Neuronal differentiation and synapse formation of PC12 and embryonic stem cells on interdigitated microelectrode arrays:

Decreasing the physical gap in the neural-electrode interface and related concepts to improve cochlear implant performance

Cochlear implants (CI) represent incredible devices that restore hearing perception for those with moderate to profound sensorineural hearing loss. However, the ability of a CI to restore complex auditory function is limited by the number of perceptually independent spectral channels provided. A major contributor to this limitation is the physical gap between the CI electrodes and the target spiral ganglion neurons (SGNs). In order for CI electrodes to stimulate SGNs more precisely, and thus better approximate natural hearing, new methodologies need to be developed to decrease this gap, (i.e., transitioning CIs from a far-field to near-field device). In this review, strategies aimed at improving the neural-electrode interface are discussed in terms of the magnitude of impact they could have and the work needed to implement them. Ongoing research suggests current clinical efforts to limit the CI-related immune response holds great potential for improving device performance. This could eradicate the dense, fibrous capsule surrounding the electrode and enhance preservation of natural cochlear architecture, including SGNs. In the long term, however, optimized future devices will likely need to induce and guide the outgrowth of the peripheral process of SGNs to be in closer proximity to the CI electrode in order to better approximate natural hearing. This research is in its infancy; it remains to be seen which strategies (surface patterning, small molecule release, hydrogel coating, etc.) will be enable this approach. Additionally, these efforts aimed at optimizing CI function will likely translate to other neural prostheses, which face similar issues.

A tissue-engineered neural interface with photothermal functionality

Neural interfaces are well-established as a tool to understand the behaviour of the nervous system via recording and stimulation of living neurons, as well as serving as neural prostheses. Conventional neural interfaces based on metals and carbon-based materials are generally optimised for high conductivity; however, a mechanical mismatch between the interface and the neural environment can significantly reduce long-term neuromodulation efficacy by causing an inflammatory response. This paper presents a soft composite material made of gelatin methacryloyl (GelMA) containing graphene oxide (GO) conjugated with gold nanorods (AuNRs). The soft hydrogel presents stiffness within the neural environment range of modulus below 5 kPa, while the AuNRs, when exposed to light in the near infrared range, provide a photothermal response that can be used to improve the spatial and temporal precision of neuromodulation. These favourable properties can be maintained at safer optical power levels when combined with electrical stimulation. In this paper we provide mechanical and biological characterization of the optical activity of the GO-AuNR composite hydrogel. The optical functionality of the material has been evaluated via photothermal stimulation of explanted rat retinal tissue. The outcomes achieved with this study encourage further investigation into optical and electrical costimulation parameters for a range of biomedical applications.

A Review on Microfluidics-Based Impedance Biosensors

Electrical impedance biosensors are powerful and continuously being developed for various biological sensing applications. In this line, the sensitivity of impedance biosensors embedded with microfluidic technologies, such as sheath flow focusing, dielectrophoretic focusing, and interdigitated electrode arrays, can still be greatly improved. In particular, reagent consumption reduction and analysis time-shortening features can highly increase the analytical capabilities of such biosensors. Moreover, the reliability and efficiency of analyses are benefited by microfluidics-enabled automation. Through the use of mature microfluidic technology, complicated biological processes can be shrunk and integrated into a single microfluidic system (e.g., lab-on-a-chip or micro-total analysis systems). By incorporating electrical impedance biosensors, hand-held and bench-top microfluidic systems can be easily developed and operated by personnel without professional training. Furthermore, the impedance spectrum provides broad information regarding cell size, membrane capacitance, cytoplasmic conductivity, and cytoplasmic permittivity without the need for fluorescent labeling, magnetic modifications, or other cellular treatments. In this review article, a comprehensive summary of microfluidics-based impedance biosensors is presented. The structure of this article is based on the different substrate material categorizations. Moreover, the development trend of microfluidics-based impedance biosensors is discussed, along with difficulties and challenges that may be encountered in the future.

