Carbon fiber on polyimide ultra-microelectrodes
Winthrop F. GillisCharles LissandrelloJun ShenBen PearreAlket MërtiriFelix DekuStuart F. CoganBradley J. HolinskiDaniel ChewAlice E. WhiteTimothy M. OtchyTimothy J. Gardner
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Abstract:
Objective. Most preparations for making neural recordings degrade over time and eventually fail due to insertion trauma and reactive tissue response. The magnitudes of these responses are thought to be related to the electrode size (specifically, the cross-sectional area), the relative stiffness of the electrode, and the degree of tissue tolerance for the material. Flexible carbon fiber ultra-microelectrodes have a much smaller cross-section than traditional electrodes and low tissue reactivity, and thus may enable improved longevity of neural recordings in the central and peripheral nervous systems. Only two carbon fiber array designs have been described previously, each with limited channel densities due to limitations of the fabrication processes or interconnect strategies. Here, we describe a method for assembling carbon fiber electrodes on a flexible polyimide substrate that is expected to facilitate the construction of high-density recording and stimulating arrays. Approach. Individual carbon fibers were aligned using an alignment tool that was 3D-printed with sub-micron resolution using direct laser writing. Indium deposition on the carbon fibers, followed by low-temperature microsoldering, provided a robust and reliable method of electrical connection to the polyimide interconnect. Main results. Spontaneous multiunit activity and stimulation-evoked compound responses with SNR >10 and >120, respectively, were recorded from a small (125 µm) peripheral nerve. We also improved the typically poor charge injection capacity of small diameter carbon fibers by electrodepositing 100 nm-thick iridium oxide films, making the carbon fiber arrays usable for electrical stimulation as well as recording. Significance. Our innovations in fabrication technique pave the way for further miniaturization of carbon fiber ultra-microelectrode arrays. We believe these advances to be key steps to enable a shift from labor intensive, manual assembly to a more automated manufacturing process.상온에서 polyimide 위에 증착한 Cu의 초기성장 과정과 Cu/polyimide의 계면의 형태에 관하여 XPS를 이용하여 관찰하였다. Polyimide 위에 Cu가 증착됨에 따라, 초기단계에는 강한 결합의 Cu-N-O complex가 주가 되어 Cu/polyimide 계면을 형성하고, Cu의 증착두께가 증가함에 따라, 약한 결합의 Cu 산화물에서 서서히 metallic Cu로서 성장하는 것을 볼 수 있었다. 이상의 결과들을 통해, Cu/polyimide의 계면은 Cu-N-O complex와 Cu 산화물이 혼합되어 있는 형태이며 polyimide 표면에 가까울수록 Cu-N-O complex가 주가 되고, Cu 쪽에 가까울수록 Cu 산화물이 주가 되는 형태를 이루고 있다는 것을 알 수 있었다.
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Abstract The adhesion of polyimide to polyimide was studied by measuring the peel strength of various polyimide–polyimide composites. Different factors such as diffusion of polyamic acid to polyimide substrate, contact angle, wettability, and the thermal expansion coefficient of polyimide films and the presence of siloxane can affect this adhesion and are discussed in this article. © 1994 John Wiley & Sons, Inc.
Siloxane
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A number of polyimide films incorporated with different amounts of octa(aminopropylsilsesquioxane) (POSS-NH2) were prepared from 1,2,4,5-Benzenetetracarboxylic anhydride, 4,4′-Oxydianiline and POSS-NH2. The structure and properties of the hybrid polyimide films were characterized and evaluated. It is found that, compared with pure polyimide without POSS-NH2, the thermal stabilities and electrical capabilities of hybrid polyimide films are improved. Meanwhile, the incorporation of POSS-NH2 also brings improvement in the flexibility of polyimide films.
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Abstract Electrical conduction characteristics in two different polyimide films prepared by the imidization of polyamic acid (PAA) and pre-imidized polyimide (PI) solution were investigated. It is found that the current density of the polyimide film from PAA was higher than that of the polyimide film from PI at the same electric field, even though the conduction mechanism in both polyimide films follows the ionic hopping model. The hopping distance was calculated to be 2.8 nm for PAA type and 3.2 nm for PI type polyimide film. It is also found that the decay rate of the residual electrostatic charges on the polyimide films becomes faster in the PAA type than in the PI type polyimide film.
