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