Miniature fiber optic pressure sensor with composite polymer-metal diaphragm for intradiscal pressure measurements.

We developed a miniature fiber optic pressure sensor system and utilized it for in vitro intradiscal pressure measurements for rodents. One of the unique features of this work is the design and fabrication of a sensor element with a multilayer polymer-metal diaphragm. This diaphragm consists of a base polyimide layer (150 nm thick), a metal reflective layer (1 microm 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 microm, 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 microm/kPa and a resolution of 0.17 kPa. To our best knowledge, this work is the first successful demonstration of rodent intradiscal pressure measurements.