Chronic neural recording using silicon-substrate microelectrode arrays implanted in cerebral cortex

An important aspect of the development of cortical prostheses is the enhancement of suitable implantable microelectrode arrays for chronic neural recording. The objective of this study was to investigate the recording performance of silicon-substrate micromachined probes in terms of reliability and signal quality. These probes were found to consistently and reliably provide high-quality spike recordings over extended periods of time lasting up to 127 days. In a consecutive series of ten rodents involving 14 implanted probes, 13/14 (93%) of the devices remained functional throughout the assessment period. More than 90% of the probe sites consistently recorded spike activity with signal-to-noise ratios sufficient for amplitudes and waveform-based discrimination. Histological analysis of the tissue surrounding the probes generally indicated the development of a stable interface sufficient for sustained electrical contact. The results of this study demonstrate that these planar silicon probes are suitable for long-term recording in the cerebral cortex and provide an effective platform technology foundation for microscale intracortical neural interfaces for use in humans.     

In vivo validation of custom-designed silicon-based microelectrode arrays for long-term neural recording and stimulation

We developed and validated silicon-based neural probes for neural stimulating and recording in long-term implantation in the brain. The probes combine the deep reactive ion etching process and mechanical shaping of their tip region, yielding a mechanically sturdy shank with a sharpened tip to reduce insertion force into the brain and spinal cord, particularly, with multiple shanks in the same array. The arrays' insertion forces have been quantified in vitro. Five consecutive chronically-implanted devices were fully functional from 3 to 18 months. The microelectrode sites were electroplated with iridium oxide, and the charge injection capacity measurements were performed both in vitro and after implantation in the adult feline brain. The functionality of the chronic array was validated by stimulating in the cochlear nucleus and recording the evoked neuronal activity in the central nucleus of the inferior colliculus. The arrays' recording quality has also been quantified in vivo with neuronal spike activity recorded up to 566 days after implantation. Histopathology evaluation of neurons and astrocytes using immunohistochemical stains indicated minimal alterations of tissue architecture after chronic implantation.     

Cultured neurons coupled to microelectrode arrays: circuit models, simulations and experimental data

The purpose of this paper is to characterize the neuron-microelectrode junction, based on the equivalent electric-circuit approach. As a result, recording of action potentials can be simulated with a general-purpose circuit simulation program such as HSPICE. The response of the microelectrode was analyzed as a function of parameters such as sealing resistance and adhesion conditions. The models of the neuron and microelectrode implemented in HSPICE were first described. These models were used to simulate the behavior of the junction between a patch of neuronal membrane (described by the compartmental model) and a microelectrode.     

Silicon-substrate microelectrode arrays for parallel recording ofneural activity in peripheral and cranial nerves

A new process for the fabrication of regeneration microelectrode arrays for peripheral and cranial nerve applications is presented. This type of array is implanted between the severed ends of nerves, the axons of which regenerate through via holes in the silicon and are thereafter held fixed with respect to the microelectrodes. The process described is designed for compatibility with industry-standard CMOS or BiCMOS processes (it does not involve high-temperature process steps nor heavily-doped etch-stop layers), and provides a thin membrane for the via holes, surrounded by a thick silicon supporting rim. Many basic questions remain regarding the optimum via hole and microelectrode geometries in terms of both biological and electrical performance of the implants, and therefore passive versions were fabricated as tools for addressing these issues in on-going work. Versions of the devices were implanted in the rat peroneal nerve and in the frog auditory nerve. In both cases, regeneration was verified histologically and it was observed that the regenerated nerves had reorganized into microfascicles containing both myelinated and unmyelinated axons and corresponding to the grid pattern of the via holes. These microelectrode arrays were shown to allow the recording of action potential signals in both the peripheral and cranial nerve settings, from several microelectrodes in parallel     

Electroluminescence from MIS silicon-based light emitters with arrays of self-assembled Ge(Si) nanoislands

We report on the electroluminescence from silicon-based metal–insulator–semiconductor (MIS) diodes with arrays of self-assembled Ge(Si) nanoislands. Aluminum oxide (Al₂O₃) is used as an insulator material in the MIS contact. Variations in the electroluminescence spectra caused by changing the metal work function are examined. The intense electroluminescence from Ge(Si) nanoislands localized at a distance of 50 nm from the insulator–semiconductor interface is observed at room temperature. The emission spectrum is found to be controlled by choosing the design of the semiconductor structure and the barrier height for injected carriers.     

Large scale,flexible organic transistor arrays and circuits based on polyimide materials

Polyimide (PI) materials are lightweight, flexible, resistant strongly to heat and chemicals, and have been widely used in electronics industry such as working as electronic packaging materials in large-scale integrated circuits. In this letter, PI materials, for the first time, are introduced into organic field-effect transistors (OFETs) and circuits as insulator layers in order to be compatible with the photolithography process. Moreover, a novel method is developed to make the PI films strong enough to endure the critical processes of photolithography (e.g., the influence of developer on polyimide layer). Based on the intact PI insulator and the modified photolithographic technique, large scale, flexible transistor arrays and circuits were fabricated with high resolution and high performance (mobility up to 0.55 cm² V⁻¹ s⁻¹ for bottom-contact bottom-gate OFETs). It provides a new way for the fabrication of large-area organic devices and circuits beyond solution printed techniques, especially for the application of organic semiconductors with poor solubility, e.g., pentacene.     

