Effect of peptide secondary structure on adsorption and adsorbed film properties

Protein adsorption at the biomaterial–tissue interface is of utmost importance to the widespread application of engineered materials. The present study asked what role the secondary structures of peptides play in their adsorption, as well as how these structures affect the physicochemical properties of the final adsorbed layer. To this end, α-helices and β-sheets were induced in poly-l-lysine, and their adsorption to Au surfaces was monitored using quartz crystal microbalance with dissipation. It was observed that secondary structures played an important role in governing both the adsorption process and the final film properties. Higher initial adsorption rates were obtained for α-helices compared with β-sheets, regardless of solution salt concentration. Adsorption half-time for β-sheets was greater than that for α-helices, and the final amount adsorbed on β-sheet was significantly higher than that on α-helix. The adsorbed amount and adsorption half-time decreased with increasing salt concentration, suggesting that electrostatic interactions played a role. It was found that the differences in Zeta potential coupled with the apparent effect of surface contact area differences between α-helix and β-sheet conformations are ultimately responsible for these different peptide adsorption behaviours at the Au interface. The initial adsorption rate of α-helix increased with salt concentrations up to 50 mM, whereas β-sheet initial adsorption rates increased with salt concentrations up to 500 mM. Viscosities for films formed from α-helices were about twice those of β-sheets films, regardless of solution ionic strength. It was evident that the peptide secondary structures influence all aspects of their adsorption, as well as affecting the adsorbed film properties.