Prevention of bacterial colonization in hospital-acquired infections using electrically conducting polymers

Abstract: Biofilms are bacterial assemblies developed as response to adverse environmental conditions and external threats. Within a biofilm, a complex and highly regulated internal architecture is developed, resulting in a network of interconnected microniches. This leads to the formation of an intricate internal electrochemical balance, key to aspects such as metabolism and inter-cell communication. Due to their highly optimized physiology, biofilms heavily influence a wide variety of aspects of the human life. In a medical context, biofilms constitute a serious health threat due to their low susceptibility to antibiotics and other biocides. In particular grave risk are patients treated with indwelling devices, as device-associated infections often result in the biofilm contamination of the implant. This requires the development of novel materials and strategies, so biofilm colonization of the device surface can be prevented. Electrically conducting polymers have recently emerged as an interesting group of materials with properties from organic polymer, metals and semiconductors. With their dual organic-conductive nature, these materials can be used to synthetize versatile electrochemical systems with which monitor and influence biological systems. In this thesis, the use of electrically conducting polymers is explored with the aim of modulating biofilm formation. First, composites of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) complexed with either chlorine (Cl), heparin (Hep) or dodecylbenzenesulfonate (DBS) were studied. In all three cases, PEDOT acted as an electron mediator for bacterial metabolism, modulating Salmonella biofilm growth with the polymer electrochemical state. Furthermore, bacteria induced an electrochromic response on PEDOT. This allowed the use of the polymer composites as visual indicators of bacterial colonization, with applications in sterility assurance of medical devices and in food packing for contamination control. To gain a deeper understanding of the effects of the PEDOT composites on biofilm growth, a fluorescence confocal microscopy study was performed. Using a custom-made image processing software tool, differences were found in the architecture of Salmonella biofilms that depended on the electrochemical state and composition of the composite. This revealed the suitability of conducting polymers as a platform for both fundamental microbiologic studies and biofilm engineering applications. Next, we investigated whether a more refined control of Salmonella biofilm formation could be obtained with a more elaborated electrochemical device. Different electrochemical gradients were established along the channel of a PEDOT:Cl-based organic electrochemical transistor (OECT) using different voltage inputs in the source, drain and gate terminals. A fluorescence confocal microscopy study with the developed custom-made software tool revealed biofilm gradients mimicking the imposed electrochemical gradients. This illustrated the potential of conducting polymers to modulate biofilms formation in complex patterns, which has applications in areas like design of antifouling surfaces, biocatalysis, and the study of bacterial colonization. Finally, we explored the functionalization of conducting polymers with biocide agents. Surfaces based on poly(hydroxymethyl 3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT-MeOH:PSS) were functionalized with silver nanoparticles (AgNPs) by means of an aminosilane linker. A nearly complete prevention of S. aureus biofilm growth was obtained when a voltage input was applied. This was not explained by the individual effects of either the AgNPs or the electrical input, indicating the presence of a synergistic effect. Moreover, it was also observed that bacterial colonization affected the electrical properties of PEDOT-MeOH:PSS, indicating a possible use of our system as real-time bacterial sensor. This opens the door to use the material as dual sensor-effector system, detecting bacterial colonization and acting when necessary. In conclusion, the work performed in this thesis shows the potential of conducting polymers as biotransducers to both monitor and influence biofilm growth. This can be applied to the systhesis of smart coatings to effectively prevent the bacterial colonization of indwelling devices as well as to many other applications.