Hydrogen bonding induced protein adsorption on polymer brushes: a Monte Carlo study

Using Monte Carlo simulations, we investigate the protein adsorption behaviors on polymer brushes in the presence of hydrogen bonding between proteins and polymer brushes. It is interesting to observe in simulation that as a function of grafting density, the amount of protein adsorbed passes through a minimum, that is, a critical grafting density with the minimum amount of adsorbed protein exists. The existence of a critical grafting density uncovers two different driving forces of protein adsorption. The driving force of protein adsorption is mainly the hydrogen bonding between proteins and polymer brushes when the grafting density is above the critical value, whereas the driving force is the attraction between proteins and the hydrophobic substrate when the grafting density is below the critical value. It is extraordinary that at the critical grafting density, increasing the hydrophilicity of the polymer brushes will lead to an increase in protein adsorption, even when the formation of hydrogen bonding between the proteins and polymer brushes is suppressed by the increasing hydrophilicity of the polymer brushes. This mainly results from the conformational transition of the polymer chains from collapsed to stretched when the hydrophilicity is increased. It is noteworthy that the relationship between protein adsorption and grafting density reported in this study is quite consistent with our previous experimental work. Beyond that, the simulation results also provide detailed information about protein adsorption location and grafting chain conformation, which helps us to better understand the protein adsorption behaviors on polymer brushes induced by hydrogen bonding.