloying Mg with zinc (Zn), silicon (Si), and tin (Sn) enhances biocompatibility and biodegradability. However, the specific influence of Sn on the microstructure and mechanical properties of Mg-Zn-Si alloys remains underexplored.

This study investigates the processing-structure-property relationships of Mg-Zn-Si-xSn alloys with varying Sn content (x = 0, 1, 2, 3, and 4 wt.%). Pressure die-cast samples underwent comprehensive microstructural characterization using scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD). The type, distribution, and volume fraction of second phases were identified through both 2D SEM and 3D X-ray tomography analyses. Mechanical properties were assessed via Vickers hardness testing and bulk compression tests. Subsequently, the alloys were hot-rolled up to 30% at 300°C, followed by further microstructural evaluations.

Corrosion behavior was examined using potentiodynamic polarization tests, hydrogen evolution measurements, and weight loss assessments in Hanks' Balanced Salt Solution (HBSS). Post-corrosion analyses employed Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Scanning Kelvin Probe Force Microscopy (SKPFM), and SEM. Furthermore, in vitro cytocompatibility was evaluated using MG-63 osteoblast-like cells, assessing cell viability and proliferation on the corroded surfaces of the rolled alloys.

The alloy with 1wt.% Sn demonstrated the lowest corrosion rate, signifying enhanced corrosion resistance with Sn addition. Conversely, the alloy with 4 wt.% Sn exhibited the greatest mechanical strength but with an elevated corrosion rate. This can be corroborated to the presence of a higher amount of second phases which increase mechanical properties but ialso elevate galvanic corrosion.