Gold-coated microelectrode array with thiol linked self-assembled monolayers for engineering neuronal cultures

Electropolymerization processing of side-chain engineered EDOT for high performance microelectrode arrays

Microelectrode Arrays (MEAs) are popular tools for in vitro extracellular recording. They are often optimized by surface engineering to improve affinity with neurons and guarantee higher recording quality and stability. Recently, PEDOT:PSS has been used to coat microelectrodes due to its good biocompatibility and low impedance, which enhances neural coupling. Herein, we investigate on electro-co-polymerization of EDOT with its triglymated derivative to control valence between monomer units and hydrophilic functions on a conducting polymer. Molecular packing, cation complexation, dopant stoichiometry are governed by the glycolation degree of the electro-active coating of the microelectrodes. Optimal monomer ratio allows fine-tuning the material hydrophilicity and biocompatibility without compromising the electrochemical impedance of microelectrodes nor their stability while interfaced with a neural cell culture. After incubation, sensing readout on the modified electrodes shows higher performances with respect to unmodified electropolymerized PEDOT, with higher signal-to-noise ratio (SNR) and higher spike counts on the same neural culture. Reported SNR values are superior to that of state-of-the-art PEDOT microelectrodes and close to that of state-of-the-art 3D microelectrodes, with a reduced fabrication complexity. Thanks to this versatile technique and its impact on the surface chemistry of the microelectrode, we show that electro-co-polymerization trades with many-compound properties to easily gather them into single macromolecular structures. Applied on sensor arrays, it holds great potential for the customization of neurosensors to adapt to environmental boundaries and to optimize extracted sensing features.

Neurons-on-a-Chip: In Vitro NeuroTools

Neurons-on-a-Chip technology has been developed to provide diverse in vitro neuro-tools to study neuritogenesis, synaptogensis, axon guidance, and network dynamics. The two core enabling technologies are soft-lithography and microelectrode array technology. Soft lithography technology made it possible to fabricate microstamps and microfluidic channel devices with a simple replica molding method in a biological laboratory and innovatively reduced the turn-around time from assay design to chip fabrication, facilitating various experimental designs. To control nerve cell behaviors at the single cell level via chemical cues, surface biofunctionalization methods and micropatterning techniques were developed. Microelectrode chip technology, which provides a functional readout by measuring the electrophysiological signals from individual neurons, has become a popular platform to investigate neural information processing in networks. Due to these key advances, it is possible to study the relationship between the network structure and functions, and they have opened a new era of neurobiology and will become standard tools in the near future.

Micropatterning of Cells on Gold Surfaces for Biophysical Applications

We developed a reproducible micropatterning method to manipulate and normalize cell shape and cell-cell separation on gold. We used methoxy polyethylene glycol thiol (PEG-SH) to create a self-assembled monolayer that can be oxidized at desired shapes through a photomask with deep UV light. The oxidized PEG can be coated with extracellular matrix proteins and seeded with cells adopting the pre-defined shape. The developed and analyzed surfaces can be used in a wide range of biophysical applications.

Simultaneous recording of electrical activity and the underlying ionic currents in NG108-15 cells cultured on gold substrate

This paper shows the simultaneous recording of electrical activity and the underlying ionic currents by using a gold substrate to culture NG108-15 cells. Cells grown on two different substrates (plastic Petri dishes and gold substrates) were characterized quantitatively through scanning electron microscopy (SEM) as well as qualitatively by optical and atomic force microscopy (AFM). No significant differences were observed between the surface area of cells cultured on gold substrates and Petri dishes, as indicated by measurements performed on SEM images. We also evaluated the electrophysiological compatibility of the cells through standard patch-clamp experiments by analyzing features such as the resting potential, membrane resistance, ionic currents, etc. Cells grown on both substrates showed no significant differences in their dependency on voltage, as well as in the magnitude of the Na+ and K+ current density; however, cells cultured on the gold substrate showed a lower membrane capacitance when compared to those grown on Petri dishes. By using two separate patch-clamp amplifiers, we were able to record the membrane current with the conventional patch-clamp technique and through the gold substrate simultaneously. Furthermore, the proposed technique allowed us to obtain simultaneous recordings of the electrical activity (such as action potentials firing) and the underlying membrane ionic currents. The excellent conductivity of gold makes it possible to overcome important difficulties found in conventional electrophysiological experiments such as those presented by the resistance of the electrolytic bath solution. We conclude that the technique here presented constitutes a solution to the problem of the simultaneous recording of electrical activity and the underlying ionic currents, which for decades, had been solved only partially.

