This study demonstrates that protein adsorption on end-grafted poly(sulfobetaine) thin films depends on the grafting density, molecular weight, and ionic strength. Zwitterionic polymers contain cationic and anionic groups, and reportedly exhibit ultralow non-specific fouling (protein adsorption) and excellent biocompatibility. This picture contrasts with a recent report that soluble pSB chains bind proteins and alter their folding stability. To address this apparent contradiction, we investigated the dependence of protein adsorption on the chain grafting parameters: namely, the grafting density, molecular weight and ionic strength. Studies compared the adsorption of PGK (phosphoglycerate kinase) and positively charged Lysozyme versus the scaled grafting parameter s/2RF Here, s is the distance between grafting sites, and RF is the Flory radius. With both proteins, plots of the adsorbed protein amount versus s/2RF exhibits a bell shaped curve, with a maximum near s/2RF ~ 1 and an amplitude that decreases with ionic strength. This behavior is qualitatively consistent with theoretical models for colloid interactions with weakly attractive, grafted chains. In such models, adsorption is controlled by competition between protein-segment attraction and osmotic repulsion, which prevents protein insertion into the brush. The model predicts a bell shaped adsorption curve, as we observe experimentally in our studies. Our results confirm that proteins do adsorb to pSB thin films. They also suggest an underlying mechanism. Comparison with polymer models further identify design rules for pSB films that effectively repel protein.

Protein adsorption on grafted zwitterionic polymer thin films

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.