Embedded Spherical Microlasers for In Vivo Diagnostic Biomechanical Performances

Abstract

In this paper, we propose to use spherical microlasers which can be attached to the surface of bones for in vivo strain monitoring applications. The sensing element is made with a mixture of polymers namely PEGDA-700 and Thiocure TMPMP mixed at 4:1 ratio in volume doped with rhodamine 6G laser dye. Solid state microlasers are fabricated by curing droplets from the liquid mixture with UV light. The sensing principle relies on the morphology dependent resonances (MDRs); any changes in the strain of the bone causes a shift of the optical resonances, which can be monitored. The bone is made of a simulated cortical bone fabricated with photopolymer resin via additive manufacturing process. The path light within the resonator is found perpendicular to the bone axis and slightly tilted. Therefore, the sensor measures, thorough Poisson effect, the strain due to bending. Two experiments are conducted: i) negative bone deflection (loading) and positive bone deflection (unloading) for a strain range from 0 to 2.35 x 10-3 m/m. Sensitivity values are ~19.489 nm/? and 19.660 nm/? for loading and unloading experiments respectively (less than 1% percentage error). In addition, the resolution of the sensor is 1x10-3 e (m/m) and the maximum range is 11.58x10-3 e (m/m). The quality factor of the microlaser is maintaining about constant (order of magnitude 104) during the experiments. This sensor can be used when bone location accessibility is problematic.

Plasmonic and Hybrid Whispering Gallery Mode–Based Biosensors: Literature Review

“…Lastly, 20 papers were used to introduce the WGM and the hybrid WGM sensing [34,35,[40][41][42][50][51][52][53][54][55][56][57][58][59][60][61][62][63]. This type of sensing methodology was not directly related to the medical literature, but biomedical applications were proposed and the future implementation of this method is likely to become the gold standard in some areas.…”

“…WGM resonators have been used for different applications, especially for high-sensitivity and resolution sensors [40,[50][51][52][53][54][55]. The WGM microstructure can be made in various types of shapes such as spheres, cylinders, and toroid [40,[50][51][52][53][54][55]. The WGMs of the resonator can be observed by coupling light to the resonator.…”

“…The WGM resonances can be observed using different techniques. For example, a study used a charge-coupled device camera and a spectrometer to observe the resonances, and therefore when doping WGM resonators with a laser dye material, the hybrid functions as tiny lasers that emit light under proper excitation conditions [40,[50][51][52][53][54][55]67]. The light emitted from the resonator could then be coupled into the spectrometer using an optical lens setup [40].…”

Whispering-gallery-mode sensors for biological and physical sensing

“…WGM microcavities in the form of liquid droplets and soft solid beads have great potential to measure the force and strain within cells and tissues. When a droplet is deformed, the WGM spectrum presents a broadening or splitting, allowing for a precise measurement of the deformation 20,204 . The force and strain may be evaluated by analysing the deformation and mechanical properties of the microcavity.…”

“…The force and strain may be evaluated by analysing the deformation and mechanical properties of the microcavity. Soft droplets are used to measure tiny forces within cells 20 while solid spheres are used for large forces and stiffer tissues 204 . In most traditional force measurement techniques, the cells are placed in contact with an artificial material while WGMbased force transducers can be placed inside tissues without much perturbation.…”