Implantable Wireless Intraocular Pressure Sensors

Abstract

The work in this thesis aims to develop a suite of biomedical microdevice implants, with an intense focus on pressure sensors, for glaucoma study and management featuring the enabling micro-electro-mechanical-system (MEMS) technologies and the use of parylene (poly-para-xylene) as a biocompatible MEMS material. The problems of the debilitating eye disease glaucoma threaten tens of millions of people worldwide with loss of vision, and are not completely resolved using the current non-optimal clinical procedures. Given the relation of neuropathy and the physiological parameter of intraocular pressure (IOP) in glaucoma from clinical findings, such parylene-based MEMS implants are investigated to realize physical IOP monitoring and regulation, and further to accomplish continuous, direct, accurate, reliable, and more effective glaucoma detection and treatment. Miniaturized parylene-based passive pressure sensors are presented in this thesis for IOP monitoring. Complete design, fabrication, characterization, and analysis of such MEMS implants are described to demonstrate their feasibility, covering both engineering and surgical/biological aspects of the proposed applications. Their passive behaviors, based on the comprised micromechanical structures, facilitate unpowered device operations. In addition, such devices are microfabricated in suitable form factors so that minimally invasive suture-less implantation procedures are possible, minimizing time and complexity of the surgeries. Two types of micromachined wireless pressure sensors are developed utilizing optical and electrical sensing methodologies, respectively, to explore the possibility of the proposed implant approach. On-bench experimental results verify that wireless pressure sensing with 1 mmHg accuracy in the 0–100 mmHg range can be achieved using both types of devices. Surgical studies, including ex vivo and in vivo animal tests, confirm the bioefficacy and biostability of the device implants in the intraocular environment. With the attempt of providing implementation concepts of the MEMS implant approaches for ultimate glaucoma study and management in practice, system-level designs and configurations involving such microdevice implants are briefly described as well. Micromachined passive-valved flow-control devices with designed surgical and engineering features are also developed (experimentally achieving 0–100 mmHg and 0–10 uL/min pressure and flow rate regulation ranges) to investigate the feasibility and possibility of such implant approach for unpowered physical IOP regulation in glaucoma treatment.