Nanopatterned Smart Polymer Surfaces for Controlled Attachment, Killing, and Release of Bacteria Qian Yu, † Janghwan Cho, † Phanindhar Shivapooja, † Linnea K. Ista, ‡ and Gabriel P. Ló pez* ,†,‡,§,⊥ † Department of Biomedical Engineering, § Department of Mechanical Engineering & Materials Science, and ⊥ NSF Research Triangle Materials Research Science & Engineering Center, Duke University, Durham, North Carolina 27708, United States ‡ Center for Biomedical Engineering and Department of Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, New Mexico 87131, United States * S Supporting Information ABSTRACT: Model surfaces with switchable functionality based on nanopatterned, thermoresponsive poly(N-isopropy- lacrylamide) (PNIPAAm) brushes were fabricated using interferometric lithography combined with surface-initiated polymerization. The temperature-triggered hydration and conformational changes of nanopatterned PNIPAAm brushes reversibly modulate the spatial concealment and exposure of molecules that are immobilized in the intervals between nanopatterned brushes. A biocidal quaternary ammonium salt (QAS) was used to demonstrate the utility of nanopatterned PNIPAAm brushes to control biointerfacial interactions with bacteria. QAS was integrated into polymer-free regions of the substrate between nanopatterned PNIPAAm brushes. The biocidal efficacy and release properties of these surfaces were tested against Escherichia coli K12. Above the lower critical solution temperature (LCST) of PNIPAAm, desolvated, collapsed polymer chains facilitate the attachment of bacteria and expose QAS moieties that kill attached bacteria. Upon a reduction of the temperature below the LCST, swollen PNIPAAm chains promote the release of dead bacteria. These results demonstrate that nanopatterned PNIPAAm/QAS hybrid surfaces are model systems that exhibit an ability to undergo noncovalent, dynamic, and reversible changes in structure that can be used to control the attachment, killing, and release of bacteria in response to changes in temperature. KEYWORDS: nanopatterned polymer brushes, poly(N-isopropylacrylamide), quaternary ammonium salt, antimicrobial, bacterial release 1. INTRODUCTION The attachment of bacterial cells to surfaces of synthetic materials often leads to colonization, resulting in the formation of biofilms; unwanted biofilms, or biofouling, can cause a variety of serious problems including failure of implanted and submerged materials and devices, as well as the spread of infection within public health and food production settings. 1-3 Developing methods to prevent biofouling on synthetic surfaces is, thus, of great interest. 4-6 Two approaches have been widely adopted to combat biofouling. First, fouling- resistant coatings, including poly(ethylene glycol) and its derivatives, 7 zwitterionic polymers, 8 and glycopolymers, 9 prevent the attachment of bacteria to materials over short time periods. While such coatings can significantly reduce the rate of bacterial attachment, colonization inevitably occurs over the long term. 10 In a second approach, antimicrobial agents, including polycations, 11 antimicrobial peptides (AMPs), 12 nano- particles, 13 enzymes, 14 and antibiotics, 15 are incorporated into materials, resulting in biocidal surfaces. Antimicrobial strategies effectively prevent the formation of viable biofilms, but the surface remains contaminated by the attached dead bacteria, which can compromise the biocidal action and can serve as a conditioning layer for further bacterial attachment and biofilm development. To overcome these limitations, an antifouling surface could combine fouling resistance and anti- microbial features in a reversible system that kills bacteria and from which dead cells and debris could be efficiently released. Our previous experience in both antimicrobial surfaces 16-18 and fouling-release surfaces 19-23 led us to explore combining these attributes into a single surface. Stimuli-responsive or “smart” materials are characterized by rapid and reversible changes in their physical properties in response to small changes in environmental conditions. 24 Poly(N-isopropylacrylamide) (PNIPAAm) is a prototypical smart polymer; it displays a sharp, reversible solubility phase transition at a lower critical solution temperature (LCST) of ∼32 °C in Special Issue: New Frontiers and Challenges in Biomaterials Received: June 8, 2013 Accepted: August 27, 2013 Published: September 16, 2013 Forum Article www.acsami.org © 2013 American Chemical Society 9295 dx.doi.org/10.1021/am4022279 | ACS Appl. Mater. Interfaces 2013, 5, 9295-9304