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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.

This work evaluated the biocompatibility and the bio-degradability/bio-solubility by comparing different bio-soluble glass materials for neural probe applications. Diboron trioxide and phosphorus oxide based bio-soluble glass materials are used as probe substrate. Two experiments conducted will be discussed in this paper. The first experiment is preliminary bench test to study the dissolution rate of the samples. Second experiment is an in vivo experiment to further investigate the dissolution rate and the biocompatibility of the material. According to the experimental results, higher content (how high?) of diboron trioxide glass has a shorter dissolution period (how long?) and evoke less inflammatory response compared to a sample with lower content of diboron trioxide and phosphorus oxide based glass. Phosphorus oxide based glass which produces an acidic medium resulting in advance inflammatory response is not suitable as base substrate material for neural probe application.

Neural probe array is utilized in neural recording, in the aim to understand the neural activity. Silicon is the common substrate used in neural probe array. However, due to the rigid nature, the silicon-based neural probe array causes cell damage during implantation into the brain tissue. This would reduce the signal-to-noise ratio. Therefore, flexible polymer probe is more suitable as it can help to minimize the tissue damage and thus increasing the signal-to-noise ratio. The lack of stiffness for the flexible probe is solved by coating it with polyethylene glycol (PEG). It stiffens the probe and can be dissolved in water, which allows the polymer probe to regain its flexibility. The proposed integrated probe with reduced distance between probe and ASIC will further help to improve the signal-to-noise ratio during neural recording. The coated flexible probe regained original impedance of 14.1 kΩ at a frequency of 1 kHz. A bench-top neural recording with the flexible probe array in saline solution will also be acquired.

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.

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.

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.