Nanoscale Characteristics and Antimicrobial Properties of (SI-ATRP)- Seeded Polymer Brush Surfaces Yoo Jin Oh,* ,† Essak S. Khan, ‡,§ Ara ́ nzazu del Campo, ‡,§ Peter Hinterdorfer, † and Bin Li* ,‡ † Institute of Biophysics, Johannes Kepler University Linz, Gruberstrasse 40, A-4020 Linz, Austria ‡ INM-Leibniz Institute for New Materials, Campus D2.2, 66123 Saarbrü cken, Germany § Chemistry Department, Saarland University, 66123 Saarbrü cken, Germany * S Supporting Information ABSTRACT: Microbial resistant coatings have raised considerable interest in the biotechnological industry and clinical scenarios to combat the spreading of infections, in particular in implanted medical devices. Polymer brushes covalently attached to surfaces represent a useful platform to identify ideal compositions for preventing bacterial settlement by quantifying bacteria-surface interactions. In this work, a series of polymer brushes with different charges, positively charged poly[2- (methacryloyloxy)ethyl trimethylammonium chloride] (PMETAC), negatively charged poly(3-sulfopropyl methacrylate potassium salt) (PSPMA), and neutral poly(2-hydroxyethyl methacrylate) (PHEMA) were grafted onto glass surfaces by surface-initiated atom transfer radical polymerization in aqueous conditions. The antimicrobial activity of the polymer brushes against Gram-negative Escherichia coli was tested at the nano- and microscopic level on different time scales, that is, from nm to 100 μm, and ms to 24 h, respectively. The interaction between the polymer brushes and E. coli was studied by single-cell force spectroscopy (SCFS) and by quantification of the bacterial density on surfaces incubated with bacterial suspensions. E. coli firmly attached to positive PMETAC brushes with high work required for de-adhesion of 28 ± 9 nN·nm, but did not significantly bind to negatively charged PSPMA and neutral PHEMA brushes. Our studies of bacterial adhesion using polymer brushes with controllable chemistry provide essential insights into bacterial surface interactions and the origins of bacterial adhesion. KEYWORDS: polymer brush, single-cell force spectroscopy, bacterial adhesion, E. coli, electrostatic interaction ■ INTRODUCTION The settlement of bacteria on synthetic material surfaces and the subsequent biofilm formation are crucial in many fields, such as the fouling of naval ship hulls, devices for medical diagnostics, and food packaging. 1-3 Material-related fouling starts with the initial adhesion of organic molecules, such as polysaccharides, proteins, and proteoglycans, as well as with inorganic compounds that rapidly accumulate on the surface to form a conditioning film for the subsequent colonization. 4 Specific ligand-receptor interactions of membrane receptors and the physicochemical properties of the materials surface together determine the type and strength of interactions with bacteria. 5 Therefore, the understanding and the control of these interactions are central questions to prevent bacterial adhesion. However, when it comes to understanding the underlying mechanisms of this dynamic phenomenon in detail, many questions remain unanswered to date because of the complexity of the dynamic fouling process and the different factors involved. A lot of effort has been undertaken to develop and identify antifouling coatings and antimicrobial materials, including self-cleaning coatings and incorporation of biocidal agents (silver, antibiotics, and nanoparticles). 5-8 However, the main problems of these strategies always lead to increased bacteria resistance or pollution to the environment. Hydro- philic polymer coatings, with a highly hydrated polymeric layer, show a strong capability to bind water around the polymer chains, leading to a repulsive osmotic force to suppress the uptake of biological entities (e.g., macromolecules, cells, larvae) and prevent biofilm formation from pathogenic bacteria. 9-11 Polymer brushes, a “forest” of densely end-grafted polymer chains onto a substrate, 12,13 are of great interest with respect to medical and bioengineering applications because of their ability of preventing bacterial adhesion. Poly(ethylene glycol) is widely used as a nonfouling coating and is extensively discussed in literature. 6,8,14 Other examples include poly- ethylene oxide, 15 peptoids, 16-19 glycerol, and carbohydrate derivatives. 20-24 The hydrophobicity and the charge of the polymer brushes are the most two important parameters for bacteria adhesion. 25-28 Cationic polymer chains can penetrate cells and thereby disrupt membrane integrity. Negatively charged polymer chains inhibit bacterial adhesion due to Received: June 6, 2019 Accepted: July 1, 2019 Published: July 1, 2019 Research Article www.acsami.org Cite This: ACS Appl. Mater. Interfaces 2019, 11, 29312-29319 © 2019 American Chemical Society 29312 DOI: 10.1021/acsami.9b09885 ACS Appl. Mater. Interfaces 2019, 11, 29312-29319 Downloaded via LEIBNIZ INST NEUE MATERIALIEN on September 26, 2019 at 12:59:00 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.