Published: May 26, 2011 r2011 American Chemical Society 2681 dx.doi.org/10.1021/bm200476g | Biomacromolecules 2011, 12, 2681–2685 ARTICLE pubs.acs.org/Biomac Chemical and Physical Factors in Design of Antibiofouling Polymer Coatings Inbal Eshet, †,‡ Viatcheslav Freger,* ,†,‡ Roni Kasher,* ,† Moshe Herzberg, † Jing Lei, § and Mathias Ulbricht § † Zuckerberg Institute for Water Research, Ben-Gurion University of the Negev, Sede Boqer Campus 84990, Israel ‡ Unit of Environmental Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel § Lehrstuhl f€ ur Technische Chemie II, Universit € at Duisburg-Essen, 45117 Essen, Germany ’ INTRODUCTION Bacterial biofilms are ubiquitous and readily form on surfaces exposed to aqueous environments. 1 Biofilm formation may inflict damage in various ways, for example, by causing persistent infec- tions, contaminating biomedical devices, damaging underwater structures and ship hulls, and impairing membrane performance in membrane-based water treatment. 2À4 Design of antibiofouling surfaces, for example, via surface modification, must consider the diversity and persistence of bacteria. 5À7 Nature provides remarkable examples of efficiently preventing attachment of bacteria and biofilms to living surfaces and emphasizes the benefits of combining different principles for this purpose. For instance, the skin of whales and dolphins keeps clean of biofilms by using both passive (a gel-like surface) and active mechanisms (ablation and enzymatic digestion of undesired biological materials). 8 Synthetic surfaces combining active and passive approaches have been reported, 9,10 but, unfortu- nately, components actively preventing bacterial growth are likely to lose activity in long-term uses. Nevertheless, there is much room for combining even simple “passive” principles to engineer efficient and sustainable biofouling-resistant surfaces. In this work, we analyze the combination of two known principles, referred to here as “chemical ” and “physical ”, in one surface engine- ering strategy. Toward this goal, we implement here a thorough quantitative separation of chemical and physical effects, which has not been common. The “chemical ” principle refers to the use of “non-fouling” building blocks that exhibit low affinity to cells and biomacromolecules such as polyethylene glycol (PEG), 11,12 zwitter- ionic moieties, 13,14 and overall neutral complexes of oppositely charged polyelectrolytes or polyampholytes built of units bearing alternating charges. 15,16 Such materials are typically incorporated to surfaces through procedures based on self-assembly or graft polymerization. 5À7 The “physical ” principle analyzed here is non- speci fic “dilution” of molecular interactions using highly hydrated materials. In general, one expects that for a given chemistry fewer interactions per contact area should always reduce the thermo- dynamic driving force for bacterial adhesion to the waterÀgel interface, provided that it is impermeable to bacteria. Both principles are apparently interrelated because the majority of “non-fouling” substances are inherently hydrophilic and the importance of hydra- tion has been recognized. 17,18 However, it is emphasized here that chemistry and hydration (swelling) may be varied indepen- dently. This is most easily realized in surface coatings based on hydrogels. 19,20 Apart from independent control of immobilized water fraction, hydrogels offer several benefits: Their mesh-like structure acts as a steric barrier for particles, bacteria, and large molecules, and no inherent limit is imposed on thickness, as is the Received: April 7, 2011 Revised: May 21, 2011 ABSTRACT: Because most “low fouling” polymers resisting bacterial attachment are hydrophilic, they are usually also significantly swollen. Swelling leads to purely physical dilution of interaction and weakens attachment; however, these nonspecific contribu- tions are usually not separated from the specificeffect of polymer chemistry. Taking advantage of the fact that chemistry and swelling of hydrogels may be independently varied through the fraction of a cross-linker, the roles of chemistry and physical dilution (swelling) in bacterial attachment are analyzed for selected hydrogels. Using as a quantitative indicator the rate of bacterial deposition in a parallel plate setup under defined flow conditions, the observed correlation of deposition rate with swelling provides a straightforward comparison of gels with different chemistries that can factor out the effect of swelling. In particular, it is found that chemistry appears to contribute similarly to bacterial deposition on hydrogels prepared from acrylamide and a zwitterioninic monomer 2-(methacryloyloxy)ethyl) dimethyl-(3-sulfopropyl) am- monium hydroxide so that the observed differences may be related to swelling only. In contrast, these gels were inferior to PEG-based hydrogels, even when swelling of the latter was lower, indicating a greater contribution of PEG chemistry to reduced bacterial deposition. This demonstrates that swelling must be accounted for when comparing different biofouling- resistant materials. Chemical and physical principles may be combined in hydrogel coatings to develop efficient antibiofouling surfaces.