Date of Award
Doctor of Philosophy (PhD)
Dr. Jeffrey N. Anker, Committee Chair
Dr. John D. DesJardins
Dr. George Chumanov
Dr. Joseph Kolis
Assessing the performance of medical devices is critical for understanding device function and monitoring pathologies. With the use of a smart device clinically relevant chemical and mechanical information regarding fracture healing may be deduced. For example, strain on the device may be used as a mechanical indicator of weight-bearing capacity. In addition, changes in chemical environment may indicate the development of implant associated infections. Although optical methods are widely used for ex vivostrain/motion analysis and for chemical analyses in cells and histological tissue sections, there utility is limited through thick tissue because light scattering reduces spatial resolution. This dissertation presents four novel luminescent sensors that overcome this limitation. The sensors are capable of detecting chemical and physical changes by measuring position or orientation-dependent color/wavelength changes through tissue. The first three sensors are spectral rulers comprised of two patterned thin films: an encoder strip and an analyzer mask. The encoder strip is either a thin film patterned with stripes of alternating luminescent materials (quantum dots, particles or dyes) or a film containing alternating stripes of a dye that absorbs luminescence from a particle film placed below. The analyzer mask is patterned with a series of alternating transparent windows and opaque stripes equal in width to the encoder lines. The analyzer is overlaid upon the encoder strip such that displacement of the encoder relative to the analyzer modulates the color/spectrum visible through the windows. Relative displacement of the sensor layers is mechanically confined to a single axis. When the substrates are overlaid in the “home position” one line spectrum is observed, and in the “end position,” another line spectrum is observed. At intermediate positions, spectra are a linear combination of the “home” and “end” spectra. The position-modulated signal is collected by a spectrometer and a spectral intensity ratio from closely spaced emission peaks is calculated. By collecting luminescent spectra, rather than imaging the device surface, the sensors eliminate the need to spatially resolve small features through tissue by measuring displacement as a function of color. We measured micron scale displacements through at least 6 mm of tissue using three types of spectral ruler based upon 1) fluorescence, 2) x-ray excited optical luminescence (XEOL), and 3) near infrared upconversion luminescence. The sensors may be used to investigate strain on orthopedic implants, study interfragmentary motion, or assess tendon/ligament tears. In addition to monitoring mechanical strain it is important to investigate clinically relevant implant pathologies such as infection. To address this application, we have developed a fourth type of sensor. The sensor monitors changes in local pH, an indicator of biofilm formation, and uses magnetic fields to modulate position and orientation-dependent luminescence. This modulation allows the sensor signal to be separated from background tissue autofluorescence for spectrochemical sensing. This final sensor variation contains a cylindrical magnet with a fluorescent pH indicating surface on one side and a mask on the other. When the pH indicating surface is oriented towards the collection optics, the spectrum generated contains both the sensor and autofluorescence signals. Conversely, when the pH sensor is oriented away, the collected signal is composed solely of background signals. All four of the sensors described can be used to build smart devices for monitoring pathologies through tissue. Future work will include the application of the strain and chemical sensors in vivo and ex vivo in animal and cadaveric models.
Rogalski, Melissa M., "Development of Position-Dependent Luminescent Sensors: Spectral Rulers and Chemical Sensing Through Tissue" (2016). All Dissertations. 1706.