(551l) Antibiofouling Behaviors of Zwitterionic Polymers

Biofouling occurs through the attachment of biomolecules onto substrate surfaces. Zwitterionic polymers have emerged as highly effective ultralow-fouling materials for both biomedical and marine vessel coatings. To understand the underlying mechanisms of fouling resistance, we conducted ab initio molecular dynamics (AIMD) simulations and atomistic MD simulations to investigate the fouling-resistant mechanisms of zwitterionic materials, such as the protein stabilizer trimethylamine N-oxide (TMAO)-derived (pTMAO) and carboxybetaine-based polymers with varying charge-separation distances at the quantum and atomistic scales. Our AIMD simulations showed that the interplay among hydration properties (hydrogen bonding, net charge, and dipole moment) is crucial to the fouling-resistant capabilities of zwitterionic polymers. Shortening the zwitterionic spacing strengthens hydrogen bonding with water, which helps prevent biomolecule attachment due to increased electrostatic and induction interactions, charge transfer, and improved structural stability. Moreover, the reduced charge separation lowers the dipole moment of zwitterionic materials with an intrinsically near-neutral net charge, thereby decreasing their electrostatic and dipole–dipole interactions with biofoulers and enhancing their resistance to fouling. Compared to carboxybetaine compounds, TMAO has the shortest zwitterionic spacing and exhibits the strongest hydrogen bonding, the smallest net charge, and the lowest dipole moment, making it an excellent nonfouling material. In alignment with sum of the frequency generation (SFG) vibrational spectroscopy, our atomistic molecular dynamics simulations showed that the ordered structure of the condensed hydration water layer on pTMAO surfaces creates a strong hydration energy barrier near the polymer surfaces, effectively resisting protein adsorption compared to other biofouling surfaces. The addition of salts has only a slight effect on the pTMAO surface’s ability to exclude proteins, due to the minimal disruption of interfacial water structure. Our fundamental study of the interfacial behavior of zwitterionic polymers will be critical to the future development of these materials for a wide range of engineering applications.