PC-12 Cell Line as a Neuronal Cell Model for Biosensing Applications

PC-12 cells have been widely used as a neuronal line study model in many biosensing devices, mainly due to the neurogenic characteristics acquired after differentiation, such as high level of secreted neurotransmitter, neuron morphology characterized by neurite outgrowth, and expression of ion and neurotransmitter receptors. For understanding the pathophysiology processes involved in brain disorders, PC-12 cell line is extensively assessed in neuroscience research, including studies on neurotoxicity, neuroprotection, or neurosecretion. Various analytical technologies have been developed to investigate physicochemical processes and the biosensors based on optical and electrochemical techniques, among others, have been at the forefront of this development. This article summarizes the application of different biosensors in PC-12 cell cultures and presents the modern approaches employed in neuronal networks biosensing.

Microfluidic platforms for single neuron analysis

Single-neuron actions are the basis of brain function, as clinical sequelae, neuronal dysfunction or failure for most of the central nervous system (CNS) diseases and injuries can be identified via tracing single-neurons. The bulk analysis methods tend to miscue critical information by assessing the population-averaged outcomes. However, its primary requisite in neuroscience to analyze single-neurons and to understand dynamic interplay of neurons and their environment. Microfluidic systems enable precise control over nano-to femto-liter volumes via adjusting device geometry, surface characteristics, and flow-dynamics, thus facilitating a well-defined micro-environment with spatio-temporal control for single-neuron analysis. The microfluidic platform not only offers a comprehensive landscape to study brain cell diversity at the level of transcriptome, genome, and/or epigenome of individual cells but also has a substantial role in deciphering complex dynamics of brain development and brain-related disorders. In this review, we highlight recent advances of microfluidic devices for single-neuron analysis, i.e., single-neuron trapping, single-neuron dynamics, single-neuron proteomics, single-neuron transcriptomics, drug delivery at the single-neuron level, single axon guidance, and single-neuron differentiation. Moreover, we also emphasize limitations and future challenges of single-neuron analysis by focusing on key performances of throughput and multiparametric activity analysis on microfluidic platforms.

Electrical Stimulation and Cellular Behaviors in Electric Field in Biomedical Research

Research on the cellular response to electrical stimulation (ES) and its mechanisms focusing on potential clinic applications has been quietly intensified recently. However, the unconventional nature of this methodology has fertilized a great variety of techniques that make the interpretation and comparison of experimental outcomes complicated. This work reviews more than a hundred publications identified mostly from Medline, categorizes the techniques, and comments on their merits and weaknesses. Electrode-based ES, conductive substrate-mediated ES, and noninvasive stimulation are the three principal categories used in biomedical research and clinic. ES has been found to enhance cell proliferation, growth, migration, and stem cell differentiation, showing an important potential in manipulating cellular activities in both normal and pathological conditions. However, inappropriate parameters or setup can have negative effects. The complexity of the delivered electric signals depends on how they are generated and in what form. It is also difficult to equate one set of parameters with another. Mechanistic studies are rare and badly needed. Even so, ES in combination with advanced materials and nanotechnology is developing a strong footing in biomedical research and regenerative medicine.

On the intersection of molecular bioelectronics and biosensors: 20 Years of C3B

Formed in 2000 at Virginia Commonwealth University, the Center for Bioelectronics, Biosensors and Biochips (C3B®) has subsequently been located at Clemson University and at Texas A&M University. Established as an industry-university collaborative center of excellence, the C3B has contributed new knowledge and technology in the areas of i) molecular bioelectronics, ii) responsive polymers, iii) multiplexed biosensor systems, and iv) bioelectronic biosensors. Noteworthy contributions in these areas include i) being the first to report direct electron transfer of oxidoreductase enzymes enabled by single walled carbon nanotubes and colloidal clays, ii) the molecular level integration of inherently conductive polymers with bioactive hydrogels using bi-functional monomers such as poly(pyrrole-co-3-pyrrolylbutyrate-conj-aminoethylmethacrylate) [PyBA-conj-AEMA] and 3-(1-ethyl methacryloylate)aniline to yield hetero-ladder electroconductive hydrogels, iii) the development of a multi-analyte physiological status monitoring biochip, and iv) the development of a bioanalytical Wien-bridge oscillator for the fused measurement to lactate and glucose. The present review takes a critical look of these contributions over the past 20 years and offers some perspective on the future of bioelectronics-based biosensors and systems. Particular attention is given to multiplexed biosensor systems and data fusion for rapid decision making.

