Bacterial Biofilms on Electrochemically Active Cathodic Titanium Surfaces

Jin Guo

Date of Award

8-2013

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biomedical and Chemical Engineering

Advisor(s)

Jeremy L. Gilbert

Keywords

Bacterial infections, Biofilms, Electrochemistry, Reduction Reactions, Titanium

Subject Categories

Biomedical Engineering and Bioengineering

Abstract

Bacterial infection is a major concern in orthopedic implants that may lead to implant failure and revisions. The resistance of bacterial biofilms to antibiotics increases the difficulties of fighting against infections. In this work, the effects of electrochemical reduction reactions on bacterial biofilm cultured on electrochemically active metal surfaces were investigated to better understand the mechanism of bacterial response to reduction electrochemistry. The influence of voltage and electrolyte were studied on the cellular behavior of bacterial cells cultured on commercially pure titanium (cpTi) surfaces held at cathodic voltages. Relatively weak potentials at -1 V (vs. Ag/AgCl) could significantly reduce the cell viability in saline solution after 24 hours compared to controls at open circuit potential (OCP, in the range of -0.2 V to -0.38 V vs. Ag/AgCl) (p < 0.05). However, bacterial biofilms cultured on cpTi surfaces in LB media require more negative voltage (below -1.2 V) to induce significant killing efficacy.

On the other hand, the cellular response was correlated with the electrochemical properties of titanium-oxide-solution interface through methods like electrochemical impedance spectroscopy (EIS) and current density monitoring. The electrochemical impedance of the oxide-bacteria-solution interface was dependent on the presence of applied voltage. Sustained voltage treatment at -1 V decreased the impedance of titanium-oxide-bacteria interface in both LB media and NaCl solution at 0.1 Hz than those at OCP (p<0.05). In LB media, the presence of bacterial biofilm significantly reduced the average current density experienced by cpTi surfaces at -1 V compared to controls without cells at -1 V in 24 hours (p < 0.05).

Significant morphological changes were found after voltage treatment in NaCl solution and LB media. In general, ruptured cells after voltage treatment at -1 V in NaCl solution ended in less length, width and height than control cells at OCP (p<0.05). The applied potential at -1 V decreased the length and height of all the cells in LB media after time-lapse photography compared to those of untreated controls (p<0.05).

Finally, time-lapse photography, which could assess cellular movement of bacteria under voltage treatment in real time, was utilized and proved to be an effective method of cellular investigation besides LIVE/DEAD assay, scanning electron microscope (SEM) and atomic force microscopy (AFM). Average bacterial cell velocity significantly increased once -1 V voltage treatment started and then dropped in two hours in NaCl solution (p<0.05), while no such difference was seen during the test in LB media.

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