Technical feasibility study for production of tailored multielectrode arrays and patterning of arranged neuronal networks

In this manuscript, we first reveal a simple ultra violet laser lithographic method to design and produce plain tailored multielectrode arrays. Secondly, we use the same lithographic setup for surface patterning to enable controlled attachment of primary neuronal cells and help neurite guidance. For multielectrode array production, we used flat borosilicate glass directly structured with the laser lithography system. The multi layered electrode system consists of a layer of titanium coated with a layer of di-titanium nitride. Finally, these electrodes are covered with silicon nitride for insulation. The quality of the custom made multielectrode arrays was investigated by light microscopy, electron microscopy and X-ray diffraction. The performance was verified by the detection of action potentials of primary neurons. The electrical noise of the custom-made MEA was equal to commercially available multielectrode arrays. Additionally, we demonstrated that structured coating with poly lysine, obtained with the aid of the same lithographic system, could be used to attach and guide neurons to designed structures. The process of neuron attachment and neurite guidance was investigated by light microscopy and charged particle microscopy. Importantly, the utilization of the same lithographic system for MEA fabrication and poly lysine structuring will make it easy to align the architecture of the neuronal network to the arrangement of the MEA electrode.. In future studies, this will lead to multielectrode arrays, which are able to specifically attach neuronal cell bodies to their chemically defined electrodes and guide their neurites, gaining a controlled connectivity in the neuronal network. This type of multielectrode array would be able to precisely assign a signal to a certain neuron resulting in an efficient way for analyzing the maturation of the neuronal connectivity in small neuronal networks.

Microfabricated, Massive Electrochemical Arrays of Uniform Ultramicroelectrodes

We report the preparation and electrochemical characterization of massive electrochemical arrays containing as many as 110,000 highly uniform ultramicroelectrodes (UMEs). These arrays were microfabricated using conventional photolithography techniques on a gold-coated silicon chip in a simple three-step method. Photoresist polymer was used as an effective insulating matrix to define 2 μm, 3 μm, and 4 μm diameter circular UMEs across a 1 × 1 mm² area. The UME arrays are high uniform and contain tens of thousands of active disk-shape UMEs slightly recessed in thin films of photoresist. These arrays were tested with cyclic voltammetry and copper electrodeposition to assess the adhesion of photoresist to the gold surface as well as to examine their electrochemical activity. Numerical simulations were performed to further validate their electrochemical response. These UME arrays can be a useful platform for fundamental understanding molecular transport in uniform electrochemical arrays and designing highly-sensitive electroanalytical sensors.

Specific Neuron Placement on Gold and Silicon Nitride-Patterned Substrates through a Two-Step Functionalization Method

The control of neuron-substrate adhesion has been always a challenge for fabricating neuron-based cell chips and in particular for multielectrode array (MEA) devices, which warrants the investigation of the electrophysiological activity of neuronal networks. The recent introduction of high-density chips based on the complementary metal oxide semiconductor (CMOS) technology, integrating thousands of electrodes, improved the possibility to sense large networks and raised the challenge to develop newly adapted functionalization techniques to further increase neuron electrode localization to avoid the positioning of cells out of the recording area. Here, we present a simple and straightforward chemical functionalization method that leads to the precise and exclusive positioning of the neural cell bodies onto modified electrodes and inhibits, at the same time, cellular adhesion in the surrounding insulator areas. Different from other approaches, this technique does not require any adhesion molecule as well as complex patterning technique such as μ-contact printing. The functionalization was first optimized on gold (Au) and silicon nitride (Si3N4)-patterned surfaces. The procedure consisted of the introduction of a passivating layer of hydrophobic silane molecules (propyltriethoxysilane [PTES]) followed by a treatment of the Au surface using 11-amino-1-undecanethiol hydrochloride (AT). On model substrates, well-ordered neural networks and an optimal coupling between a single neuron and single micrometric functionalized Au surface were achieved. In addition, we presented the preliminary results of this functionalization method directly applied on a CMOS-MEA: the electrical spontaneous spiking and bursting activities of the network recorded for up to 4 weeks demonstrate an excellent and stable neural adhesion and functional behavior comparable with what expected using a standard adhesion factor, such as polylysine or laminin, thus demonstrating that this procedure can be considered a good starting point to develop alternatives to the traditional chip coatings to provide selective and specific neuron-substrate adhesion.

Surface Engineering of Triboelectric Nanogenerator with an Electrodeposited Gold Nanoflower Structure

A triboelectric nanogenerator composed of gold nanoflowers is demonstrated. The proposed triboelectric nanogenerator creates electricity by contact-separation-based electrification between an anodic metal and a cathodic polymer. For the improvement of output power via the enlargement of the effective surface area in the anodic metal, gold nanoflowers that produce a hierarchical morphology at a micro-to-nano scale by electrodeposition are utilized. The hierarchical morphology is controlled by the applied voltage and deposition time. Even though the triboelectric coefficient of gold is inferior to those of other metals, gold is very attractive to make a flower-like structure by electrodeposition. Moreover, gold is stable against oxidation by oxygen in air. From a reliability and practicality point of view, the aforementioned stability against oxidation is preferred.

Toward on-chip functional neuronal networks: computational study on the effect of synaptic connectivity on neural activity

This paper presents a new unified computational-experimental approach to study the role of the synaptic activity on the activity of neurons in the small neuronal networks (NNs). In a neuronal tissue/organ, this question is investigated with higher complexities by recording action potentials from population of neurons in order to find the relationship between connectivity and the recorded activities. In this approach, we study the dynamics of very small cortical neuronal networks, which can be experimentally synthesized on chip with constrained connectivity. Multi-compartmental Hodgkin-Huxley model is used in NEURON software to reproduce cells by extracting the experimental data from the synthesized NNs. We thereafter demonstrate how the type of synaptic activity affects the network response to specific spike train using the simulation results.