Morphometric and computational assessments to evaluate neuron survival and maturation within compartmentalized microfluidic devices: The influence of design variation on diffusion-driven nutrient transport

Burgeoning use of segregated microfluidic platforms that parse somas and neurites into discrete compartments is fueling unique examinations of neuronal structure and physiology in a manner impossible to achieve with non-compartmentalized systems. However, even though this line of axon-soma polarizing microfluidic devices stems from the same general design of a Campenot chamber set-up, slight deviations in device geometry appear to induce vastly different nutrient transport profiles that influence neuron survival and maturation. Here we examine the uptake of nerve growth factor (NGF) by a pheochromocytoma PC12 cell line cultured using two Campenot-like device designs, a "Standard" layout, representative of a commercial device, and a custom "Notch" layout, predicted to encourage more efficient nutrient transfer that gives rise to sustained neuron viability and extensive neurite elaboration. Exploiting in vitro culture schemes coupled with computational analyses, we identify the influence of device design geometry on the interplay between neuronal survival and maturation, gauged from morphometric assessments and the spatiotemporal distribution of NGF. Computer simulations of NGF transport within the devices revealed that the microfluidic neuron culture system is highly sensitive to change, where nutrient transport is intricately linked to device geometry and cell plating density, and premature depletion of nutrients is observed if specific design criteria are not met. This study underscores the importance of validating specific device geometries for a particular neuro-based assessment, while showcasing computational modeling as a powerful tool to achieve this goal.

Microfabricated and 3-D Printed Soft Bioelectronic Constructs from PAn-PAAMPSA-Containing Hydrogels

The formation of hybrid bioactive and inherently conductive constructs of composites formed from polyaniline-polyacrylamidomethylpropane sulfonic acid (PAn-PAAMPSA) nanomaterials (0.00–10.0 wt%) within poly(2-hydroxy ethyl methacrylate-co-N-{Tris(hydroxymethyl)methyl} acrylamide)-co-polyethyleneglycol methacrylate) p(HEMA-co-HMMA-co-PEGMA) hydrogels was made possible using microlithographic fabrication and 3-D printing. Hybrid constructs formed by combining a non-conductive base (0.00 wt% PAn-PAAMPSA) and electroconductive (ECH) (varying wt% PAn-PAAMPSA) hydrogels using these two production techniques were directly compared. Hydrogels were electrically characterized using two-point probe resistivity and electrochemical impedance spectroscopy. Results show that incorporation of >0.10 wt% PAn-PAAMPSA within the base hydrogel matrices was enough to achieve percolation and high conductivity with a membrane resistance (R_M) of 2140 Ω and 87.9 Ω for base (0.00 wt%) and ECH (10.0 wt%), respectively. UV-vis spectroscopy of electroconductive hydrogels indicated a bandgap of 2.8 eV that was measurable at concentrations of >0.10 wt% PAn-PAAMPSA. Both base and electroconductive hydrogels supported the attachment and growth of NIH/3T3 fibroblast cells. When the base hydrogel was rendered bioactive by the inclusion of collagen (>200 µg/mL), it also supported the attachment, but not the differentiation, of PC-12 neural progenitor cells.

Controlling Differentiation of Stem Cells for Developing Personalized Organ-on-Chip Platforms

Organ-on-chip (OOC) platforms have attracted attentions of pharmaceutical companies as powerful tools for screening of existing drugs and development of new drug candidates. OOCs have primarily used human cell lines or primary cells to develop biomimetic tissue models. However, the ability of human stem cells in unlimited self-renewal and differentiation into multiple lineages has made them attractive for OOCs. The microfluidic technology has enabled precise control of stem cell differentiation using soluble factors, biophysical cues, and electromagnetic signals. This study discusses different tissue- and organ-on-chip platforms (i.e., skin, brain, blood-brain barrier, bone marrow, heart, liver, lung, tumor, and vascular), with an emphasis on the critical role of stem cells in the synthesis of complex tissues. This study further recaps the design, fabrication, high-throughput performance, and improved functionality of stem-cell-based OOCs, technical challenges, obstacles against implementing their potential applications, and future perspectives related to different experimental platforms.

