Synthesis and Grafting To of Biomimetic Bottlebrush Polymers
Specifically-adsorbed bottlebrush coatings are found in nature as brush-like glycoproteins that decorate biointerfaces and provide anti-fouling, lubrication, or wear-protection. These molecules contain a surface-adhesive headgroup to anchor macromolecules to a target surface and a bottlebrush polymer that endows the surface with a beneficial property, like antifouling. These glycoproteins can be effectively mimicked using protein-bottlebrush hybrids, but many challenges still exist to robustly produce such polymers. Furthermore, the use of glycoprotein-like bottlebrush coatings is limited by the current lack of understanding of their adsorption behavior and surface conformation. In this work, I first develop a modular synthesis to facilitate the production of protein-brush hybrids. I successfully made a range of protein-brush hybrids baring elastin-like polypeptides (ELP) as model proteins by using copper-catalyzed azide-alkyne cycloaddition and newly discovered diazotransfer reagents. I demonstrated the effectiveness of this synthetic path at each step through careful characterization with 1H-NMR, FTIR, GPC, and diagnostic test reactions on SDS-PAGE. In the second half of this work, I determine the relationships between the dimensions of end-adsorbing bottlebrush polymers and their adsorption behavior. Specifically, I examine the adsorption behavior of PEG-based, biotinylated bottlebrushes with different backbone and bristle lengths to streptavidin model surfaces in PBS. By using QCM, LSPR, and AFM, I learned how bottlebrush dimensions impact their adsorption kinetics, surface conformation, mechanical properties, and anti-fouling 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, bristle length more dramatically affects brush properties than backbone length. Generally, larger bottlebrush dimensions lead to reduced molar adsorption, retarded kinetics, weaker anti-fouling, and softer brush coatings. Longer bristles also lead to less mass adsorption, while the opposite trend is observed for increasing backbone length. In summary, these 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.
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