Graduate Research and Discovery Symposium (GRADS)


Luminescent spectral rulers for non-invasive strain measurement through tissue

Document Type


Publication Date

Spring 2015


Dynamic compression plates and orthopedic screws maintain proper bone alignment and share load with bone as a fracture heals. We are developing luminescent spectral rulers to evaluate strain on the surface of these devices to mechanically monitor fracture healing and aid in detection of hardware fatigue (e.g. load sharing, implant loosening, and non-union). The strain sensors contain two patterned surfaces: (1) an “encoder” patterned with alternating luminescent lines, and (2) a transparent “analyzer mask” patterned with opaque lines that overlay and mask a portion of the encoder below. Moving the encoder with respect to the analyzer generates a color change that is detected by spectrometer and analyzed in MATLAB. We have fabricated a bromocresol purple patterned encoder that overlays an X-ray scintillator film (Gd2O2S:Eu). The dye absorbs a portion of the Gd2O2S:Eu luminescence spectrum in a position-dependent manner. With our x-ray scintillator sensors reproducible small displacements (~13 microns) through 6 mm thick chicken breast tissue have been detected. Additionally, we have fabricated sensors that do not require ionizing radiation; a 633 nm laser is used for excitation. The sensors contain an encoder patterned with alternating spectrally distinct fluorescent materials. Both sensors provide a non-invasive method for strain analysis through tissue.

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