External factors influencing mesenchymal stem cell fate in vitro

Mesenchymal stem cells (MSCs) have extensive potentials, which make them attractive candidates for the developmental biology, drug discovery and regenerative medicine. However, the use of MSCs is limited by their scarceness in tissues and in culture conditions. They also exhibit various degrees of potency which subsequently influencing their applications. Nowadays, questions remain about how self-renewal and differentiation of MSCs can be controlled in vitro and in vivo, how they will behave and migrate to the right place and how they modulate the immune system. Therefore, identification of factors and culture conditions to affect the fate and function of MSCs may be effective to enhance their applications in clinical situations. Studies have indicated that the fate of MSCs in culture is influenced by various external factors, including the specific cell source, donor age, plating density, passage number and plastic surface quality. Some other factors such as cell culture media and their supplementary factors, O₂ concentration, mechano-/electro-stimuli and three-dimensional scaffolds are also shown to be influential. This review addresses the current state of MSC research for describing and discussing the findings about external factors that influence the fate and function of MSCs. Additionally, the new discoveries and suggestions regarding their molecular mechanisms will be explained.

Continuous-flow sorting of stem cells and differentiation products based on dielectrophoresis

This paper presents a continuous-flow microfluidic device for sorting stem cells and their differentiation progenies. The principle of the device is based on the accumulation of multiple dielectrophoresis (DEP) forces to deflect cells laterally in conjunction with the alternating on/off electric field to manipulate the cell trajectories. The microfluidic device containing a large array of oblique interdigitated electrodes was fabricated using a combination of standard and soft lithography techniques to generate a PDMS-gold electrode construct. Experimental testing with human mesenchymal stem cells (hMSC) and their differentiation progenies (osteoblasts) was carried out at different flow rates, and clear separation of the two populations was achieved. Most of the osteoblasts experiencing stronger DEP forces were deflected laterally and continuously, following zig-zag trajectories, and moved towards the desired collection outlet, whereas most of the hMSCs remained on the original trajectory due to weaker DEP forces. The experimental measurements were characterized and evaluated quantitatively, and consistent performance was demonstrated. Collection efficiency up to 92% and 67% for hMSCs and osteoblasts, respectively, along with purity up to 84% and 87% was obtained. The experimental results established the feasibility of our microfluidic DEP sorting device for continuous, label-free sorting of stem cells and their differentiation progenies.

Successful differentiation of neural stem/progenitor cells cultured on electrically adjustable indium tin oxide (ITO) surface

In order to control differentiation of neural cells and guide the developed neurites to targets, polyelectrolyte multilayer (PEM) films were used because of their capability of modulation of electrical charged characteristics, thickness, and stiffness. In this work, we suggested that indium tin oxide (ITO) is an alternative surface to achieve the above-mentioned objectives. A microfluidic system with four culture chambers was developed and each chamber consisted of parallel ITO surfaces for the application of adjustable electrical field. Neural stem/progenitor cells (NSPCs) were respectively cultured on the ITO surfaces with and without PEM film, constructed by alternate adsorption of poly(L-lysine) (PLL) and poly(L-glutamic acid) (PLGA). Analyses of cell morphology, cytotoxicity, process outgrowth, differentiated cell types, and neuron functionality were compared between both surfaces. In this study, NSPCs successfully differentiated on ITO surface with electrical stimulation. The optimal electrical potential was found to be 80 mV that could stimulate the longest process, i.e., >300 μm, after 3 days culture. Cell differentiation, process development, and functionality of differentiated neuron on ITO surface were shown to be strongly controlled by the electrical stimulation that can be simply adjusted by external equipment. The electrically adjustable cell differentiation reported here could potentially be applied to neurochip for the study of neural signal transmission in a well-constructed network.

