Date of Award

August 2020

Document Type


Degree Name

Doctor of Philosophy (PhD)



Committee Member

Jeffrey N Anker

Committee Member

Tzuen-Rong Tzeng

Committee Member

Stephen Creager

Committee Member

Carlos D Garcia

Committee Member

Jason D McNeil


Implant-associated infection is a leading cause of fixation failures and these infections are resistant to antibiotics especially after mature biofilms have been established on the implant surface. These infections can also be challenging to detect, especially at early stages or during antibiotic treatment, due to lack of symptoms and specific tests to detect localized infection. Low pH is believed to be associated with infection as bacteria and inflammatory responses can cause a pH drop in the affected area. Detecting changes in pH on the implant surface can provide a better understanding and help to detect, treat and monitor such infections more effectively thereby reducing the need for revision surgeries. We developed a novel X-ray Excited Luminescence Chemical Imaging (XELCI) technique to measure surface specific chemical concentrations with sub-millimeter spatial resolution. A focused X-ray beam (~0.3 mm) passes through tissue and irradiates scintillators coated on an orthopedic implant; these scintillators generate visible and near infrared light which is partially absorbed by a pH indicator film (e.g., bromocresol green or bromothymol blue pH dye encapsulated in a PEG hydrogel) altering the luminescence spectrum in a pH-dependent manner. Images are acquired by scanning the beam point-by-point and measuring the spectrum at each point. We developed, synthesized and tested pH indicator films and measured the signal intensity, noise level, and knife-edge spatial resolution through varying thicknesses of chicken breast tissue and through 11 mm of human cadaveric tissue in a tibial fixation specimen. For example, we observed a knife-edge (80/20) spatial resolution of ~0.5 mm through up to 1 cm of tissue and an average pH noise level of 0.25 ±0.05 pH units. We also implanted the pH sensor in rabbits to image pH during infection. The in vivo studies found that the sensors continued to function well for the 11-day experiments. During infection, the pH did not significantly drop compared to uninfected implants on opposite legs (<0.5 pH unit change). For sensors that were initially acidic and infected, the pH neutralized in time, and this neutralization could be delayed by enclosing the implant in cavity with a 1 mm aperture to slow perfusion and diffusion. These studies show applicability provide useful insight into the pH changes that occur on implant surface during infection and can have important implications for antibiotic treatments. Future directions include improving the collection efficiency, adding an X-ray chopper to measure background signal and luminescence lifetime, scanning scintillator nanoparticles in three dimensions for tomography, detecting additional analytes, and studying pH changes on the device surface during infection followed by antibiotic treatment in animal models and to develop a model for pH changes during osteomyelitis.



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