Tuning neuron adhesion and neurite guiding using functionalized AuNPs and backfill chemistry

Gold nanoparticles are used to investigate the dependence of neuron adhesion on the density of cell binding sites and particle backfill. Neurons viability and neurite development depend differently on cell attractive and cell repellant surface cues.

Fabricating complex culture substrates using robotic microcontact printing (R-µCP) and sequential nucleophilic substitution

In tissue engineering, it is desirable to exhibit spatial control of tissue morphology and cell fate in culture on the micron scale. Culture substrates presenting grafted poly(ethylene glycol) (PEG) brushes can be used to achieve this task by creating microscale, non-fouling and cell adhesion resistant regions as well as regions where cells participate in biospecific interactions with covalently tethered ligands. To engineer complex tissues using such substrates, it will be necessary to sequentially pattern multiple PEG brushes functionalized to confer differential bioactivities and aligned in microscale orientations that mimic in vivo niches. Microcontact printing (μCP) is a versatile technique to pattern such grafted PEG brushes, but manual μCP cannot be performed with microscale precision. Thus, we combined advanced robotics with soft-lithography techniques and emerging surface chemistry reactions to develop a robotic microcontact printing (R-μCP)-assisted method for fabricating culture substrates with complex, microscale, and highly ordered patterns of PEG brushes presenting orthogonal 'click' chemistries. Here, we describe in detail the workflow to manufacture such substrates.

Hippocampal networks on reliable patterned substrates

Toward the goal of reproducible live neuronal networks, we investigated the influence of substrate patterns on neuron compliance and network activity. We optimized process parameters of micro-contact printing for reproducible geometric patterns of 10 μm wide lines of polylysine with 4, 6, or 8 connections at a constant square array of nodes overlying the recording electrodes of a multielectrode array (MEA). We hypothesized that an increase in node connections would give the network more inputs resulting in higher neuronal outputs as network spike rates. We also chronically stimulated these networks during development and added astroglia to enhance network activity. Our results show that despite frequent localization of neuron somata over the electrodes, the number of spontaneously active electrodes was reduced 3-fold compared to random networks, independent of pattern complexity. Of the electrodes active, the overall spike rate was independent of pattern complexity, consistent with homeostasis of activity. Lower mean burst rates were seen with higher levels of pattern complexity; however, burst durations increased 1.6-fold with pattern complexity (n=6027 bursts, p<0.001). Inter-burst interval and percentage of active electrodes displaying bursts also increased with pattern complexity. The extra-burst (non-burst or isolated) spike rate increased 4-fold with pattern complexity, but this relationship was reversed with either chronic stimulation or astroglia addition. These studies suggest for the first time that patterns which limit the distribution of branches and inputs are deleterious to activity in a hippocampal network, but that higher levels of pattern complexity promote non-burst activity and favor longer lasting, but fewer bursts.

Extreme hardening of PDMS thin films due to high compressive strain and confined thickness

Polymers confined to small dimensions and that undergo high strains can show remarkable nonlinear mechanics, which must be understood to accurately predict the functioning of nanoscale polymer devices. In this paper we describe the determination of the mechanical properties of ultrathin polydimethylsiloxane (PDMS) films undergoing large strains, using atomic force microscope (AFM) indentation with a spherical tip. The PDMS was molded into extremely thin films of variable thickness and adhered to a hard substrate. We found that for films below 1 μm in thickness the Young's modulus increased with decreasing sample thickness with a power law exponent of 1.35. Furthermore, as the soft PDMS film was indented, significant strain hardening was observed as the indentation depth approached 45% of the sample thickness. To properly quantify the nonlinear mechanical measurements, we utilized a pointwise Hertzian model which assumes only piecewise linearity on the part of the probed material. This analysis revealed three regions within the material. A linear region with a constant Young's modulus was seen for compression up to 45% strain. At strains higher than 45%, a marked increase in Young's modulus was measured. The onset of strain induced stiffening is well modeled by finite element modeling and occurs as stress contours expanding from the probe and the substrate overlap. A third region of mechanical variation occurred at small indentations of less than 10 nm. The pointwise Young's modulus at small indentations was several orders of magnitude higher than that in the linear elasticity region; we studied and ruled out causes responsible for this phenomenon. In total, these effects can cause thin elastomer films to become extremely stiff such that the measured Young's modulus is over a 100-fold higher than the bulk PDMS. Therefore, the mechanics of a polymer can be changed by adjusting the geometry of a material, in addition to changing the material itself. In addition to understanding the mechanics of thin polymer films, this work provides an excellent test of experimental techniques to measure the mechanics of other nonlinear and heterogeneous materials such as biological cells.

