Methods for Determining Strain and Localized pH on Implanted Medical Device Surfaces Through Tissue
Due to an aging population in the United States the demand for implantable medicaldevices such as fracture fixators is increasing. Failures of these devices due to factors suchas implant loosening and infections come at a high cost both monetarily and in patientsuffering when surgical revisions are needed. In order to combat these problemsimplantable optical sensors have been developed which consist of two blinking LEDs orare multilayer radioluminescent sensors for detecting localized pH or strain which canindicate infection and hardware failures respectively. The active approach using two LEDSdriven by a resistance to frequency circuit which contains a thin foil strain gauge is anexcellent approach for making measurements through thick tissues due to high opticaloutpu but suffers from needing a power source and the need for multiple sensors to achievea full understanding of the device’s surface. Radioluminescent sensors provide a highresolution, low background and low noise image of localized pH and strain fields on theimplant surface using low energy focused x-rays that are scanned with an x-y moveablestage in addition to collection optics and photomultiplier tubes but may not be suitable forthicker tissues and abstractly shaped devices. Both the LED sensor and theradioluminescent sensors need further development and characterization with both cadaverand animal studies in the future.