Cytocompatibility of novel extracellular matrix protein analogs of biodegradable polyester polymers derived from α-hydroxy amino acids

One of the challenges in regenerative medicine is the development of novel biodegradable materials to build scaffolds that will support multiple cell types for tissue engineering. Here we describe the preparation, characterization, and cytocompatibility of homo- and hetero-polyesters of α-hydroxy amino acid derivatives with or without lactic acid conjugation. The polymers were prepared by a direct condensation method and characterized using gel permeation chromatography, (1)H-nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, optical activity, and solubility. The surface charge of the polymers was evaluated using zeta potential measurements. The polymers were coated onto glass cover slips followed by characterization using nano-surface profiler, thin film reflectometry, and atomic force microscopy (AFM). Their interaction with endothelial and neuronal cells was assessed using adhesion, proliferation, and differentiation assays. Of the characterized polymers, Poly-HOVal-LA, but not Poly-(D)HOPhe, significantly augmented nerve growth factor (NGF)-induced neuronal differentiation of the PC12 pheochromcytoma cells. In contrast, Poly-HOLeu increased by 20% the adhesion of endothelial cells, but did not affect PC12 cell differentiation. NGF-induced Erk1/2 phosphorylation in PC12 cells grown on the different polymers was similar to the effect observed for cells cultured on collagen type I. While no significant association could be established between charge and the differentiative/proliferative properties of the polymers, AFM analysis indicated augmentation of NGF-induced neuronal differentiation on smooth polymer surfaces. We conclude that overall selective cytocompatibility and bioactivity might render α-hydroxy amino acid polymers useful as extracellular matrix-mimicking materials for tissue engineering.

A microfluidic impedance flow cytometer for identification of differentiation state of stem cells

This paper presents a microfluidic electrical impedance flow cytometer (FC) for identifying the differentiation state of single stem cells. This device is comprised of a novel dual micropore design, which not only enhances the processing throughput, but also allows the associated electrodes to be used as a reference for one another. A signal processing algorithm, based on the support vector machine (SVM) theory, and a data classification method were developed to automate the identification of sample types and cell differentiation state based on measured impedance values. The device itself was fabricated using a combination of standard and soft lithography techniques to generate a PDMS-gold electrode construct. Experimental testing with non-biological particles and mouse embryonic carcinoma cells (P19, undifferentiated and differentiated) was carried out using a range of excitation frequencies. The effects of the frequency and the interrogation parameters on sample identification performance were investigated. It was found that the real and imaginary part of the detected impedance signal were adequate for distinguishing the undifferentiated P19 cells from non-biological polystyrene beads at all tested frequencies. A higher frequency and an opacity index were required to resolve the undifferentiated and differentiated P19 cells by capturing capacitive changes in electrophysiological properties arising from differentiation. The experimental results demonstrated salient accuracy of the device and algorithm, and established its feasibility for non-invasive, label-free identification of the differentiation state of the stem cells.

Topography and coating of platinum improve the electrochemical properties and neuronal guidance

To improve neuronal-electrode interfaces, we analyzed the influence of surface topographies combined with coating on the electrochemistry of platinum and neuronal differentiation of PC-12 cells. Surface structuring on nanoscale was realized by femtosecond laser ablation. Additional coating with laminin (LA), collagen type I (COL) or poly-d-lysine (PDL) did not change the produced topography. We further demonstrated that impedance could be improved in all cases. The pre-requisites of differentiation - viability and attachment - were fulfilled on the topography. Cell attachment of non-differentiated and differentiated cells and their formation of focal adhesion complexes were even enhanced compared to unstructured platinum. However, without the nerve growth factor (NGF) no cellular outgrowth and differentiation were possible. The topography enabled cell elongation and reduced the amount of rounded cells, but less effective than coating. Differentiation was either comparable or increased on the structures when compared with unstructured coatings. For instance, microtubule associated protein (MAP2) was detected most on the topography alone. But a combination of surface structuring and coating had the strongest impact on differentiation: the usage of COL provoked best cell elongation and beta III tubulin expression, PDL best synaptophysin. LA-coating had no noteworthy effect. These findings point out that innovative electronic devices like cochlear implants include two aspects: (a) nanotopography to improve the transmission of electrical signals and neuronal attachment; and (b) an additional coating to stimulate neuronal differentiation.

