Optimizing the Limit of Detection of Waveguide-Based Interferometric Biosensor Devices.

Waveguide-based photonic sensors provide a unique combination of high sensitivity, compact size and label-free, multiplexed operation. Interferometric configurations furthermore enable a simple, fixed-wavelength read-out making them particularly suitable for low-cost diagnostic and monitoring devices. Their limit of detection, i.e., the lowest analyte concentration that can be reliably observed, mainly depends on the sensors response to small refractive index changes, and the noise in the read-out system. While enhancements in the sensors response have been extensively studied, noise optimization has received much less attention. Here we show that order-of-magnitude enhancements in the limit of detection can be achieved through systematic noise reduction, and demonstrate a limit of detection of ∼ 10 - 8 RIU with a silicon nitride sensor operating at telecom wavelengths.

Computational analyses of different intervertebral cages for lumbar spinal fusion.

Lumbar spinal fusion is the most common approach for treating spinal disorders such as degeneration or instability. Although this procedure has been performed for many years, there are still important challenges that must be overcome and questions that need to be addressed regarding the high rates of non-union. The present finite element model study aimed to investigate the influence of different cage designs on the fusion process. An axisymmetric finite element model of a spinal segment with an interbody fusion cage was used. The fusion process was based on an existing mechano-regulation algorithm for tissue formation. With this model, the following principal concepts of cage design were investigated: (1) different cage geometries with constant compressive stiffness and (2) cage designs optimized to provide the ideal mechanical stimulus for bone formation, first at the beginning of fusion and then throughout the entire fusion process. The cage geometry substantially influenced the fusion outcome. A cage that created an optimized initial mechanical stimulus did not necessarily lead to accelerated fusion, but rather resulted in delayed fusion or non-union. In contrast, a cage made of a degradable material produced a significantly higher amount of bone and resulted in higher segmental stiffness. However, different compressive loads (250, 500 and 1000 N) substantially affected the amount of newly formed bone tissue. The results of the present study suggest that aiming for an optimal initial mechanical stimulus may be misleading because the initial mechanical environment is not preserved throughout the bone modeling process.

Investigation of different cage designs and mechano-regulation algorithms in the lumbar interbody fusion process - a finite element analysis.

Lumbar interbody fusion cages are commonly used to treat painful spinal degeneration and instability by achieving bony fusion. Many different cage designs exist, however the effect of cage morphology and material properties on the fusion process remains largely unknown. This finite element model study aims to investigate the influence of different cage designs on bone fusion using two mechano-regulation algorithms of tissue formation. It could be observed that different cages play a distinct key role in the mechanical conditions within the fusion region and therefore regulate the time course of the fusion process.