Teimour Maleki

A Minimally Invasive Implantable Wireless Pressure Sensor for Continuous IOP Monitoring

This paper presents a minimally invasive implantable pressure sensing transponder for continuous wireless monitoring of intraocular pressure (IOP). The transponder is designed to make the implantation surgery simple while still measuring the true IOP through direct hydraulic contact with the intraocular space. Furthermore, when IOP monitoring is complete, the design allows physicians to easily retrieve the transponder. The device consists of three main components: 1) a hypodermic needle (30 gauge) that penetrates the sclera through pars plana and establishes direct access to the vitreous space of the eye; 2) a micromachined capacitive pressure sensor connected to the needle back-end; and 3) a flexible polyimide coil connected to the capacitor forming a parallel LC circuit whose resonant frequency is a function of IOP. Most parts of the sensor sit externally on the sclera and only the needle penetrates inside the vitreous space. In vitro tests show a sensitivity of 15 kHz/mmHg with approximately 1-mmHg resolution. One month in vivo implants in rabbits confirm biocompatibility and functionality of the device.

An Ultrasonically Powered Implantable Micro-Oxygen Generator (IMOG)

In this paper, we present an ultrasonically powered implantable micro-oxygen generator (IMOG) that is capable of in situ tumor oxygenation through water electrolysis. Such active mode of oxygen generation is not affected by increased interstitial pressure or abnormal blood vessels that typically limit the systemic delivery of oxygen to hypoxic regions of solid tumors. Wireless ultrasonic powering (2.15 MHz) was employed to increase the penetration depth and eliminate the directional sensitivity associated with magnetic methods. In addition, ultrasonic powering allowed for further reduction in the total size of the implant by eliminating the need for a large area inductor. IMOG has an overall dimension of 1.2 mm × 1.3 mm × 8 mm, small enough to be implanted using a hypodermic needle or a trocar. In vitro and ex vivo experiments showed that IMOG is capable of generating more than 150 μA which, in turn, can create 0.525 μL/min of oxygen through electrolytic disassociation. In vivo experiments in a well-known hypoxic pancreatic tumor models (1 cm3 in size) also verified adequate in situ tumor oxygenation in less than 10 min.

A Biaxial Stretchable Interconnect With Liquid-Alloy-Covered Joints on Elastomeric Substrate

This paper reports a biaxial stretchable interconnect on an elastomeric substrate. To increase the stretchability of interconnects, a 2-D diamond-shaped geometry of gold on a polydimethylsiloxane substrate was adopted in which the potentially breakable points were covered with room temperature liquid alloy. Finite element model simulations were performed to identify the most vulnerable points subjected to stress concentration and optimize the design process. Simulations also indicated an optimum gold thickness and linewidth that result in a minimum stress when the substrate is stretched. Four different geometries were designed, fabricated, and characterized. These included: 1) 2-D diamond-shaped gold lines connected at circular junctions with an intersection angle of 90deg; 2) 2-D diamond-shaped gold lines connected at circular junctions with intersection angles of 120deg and 60deg; 3) 2-D diamond-shaped gold lines separated at circular junctions with an intersection angle of 90deg; and 4) 2-D diamond-shaped gold lines separated at circular junctions with intersection angles of 120 deg and 60deg. A maximum stretchability (DeltaL/L) of ~ 60% was achieved for the design in which the lines and circles were separated and had intersection angles of 120deg and 60deg. A resistance variation of (DeltaR/R) ~ 30% was measured for this configuration.

A nanofluidic channel with embedded transverse nanoelectrodes

In this paper, we demonstrate fabrication and characterization of a nanofluidic channel with embedded transverse nanoelectrodes using a combination of conventional photolithography and focused ion beam technologies. Glass-capped silicon dioxide nanochannels having 20 nm depth, 50 nm width, and 2 microm length with embedded platinum nanoelectrodes were fabricated. Channel patency was verified through measurements of the resistivity in phosphate buffered saline and electrostatic action on charged fluorescent nanospheres. Platinum nanoelectrode functionality was also tested using transverse resistance measurements in nanochannels filled with air, deionized water, and saline solution.

Magnetic Tracking System for Radiation Therapy

Intensity-modulated radiation therapy (IMRT) requires precise delivery of the prescribed dose of radiation to the target and surrounding tissue. Irradiation of moving body anatomy is possible only if stable, accurate, and reliable information about the moving body structures are provided in real time. This paper presents a magnetic position tracking system for radiation therapy. The proposed system uses only four transmitting coils and an implantable transponder. The four transmitting coils generate a magnetic field which is sensed and measured by a biaxial magnetoresistive sensor in the transponder in the tumor. The transponder transmits the information back to a computer to determine the position of the transponder allowing it to track the tumor in real time. The transmission of the information from the transponder to the computer can be wired or wireless. Measurements using a biaxial sensor agree well with the field strength calculated from the ideal equations. The translation from the measurement data to the 3-D location and orientation requires a numerical technique because the equations are in nonclosed forms. The algorithm of tracking is implemented using MATLAB. Each calculation of the position along the target trajectory takes 30 ms, which makes the proposed system suitable for real-time tracking of the transponder for radiation assessment and delivery. An error of less than 2 mm is achieved in the demonstration.

