Kwan Ling Tan

3D probe array integrated with a front-end 100-channel neural recording ASIC

Brain–machine interface technology can improve the lives of spinal cord injury victims and amputees. A neural interface system, consisting of a 3D probe array and a custom low-power (1 mW) 100-channel (100-ch) neural recording application-specific integrated circuit (ASIC), was designed and implemented to monitor neural activity. In this study, a microassembly 3D probe array method using a novel lead transfer technique was proposed to overcome the bonding plane mismatch encountered during orthogonal assembly. The proposed lead transfer technique can be completed using standard micromachining and packaging processes. The ASIC can be stacking-integrated with the probe array, minimizing the form factor of the assembled module. To minimize trauma to brain cells, the profile of the integrated probe array was controlled within 730 μm. The average impedance of the assembled probe was approximately 0.55 MΩ at 1 kHz. To verify the functionality of the integrated neural probe array, bench-top signal acquisitions were performed and discussed.

Biopackaging of Intracranial Pressure Microsystem for Multimodality Neuro Monitoring of Severe Head Injury Patients

In this work, we present the biopackaging and integration method of an intracranial pressure microsystem for multimodal neural monitoring. The neural monitoring chip used is a System-on-Chip (SoC) which has Microelectromechanical Systems (MEMS) capacitive pressure sensor that is fabricated in-house after Complementary Metal-Oxide Semiconductor (CMOS) wafer fabrication process, with a temperature sensor and an oxygen sensor in order to achieve multimodal neural monitoring functions. Polyimide is used for the substrate of the SoC die and passive component due to its biocompatibility and flexibility. A reversed stand-off stitch wire bonding process was employed in order to achieve a low-profile wire looping for the interconnection of the SoC die to the substrate. The biocompatible coatings of this implantable system consist of Parylene-C (for covering temperature and pressure sensors), Nafion® (for covering oxygen sensor), and medical grade silicone elastomer (for overall device encapsulation). The ICP microsystem wireless reader module was packaged in a customized biocompatible hermetic Teflon housing. To reinforce and seal the catheter, which is integrated with the microsystem, during the device implantation into the brain tissue, it is filled until the wire bonded portion with polydimethylsiloxane. Similarly, the guiding tip of the catheter which will facilitate the sensor device to penetrate into the brain tissue is made and casted from a specially designed mold using polydimethylsiloxane as the material. Verification of the packaging feasibility was measured by measuring the sensitivities of the pressure sensor, oxygen sensor, and temperature sensor. The whole microsystem also passed the ISO 10993-5 standards in vitro cytotoxicity test with a conclusion of no reactivity and no cell lysis cell growth in cell culture, verifying its biocompatibility

Evaluation of biodegradable coating on the stiffness control of the polyimide-based probe used in neural devices

In this work, an assembled and integrated flexible probe array with biodegradable coating for stiffness control is demonstrated. The proposed method will help to overcome the stiffness issue faced by polymeric probe array during insertion into the brain tissue. It is proposed to do coating with biodegradable material to increase the stiffness of the probe shanks. Assembly process is simplified as polymer probe and cable were being monolithically fabricated, only the connector needs to be soldered onto the bonding pads. To enhance the soldering between connector and bonding pads, rigid stiffener is designed at the bonding pads region to provide robust support for soldering process and for insertion process.

Three-Dimensional Flexible Polyimide Based Probe Array with Stiffness Improvement by Using Biodegradable Polymer

This work presents a three-dimensional flexible polyimide (PI) probe array with biodegradable polymer that offers desirable insertion capability. In order to avoid the recording sites position shifts slightly and damage neuron cells when the body moves, the flexible neural probes are more preferable than traditional Si-based neural probes. A sufficient buckling strength of flexible probe is critical for inserting flexible probe into the brain. Here, we used a biodegradable polymer, polyethylene glycol (PEG), to improve the mechanical stiffness of flexible probe. PEG, which is solid state at room temperature and dissolves when immersing in water, was coated onto the flexible probe and the mechanical stiffness of the flexible probe was increased before insertion into the biological tissue. The buckling strength of different probes was simulated using finite element analysis and measured by compression tester. The coated PEG flexible probe maintains sufficient stiffness to facilitate tissue penetration with solid PEG elastic modulus of 660±19 MPa but loses its strength within 25 minutes once immersed in saline. A microassembly method of three-dimensional flexible probe array was also proposed to integrate the flexible probe and their interconnections. In vitro test, the coated PEG flexible probe regained their original impedance of 12.8 kΩ at 1 kHz within 30 minutes of immersing in saline via water absorption and polymer’s biodegradable response.

