Impact of conformational change of immunoglobulin G induced by silver ions on Escherichia coli and macrophage adhesion to biomaterial surfaces

Silver ions (Ag+) are widely employed in biomedical devices and implants to minimize the risk of microbial contamination owing to their superior antibacterial properties. Surface adsorption of serum proteins occurs within seconds after biomaterials come into contact with the blood and is a decisive step prior to cell-surface interactions. However, investigation on the interactions between Ag+ and serum proteins, and the impact of such interactions on the antibacterial and anti-inflammatory performance of biomaterials are critical but rather scarce. In this study, using TiSiN/Ag coatings as a model, in vitro investigation was performed to explore the synergistic effect of Ag+ and immunoglobulin G (IgG), one of the major serum proteins involved in primary immune responses towards bacterial infections, on Escherichia coli and macrophage adhesion to biomaterial surfaces. The molecular interactions between Ag+ and IgG were further explored using dynamic light scattering (DLS), atomic force microscopy (AFM), circular dichroism (CD) spectroscopy and inductively coupled plasmamass spectrometry (ICP-MS). The results show that the presence of Ag+ altered the impact of IgG on E. coli and macrophage adhesion from promotion to inhibition. DLS, AFM and CD analyses further disclosed that the existence of Ag+ altered the secondary structure of the Fab and Fc domains of IgG from the typical 13-sheet structure to random coils, and changed the "Y" structure of IgG into a linear structure, accounting for the switch of the role of IgG. These results would give insights into the interactions between Ag+ and IgG, and provide guidance for more rational design of antibacterial biomaterial surfaces.