INTEGRATED THRESHOLD-ACTIVATED FEEDBACK MICROSYSTEM FOR REAL-TIME CHARACTERIZATION, SENSING AND TREATMENT OF BACTERIAL BIOFILMS

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Date

2016

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Abstract

Biofilms are the primary cause of clinical bacterial infections and are impervious

to typical amounts of antibiotics, necessitating very high doses for treatment.

Therefore, it is highly desirable to develop new alternate methods of treatment that

can complement or replace existing approaches using significantly lower doses of

antibiotics. Current standards for studying biofilms are based on end-point studies

that are invasive and destroy the biofilm during characterization. This dissertation

presents the development of a novel real-time sensing and treatment technology to aid

in the non-invasive characterization, monitoring and treatment of bacterial biofilms.

The technology is demonstrated through the use of a high-throughput bifurcation based

microfluidic reactor that enables simulation of flow conditions similar to

indwelling medical devices. The integrated microsystem developed in this work

incorporates the advantages of previous in vitro platforms while attempting to

overcome some of their limitations.

Biofilm formation is extremely sensitive to various growth parameters that cause

large variability in biofilms between repeated experiments. In this work we

investigate the use of microfluidic bifurcations for the reduction in biofilm growth

variance. The microfluidic flow cell designed here spatially sections a single biofilm

into multiple channels using microfluidic flow bifurcation. Biofilms grown in the

bifurcated device were evaluated and verified for reduced biofilm growth variance

using standard techniques like confocal microscopy. This uniformity in biofilm

growth allows for reliable comparison and evaluation of new treatments with

integrated controls on a single device.

Biofilm partitioning was demonstrated using the bifurcation device by exposing

three of the four channels to various treatments. We studied a novel bacterial biofilm

treatment independent of traditional antibiotics using only small molecule inhibitors

of bacterial quorum sensing (analogs) in combination with low electric fields. Studies

using the bifurcation-based microfluidic flow cell integrated with real-time

transduction methods and macro-scale end-point testing of the combination treatment

showed a significant decrease in biomass compared to the untreated controls and

well-known treatments such as antibiotics.

To understand the possible mechanism of action of electric field-based treatments,

fundamental treatment efficacy studies focusing on the effect of the energy of the

applied electrical signal were performed. It was shown that the total energy and not

the type of the applied electrical signal affects the effectiveness of the treatment. The

linear dependence of the treatment efficacy on the applied electrical energy was also

demonstrated.

The integrated bifurcation-based microfluidic platform is the first microsystem

that enables biofilm growth with reduced variance, as well as continuous real-time

threshold-activated feedback monitoring and treatment using low electric fields. The

sensors detect biofilm growth by monitoring the change in impedance across the

interdigitated electrodes. Using the measured impedance change and user inputs

provided through a convenient and simple graphical interface, a custom-built

MATLAB control module intelligently switches the system into and out of treatment

mode. Using this self-governing microsystem, in situ biofilm treatment based on the

principles of the bioelectric effect was demonstrated by exposing two of the channels

of the integrated bifurcation device to low doses of antibiotics.

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