Floating-disk parylene microvalve for self-regulating biomedical flow controls

A novel self-regulating parylene micro valve is presented in this paper with potential applications for biomedical flow controls. Featuring a free-floating bendable valve disk and two-level valve seat, this surface-micromachined polymeric valve accomplishes miniature pressure/flow rate regulation in a band-pass profile stand-alone without the need of power sources or active actuation. Experimental data of underwater testing results have successfully demonstrated that the microfabricated in-channel valve can regulate water flow at 0-80 mmHg and 0-10 µL/min pressure/flow rate level, which is perfectly suitable for biomedical and lab-on-a-chip applications. For example, such biocompatible microvalve can be incorporated in ocular implants for control of eye fluid drainage to fulfill intraocular pressure (IOP) regulation in glaucoma patients

Implantable parylene-based wireless intraocular pressure sensor

This paper presents a novel implantable, wireless, passive pressure sensor for ophthalmic applications. Two sensor designs incorporating surface-micromachined variable capacitor and variable capacitor/inductor are implemented to realize the pressure sensitive components. The sensor is monolithically microfabricated using parylene as a biocompatible structural material in a suitable form factor for increased ease of intraocular implantation. Pressure responses of the microsensor are characterized on-chip to demonstrate its high pressure sensitivity (> 7000 ppm/mmHg) with mmHg level resolution. An in vivo animal study verifies the biostability of the sensor implant in the intraocular environment after more than 150 days. This sensor will ultimately be implanted at the pars plana or iris of the eye to fulfill continuous intraocular pressure (IOP) monitoring in glaucoma patients

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

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

Microfabricated Implantable Parylene-Based Wireless Passive Intraocular Pressure Sensors

This paper presents an implantable parylene-based wireless pressure sensor for biomedical pressure sensing applications specifically designed for continuous intraocular pressure (IOP) monitoring in glaucoma patients. It has an electrical LC tank resonant circuit formed by an integrated capacitor and an inductor coil to facilitate passive wireless sensing using an external interrogating coil connected to a readout unit. Two surface-micromachined sensor designs incorporating variable capacitor and variable capacitor/inductor resonant circuits have been implemented to realize the pressure-sensitive components. The sensor is monolithically microfabricated by exploiting parylene as a biocompatible structural material in a suitable form factor for minimally invasive intraocular implantation. Pressure responses of the microsensor have been characterized to demonstrate its high pressure sensitivity (> 7000 ppm/mmHg) in both sensor designs, which confirms the feasibility of pressure sensing with smaller than 1 mmHg of resolution for practical biomedical applications. A six-month animal study verifies the in vivo bioefficacy and biostability of the implant in the intraocular environment with no surgical or postoperative complications. Preliminary ex vivo experimental results verify the IOP sensing feasibility of such device. This sensor will ultimately be implanted at the pars plana or on the iris of the eye to fulfill continuous, convenient, direct, and faithful IOP monitoring

Implantable Unpowered Parylene MEMS Intraocular Pressure Sensor

This paper presents the first implantable, unpowered, parylene-based micro-electro-mechanical-systems (MEMS) pressure sensor for intraocular pressure (IOP) sensing. From in situ mechanical deformation of the compliant structures, this sensor registers pressure variations without power consumption/transduction. Micromachined high-aspect-ratio thin-walled tubes in different geometric layouts are exploited to obtain a high-sensitivity pressure response. An integrated packaging method has been successfully developed to realize suture-less implantation of the device. In vitro testing results have demonstrated that the IOP sensor can achieve 0.67 degree/mmHg angular sensitivity with a spiral-tube design, 3.43 µm/mmHg lateral sensitivity with a long-armed-tube design, and 0.38 µm/mmHg longitudinal sensitivity with a serpentine-tube design. This IOP sensor is designed to be implanted in the anterior chamber of the eye and anchored directly on the iris so that, under incident visible light, the pressure response of the implant can be directly observed from outside the eye, which enables faithful and unpowered IOP monitoring in glaucoma patient

Wafer-Level Parylene Packaging With Integrated RF Electronics for Wireless Retinal Prostheses

This paper presents an embedded chip integration technology that incorporates silicon housings and flexible Parylene-based microelectromechanical systems (MEMS) devices. Accelerated-lifetime soak testing is performed in saline at elevated temperatures to study the packaging performance of Parylene C thin films. Experimental results show that the silicon chip under test is well protected by Parylene, and the lifetime of Parylenecoated metal at body temperature (37°C) is more than 60 years, indicating that Parylene C is an excellent structural and packaging material for biomedical applications. To demonstrate the proposed packaging technology, a flexible MEMS radio-frequency (RF) coil has been integrated with an RF identification (RFID) circuit die. The coil has an inductance of 16 μH with two layers of metal completely encapsulated in Parylene C, which is microfabricated using a Parylene–metal–Parylene thin-film technology. The chip is a commercially available read-only RFID chip with a typical operating frequency of 125 kHz. The functionality of the embedded chip has been tested using an RFID reader module in both air and saline, demonstrating successful power and data transmission through the MEMS coil

Implantable micromechanical parylene-based pressure sensors for unpowered intraocular pressure sensing

This paper presents the first implantable, unpowered, parylene-based microelectromechanical system (MEMS) pressure sensor for intraocular pressure (IOP) sensing. From in situ mechanical deformation of the compliant spiral-tube structures, this sensor registers pressure variations without electrical or powered signal transduction of any kind. Micromachined high-aspect-ratio polymeric hollow tubes with different geometric layouts are implemented to obtain high-sensitivity pressure responses. An integrated device packaging method has been developed toward enabling minimally invasive suture-less needle-based implantation of the device. Both in vitro and ex vivo device characterizations have successfully demonstrated mmHg resolution of the pressure responses. In vivo animal experiments have also been conducted to verify the biocompatibility and functionality of the implant fixation method inside the eye. Using the proposed implantation scheme, the pressure response of the implant can be directly observed from outside the eye under visible light, with the goal of realizing convenient, direct and faithful IOP monitoring in glaucoma patients

Systems design of a high resolution retinal prosthesis

Simulations of artificial vision suggest that 1000 electrodes may be required to restore vision to individuals with diseases of the outer retina. In order to achieve such an implant, new technology is needed, since the state-of-the-art implantable neural stimulator has at most 22 contacts with neural tissue. Considerable progress has been made towards that goal with the development of image processing, microelectronics, and polymer based MEMS. An image processing system has been realized that is capable of real-time implementation of image decimation and filtering (for example, edge detection). Application specific integrated circuits (ASICs) have been designed and tested to demonstrate closed loop power control and efficient microstimulation. A novel packaging process has been developed that is capable of simultaneously forming communication coils, interconnects, and stimulating electrodes