Takafumi Suzuki

3D flexible multichannel neural probe array

A 3D flexible multichannel microprobe array was designed, fabricated and tested. Since each probe had several recording pads, the probe array could be used to measure neural activity at various depths in the brain. They were batch fabricated with interconnections, using a specific folding process to fold the planar probe structures. This flexible probe array was inserted into a rats brain without fracturing and was successfully used to measure neural signals.

Fabrication of Flexible Neural Probes With Built-In Microfluidic Channels by Thermal Bonding of Parylene

This paper describes the fabrication technology and characterization of Parylene neural probes containing fluidic channels for delivery of small amounts of drugs into biological tissue as well as neural recording. We present a first attempt to realize such neural probes by micromolding and thermal bonding of Parylene. Compared to the common fabrication method, where a sacrificial photoresist layer is sandwiched between two Parylene layers, the major advantages of this process are, that the time consuming photoresist dissolution is omitted, and that the adhesion between the Parylene layers could be improved. The electrodes were characterized by impedance measurements, in which an impedance sufficiently low for neural recording was observed. Fluidic injection experiments with the microchannel have shown that nanoliter volumes can be injected

Parylene flexible neural probe with micro fluidic channel

A flexible neural probe with an integrated fluidic channel is proposed. Since parylene thin film is used as the main structure, the probe is sufficiently flexible to perform a less invasive implant for neural recording. The micro fluidic channel of this probe can be used not only to inject certain chemicals into biological tissues but also to improve mechanical stiffness prior to the insertion when the channel is filled with rigid polymer, such as polyethylene glycol (PEG), which is dissolved into the tissues. We have succeeded in inserting the probe into a rats brain and measuring the neural signals from it.

Preliminary study of multichannel flexible neural probes coated with hybrid biodegradable polymer.

Two types of intracortical multichannel flexible neural probes coated with a hybrid biodegradable polymer were designed and fabricated. The hybrid biodegradable polymer was made of polyethylene glycol and biodegradable polymeric microspheres containing nerve growth factor (NGF) and incorporated to improve the stiffness for flexible neural probe insertion, and promote regrowth of damaged neural tissues around the probe. The type-A neural probe has a groove structure designed to be seeded with a large amount of the hybrid biodegradable polymer. The type-B neural probe has a unique configuration like skeleton to minimize the volume of the flexible probe and buffer injurious micromotion between the probe and the tissues after implantation. In this preliminary study, the efficacy of the released NGF from the microspheres with the PC12 cells was examined. Further, neural probe implantation and neural signal recording with an acute experiment were studied

A new multi-electrode array design for chronic neural recording, with independent and automatic hydraulic positioning

We report on a new microdrive design, which enables the construction of multi-electrode arrays capable of chronically recording the multi-unit neural activity of waking animals. Our principal motivation for inventing this device was to simplify the task of positioning electrodes, which consumes a considerable amount of time and requires a high level of skill. With the new microdrives, each electrode is independently and automatically driven into place. A hydraulic drive system is adopted to reduce the size, weight, and cost of the structure. The hydraulic fluid is also used as a part of the electrical circuit, and facilitates the wiring of the electrodes. A routing system has been attached to reduce the number of tube connections. The microdrive is cylindrical, has a diameter of 23.5 mm, a height of 37 mm, and a weight of 15 g. It allows for up to 22 electrodes, which are arranged on a 0.35 mm grid. Each electrode can be positioned at any depth up to approximately 4mm. The microdrive was evaluated under acute and chronic recording experiments, and is shown to be capable of automatically positioning each electrode and successfully recording the neural signals of waking rats.

Flexible neural probes with micro-fluidic channels for stable interface with the nervous system

A flexible neural probe with micro-fluidic channels has been developed. The probe is sufficiently flexible to enable minimally invasive recording. The fluidic channel integrated on the probe is capable of injecting chemicals into neural tissues. In addition, it permits a stable interface with the nervous system. We focus on issues concerning: 1) stable recording with electrodes placed in fluidic channels, 2) improved mechanical stiffness by filling channels with a solid that dissolves in neural tissues, and 3) the probes application to a nerve regeneration electrode.