Hydrogel-electrospun fiber mat composite coatings for neural prostheses

Achieving stable, long-term performance of implanted neural prosthetic devices has been challenging because of implantation related neuron loss and a foreign body response that results in encapsulating glial scar formation. To improve neuron–prosthesis integration and form chronic, stable interfaces, we investigated the potential of neurotrophin-eluting hydrogel–electrospun fiber mat (EFM) composite coatings. In particular, poly(ethylene glycol)-poly(ε-caprolactone) (PEGPCL) hydrogel–poly(ε-caprolactone) EFM composites were applied as coatings for multielectrode arrays. Coatings were stable and persisted on electrode surfaces for over 1 month under an agarose gel tissue phantom and over 9 months in a PBS immersion bath. To demonstrate drug release, a neurotrophin, nerve growth factor (NGF), was loaded in the PEGPCL hydrogel layer, and coating cytotoxicity and sustained NGF release were evaluated using a PC12 cell culture model. Quantitative MTT assays showed that these coatings had no significant toxicity toward PC12 cells, and neurite extension at day 7 and 14 confirmed sustained release of NGF at biologically significant concentrations for at least 2 weeks. Our results demonstrate that hydrogel–EFM composite materials can be applied to neural prostheses to improve neuron–electrode proximity and enhance long-term device performance and function.

In vivo impedance evaluation of Au/PI microelectrode with surface modulated by alkanethiolate self-assembled monolayers

The goal of this study was to verify that a fully implanted microelectrode with modulated surface may have a reduced rising rate of total impedance and a longer life time. In the previous work, alkanethiolate self-assembled monolayers (SAMs) surface as protein-resistant spacer or cell-repulsive dense-packed spacer has been verified from in vitro experiments. In this study, microelectrodes with the same surface modulation were implanted into the subcutaneous layers of Wistar rats. Nine rats were implanted with the microelectrodes and the total impedance data were measured every 24 h for 2 weeks after implantation. An equivalent electrical circuit model of the electrode-tissue interface was established and parameters were estimated by using an optimization algorithm. Four out of nine rats had manifested acute inflammation reaction and the rests revealed only slight tissue response. Histological examination for the inflammatory group showed fibroblasts, macrophages, and polymorphonuclear leukocytes in adjacent to the electrode contact surface. In the inflammatory group, no significantly difference in total impedance was found in both types of electrodes. However, the trend of total impedance of SAMs-treated electrodes could maintain a steady state value after 1 week. For the non-inflammatory group, both types of electrodes could reduce the impedance value within implanted days. The tissue resistance might be related to the thickness of cells adhered upon the electrode contacts.

Microcup arrays for the efficient isolation and cloning of cells

Arrays of transparent, releasable micrometer-scale structures termed "microcups" were created for the purpose of patterning and isolating viable cells from small cell samples. Cells were captured by the microcups without the need for barriers or walls on the intervening substrate. Furthermore, in contrast to prior methods for creating cell arrays with releasable elements, no chemical modification of the substrate was required. Individual microcups were released from the array using a pulsed laser at very low energy. Improvements in microcup design enabled cells in suspension to be loaded into the microcups with greater than 90% efficiency. Cells cultured within the microcups displayed 100% viability and were cultured over 4 days yielding colonies that remained sequestered within the microcups to generate pure clonal populations. Standard microscopic imaging was used to identify cells or colonies of interest, and the microcups containing these cells were then released and collected. Individual target cells isolated in this manner remained viable as demonstrated by clonal expansion of 100% of collected cells. Direct comparisons with cell isolation by fluorescence-activated cell sorting and magnetic-bead-based isolation systems demonstrated that the microcup cell isolation procedure yielded higher purity, yield, and viability than these standard technologies when separating samples with small numbers of cells. The power of this technique was demonstrated by the isolation of hematopoietic stem cells from a human bone marrow aspirate possessing only 4000 total cells.

Surface-modified microelectrode array with flake nanostructure for neural recording and stimulation

A novel microelectrode modification method is reported for neural electrode engineering with a flake nanostructure (nanoflake). The nanoflake-modified electrodes are fabricated by combining conventional lithography and electrochemical deposition to implement a microelectrode array (MEA) on a glass substrate. The unique geometrical properties of nanoflake sharp tips and valleys are studied by optical, electrochemical and electrical methods in order to verify the advantages of using nanoflakes for neural recording devices. The in vitro recording and stimulation of cultured hippocampal neurons are demonstrated on the nanoflake-modified MEA and the clear action potentials are observed due to the nanoflake impedance reduction effect.

Response characteristics of single-cell impedance sensors employed with surface-modified microelectrodes

The underlying sensing mechanism of single-cell-based integrated microelectrode array (IMA) biosensors was investigated via experimental and modeling studies. IMA chips were microfabricated and single-cell-level manipulation was achieved through surface chemistry modification of IMA chips. Individual fibroblast cells (NIH3T3) were immobilized on either lysine-arginine-glycine-aspartic acid (KRGD) short peptide-modified or fibronectin extracellular-cell-adhesion-molecule-modified microelectrodes to record the impedance variations of cell-electrode heterostructure over a frequency range of 1-10 kHz. By fitting experimental data to an application-specific single-cell-level equivalent circuit model, important sensing parameters, including specific cell membrane capacity, cell membrane resistivity, and averaged cell-to-substrate separation, were determined. It was demonstrated that biofunctionalization of planar microelectrode surface by covalently linking short peptides or fibronectin molecules could achieve strong or tight cell adhesion (with an estimated averaged cell-to-substrate separation distance of 11-16 nm), which, in turn, improves the transduced electrical signal from IMA chips. Analyses on frequency-dependent characteristics of single-cell-covered microelectrode impedance and of IMA sensor circuitry response have revealed an addressable frequency band wherein electrical properties of single cells can be distinctively determined and monitored for cellular biosensing applications. The presented work addresses some major limitations in single-cell-based biosensing schemes, i.e., the manipulation of a single cell, the transduction of weak biological signals, and the implementation of a proper model for data analysis, and demonstrates the potential of IMA devices as single-cell biosensors.