Microfabricated electrochemical cell-based biosensors for analysis of living cells in vitro

Cellular biochemical parameters can be used to reveal the physiological and functional information of various cells. Due to demonstrated high accuracy and non-invasiveness, electrochemical detection methods have been used for cell-based investigation. When combined with improved biosensor design and advanced measurement systems, the on-line biochemical analysis of living cells in vitro has been applied for biological mechanism study, drug screening and even environmental monitoring. In recent decades, new types of miniaturized electrochemical biosensor are emerging with the development of microfabrication technology. This review aims to give an overview of the microfabricated electrochemical cell-based biosensors, such as microelectrode arrays (MEA), the electric cell-substrate impedance sensing (ECIS) technique, and the light addressable potentiometric sensor (LAPS). The details in their working principles, measurement systems, and applications in cell monitoring are covered. Driven by the need for high throughput and multi-parameter detection proposed by biomedicine, the development trends of electrochemical cell-based biosensors are also introduced, including newly developed integrated biosensors, and the application of nanotechnology and microfluidic technology.

A digital microfluidic method for multiplexed cell-based apoptosis assays

Digital microfluidics (DMF), a fluid-handling technique in which picolitre-microlitre droplets are manipulated electrostatically on an array of electrodes, has recently become popular for applications in chemistry and biology. DMF devices are reconfigurable, have no moving parts, and are compatible with conventional high-throughput screening infrastructure (e.g., multiwell plate readers). For these and other reasons, digital microfluidics has been touted as being a potentially useful new tool for applications in multiplexed screening. Here, we introduce the first digital microfluidic platform used to implement parallel-scale cell-based assays. A fluorogenic apoptosis assay for caspase-3 activity was chosen as a model system because of the popularity of apoptosis as a target for anti-cancer drug discovery research. Dose-response profiles of caspase-3 activity as a function of staurosporine concentration were generated using both the digital microfluidic method and conventional techniques (i.e., pipetting, aspiration, and 96-well plates.) As expected, the digital microfluidic method had a 33-fold reduction in reagent consumption relative to the conventional technique. Although both types of methods used the same detector (a benchtop multiwell plate reader), the data generated by the digital microfluidic method had lower detection limits and greater dynamic range because apoptotic cells were much less likely to de-laminate when exposed to droplet manipulation by DMF relative to pipetting/aspiration in multiwell plates. We propose that the techniques described here represent an important milestone in the development of digital microfluidics as a useful tool for parallel cell-based screening and other applications.

Real-time detection of β1 integrin expression on MG-63 cells using electrochemical impedance spectroscopy

Beta 1 integrin is a membrane protein responsible for attachment and migration of osteosarcoma cells. In this study, expression of β1 integrin on MG-63 cells, a human osteogenic sarcoma cell line, was monitored using electrochemical impedance spectroscopy (EIS). ITO-based biochips were developed using a semiconductor technique. Differences in electric resistance (ΔR) were measured continuously when cells binding with anti-β1 integrin antibody coagulated with nano-scale gold particles. The results of the EIS system were compared with traditional immunofluorescence staining. We found that sample chambers with higher cell densities had larger ΔR values. When the cell densities increased from 5 × 10(4) cells/ml to 5 × 10(5) cells/ml, the ΔR value dose-dependently increased from 14 Ω to 37 Ω. In addition, a highly linear relationship (correlation coefficient, 0.921) was found between the ΔR values and the corresponding fluorescence intensities (p<0.05). These results suggest that electrochemical impedance spectroscopy can be a useful tool for evaluating β1 integrin expression on cell membranes.

