Self-Sterilizing, Self-Cleaning Mixed Polymeric Multifunctional Antimicrobial Surfaces

Mitigation of bacterial adhesion and subsequent biofilm formation is quickly becoming a strategy for the prevention of hospital-acquired infections. We demonstrate a basic strategy for surface modification that combines the ability to control attachment by microbes with the ability to inactivate microbes. The surface consists of two active materials: poly(p-phenylene ethynylene)-based polymers, which can inactivate a wide range of microbes and pathogens, and poly(N-isopropylacrylamide)-based polymers, which can switch between an hydrophobic "capture" state and a hydrophilic "release" state. The combination of these materials creates a surface that can both bind microbes in a switchable way and kill surface-bound microbes efficiently. Considerable earlier work with cationic poly(p-phenylene ethynylene) polyelectrolytes has demonstrated and characterized their antimicrobial properties, including the ability to efficiently destroy or deactivate Gram-negative and Gram-positive bacteria, fungi, and viruses. Similarly, much work has shown (1) that surface-polymerized films of poly(N-isopropylacrylamide) are able to switch their surface thermodynamic properties from a swollen, relatively hydrophilic state at low temperature to a condensed, relatively hydrophobic state at higher temperature, and (2) that this switch can control the binding and/or release of microbes to poly(N-isopropylacrylamide) surfaces. The active surfaces described herein were fabricated by first creating a film of biocidal poly(p-phenylene ethynylene) using layer-by-layer methods, and then conferring switchable adhesion by growing poly(N-isopropylacrylamide) through the poly(p-phenylene ethynylene) layer, using surface-attached polymerization initiators. The resulting multifunctional, complex films were then characterized both physically and functionally. We demonstrate that such films kill and subsequently induce widespread release of Gram-negative and Gram-positive bacteria.