Tin Silver Alloy as a Biomaterial: Corrosion Characteristics and Cellular Behavior

Tin-silver (Sn-Ag) has been used as a permanently implanted biomaterial within the Essure female sterilization device and in dental amalgams; however, little data exist for Sn-Ag's corrosion characteristics and/or cellular interactions. In this study, to assess its suitability as a degradable metallic biomaterial, 95-5 wt% Sn-Ag solder was subjected to corrosion testing including open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and anodic potentiodynamic polarization in phosphate-buffered saline (PBS) and cell culture media (with serum proteins) at room temperature (25°C) and body temperature (37°C). Cell culture studies were also performed. Mouse pre-osteoblast cells (MC3T3-E1) were cultured in media on Sn-Ag discs and monitored over 24 h at potentials below, around, or above Sn-Ag's breakdown potential, fixed, and then viewed using SEM. Separately, cells on tissue culture plastic were subjected to increasing concentrations of SnCl₂ in media for 24 h before a live-dead imaging at each concentration to determine cell viability and area fraction covered when compared with a control well. The results show both passive (in PBS), with a breakdown potential of -250 mV versus Ag/AgCl and active polarization behavior (in AMEM with proteins). EIS results showed polarization resistance (R _p ) in the 10⁵ Ωcm² range but decreased generally with increasing temperature (p < 0.05). Cells were well attached on Sn-Ag surfaces at OCP and below the breakdown potential, but when anodically polarized, cells reduced their spread area and became more spherical, indicating less viability. SnCl₂ exhibited a dose-dependent killing effect on MC3T3 cells with a lethal dose for 50% of about 0.5 mM. The results of these experiments show that Sn-Ag alloys can be considered as degradable metallic biomaterials.