Triangular neuronal networks on microelectrode arrays: an approach to improve the properties of low-density networks for extracellular recording

Multi-unit recording from neuronal networks cultured on microelectrode arrays (MEAs) is a widely used approach to achieve basic understanding of network properties, as well as the realization of cell-based biosensors. However, network formation is random under primary culture conditions, and the cellular arrangement often performs an insufficient fit to the electrode positions. This results in the successful recording of only a small fraction of cells. One possible approach to overcome this limitation is to raise the number of cells on the MEA, thereby accepting an increased complexity of the network. In this study, we followed an alternative strategy to increase the portion of neurons located at the electrodes by designing a network in confined geometries. Guided settlement and outgrowth of neurons is accomplished by taking control over the adhesive properties of the MEA surface. Using microcontact printing a triangular two-dimensional pattern of the adhesion promoter poly-D-lysine was applied to the MEA offering a meshwork that at the same time provides adhesion points for cell bodies matching the electrode positions and gives frequent branching points for dendrites and axons. Low density neocortical networks cultivated under this condition displayed similar properties to random networks with respect to the cellular morphology but had a threefold higher electrode coverage. Electrical activity was dominated by periodic burst firing that could pharmacologically be modulated. Geometry of the network and electrical properties of the patterned cultures were reproducible and displayed long-term stability making the combination of surface structuring and multi-site recording a promising tool for biosensor applications.

Action potential recording from dielectrophoretically positioned neurons inside micro-wells of a planar microelectrode array

To organise in vitro neural networks at the cellular level and study their electrical patterns, we have fabricated 4 x 4 planar microelectrode arrays using conventional photolithography. The electrode sites of these arrays are located inside micro-wells, for confining the neurons, which are connected with neighbouring wells via micro-trenches capable of guiding the outgrowth of neurites. In order to load a single neuron inside each micro-well, a simple system has been developed that utilises the phenomenon of dielectrophoresis. It operates by moving neurons towards each electrode site of an array using a dielectrophoretic force, checking for the presence of a neuron inside each micro-well using image processing, and stopping the dielectrophoretic force when detecting a neuron inside a micro-well in order to prevent more cells from being trapped. This system provides a fast, effective and inexpensive way to assemble neural grids consisting of contacts between electrodes and single neurons, as the use of micromanipulator guided micropipettes can be avoided. Spontaneous and evoked action potentials from trapped neurons were successfully recorded using a 16-channel acquisition/stimulation unit.

Comment on "Detection, stimulation, and inhibition of neuronal signals with high-density nanowire transistor arrays"

Patolsky et al. (Reports, 25 August 2006, p. 1100) used silicon nanowires to record action potentials in rat neuronal axons and found increases in conductance of about 85 nanosiemens. We point out that the data correspond to voltage changes of about -85 millivolts on the nanowire and that conceivable mechanisms of axon-nanowire interaction lead to signals that are opposite in sign or smaller by orders of magnitude.

Moving live dissociated neurons with an optical tweezer

The use of an optical tweezer for moving dissociated neurons was studied. The main features of the tweezers are outlined as well as the general principles of its operation. Infrared beams at 980 and 1064 nm were used, focused so as to make a trap for holding neurons and moving them. Absorption by cells at those wavelengths is very small. Experiments were done to evaluate nonsticky substrate coatings, from which neurons could be easily lifted with the tweezers. The maximum speed of cell movement as a function of laser power was determined. Detailed studies of the damage to cells as a function of beam intensity and time of exposure were made. The 980 nm beam was much less destructive, for reasons that are not understood, and could be used to safely move cells through distances of millimeters in times of seconds. An illustrative application of the use of the tweezers to load neurons without damage into plastic cages on a glass substrate was presented. The conclusion is that optical tweezers are an accessible and practical tool for helping to establish neuron cultures of cells placed in specific locations.

Topography and biocompatibility of patterned hydrophobic/hydrophilic zein layers

The topography and biocompatibility of zein layers adsorbed on patterned templates containing hydrophilic and hydrophobic regions were investigated. Nanopatterned templates consisting of hydrophilic lines on a hydrophobic background were drawn by dip-pen nanolithography (DPN) on gold-coated surfaces. 16-Mercaptohexadecanoic acid (COOH(CH(2))(15)SH, MHA) was used as primary ink to generate hydrophilic lines. Unpatterned surfaces were backfilled with 18-octadecanethiol (CH(3)(CH(2))(17)SH, ODT), which generated hydrophobic regions. Zein was allowed to adsorb on patterned surfaces from alcohol-water solutions. The topography of zein deposits was observed by atomic force microscopy (AFM). Height profiles from AFM measurements revealed that zein deposits followed closely the nanopatterned templates. The biocompatibility of zein layers assembled over hydrophilic/hydrophobic micropatterned templates was investigated. Templates containing MHA lines and ODT regions were generated by micro-contact printing (microCP). Mouse fibroblasts seeded on patterned zein layers proliferated on zein deposited over MHA lines, but not on zein over ODT. The experiment indicated that fibroblast cells were able to respond to variations in the underlying surface chemistry, transmitted by the different orientation adopted by zein on the different substrates. This property may be useful in controlling the spatial distribution of cells on patterned protein layers.