Effect of insertion speed on tissue response and insertion mechanics of a chronically implanted silicon-based neural probe

In this study, the effect of insertion speed on long-term tissue response and insertion mechanics was investigated. A dummy silicon parylene-coated probe was used in this context and implanted in the rat brain at 10?μm/s (n = 6) or 100?μm/s (n = 6) to a depth of 9?mm. The insertion mechanics were assessed by the dimpling distance, and the force at the point of penetration, at the end of the insertion phase, and after a 3-min rest period in the brain. After 6 weeks, the tissue response was evaluated by estimating the amount of gliosis, inflammation, and neuronal cell loss with immunohistochemistry. No difference in dimpling, penetration force, or the force after a 3-min rest period in the brain was observed. However, the force at the end of the insertion phase was significantly higher when inserting the probes at 100?μm/s compared to 10?μm/s. Furthermore, an expected tissue response was seen with an increase of glial and microglial reactivity around the probe. This reaction was similar along the entire length of the probe. However, evidence for a neuronal kill zone was observed only in the most superficial part of the implant. In this region, the lesion size was also greatest. Comparison of the tissue response between insertion speeds showed no differences.     

Aligned microcontact printing of micrometer-scale poly-L-lysine structures for controlled growth of cultured neurons on planar microelectrode arrays

We describe a method for producing high-resolution chemical patterns on surfaces to control the attachment and growth of cultured neurons. Microcontact printing has been extended to allow the printing of micron-scale protein lines aligned to an underlying pattern of planar microelectrodes. Poly-L-lysine (PL) lines have been printed on the electrode array for electrical studies on cultured neural networks. Rat hippocampal neurons showed a high degree of attachment selectivity to the PL and produced neurites that faithfully grew onto the electrode recording sites.     

Integration of VLSI circuits and mechanics for vibration control of flexible structures

The approach to modeling and control of smart flexible structures presented in this paper is based on the concept that an intelligent structure requires an internal knowledge of self to act intelligently. This knowledge can be acquired from local analog models of substructure dynamics and can be used in model-based controller designs. The key to this approach is the synergistic integration of analog VLSI circuit models and control with the sensing and actuation which are then to be embedded into the mechanical structure. This paper presents the motivation, development, and test results of analog VLSI circuit models for use in model-based control of smart flexible structures. Furthermore, control applications for these VLSI circuits are developed and simulation results are presented in which the VLSI circuits are used in adaptive vibration control of a simple mass-spring system.     

Factors influencing the biocompatibility of insertable siliconmicroshafts in cerebral cortex

Insertable microelectrode arrays can be used to activate neurons or to sense neural signals for use in prosthetics. The relationship of the microelectrodes to the neurons is determined by random alignment and by biocompatibility. Issues that determine the biocompatibility of insertable microelectrode arrays were investigated. Arrays were implanted into the cortex of rabbit brain and fixed to the skull. Following six-month survival, neuron density as a function of distance from the shafts of the arrays was measured to assess destruction of neurons. Results from a limited number of tests indicated that there was minimal tissue response along the sides of the shafts when shafts were well sharpened, had sufficiently small tip angles, and were clean. Tissue was usually more reactive at the tips of the shafts. It was concluded that silicon microshafts of appropriate shaft and tip design were biocompatible along the sides of the shaft, but that relatively severe reactions could be anticipated at the tips. Recording or stimulation sites should be located away from the tips on the sides of the shafts for better coupling with individual neurons. Measurement of neuron density as a function of distance from the shafts was a sensitive and quantitative technique for assessing biocompatibility. Additional measures such as glial density as a function of distance from the shafts, and incidence of microhematoma formation were proposed.     

Efficient time-space mappings of nested loops onto multidimensionalsystolic arrays with a flexible buffer scheme

The task of mapping a nested loop algorithm onto a multidimensional systolic array is considered. A buffer structure for the processing elements (PEs) that allows the data tokens to arrive at the PE earlier than when they are needed is proposed. Necessary and sufficient conditions for valid mappings using this buffer structure are then given. A refinement technique for deriving efficient statement level mappings from iteration level mappings is then proposed     

Reconstruction of the human cerebral cortex from magnetic resonanceimages

Reconstructing the geometry of the human cerebral cortex from MR images is an important step in both brain mapping and surgical path planning applications. Difficulties with imaging noise, partial volume averaging, image intensity inhomogeneities, convoluted cortical structures, and the requirement to preserve anatomical topology make the development of accurate automated algorithms particularly challenging. In this paper we address each of these problems and describe a systematic method for obtaining a surface representation of the geometric central layer of the human cerebral cortex. Using fuzzy segmentation, an isosurface algorithm, and a deformable surface model, the method reconstructs the entire cortex with the correct topology, including deep convoluted sulci and gyri. The method is largely automated and its results are robust to imaging noise, partial volume averaging, and image intensity inhomogeneities. The performance of this method is demonstrated, both qualitatively and quantitatively, and the results of its application to six subjects and one simulated MR brain volume are presented.     