MEMS Tri-Axial Tactile Sensor for Sensorized Guide Wire in Catheterization Application

This paper describes the integration of micro-electro-mechanical systems (MEMS) tri-axial force sensor using polyimide-based substrate for sensorised guide wire application. For tri-axial force sensor, piezoresistive silicon nanowires (SiNWs) are embedded into a cross cantilever design with a maneuverable stylus to allow the detection of force in all directions, and amplify the tactile forces at the tip for transverse directions. The electrical resistance changes in the four SiNWs are used to decode an arbitrary force applied onto the force sensor. Robustness of the force sensor is improved due to the novel design by incorporating a mechanical stopper at the tip of the stylus. Flip chip bonding using gold stud bumps is used to mount the force sensor on a substrate for characterization and to simplify the assembly process. The packaging process of the miniaturized sensorised guide wire was presented in this work.

Forward Tactile Sensing Device Development and Biopackaging for Endovasular Guidewire Intervention Application

Revascularization procedure for peripheral artery disease is dependent on surgeons skill and experience for a successful procedure. An integrated sensor on guidewire is proposed to reduce such dependency during the procedure. The development and packaging of the sensor with a hybrid-silicone-polymer substrate (HSPS) and a silicon stopper arepresented in this paper. A compact HSPS (0.4mm x 10mm x0.31mm) with trace width/spacing of 20μm/20μm for five output signals and Si stopper with safety displacement feature to prevent force overloading are fabricated. It is able to enhanced current sensor integrated guidewire by improving the robustness and provides a forward sensing mechanism (orthogonal assembly). The assembled device is able to measure up till 42mN force with a resolution of 0.2mN. Detail of characterization testing and result will be presented in the paper.

Ultra slim packaging and assembly method for 360-μm diameter guide wires

In this work, we present an ultra-slim profile packaging and assembly solution of a 360-μm diameter medical guide wire fitted and integrated with silicon based fractional flow reserve (FFR) sensor. The miniaturization of the whole sensorized guide wire assembly without sacrificing its sensing functionality was made possible by the use of polyimide flexible printed circuit board (FPCB) as the substrate material for the silicon platform and by the use of lowest possible wire looping profile to create interconnection between the FFR sensor and the FPCBs bonding pads using the gold wires. In order to reinforce and protect the wire interfaces, as well as to maintain the required biocompatibility of the whole system, a thin layer of Polydimethylsiloxane (PDMS) was used for the encapsulation process. Long signal wires were then attached to the bonding pads of FPCB before finally fitted inside a miniaturized metal housing. This whole system has easily fit and integrated with the 360-μm diameter medical guide wire. In order to verify the packaging feasibility, the electrical short testing of the bonding pads and SEM observations were conducted.

Silicon cap structure development and microassembly for forward tactile sensing in endovascular guidewire intervention

Guidewire procedure for peripheral artery disease treatment is heavily dependent on the surgeons skills and experiences. In order to reduce such dependency, sensor-enhanced forward sensing guidewire is proposed. In this paper, we proposed a silicon cap structure that increases the robustness and efficient force transfer of the existing sensor-enhanced forward sensing guidewire. Silicon cap structure of 0.32 × 0.32 × 0.40mm has been fabricated using two masks process. Assembly of silicon structure with sensor having a 30μm overloading protection limit and resistance changes of 25kΩ with applied force ranging from 0∼40mN has been demonstrated.

Silicon-Based Multichannel Probe Integrated with a Front End Low Power Neural Recording IC for Acute Neural Recording

This work presents a silicon-based multichannel probe integrated with a front end low power neural recording integrated circuit (IC) which is used in acute neural recording application. The low power neural recording IC contains 100-channel analog recording front-ends, 10 multiplexing successive approximation register ADCs, digital control modules and power management circuits. The 100-channel neural recording IC consumes 1.16-mW, making it the optimum solution for multi-channel neural recording systems. The neural recording IC and Si probe are integrated in a printed circuit board (PCB) which is fixed on the skull using dental resin. Digital neural signal is converted to analog signal and output by neural recording IC. The signal-to-noise ratio of neural recording signal can be increased through the reduction of interconnect length. The buckling strength of the fabricated probes was simulated using finite element analysis and measured by compression tester. The packaging method of 2D probe and neural recording IC was successfully demonstrated. The impedance of the assembled probe is also measured and discussed. To verify the functionality of Si probe integrated with neural recording IC, a pseudo neural signal acquisitions have been perform.

Bio-Degradable Glass for Neural Probe Application

This work presents a bio-degradable glass probes and its biocompatibility assessment for neural applications. The probes can be implanted into different sites of the human brain for recording and stimulating purposes. Current existing neural probe address the probe stiffness requirement for the penetration of brain tissue. However, this requirement normally resulted in the rigidity of the probe which is non-compatible with the brain tissue movement for long term implantation. The brain neuron cells will be damaged by too rigid probe substrate. In order to address this issue, bio-degradable glass probes having sufficient stiffness for a smooth brain insertion as well as ability to degrade after implantation; leaving behind the flexible circuitry substrate was being explored. The biodegradability of the proposed probe was evaluated.