Characterization of surface modification on microelectrode arrays for in vitro cell culture

This study aims to investigate surface-modified microelectrodes on the microelectrode arrays (MEAs) for neuronal interfaces with in vitro cell culture. The polyimide (PI) MEA was fabricated by using micro-electro-mechanical systems (MEMS) techniques. Self-assembled monolayers (SAMs) of 11-mercaptoundecanoic acid (MUA) were utilized to modify the microelectrode surface of the MEA. The SAMs' modified surface of microelectrodes offered a reliable interface to immobilize biological ligands through covalent bonding. To increase biocompatibility, the poly-D-lysine (PDL) was immobilized on the SAMs' modified microelectrodes. Several analytical techniques were used to define the physical structure and functional groups of surface-modified gold microelectrodes on the MEA. Spectra of the Fourier transform infrared reflection (FTIR) were applied to characterize the molecular structure of MUA-SAMs and PDL on the microelectrodes. The spectra, two peaks of amide I (at 1,613 cm(-1)) and amide II (at 1,548 cm(-1)), revealed that covalent amide bonding existed in PDL-MUA-SAMs modified surfaces. The thickness and formation of the MUA and PDL were also observed and quantified by using an atomic force microscope (AFM). The impedance measurement of PDL-MUA-SAMs modified MEA only increased slightly to an average of 524.6 +/- 55.8 kOmega from 352.9 +/- 34.4 kOmega of bare gold microelectrode (p < 0.05, N = 20). In addition, the time-course changes of total impedance resulting from cell sealing resistance and gap reactance were recorded for 7 days for inferring the growth of cell lines on the electrode contact of modified MEA. The experiment of 3T3 fibroblasts, PC12 cells, primary glial cells, and primary cortical neurons cultured on the modified MEAs displayed a good adhesion rate. These biocompatibility assays demonstrated that the neuronal cells are able to grow in a proximity to PDL-MUA-SAMs modified microelectrodes of the MEAs for effective electrophysiological stimulation/sensing schemes and for future implantation purposes.

Automatic positioning and sensing microelectrode array (APSMEA) for multi-site electrophysiological recordings

Technological improvement of measurements for the electrical recordings from individual neurons within network is essential in neuroscience today. Here, we present a novel automatic positioning and sensing microelectrode array (APSMEA), which simultaneously positioned desired number of neurons onto 48 recording microelectrodes automatically and scathelessly by use of negative dielectrophoretic (DEP) forces, and facilitated the measurement of the electrophysiological activities of neuronal populations after functional synaptic connections formed between neurons. The results of multi-site electrophysiological recordings during drug administration also demonstrated the application of APSMEA in bioassay with cultured rat cortical neurons. Therefore, this device should benefit the investigation of neuronal networks in vitro with more comprehensive electrophysiological experiments, and also promise the possibility of a modular device for both cell manipulation and cell-based biosensor on microchip.

Development of astroglial cells in patterned neuronal cultures

The purpose of this work was to study the development of astroglial cells in patterned neuronal cultures. Hippocampal neurons, derived from embryonic stage (E18) rats and cultured in serum-free Neurobasal/B27 medium, grew to follow patterns of poly(D-lysine) created by micro-contact printing. The growth of the astroglial cells and the co-localization of neurons and astroglial cells were measured for up to one month using fluorescence immunostaining of neurons and astroglial cells. Neurons grew to form square patterns within 2 weeks, while astroglia only started to emerge in the same period. Astroglial cells continued to proliferate for a month following a general growth curve. Over 90% of the astroglial cell area co-localized with neurons (within 2 mum) at an early stage of astroglial development (13 DIV). Over the remaining period, astroglial cells proliferated and the co-localization was 80%. Hence, in these culture conditions astroglial cells develop 2-3 weeks later than neurons but remain highly co-localized with neurons.

Multichannel recording and stimulation of neuronal cultures grown on microstamped poly-D-lysine

We report progress toward designable, reproducible, patterned in vitro neuronal cultures. Cell adhesive proteins were directly microcontact printed on microelectrode arrays (MEAs) used as substrates for hippocampal neurons grown in a defined culture medium. The patterned neuronal network circuits were maintained up to one month. The recorded activity was comparable to that of cultures grown on unpatterned uniform surfaces. Time-locked evoked responses were recorded across the networks.

Alkyl-thiol Langmuir films on the surface of liquid mercury

The coverage dependent phase behavior of monolayers of alkyl thiols (CH3(CH2)(n-1)SH, denoted as CnSH) on mercury was studied for chain lengths 9 <or= n <or= 22, using surface tensiometry and surface-specific X-ray scattering methods. At low coverage, a disordered single layer of surface-parallel molecules is found for all n. At high coverage, a monolayer of standing-up molecules is formed, exhibiting well-ordered phases, the structure of which is n- and coverage-dependent. The molecular chains pack in a centered rectangular unit cell, with an approximately 27 degrees tilt from the surface normal toward nearest neighbors. The strong sulfur-mercury bond induces a noncentered unit cell for the headgroups, incorporating one mercury atom per two thiol molecules. The small but significant differences in structure of these films on gold and on mercury are discussed and assigned to the different structure of the subphase: long-range-ordered crystal for gold and short-range-ordered liquid for mercury.

