Reduction of protein adsorption on well-characterized polymer brush layers with varying chemical structures

To clarify protein adsorption behavior on polymer brush layers, surface characteristics and protein adsorption repellency on polymer brush layers should be precisely determined. Here, we clearly delineated the chemical structure of the polymer brush layers containing various hydrophilic groups, namely, phosphorylcholine, sulfoxybetaine, carboxybetaine (zwitterionic), and hydroxyl group (nonionic) and examined the effects of the chemical structure on initial protein adsorption behavior. Kinetic analysis performed during surface-initiated atom transfer radical polymerization revealed that graft polymerization proceeded in a living manner. The graft density of each type of polymer chain and its surface coverage were high enough to form dense polymer brush structures. The hydroxyl group-bearing polymer brush structure exhibited the highest graft density. Among the zwitterionic polymer brush structures, the graft density and surface coverage of sulfoxybetaine- and carboxybetaine-bearing polymer chains were higher than those of the phosphorylcholine-bearing polymer chains. The amount of protein relative to 100% serum adsorbed on polymer brush layers was quantified using quartz crystal microbalance with dissipation (QCM-D). Protein adsorption on all zwitterionic polymer brush layers apparently decreased with increasing thickness of the grafted polymer layers. Protein adsorption was highly suppressed on thick polymer brush layers bearing phosphorylcholine or sulfoxybetaine groups. However, the amount of proteins adsorbed on thick polymer brush layers bearing hydroxyl groups was 10 times more than that adsorbed on polymer brush layers bearing phosphorylcholine groups. Thus, we concluded that the chemical structure of the polymer brush layer is a significant factor affecting resistance to protein adsorption even for dense polymer brush structures.