Development of a regeneration-type neural interface : A microtube guide for axon growth of neuronal cells fabricated using focused-ion-beam chemical vapor deposition

The authors’ goal is to develop a neural interface system that enables connection of the human nervous system with external devices and allows transmission of information in both directions. One way to connect interface to neurons is a regenerative electrode, where the electrode is placed between the two cut ends of a nerve. The cut nerve fiber can regenerate through channels in a metallic electrode on a two-dimensional (2D) plane of the regenerative electrode. As this type of electrode enables both the recording of signals from a single nerve fiber and the stimulation of a single nerve fiber, attempts have been made to develop it using traditional 2D microfabrication techniques. However, it is difficult to process such electrodes with these 2D microfabrication techniques, particularly the high-density integrated structure of the electrical wiring. The authors previously designed a neural interface system—a type of regenerative electrode consisting of an electrode segment and many carbon microtubes for gu...

Three-dimensional and multimaterial microfabrication using focused-ion-beam chemical-vapor deposition and its application to processing nerve electrodes

One of the ways to interface electrodes to neurons is a regenerative electrode. The electrode is between the two cut end of a nerve. The cut nerve fiber regenerates through a metalized hold electrode in a two-dimensional (2D) planar of regenerative electrode. As this type of electrode has advantages enabling both the recording of signals of a single nerve fiber and the stimulation of a single nerve fiber, attempts have been made to develop it using traditional 2D microfabrication techniques. However, these traditional 2D techniques have made it difficult to process such electrodes, in particular, electrical wires that have a high density and an integrated structure. In this study, we developed a novel microfabrication method that enables three-dimensional (3D) micro/nanostructures to be fabricated that are made of several kinds of materials with focused-ion-beam chemical-vapor deposition (FIB-CVD). To demonstrate the feasibility of this technique, we designed and fabricated a modified type of regenerative...

Fast Automatic Template Matching for Spike Sorting Based on Davies-Bouldin Validation Indices

The present study introduces an approach to detecting and classifying the extracellular action potentials of neurons, a process usually referred to as spike sorting. Our approach is based on template matching which is an optimal filter under Gaussian noise. However, this is usually expensive in terms of computational time, and constructing appropriate templates can be also problematic. Despite its theoretical consistency, only a few algorithms have been proposed to efficiently solve this problem. To speed up the filter, it is important to curtail the matching process when the distance between the template and waveform exceeds some threshold. We approach this aspect of the problem using Davies-Bouldin validation indices (DBVIs), which are a function of the ratio of the sum of within-cluster scatter to between-cluster separation to prioritize point-by-point calculation. The templates are also constructed automatically by combining principle component analysis (PCA) and k-means clustering. This matching process performed well, with a shorter computational time and fewer incorrect classifications than other ordering methods.

Flexible Intracortical Neural Probe with Biodegradable Polymer for Delivering Bioactive Components

A flexible intracortical neural probe containing a biodegradable polymer for delivering bioactive components was developed. This was designed to promote regrowth of damaged neural tissues around the implanted neural probe for a long-term recording. The neural probe was based on the flexible and biocompatible material of parylene C incorporated a drug delivery system (DDS). A groove structure of the probe was designed to seed the degradable polymeric microspheres with bioactive components, to promote recovery of the damaged tissues, and improve mechanical stiffness for the probe implantation. The efficacy of released nerve growth factor (NGF) from the microspheres was observed in in vitro experiments with PC12 cells. The neural probe was successfully inserted in the cerebral cortex of a rat, and neural signals were recorded. These results have shown the possibility that the flexible intracortical neural probe can be applied for chronic recording along with neural regeneration