Inhibition of Bacterial Adhesion, Biofilm Formation, and Endotoxin Accumulation in a Prototype Dialysis Regeneration System

Abstract

Renal physicians and clinical investigators envision portable dialysis systems as a paradigm shift, markedly enhancing patient quality of life and clinical prognoses through continuous, low-shear filtration, enhanced autonomy, and minimized water consumption. However, developing such a patient-friendly machine presents significant engineering challenges, including: urea removal (the primary byproduct of protein metabolism), reliable, sterile vascular access, patient movement, and prevention of microbiological contamination. At the University of Washington, we have developed a platform comprising multiple titanium dioxide (TiO₂) photooxidation cells to remove urea from spent dialysate. This dissertation explores an additional function of these TiO₂ photooxidation cells: inhibiting bacterial suspended growth and biofilm formation while addressing associated bacterial byproducts, thereby targeting the major microbiological challenges in portable dialysis systems. This dissertation evaluates the performance of the TiO₂ photocatalytic process in reducing bacterial viability and biofilm attachment to material surfaces. Four dialysis-related bacteremia pathogens—Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa, and Escherichia coli—were inoculated into a dialysate-mimicking solution containing 10 mM urea and 0.9% saline. Bacterial viability assays, including colony-forming unit (CFU) enumeration and Live/Dead staining, demonstrated a 99.9% reduction in viable bacterial counts within 60 minutes of UV illumination of the TiO₂ cells, with extensive cell membrane disruption observed within 4 hours. Viable bacterial attachment to the internal surfaces of polyvinyl chloride tubing was reduced to undetectable levels. In addition, the photooxidation process achieved 45–65% urea decomposition while simultaneously eliminating 99.9% of pathogenic bacteria within the recirculating loop. Although endotoxin concentrations increased during photocatalytic treatment, likely due to the release of lipopolysaccharides following bacterial lysis, incorporating activated carbon may help adsorb and remove endotoxins from the recirculating solution. These findings demonstrate that the TiO₂-based photooxidation system effectively inactivates planktonic pathogenic bacteria while removing urea from a dialysate-mimicking solution, highlighting its dual functionality and potential application in portable dialysis systems.