Self-Propelling Microbubblers for Active Cleaning of Biofilm in Confined Spaces

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PART 1: NON-TECHNICAL SUMMARYDense microbial films called “biofilm” often foul medical tools, household items, and infrastructures such as an endoscopes, bathroom tiles, and water supply pipes, and can lead to dangerous infections. These biofilms are slimy aggregates of bacterial cells surrounded by scaffolds adhering to anything they touch. About 80 percent of all medical infections originate from biofilms that invade the inner workings of clinical devices and implants inside patients. Cleaning of biofilms in such a hard-to-reach area is extremely difficult because traditional disinfectants and antibiotics cannot penetrate a biofilm's tough scaffolds. How can we let antibacterial reagents cross over such a barrier of biofilms? This proposed study attempts to develop a small particle that can penetrate and destroy tough scaffolds by generating oxygen bubbles. The particle named “self-propelling microbubbler” would be prepared by loading an oxygen-generating chemical on diatoms – the tiny skeletons of algae. As a consequence, this system would improve the delivery of antibacterial deathblow to the bacterial cells living inside. While tuning the oxygen bubble generation rate and subsequent propulsion speed of the micrububblers, this proposed study will examine extents that the microbubblers can penetrate biofilm clinging to a material with complex topology, damages the scaffold of biofilms, kill bacterial cells protected by the scaffolds, and, ultimately, prevent the return of biofilm formation. In parallel, for broad impacts, the unique microbubblers will be used as education and training tools for a new generation of bioscientists and bioengineers. Overall, this project will serve to improve people’s health, safety, and life quality against infectious diseases and fouling.PART 2: TECHNICAL SUMMARY Biofilms composed of microbial cell colonies and surrounding extracellular polymer substances (EPS) are major causes of medical infection and material deterioration, thus threatening both human health and sustainability. A variety of disinfectants were developed to date, but none of these systems are active in removing biofilms forming in confined spaces. To this end, this proposed study aims to assemble and analyze a “self-propelling microbubbler” that can invade biofilms grown in the hard-to-reach area and, subsequently, clean out both bacterial colonies and EPS. This study hypothesizes that diatom particles doped with zinc oxide (ZnO) or manganese dioxide (MnO2) catalysts decomposing hydrogen peroxide (H2O2) eject oxygen bubbles and, in turn, act as the self-propelling microbubbler in the antiseptic 3% H2O2 solution. After the invasion, the microbubblers would continue to generate oxygen bubbles that fuse to produce a wave of mechanical energy capable of destroying the biofilms. The self-propulsion of microbubblers will be studied by analyzing the activation energy for H2O2 decomposition, the H2O2 decomposition rate, and the kinetic energy. In parallel, the extent that the microbubblers remove biofilm in the micro-grooved substrate will be examined by monitoring invasion of particles into the biofilm and subsequent changes in stiffness, adhesion force, and chemical composition of the biofilms formed by Escherichia coli and Pseudomonas aeruginosa. Finally, the efficacy of microbubblers to killing biofilm bacteria will be evaluated by monitoring the increase of intracellular oxidative stress, the reduction of viable cells, and the recurrence of biofilm. The successful completion of this study will elucidate the unique cleaning mechanism attained by chemical-to-mechanical energy conversion and transform current disinfection strategies that rely on chemicals mostly. In parallel, this project will make broad impacts by incorporating the proposed research modules into several educational programs developed for students at various educational levels and also disseminating the research outcomes to a broad spectrum of communities.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.