Patterning to influence in vitro neuronal interfaces

Microlithographic techniques applied to control surface chemistry can be used to guide neurons to surface electrodes in in vitro culture. Here we report on the effectiveness of these techniques as measured by the likelihood of recording electrical signals and detecting propagation of network activity.

Detection of tetanus-induced effects in linearly lined-up micropatterned neuronal networks: Application of a multi-electrode array chip combined with agarose microstructures

One of the best approaches to understanding the mechanism of information acquisition and storage is to characterize the plasticity of network activity by monitoring and stimulating individual neurons in a topologically defined network and doing this for extended periods of time. We therefore previously developed an on-chip multi-electrode array (MEA) system combined with an array of agarose microchambers (AMCs). It is possible to record the firing at multiple cells simultaneously for long term and topographically control the cells position and their connections. In our present study, we demonstrated the effect of tetanic stimulation in a linearly lined-up patterned network on the AMC/MEA chip. We detected reproducible activity changes that were induced by tetanic stimulation and saw that these changes were maintained for 6-24 h. The results show the advantage of our AMC/MEA cultivation and measurements methods and suggest they will be useful for investigating the long-term plasticity depending on network topology and size.

Applications of microfluidics for neuronal studies

Microfabrication processes have changed the technology used in consumer goods, and have now advanced into applications in biology. Microfluidic platforms are microfabricated tools that are gaining popularity for studies of molecular and cellular biology. These platforms can allow precise control of the environment surrounding individual cells and they have been used to study physiologic and pharmacologic responses at the single-cell level. This article reviews microfluidic technology with emphasis on advances that could apply to the study of the nervous system, including architecture for isolation of axons, integrated electrophysiology, patterned physical and chemical substrate cues, and devices for the precisely controlled delivery of possible therapeutic agents such as trophic factors and drugs. The potential of these chips for the study of neurological diseases is also discussed.

Neurotrophin-eluting hydrogel coatings for neural stimulating electrodes

Improved sensory and motor prostheses for the central nervous system will require large numbers of electrodes with low electrical thresholds for neural excitation. With the eventual goal of reducing stimulation thresholds, we have investigated the use of biodegradable, neurotrophin-eluting hydrogels (i.e., poly(ethylene glycol)-poly(lactic acid), PEGPLA) as a means of attracting neurites to the surface of stimulating electrodes. PEGPLA hydrogels with release rates ranging from 1.5 to 3 weeks were synthesized. These hydrogels were applied to multielectrode arrays with sputtered iridium oxide charge-injection sites. The coatings had little impact on the iridium oxide electrochemical properties, including charge storage capacity, impedance, and voltage transients during current pulsing. Additionally, we quantitatively examined the ability of neurotrophin-eluting, PEGPLA hydrogels to promote neurite extension in vitro using a PC12 cell culture model. Hydrogels released neurotrophin (nerve growth factor, NGF) for at least 1 week, with neurite extension near that of an NGF positive control and much higher than extension seen from sham, bovine serum albumin-releasing boluses, and a negative control. These results show that neurotrophin-eluting hydrogels can be applied to multielectrode arrays, and suggest a method to improve neuron-electrode proximity, which could result in lowered electrical stimulation thresholds. Reduced thresholds support the creation of smaller electrode structures and high density electrode prostheses, greatly enhancing prosthesis control and function.

Epoxy-silane linking of biomolecules is simple and effective for patterning neuronal cultures

Surface chemistry is one of the main factors that contributes to the longevity and compliance of cell patterning. Two to three weeks are required for dissociated, embryonic rat neuronal cultures to mature to the point that they regularly produce spontaneous and evoked responses. Though proper surface chemistry can be achieved through the use of covalent protein attachment, often it is not maintainable for the time periods necessary to study neuronal growth. Here we report a new and effective covalent linking approach using (3-glycidoxypropyl) trimethoxysilane (3-GPS) for creating long term neuronal patterns. Micrometer scale patterns of cell adhesive proteins were formed using microstamping; hippocampal neurons, cultured up to 1 month, followed those patterns. Cells did not grow on unmodified 3-GPS surfaces, producing non-permissive regions for the long-term cell patterning. Patterned neuronal networks were formed on two different types of MEA (polyimide or silicon nitride insulation) and maintained for 3 weeks. Even though the 3-GPS layer increased the impedance of metal electrodes by a factor of 2-3, final impedance levels were low enough that low noise extracellular recordings were achievable. Spontaneous neural activity was recorded as early as 10 days in vitro. Neural recording and stimulation were readily achieved from these networks. Our results showed that 3-GPS could be used on surfaces to immobilize biomolecules for a variety of neural engineering applications.

