Ning Xue

A SU-8-Based Microfabricated Implantable Inductively Coupled Passive RF Wireless Intraocular Pressure Sensor

With the growing demand in noncontact detection of human diseases, this paper presents an implantable passive wireless pressure sensor using an inductively coupled wireless sensing technique, particularly designed to monitor the intraocular pressure (IOP) of glaucoma patients. The microfabricated IOP sensor consists of a planar spiral gold coil inductor, a two-parallel-gold-plate (metal-insulator-metal) capacitor, and a SU-8 pressure-sensitive diaphragm. The IOP sensor is fully encapsulated inside biocompatible SU-8 stacking layers to isolate the IOP sensor from the biological tissue medium environment. By measuring the impedance phase dip frequency shift from the external coil, the IOP signal can be obtained through the implanted IOP sensor. The optimized size of the manually wound external coil was investigated. The readout distance is up to 6 mm from the implanted sensor. Characterization results show that the microfabricated IOP sensor has relatively high sensitivities-7035 ppm/mmHg in air and 3770 ppm/mmHg in saline medium-with pressure resolution lower than 1 mmHg, which is adequate for IOP monitoring application.

Ultra-thin flexible polyimide neural probe embedded in a dissolvable maltose-coated microneedle

The ultra-thin flexible polyimide neural probe can reduce the glial sheath growth on the probe body while its flexibility can minimize the micromotion between the probe and brain tissue. To provide sufficient stiffness for penetration purposes, we developed a drawing lithography technology for uniform maltose coating to make the maltose-coated polyimide neural probe become a stiff microneedle. The coating thicknesses under different temperature and the corresponding stiffness are studied. It has been proven that the coated maltose is dissolved by body fluids after implantation for a few seconds. Moreover, carbon nanotubes are coated on the neural probe recording electrodes to improve the charge delivery ability and reduce the impedance. Last but not least, the feasibility and recording characteristic of this ultra-thin polyimide neural probe embedded in a maltose-coated microneedle are further demonstrated by in vivo tests.

A SU-8-Based Fully Integrated Biocompatible Inductively Powered Wireless Neurostimulator

A fully integrated minimally invasive compact polymer-based wireless neurostimulator was designed, fabricated, and characterized both in open air and in vivo. The neurostimulator (3.1 × 1.6 × 0.3 mm) consists of a planar spiral coil for wireless power supply through inductive coupling, two Schottky diodes for full-wave rectification, an application-specific integrated circuit neurostimulator circuit chip for stimulus spike signal generation, and two biphasic platinum-iridium (PtIr) stimulation electrodes. The device is fully integrated and completely embedded in biocompatible SU-8 packaging. For in vivo testing, the wireless neurostimulator was implanted subcutaneously in a rat hind limb. At the coupling power of 21 dBm (125 mW) at 394-MHz resonant frequency, stable and robust cortical responses during extended periods of wireless stimulation were recorded.

Flexible Epineural Strip Electrode for Recording in Fine Nerves

This paper demonstrates flexible epineural strip electrodes (FLESE) for recording from small nerves. Small strip-shaped FLESE enables us to easily and closely stick on various sized nerves for less damage in a nerve and optimal recording quality. In addition, in order to enhance the neural interface, the gold electrode contacts were coated with carbon nanotubes, which reduced the impedance of the electrodes. We used the FLESEs to record electrically elicited nerve signals (compound neural action potentials) from the sciatic nerve in rats. Bipolar and differential bipolar configurations for the recording were investigated to optimize the recording configuration of the FLESEs. The successful results from differential bipolar recordings showed that the total length of FLESEs could be further reduced, maintaining the maximum recording ability, which would be beneficial for recording in very fine nerves. Our results demonstrate that new concept of FLESEs could play an important role in electroceuticals in near future.

A SU-8-based compact implantable wireless pressure sensor for intraocular pressure sensing application

Telemetric sensing has received a great deal of attention in noncontact human disease detection. To take advantage of this method, this paper presents a SU-8-based compact (1.52 mm × 3.23 mm × 0.2 mm) passive wireless pressure sensor, especially designed to measure the intraocular pressure. The sensor was microfabricated using biocompatible materials such as gold and SU-8 [1] to form the LC parallel circuit and the pressure sensitive diaphragm. The surface of the sensor is fully covered by SU-8, which isolates the working circuit from the biological tissue medium. The pressure signal can be detected by an external readout coil with up to 6 mm distance from the implanted sensor. The pressure sensitivity of the sensor was characterized in both air and saline environment. The microfabricated sensor has high sensitivity (>7,000 ppm/mmHg).

