Implanted medical device-associated infections are a major cause of fixation failure. Detection and treatment of these infections remain as a challenge as clinical symptoms are often delayed or completely absent till the infection reaches a later stage and harder to treat with antibiotics. Once diagnosed early, infections can be treated without removal of implants and undergoing a second surgery. Herein, we describe a X-ray Excited Luminescence Chemical Imaging (XELCI) based pH sensor for noninvasive detection and imaging of changes in local pH with high spatial and pH resolution. The sensor is fabricated as a coating on an implant (orthopedic plates, Intramedullary nails, etc). It has two layers: a layer of Gd2O2S:Eu scintillators that produces 620 nm and 700 nm luminescence upon X-ray irradiation, and a pH-indicating film containing BTB (Bromothymol Blue) which covers the scintillators and alters the luminescence spectrum in a pH dependent manner. The spectrum escaping through the tissue is measured to determine the local pH as a focused X-ray beam irradiates one spot on the implant. The X-ray beam scans across the sensor surface to generate an image and measures pH point by point which enables high spatial resolution, low background measurements of local pH for studying implant associated infections. We are interested in detecting pH changes through bone and infections associated with intramedullary nails. These are a type of orthopedic implants which are commonly forced into the medullary cavity of the bone to fix comminuted femoral and tibial fractures. They are commonly associated with osteomyelitis. As a preliminary study, we have imaged an epoxy-PEG coated stainless-steel rod with two distinct pH regions (pH 4 and pH 8) in a reamed rabbit cadaver tibia. We were successfully able to image the above pH changes through bone in vitro with XELCI imaging. In future studies, we will be applying these sensors in the rabbit model to detect pH changes through bone in vivo.

Noninvasive imaging of pH changes associated with implanted medical devices using X-ray excited luminescence chemical imaging (XELCI)

ACS Spring 2022

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