Study of energy transfer in silicon-based micro-ring resonators

Physical model, time-domain model, transmission spectra and energy transfer diagram of silicon-based micro-ring resonators based on the parallel waveguide structure are analyzed in this paper, in which transmission spectrum is ob- tained by Matlab, and the energy transfer process is analyzed by Rsoft. According to the analyses of the models and results, the energy transfer process in this type of resonator is clear to a great extent. The experimental results show that when the input signal is stable, the energy of the micro-ring resonator and the drop port tends to be steady after the input optical signal is coupled in the coupling region, which proves that the silicon-based micro-ring resonators can select specific optical signal if the input optical signal satisfies the resonance condition. However, if the resonance condition is not met, filtering function, optical switch function and signal selection function can be realized. Therefore, the analysis and simulation of energy transfer in silicon-based micro-ring resonators can not only enrich the silicon micro-ring resonator theory, but also provide new theoretical basis and method for the design and optimization of ex- isting, ontoelectronie devices.     

硅基光电子在通信中的应用和挑战

硅基光电子技术拥有光的宽带、高速和抗干扰特性以及微电子技术在大规模集成、低能耗、低成本等方面的优势。最近十年,硅基光电子技术开始进入通信产业领域,在800 Gbit/s以上的高速短距应用场景中发挥优势,对传统磷化铟（InP）的通信光模块形成挑战。浅谈硅基光电子技术在通信中的应用和发展,同时简要介绍硅基光电子技术在应用中的一些挑战。解决器件性能、封装技术、自动化软件等方面的不足,才能实现硅基光电子技术长足发展。     

Experimental validation of a tissue-joining implant providing flexible adaptation to the thickness of the stomach wall

Endoscopy is gradually replacing open surgery in the gastrointestinal tract. Therefore, novel medical devices and instrumentation are required, such as flexible miniaturized mechanisms for tissue joining and manipulation. In this paper, an absorbable implant for the purpose of long-term tissue fixation is presented. An experimental validation of the implant design and functionality is introduced. The implant achieves tissue penetration and provides flexible adaptation according to the thickness of two stomach walls. This mechanism is easy as it is based on push-pull principle using unidirectional forces. The shape optimization of each implant part occurs by varying design-influencing factors. The load transmission on postmortem porcine tissue was measured in the frame of the experimental setup. The feasibility of the implant was tested, and the forces needed for the intended application quantified. The implant successfully achieves tissue penetration, load transmission, adjustment, and fixation. It is a new alternative to conventional tissue-joining mechanisms.     

Changes in the complex permittivity during spreading depression in rat cortex

With recent developments in current density imaging (CDI), it is feasible to utilize this new technique in brain imaging applications. Since CDI's ability to measure changes in current density depends on a concomitant activity-dependent change in the conductivity of the brain tissue, we have examined the changes in complex conductivity during spreading depression (SD) in rodent neocortex using a coaxial probe. SD was chosen because it is often referred to as an animal model of cerebral ischemia and migraine with aura. The conductivity measurements revealed a change with short latency (30-60 s) followed by a change with a longer latency (200-300 s). This change in conductivity with short latency has not been reported before, and we conjecture that it may be the priming or triggering mechanism prior to the main SD episode. A 20% change in conductivity during SD is sufficiently large to be measured by CDI. Therefore, the ability to measure changes in the conductivity, as opposed to metabolic changes, makes CDI a viable approach to the study of ischemia and migraine with aura.     

Constrained least squares in adaptive, imperfect arrays

Two new constrained deterministic least-squares algorithms are presented which are capable of enabling a narrow-band zero-order generalized sidelobe canceller (SLC), in the presence of array imperfections, to null out jammers while preserving the friendly look-direction signal with minimal a priori knowledge of the signal environment. The algorithms are capable of solving deterministic least-squares optimization problems subject to an equality constraint in an iterative, adaptive manner by imposing a `soft' constraint via the quadratic penalty function optimization method. The first algorithm is based on the matrix inversion lemma while the second is obtained by means of QR-decomposition using new three-dimensional Givens (1958) rotations and implemented with a systolic array architecture. These new constrained algorithms improve system performance when an artificial injection of a receiver noise vector is introduced     

太赫兹硅基微环谐振器的设计与分析

设计了一个工作频率在太赫兹大气传输第一窗口的硅基波导型微环谐振器。利用传输矩阵法和耦合模理论计算微环谐振器的传输函数,并对波导耦合系数进行分析,获得微环谐振器的临界耦合条件。采用时域有限差分法分析微环谐振器的性能参数,并与串联双环谐振器性能参数相比较。结果表明：单环谐振器的自由谱宽范围为27 GHz,插入损耗为0.3 dB。单环与双环谐振器的响应谱线形状因子分别为0.16和0.52,即串联双环谐振器使谐振谱线顶端更平坦,滚降度增高。Abstract：关键词：