Introduction to the fractality principle of consciousness and the sentyon postulate

Recently, consciousness research has gained much attention. Indeed, the question at stake is significant: why is the brain not just a computing device, but generates a perception from within? Ambitious endeavors trying to simulate the entire human brain assume that the algorithm will do the trick: as soon as we assemble the brain in a computer and increase the number of operations per time, consciousness will emerge by itself. I disagree with this simplistic representation. My argument emerges from the "atomism paradox": the irreducible space of the consciously perceived world, the endospace is incompatible with the reducible and decomposable architecture of the brain or a computer. I will first discuss the fundamental challenges in current consciousness models and then propose a new model based on the fractality principle: "the whole is in each of its parts". This new model copes with the atomism paradox by implementing an iterative mapping of information from higher order brain structures to smaller scales on the cellular and molecular level, which I will refer to as "fractalization". This information fractalization gives rise to a new form of matter that is conscious ("bright matter"). Bright matter is composed of conscious particles or units named "sentyons". The internal fractality of these sentyons will close a loop (the "psychic loop") in a recurrent fractal neural network (RFNN) that allows for continuous and complete information transformation and sharing between higher order brain structures and the endpoint substrate of consciousness at the molecular level.

Neural cell-cell and cell-substrate adhesion through N-cadherin, N-CAM and L1

In this study neural (N)-cadherin, neural cell adhesion molecule (N-CAM) and L1 proteins and their antibody equivalents were covalently immobilized on a polyethylene-imine (PEI)-coated glass surface to form neuron-adhesive coatings. Impedance sensing and (supplementary) image analysis were used to monitor the effects of these CAMs. Immobilization of high concentrations of both N-cadherin protein and antibody led to good adhesion of neurons to the modified surface, better than surfaces treated with 30.0 and 100.0 µg ml(-1) N-CAM protein and antibody. L1 antibody and protein coating revealed no significant effect on neuronal cell-substrate adhesion. In a second series of combinatorial experiments, we used the same antibodies and proteins as medium-additives to inhibit cell-cell adhesion between neurons. Adhesion of neurons cultured on N-cadherin protein or antibody-modified surfaces was lowered by the addition of a soluble N-cadherin protein and antibody to the culturing medium, accelerating neuronal aggregation. The presence of a soluble N-CAM antibody or protein had no effect on the adhesion of neuronal cells on a N-cadherin protein-modified surface. On a N-cadherin antibody-coated surface, the addition of a soluble N-CAM protein led to cell death of neurons after 48 h, while a N-CAM antibody had no effect. In the presence of a soluble N-cadherin protein and antibody the aggregation of neurons was inhibited, both on N-CAM protein and N-CAM antibody-modified surfaces. Neurons cultured on immobilized antibodies were less affected by the addition of soluble CAM blockers than neurons cultured on immobilized proteins, indicating that antibody-protein bonds are more stable compared to protein-protein bonds.

Impedance sensing for monitoring neuronal coverage and comparison with microscopy

We investigated the applicability of electric impedance sensing (IS) to monitor the coverage of adhered dissociated neuronal cells on glass substrates with embedded electrodes. IS is a sensitive method for the quantification of changes in cell morphology and cell mobility, making it suitable to study aggregation kinetics. Various sizes of electrodes were compared for the real-time recording of the impedance of adhering cells, at eight frequencies (range: 5 Hz-20 kHz). The real part of the impedance showed to be most sensitive at frequencies of 10 and 20 kHz for the two largest electrodes (7850 and 125,600 μm(2)). Compared to simultaneous microscopic evaluation of cell coverage and cell spreading, IS shows more detail.

Physicochemical control of adult stem cell differentiation: shedding light on potential molecular mechanisms

Realization of the exciting potential for stem-cell-based biomedical and therapeutic applications, including tissue engineering, requires an understanding of the cell-cell and cell-environment interactions. To this end, recent efforts have been focused on the manipulation of adult stem cell differentiation using inductive soluble factors, designing suitable mechanical environments, and applying noninvasive physical forces. Although each of these different approaches has been successfully applied to regulate stem cell differentiation, it would be of great interest and importance to integrate and optimally combine a few or all of the physicochemical differentiation cues to induce synergistic stem cell differentiation. Furthermore, elucidation of molecular mechanisms that mediate the effects of multiple differentiation cues will enable the researcher to better manipulate stem cell behavior and response.

