Unpowered spiral-tube parylene pressure sensor for intraocular pressure sensing

This paper presents the first biocompatible, unpowered, micromachined pressure sensor for intraocular pressure (IOP) sensing. This device is designed for implantation in the eye so that IOP can be faithfully measured externally. It features a parylene-based high-aspect-ratio spiral-tube structure fabricated using a buried-channel process. This passive sensor requires no power from other physical (i.e. electrical and/or magnetic) domains and registers pressure variations by changes of a mechanical in-plane spiral rotation that can be gauged by direct and convenient optical observation. The fabricated device has been tested in various media, and a 1 mm-radius device with a 10-turn spiral has successfully demonstrated continuous spiral rotation when immersed in liquids, with 0.22°/mmHg sensitivity in isopropyl alcohol (IPA) and 0.13°/mmHg sensitivity in water. This pressure sensing technology is proposed as a convenient method to monitor in situ IOP in glaucoma patients and to facilitate treatment and scientific study of the disease.