Metabolic expression of thiol-derivatized sialic acids on the cell surface and their quantitative estimation by flow cytometry

The N-acetyl-D-mannosamine (ManNAc) analog Ac5ManNTGc, a non-natural metabolic precursor for the sialic acid biosynthetic pathway, can be used to display thiols on the cell surface. Sugar-expressed cell-surface thiols are readily accessible compared to their protein counterparts, making them ideal for exploitation in cell-adhesion and tissue-engineering applications. This report describes a protocol for the incubation of Jurkat (human acute T-cell leukemia) cells with Ac5ManNTGc and the quantitative estimation of the resulting sialic acid displayed thiols by flow cytometry after a reaction with a water-soluble biotin-conjugated maleimide reagent and fluorescein isothiocyanate-conjugated (FITC) avidin staining. These methods, with minimal optimization, are generally also applicable to other human cell lines. The labeling and flow cytometry steps of this protocol can be performed in five to eight hours.

Combined topographical and chemical micropatterns for templating neuronal networks

In vitro neuronal networks with geometrically defined features are desirable for studying long-term electrical activity within the neuron assembly and for interfacing with external microelectronic circuits. In standard cultures, the random spatial distribution and overlap of neurites makes this aim difficult; hence, many recent efforts have been made on creating patterned cellular circuits. Here, we present a novel method for creating a planar neural network that is compatible with optical devices. This method combines both topographical and chemical micropatterns onto which neurons can be cultured. Compared to other reported patterning techniques, our approach and choice of template appears to show both geometrical control over the formation of specific neurite connections at low plating density and compatibility with microelectronic circuits that stimulate and record neural activity.

Culturing neuron cells on electrode with self-assembly monolayer

The success of neuronal implantable microsystems relies on the quality of the interface with neuronal cells. Depending on the application, specifically engineered surfaces may either prevent or enhance cell/tissue growth with an appropriate host response. The surface chemistry and topography have major effects on the cell adherence and the interaction between the tissue and devices. We report on a simple technique to precisely explant cortical neurons in a serum-free medium on 2D electrode arrays and investigated the pad size effect on neuron cell culture and immobilization. We produced gold patterns on glass substrates using microfabrication processes. 11-Amino-1-undecanethiol self-assembled monolayer was coated only on the gold surface. Cortical neurons were cultured on the arrays to examine the dependence of neuron growth and cells distribution on pad size. We found that the terminal functional groups of the highly oriented 11-amino-1-undecanethiol thin film are essential for generating cell-adhesive areas for the rat cortical neurons. A 50 microm x 50 microm SAM pad size was found to be suitable for single cortical neuron immobilization, while the larger pads provide excellent neuron coverage. This technology may enable precise and localized neuron stimulation and surveillance for both biological research and medical applications.

Functional screening of traditional antidepressants with primary cortical neuronal networks grown on multielectrode neurochips

We optimized the novel technique of multielectrode neurochip recordings for the rapid and efficient screening of neuroactivity. Changes in the spontaneous activity of cultured networks of primary cortical neurons were quantified to evaluate the action of drugs on the firing dynamics of complex network activity. The multiparametric assessment of electrical activity changes caused by psychoactive herbal extracts from Hypericum, Passiflora and Valeriana, and various combinations thereof revealed a receptor-specific and concentration-dependent inhibition of the firing patterns. The spike and burst rates showed significant substance-dependent effects and significant differences in potency. The effects of specific receptor blockades on the inhibitory responses provided evidence that the herbal extracts act on gamma-amino butyric acid (GABA) and serotonin (5-HT) receptors, which are recognized targets of pharmacological antidepressant treatment. A biphasic effect, serotonergic stimulation of activity at low concentrations that is overridden by GABAergic inhibition at higher concentrations, is apparent with Hypericum alone and the triple combination of the extracts. The more potent neuroactivity of the triple combination compared to Hypericum alone and the additive effect of Passiflora and Valeriana suggest a synergy between constituent herbal extracts. The extracts and their combinations affected the set of derived activity parameters in a concomitant manner suggesting that all three constituent extracts and their combinations have largely similar modes of action. This study also demonstrates the sensitivity, selectivity and robustness of neurochip recordings for high content screening of complex mixtures of neuroactive substances and for providing multiparametric information on neuronal activity changes to assess the therapeutic potential of psychoactive substances.

Application of a PDMS microstencil as a replaceable insulator toward a single-use planar microelectrode array

Here we present a novel idea for a replaceable insulator, and thus advance toward the goal of a single-use planar microelectrode array (MEA) for the study of electrogenic tissues. The concept of a replaceable insulator is motivated by insulator degradation after repeated usage of an MEA. Instead of fabricating a more durable insulator for repeated MEA usage, we propose replacing the insulator and effectively producing a fresh MEA for each experiment. We chose a polydimethylsiloxane (PDMS) microstencil as a candidate for the replaceable insulator as it is biocompatible, shows reversible adhesion to surfaces, and can be easily and controllably fabricated. As a proof-of-concept, we demonstrate two applications using microstencils: the rejuvenation of an old MEA and the fabrication of a single-use MEA. These MEAs were tested with dissociated neural cell cultures and neural recordings were performed at 14 days in vitro. Inexpensive and quick supply of insulators with micrometer-sized holes provides a way of constructing an MEA that can be treated as a disposable component in high throughput cell-based biosensor applications.