Miniaturized fiber optic sensor for measuring intervertebral disc pressure

This paper reports the development of a miniature fiber optic pressure sensor system for in vitro intradiscal pressure measurements for rodents. The primary focus of this work is the design and fabrication of a sensor element with a multi-layer polymer-metal diaphragm. This diaphragm consists of a base polyimide layer (150 nm thick), a metal reflective layer (1 μm thick), and another polyimide layer for protection and isolation (150 nm thick). The sensor element is biocompatible and can be fabricated by simple, batch-fabrication methods in a non- cleanroom environment with good device-to-device uniformity. The fabricated sensor element has an outer diameter of only 366 μn, which is small enough to be inserted into the rodent discs without disrupting the structure or altering the intradiscal pressures. In the calibration and in vitro rodent intradiscal pressure measurements, the sensor element exhibits a linear response to the applied pressure over the range of 0 - 70 kPa, with a sensitivity of 0.0206 μm/kPa and a resolution of 0.17 kPa.