Mapping of Small Nerve Trunks and Branches Using Adaptive Flexible Electrodes

Selective stimulation is delivered to the sciatic nerve using different paris of contacts on a split‐ring electrode, while simulatneous recordings are acquired by the neural ribbon electrodes on three different branches. Two hook electrodes are also implanted in the muscle to monitor the activated muscle responses. It shows that the high precision implantation of electrodes, increases the efficacy and reduces the incidence of side effects.

Glass-Based Continuous-Flow PCR Chip With a Portable Control System for DNA Amplification

A glass-based continuous-flow polymerase chain reaction (PCR) chip has been designed and fabricated. The device consists of a glass microfluidic channel, three NiCr heaters, and three Ni thermometers on the silicon substrate. An intelligent temperature-control circuit system has been designed to achieve desirable temperature control (95, 72, and 55°C) at the three temperature zones of the PCR chip. Simulation underneath the microfluidic channel using the finite element method shows that the temperature distribution through the three temperature zones are relatively uniform. A mixture of DNA samples for PCR was allowed to flow through the microfluidic channel under different flow rates. The amplified sample of the target DNA obtained from the PCR chip was then separated by electrophoresis and was analyzed using an ultraviolet analyzer. The result indicates that DNA amplification can be achieved and that its amplification factor depends greatly on the injection rate of the sample. The optimum sample-flow rate is 0.6 μl/min.

Biocompatible polymeric wireless pressure sensor for intraocular pressure sensing application

Telemetric sensing is a promising method to accomplish non-contact and continuous disease diagnoses. Implantable intraocular pressure (IOP) sensor using wireless telemetric technology is highly desirable. This paper presents a fully integrated SU-8-based passive wireless inductively-coupled pressure sensor, especially designed for IOP sensor. The sensor was microfabricated using biocompatible materials - gold and SU-8 - to form the LC parallel circuit and the pressure sensitive diaphragm. Multi-SU-8-layers were stacked to completely isolate the working circuit from the biological tissue medium. The characterization result of IOP sensor shows that it has relatively high responsivity (683 KHz/mmHg) in the pressure range of 0 – 60 mmHg and has pressure resolution much lower than 1 mmHg in both air and saline medium.

Highly Integrated MEMS-ASIC Sensing System for Intracorporeal Physiological Condition Monitoring

In this paper, a highly monolithic-integrated multi-modality sensor is proposed for intracorporeal monitoring. The single-chip sensor consists of a solid-state based temperature sensor, a capacitive based pressure sensor, and an electrochemical oxygen sensor with their respective interface application-specific integrated circuits (ASICs). The solid-state-based temperature sensor and the interface ASICs were first designed and fabricated based on a 0.18-μm 1.8-V CMOS (complementary metal-oxide-semiconductor) process. The oxygen sensor and pressure sensor were fabricated by the standard CMOS process and subsequent CMOS-compatible MEMS (micro-electromechanical systems) post-processing. The multi-sensor single chip was completely sealed by the nafion, parylene, and PDMS (polydimethylsiloxane) layers for biocompatibility study. The size of the compact sensor chip is only 3.65 mm × 1.65 mm × 0.72 mm. The functionality, stability, and sensitivity of the multi-functional sensor was tested ex vivo. Cytotoxicity assessment was performed to verify that the bio-compatibility of the device is conforming to the ISO 10993-5:2009 standards. The measured sensitivities of the sensors for the temperature, pressure, and oxygen concentration are 10.2 mV/°C, 5.58 mV/kPa, and 20 mV·L/mg, respectively. The measurement results show that the proposed multi-sensor single chip is suitable to sense the temperature, pressure, and oxygen concentration of human tissues for intracorporeal physiological condition monitoring.

Recent Progress in Technologies for Tactile Sensors

Over the last two decades, considerable scientific and technological efforts have been devoted to developing tactile sensing based on a variety of transducing mechanisms, with prospective applications in many fields such as human–machine interaction, intelligent robot tactile control and feedback, and tactile sensorized minimally invasive surgery. This paper starts with an introduction of human tactile systems, followed by a presentation of the basic demands of tactile sensors. State-of-the-art tactile sensors are reviewed in terms of their diverse sensing mechanisms, design consideration, and material selection. Subsequently, typical performances of the sensors, along with their advantages and disadvantages, are compared and analyzed. Two major potential applications of tactile sensing systems are discussed in detail. Lastly, we propose prospective research directions and market trends of tactile sensing systems.