Systematic Comparison of Zwitterionic and Non-Zwitterionic Antifouling Polymer Brushes on a Bead-Based Platform

We report the first direct comparison made between a sulfobetaine with opposite charges separated by two and three methylene groups and a carboxybetaine bearing two separating methylene groups

Esther van Andel

2018

Scholarcy highlights

  • Nonspecific adsorption of biomolecules to surfaces is a major concern in many applications, including drug-delivery systems, medical implants, and diagnostic devices. Compromised sensitivity of diagnostic tests and adverse immune responses against drug-delivery carriers and indwelling medical devices illustrate the great need for effective nonfouling materials.Two decades ago, Whitesides and co-workers performed a systematic study on the efficiency of different monolayers to suppress protein adsorption, leading to a set of empirical guidelines that is often referred to as the “Whitesides rules”.7 These guidelines state that good antifouling layers have polar functional groups, i.e., are hydrophilic, hydrogen bond acceptors, no hydrogen bond donors, and zero net charge
  • We compare the antifouling performance of polymer brushes derived from two sulfobetaines, SBMAA-3 and SBMAA-2, the carboxybetaine CBMAA-2, the phosphocholine PCMA-2 and, the hydroxyl acrylamide HPMAA
  • SBMAA-3 and CBMAA-2 were synthesized in a similar fashion using DMAPMAA with 1,3-propane sultone and 1,3-propiolactone, respectively
  • In selecting the optimal antifouling coating, besides the actual antifouling performance, several other factors come into play depending on the application. pH of the medium: the antifouling performance of poly(CBMAA-2) is pH-dependent as the zwitterionic character is lost upon protonation of the carboxylic acid at low pH. Ionic strength and temperature: the antifouling characteristics of sulfobetaines are highly dependent on ionic strength and temperature− due to strong intra/interchain interactions between the sulfobetaine moieties. These are so strong that, without any added ions, sulfobetaine-based polymers can even be used as the basis of self-healing antifouling materials. Biofunctionalization: CBMAA-2 and HPMAA are the only monomers that can directly be functionalized within the brush with biorecognition elements, albeit at the cost of diminished antifouling properties; for sulfobetaines, an efficient synthesis of azide-functionalized monomers is available that allows azide−alkyne click-based biofunctionalizations to take place without loss of the zwitterionic character. Ease of use: The growth of sulfobetaine brushes is extremely reproducible and allows for minor deviations from the protocol
  • Our observations lead to the following antifouling ranking based on the amount of adsorbed serum proteins: HPMAA ≥ CBMAA-2 ≈ PCMA-2 > SBMAA-2 > SBMAA-3 ≫ nonmodified beads
  • Of the family of sulfobetaines, we show for the first time that poly(SBMAA-2) performs consistently better in antifouling studies than poly(SBMAA-3) due to the reduced spacer length between opposing charges
  • The excellent performance of poly(HPMAA), equal to or better than any of the zwitterionic monomers under study, is likely related to strong and multiple hydrogen bond formation and/or low surface charge

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