A batch-fabricated laser-micromachined PDMS actuator with stamped carbon grease electrodes

In this note, we report on the development of a batch-fabricated laser-micromachined elastomeric cantilever actuator composed of a polydimethylsiloxane (PDMS) bilayer (active/inactive) and soft-lithographically patterned conductive carbon grease electrodes. The described unimorph structure has a low actuation voltage and large out-of-plane displacement. For a 4 mm long, 1 mm wide, and 80 µm thick actuator, an out-of-plane displacement of 1.2 mm and a maximum force of 25 µN were measured using 450 V actuation voltage.

A self-assembled 3D microelectrode array

Recording a neural ensemble has been an extremely successful experimental paradigm allowing real-time interpretation of neural codes as well as the detection of dynamic changes within a process. In recent years, microfabricated electrodes have attracted a great deal of attention for recording neural ensembles with superior resolution and spatial density. A 3D microfabricated electrode is particularly attractive since it yields enhanced performance with regard to spike sorting and single unit detection. In this paper, we describe a self-assembly process for fabricating 3D microelectrode arrays in silicon. The electrode array is composed of four silicon shanks (200 µm wide, 4 mm long and 30 µm thick) with polyimide-filled V-groove joints at the back end and four 20 × 20 µm2 recording sites (200 µm separation) at the tip. The shanks automatically fold to a vertical configuration upon proper heat treatment, hence creating a 3D configuration without the need for any manual assembly. Impedance and electrical test-signal measurements were used to verify the electrode functionality after the folding process.

Point-of-care, portable microfluidic blood analyzer system

Recent advances in MEMS technology have provided an opportunity to develop microfluidic devices with enormous potential for portable, point-of-care, low-cost medical diagnostic tools. Hand-held flow cytometers will soon be used in disease diagnosis and monitoring. Despite much interest in miniaturizing commercially available cytometers, they remain costly, bulky, and require expert operation. In this article, we report progress on the development of a battery-powered handheld blood analyzer that will quickly and automatically process a drop of whole human blood by real-time, on-chip magnetic separation of white blood cells (WBCs), fluorescence analysis of labeled WBC subsets, and counting a reproducible fraction of the red blood cells (RBCs) by light scattering. The whole blood (WB) analyzer is composed of a micro-mixer, a special branching/separation system, an optical detection system, and electronic readout circuitry. A droplet of un-processed blood is mixed with the reagents, i.e. magnetic beads and fluorescent stain in the micro-mixer. Valve-less sorting is achieved by magnetic deflection of magnetic microparticle-labeled WBC. LED excitation in combination with an avalanche photodiode (APD) detection system is used for counting fluorescent WBC subsets using several colors of immune-Qdots, while counting a reproducible fraction of red blood cells (RBC) is performed using a laser light scatting measurement with a photodiode. Optimized branching/channel width is achieved using Comsol Multi-Physics™ simulation. To accommodate full portability, all required power supplies (40v, ±10V, and +3V) are provided via step-up voltage converters from one battery. A simple onboard lock-in amplifier is used to increase the sensitivity/resolution of the pulse counting circuitry.

Enhanced 3-D Folding of Silicon Microstructures via Thermal Shrinkage of a Composite Organic/Inorganic Bilayer

Although 3-D out-of-plane structures based on the thermal shrinkage of polyimide-filled V-grooves have already been demonstrated, for large bending angles, this method typically requires several V-grooves and high curing temperatures, which are real-estate consuming and can damage temperature-sensitive components. In this paper, we show that the addition of an inorganic layer (called the boosting layer) beneath the V-grooves can significantly enlarge the bending angle without requiring more V-grooves or higher curing temperatures. For example, a 2- -thick boosting layer can raise the bending angle of a single V-groove joint by a factor of seven. In addition, the boosting layer removes the requirement for a V-groove and permits the use of straight-wall dry-etched grooves, hence allowing a sharper curvature in a smaller area.

A batch fabricated capacitive pressure sensor with an integrated Guyton capsule for interstitial fluid pressure measurement

In this paper, we present the design, fabrication and test of a batch fabricated capacitive pressure sensor with an integrated Guyton capsule for interstitial fluid pressure measurement. The sensor is composed of 12 µm thick single crystalline silicon membrane and a 3 µm gap, hermetically sealed through silicon–glass anodic bonding. A novel batch scale method for creating electrical feed-throughs inside the sealed capacitor chamber is developed. The Guyton capsule consists of an array of 10 µm diameter access holes etched onto a silicon back-plate separated from the silicon sensing membrane by a gap of 5 µm. The presence of the Guyton capsule (i.e. plates with access holes plus the gap separating them from the sensing membrane) allows for the ingress of interstitial fluid inside the 5 µm gap following the implantation, thus, providing an accurate measurement of interstitial fluid pressure. The fabricated sensor is 3 × 2 × 0.42 mm3 in dimensions and has a maximum sensitivity of 10 fF mmHg−1.