Grafting To of Bottlebrush Polymers: Conformation and Kinetics

Specifically adsorbed bottlebrush coatings are found in nature as brush-like glycoproteins that decorate biointerfaces and provide antifouling, lubrication, or wear-protection. Although various synthetic strategies have been developed to mimic glycoprotein structure and function, the use of these mimics is still limited because of the current lack of understanding of their adsorption behavior and surface conformation. In this paper, we examine the adsorption behavior of PEG-based, biotinylated bottlebrushes with different backbone and bristle lengths to streptavidin model surfaces in phosphate-buffered saline. By using quartz crystal microbalance, localized surface plasmon resonance, and atomic force microscopy, we learn how bottlebrush dimensions impact their adsorption kinetics, surface conformation, mechanical properties, and antifouling properties. Our bottlebrushes qualitatively mirror the adsorption behavior of linear polymers and exhibit three kinetic regimes of adsorption: (I) a transport-limited regime, (II) a pause, and (III) a penetration-limited regime. Furthermore, we find that the bristle length more dramatically affects brush properties than the backbone length. Generally, larger bottlebrush dimensions lead to reduced molar adsorption, retarded kinetics, weaker antifouling, and softer brush coatings. Longer bristles also lead to less mass adsorption, while the opposite trend is observed for increasing backbone length. In summary, our findings aid the rational design of new bottlebrush coatings by elucidating how their dimensions impact adsorption, surface conformation, and the properties of the final coating.