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Abstract High‐performance polyimide fibre is well known for its outstanding thermal stability, fire resistance and chemical stability, and it has great potential for use in fire‐protective textiles. One major drawback of polyimide fibre is that it is difficult to dye under regular conditions. In this work, it was found that polyimide fibre could be dyed with disperse dyes with the assistance of N ‐methylformanilide. Thus, it was proposed that there might exist an interaction between polyimide fibre and N ‐methylformanilide that plays an important role in dyeing. Experimental results showed that N ‐methylformanilide penetrated into polyimide fibre, resulting in a slight swell in diameter and decrease in the breaking strength of polyimide fibre. X‐ray diffractometric data showed no apparent solvent‐introduced increase on the crystallinity of polyimide fibres but an orderly change on the interplanar spacing. When N ‐methylformanilide was removed from polyimide fibre by thermal treatment, the diameter, breaking strength and interplanar spacing of the polyimide fibres were all recovered to some extent. This indicated that the interactions between polyimide macromolecular chains were broken because of the penetration of N ‐methylformanilide, and new interactions occurred between polyimide macromolecular chains and N ‐methylformanilide that played a role in lubricating dye molecules to diffuse into polyimide fibres.
Thermal Stability
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Electrical conduction characteristics in two different polyimide films prepared by the imidization of polyamic acid (PAA) and pre-imidized polyimide (PI) solution were investigated. It is found that the current density of the polyimide film from PAA was higher than that of the polyimide film from PI at the same electric field, even though the conduction mechanism in both polyimide films follows the ionic hopping model. The hopping distance was calculated to be 2.8 nm for PAA type and 3.2 nm for PI type polyimide film. It is also found that the decay rate of the residual electrostatic charges on the polyimide films becomes faster in the PAA type than in the PI type polyimide film.
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Abstract Thousands of different copolyimide combinations render it technically impossible to have a single universal synthesis method to produce aromatic polyimide film. This study aimed to outline the selection of synthesis protocol, either through the casting of chemically imidized polyimide solution or thermal imidization of polyamic acid (PAA), to produce the polyimide film. The rheological behaviour, molecular weight, and solubility of five structurally different PAA were analysed and correlated to both imidization methods. In this work, a tough polyimide film was successfully synthesized by casting the chemically imidized polyimide derived from high viscosity (> 81 cP) and high molecular weight (≥ 1.35 x 10 6 g/mol) PAA. On the contrary, both low viscosity (< 13 cP) and high viscosity (> 81 cP) PAA demonstrated the possibility to produce polyimide film via thermal imidization route. The longer molecular chain of ODPA-6FpDA:DABA (3:2) polyimide produced from thermal imidization had restricted the passage of CO 2 across the polyimide film when it was applied in the gas separation application. The outcome from this work serves as a guideline for the selection of suitable polyimide film synthesis protocol, which will minimize the time and chemical consumption in future exploration of new polyimide structure.
Tape casting
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To improve AO resistance of polyimide, a type of polyimide/silica (PI/SiO2) hybrid film was prepared by the sol-gel process. The coupling agent p-aminophenyltrimeth- oxysilane (APTMOS) was chosen to enhance the compatibility between the polyimide (PI) and silica (SiO2). AO resistance of the PI/SiO2 hybrid films were tested in the ground-based simulation AO facility. The erosion yield of the films was 4.7×10-26 cm3/atom, decreased by two orders of magnitude compared with the value of 3.0×10-24 cm3/atom of the polyimide film. Results from FTIR, XPS, AFM on AO treated polyimide/silica hybrid films indicate the formation of a passivating inorganic SiO2 layer. The layer significantly retards the penetration of oxygen atoms, preventing further degradation of the polymer in the bulk. The addition of SiO2 in polyimide does not significantly alter the optical properties of polyimide during AO exposure.
Siloxane
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Photoconductivity of an aliphatic polyimide, PI(PMDA/DCHM), was investigated, comparing with that of an aromatic polyimide, PI(PMDA/ODA). An enhanced photocurrent was observed for the aliphatic polyimide. The quantum efficiency of the aliphatic polyimide and the aromatic polyimide was 2.1×10-5 at 370nm, as 5.6×10-6 at 420nm respectively, where the film thickness is 1.0μ. Initial photoresponse behavior was observed to investigate the photoconduction mechanism of the aliphatic polyimide, which shows a different behavior from the aromatic polyimide. The nature of the aliphatic polyimide film is investigated by using the model compounds. The emission spectra of the aliphatic polyimide shows the red-shifting with increasing of the excitation intensity, which indicates the existence of an aggregation of pyromellitic groups intra-and intermolecularly.
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