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.

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Bones experience mechanical loads on a daily basis. It is difficult to obtain biomechanical performances in-vivo measurements. When implants are integrated with bones after surgery, especially in aged individuals, their osseointegration can compromise the structural integrity of bones; for this reason, it is important to monitor the evolution of the mechanical properties of bones with some in-vivo diagnostic technique. In this study, we propose to integrate optical microsensing devices into bones. To simulate the working principle, a sensor is integrated with a 3-D printed bone. The sensing element is a dye-doped optical microlaser based on the morphology dependent resonance (MDR) shifts also called the whispering gallery mode phenomenon (WGM). When the microlaser is excited by a light source, the fluorescence from the dye couples with the optical resonances. These optical resonances are very sensitive to any perturbation of the microlasers’s morphology. Therefore, the local strain variation of the bone can be related to the shift of the optical resonances. This in-vivo technique monitors the biomechanical performance of bones with implants and prosthetics.

Background The term “plasmonic” describes the relationship between electromagnetic fields and metallic nanostructures. Plasmon-based sensors have been used innovatively to accomplish different biomedical tasks, including detection of cancer. Plasmonic sensors also have been used in biochip applications and biosensors and have the potential to be implemented as implantable point-of-care devices. Many devices and methods discussed in the literature are based on surface plasmon resonance (SPR) and localized SPR (LSPR). However, the mathematical background can be overwhelming for researchers at times. Objective This review article discusses the theory of SPR, simplifying the underlying physics and bypassing many equations of SPR and LSPR. Moreover, we introduce and discuss the hybrid whispering gallery mode (WGM) sensing theory and its applications. Methods A literature search in ScienceDirect was performed using keywords such as “surface plasmon resonance,” “localized plasmon resonance,” and “whispering gallery mode/plasmonic.” The search results retrieved many articles, among which we selected only those that presented a simple explanation of the SPR phenomena with prominent biomedical examples. Results SPR, LSPR, tilted fiber Bragg grating, and hybrid WGM phenomena were explained and examples on biosensing applications were provided. Conclusions This minireview presents an overview of biosensor applications in the field of biomedicine and is intended for researchers interested in starting to work in this field. The review presents the fundamental notions of plasmonic sensors and hybrid WGM sensors, thereby allowing one to get familiar with the terminology and underlying complex formulations of linear and nonlinear optics.

In this paper, we propose the use of a microfluidic channel with flow focusing technique to fabricate solid state polymeric microlasers to precisely control sizes for mass production. Microlasers are made from a solution of UV curable polymer, namely polyethylene glycol diacrylate (PEGDA) with a molecular weight of 700 and rhodamine 6G laser dye at two different volumetric ratios (polymer to dye) of 4:1 and 2:1, respectively, which are used as the dispersed phase. A reservoir filled with liquid polydimethylsiloxane (PDMS) was used to cure the microlasers via UV lamp. A microchannel made of (PDMS) and size of 200 µm was used in this paper; mineral oil was selected as the continuous phase. Two experiments are conducted by fixing the pressure flow for the dispersed phase to 188 mbar and 479.9 mbar, respectively. In both experiments, the pressure of the continuous phase (mineral oil) was varied between 1666.9 mbar and 1996.9 mbar. The measurement of the fabricated microlasers’ size was performed with the aid of the MATLAB Image Processing Toolbox by using photographs taken with a CMOS camera. The tunability of the highest size, ranging from 109 µm to 72 µm, was found for the PEGDA to dye ratio of 2:1 (188 mbar) and average standard deviation of 1.49 µm, while no tunability was found for the 4:1 ratio (188 mbar). The tunability of the microlaser’s size, ranging from 139 µm to 130 µm and an average standard deviation value of 1.47 µm, was found for the 4:1 ratio (479.9 mbar). The fabricated microlasers presented a quality factor Q of the order 104, which is suitable for sensing applications. This technique can be used to control the size of the fabrication of a high number of solid state microlaser based UV polymers mixed with laser dyes.