Wireless Intraocular Pressure Sensing Using Microfabricated Minimally Invasive Flexible-Coiled LC Sensor Implant

Abstract

Abstract-This paper presents an implant-based wireless pressure sensing paradigm for long-range continuous intraocular pressure (IOP) monitoring of glaucoma patients. An implantable parylene-based pressure sensor has been developed, featuring an electrical LC-tank resonant circuit for passive wireless sensing without power consumption on the implanted site. The sensor is microfabricated with the use of parylene C (poly-chlorop-xylylene) to create a flexible coil substrate that can be folded for smaller physical form factor so as to achieve minimally invasive implantation, while stretched back without damage for enhanced inductive sensor-reader coil coupling so as to achieve strong sensing signal. A data-processed external readout method has also been developed to support pressure measurements. By incorporating the LC sensor and the readout method, wireless pressure sensing with 1-mmHg resolution in longer than 2-cm distance is successfully demonstrated. Other than extensive on-bench characterization, device testing through six-month chronic in vivo and acute ex vivo animal studies has verified the feasibility and efficacy of the sensor implant in the surgical aspect, including robust fixation and long-term biocompatibility in the intraocular environment. With meeting specifications of practical wireless pressure sensing and further reader development, this sensing methodology is promising for continuous, convenient, direct, and faithful IOP monitoring.[ 2009-0111]Index Terms-Implantable microdevice, intraocular pressure (IOP), LC pressure sensor, parylene, wireless sensing.

Continuous wireless pressure monitoring and mapping with ultra-small passive sensors for health monitoring and critical care

“…We first describe a size scaling path to achieve the smallest passive sensors reported for wireless pressure monitoring, with dimensions of 1 Â 1 Â 0.1 mm 3 . At a volume of 0.1 mm 3 , this is more than an order of magnitude smaller than previously reported research devices [22][23][24][25][26] and more than two orders smaller than commercial solutions [15][16][17][18] . We apply this system to capturing human radial pulse waveforms in real-time with externally placed wireless sensors.…”

“…These devices are more than an order of magnitude smaller in volume than recent research devices for intraocular pressure sensing [22][23][24][25][26] and more than two orders smaller than commercial solutions [15][16][17][18] . We are able to achieve this level of scaling by leveraging the presented GDD detection scheme, which overcomes the operating frequency limits of traditional strategies and exhibits insensitivity to lossy tissue environments.…”

“…In contrast, traditional methods in passive sensing can only be operated at low frequencies, below the self-resonance of the readout coil. These techniques rely on detecting the maxima in the real part or the magnitude 3-10,22-23,34 of the input impedance or the phase minimum [24][25][26]35,36 . Most operate in the MHz range as a result.…”

“…Recently, microfabrication techniques and microelectromechanical system technology have been applied to reduce device footprints in passive wireless sensing of intraocular pressures [18][19][20][21][22] . However, with all the sensors operating below a few hundred MHz, none has been able to miniaturize below a few mm 3 in volume [3][4][5][6][7][8][9][10][22][23][24][25][26] . Traditional passive strategies have been inherently limited by the self-resonant frequency of readout circuitry because interference effects make it difficult to detect sensors operating near and above this frequency [27][28][29] .…”

Modelling Nonlinear Responses of Resonance Sensors in Pressure Garment Application

“…In addition, the simple structure of the sensor may enable the use of the new fabrication methods like printing the structures directly on supporting material. Other tested applications of the passive resonance sensors in the field of medicine are intra-ocular pressure sensing [5] and ECGmeasurements [6].…”