Surface-patterned electrode bioreactor for electrical stimulation

We present a microscale cell culture system with an interdigitated microarray of excimer-laser-ablated indium tin oxide electrodes for electrical stimulation of cultured cells. The system has been characterized in a range of geometeries and stimulation regimes via electrochemical impedance spectroscopy and used to culture primary cardiomyocytes and human adipose derived stem cells. Over 6 days of culture with electrical stimulation (2 ms duration, 1 Hz, 180 microm wide electrodes with 200 microm spacing), both cell types exhibited enhanced proliferation, elongation and alignment, and adipose derived stem cells exhibited higher numbers of Connexin-43-composed gap junctions.

Micropatterning of proteins and mammalian cells on indium tin oxide

This paper describes a novel surface engineering approach that combines oxygen plasma treatment and electrochemical activation to create micropatterned cocultures on indium tin oxide (ITO) substrates. In this approach, photoresist was patterned onto an ITO substrate modified with poly(ethylene) glycol (PEG) silane. The photoresist served as a stencil during exposure of the surface to oxygen plasma. Upon incubation with collagen (I) solution and removal of the photoresist, the ITO substrate contained collagen regions surrounded by nonfouling PEG silane. Chemical analysis carried out with time-of-flight secondary ion mass spectrometry (ToF-SIMS) at different stages in micropatterned construction verified removal of PEG-silane during oxygen plasma and presence of collagen and PEG molecules on the same surface. Imaging ellipsometry and atomic force microscopy (AFM) were employed to further investigate micropatterned ITO surfaces. Biological application of this micropatterning strategy was demonstrated through selective attachment of mammalian cells on the ITO substrate. Importantly, after seeding the first cell type, the ITO surfaces could be activated by applying negative voltage (-1.4 V vs Ag/AgCl). This resulted in removal of nonfouling PEG layer and allowed to attach another cell type onto the same surface and to create micropatterned cocultures. Micropatterned cocultures of primary hepatocytes and fibroblasts created by this strategy remained functional after 9 days as verified by analysis of hepatic albumin. The novel surface engineering strategy described here may be used to pattern multiple cell types on an optically transparent and conductive substrate and is envisioned to have applications in tissue engineering and biosensing.

Microfluidics: a new cosset for neurobiology

Recently, microfluidic systems have shown great potential in the study of molecular and cellular biology. With its excellent properties, such as miniaturization, integration and automation, to name just a few, microfluidics creates new opportunities for the spatial and temporal control of cell growth and environmental stimuli in vitro. In the field of neuroscience, microfluidic devices offer precise control of the microenvironment surrounding individual cells, and the delivery of biochemical or physical cues to neural networks or single neurons. The intent of this review is to outline recent advances in microfluidic-based applications in neurobiology, with emphasis on neuron culture, neuron manipulation, neural stem cell differentiation, neuropharmacology, neuroelectrophysiology, and neuron biosensors. It also aims to stimulate development of microfluidic-based applications in neurobiology by involving scientists from various disciplines, especially neurobiology and microtechnology.

Quantitative assessment of neuronal differentiation in three-dimensional collagen gels using enhanced green fluorescence protein expressing PC12 pheochromocytoma cells

There is a paucity of quantitative methods for evaluating the morphological differentiation of neuronal cells in a three-dimensional (3-D) system to assist in quality control of neural tissue engineering constructs for use in reparative medicine. Neuronal cells tend to aggregate in the 3-D scaffolds, hindering the application of two-dimensional (2-D) morphological methods to quantitate neuronal differentiation. To address this problem, we developed a stable transfectant green fluorescence protein (GFP)-PC12 neuronal cell model, in which the differentiation process in 3-D can be monitored with high sensitivity by fluorescence microscopy. Under 2-D conditions, the green cells showed collagen adherence, round morphology, proliferation properties, expression of the nerve growth factor (NGF) receptors TrkA and p75(NTR), stimulation of extracellular signal-regulated kinase phosphorylation by NGF and were able to differentiate in a dose-dependent manner upon NGF treatment, like wild-type (wt)-PC12 cells. When grown within 3-D collagen gels, upon NGF treatment, the GFP-PC12 cells differentiated, expressing long neurite outgrowths. We describe here a new validated method to measure NGF-induced differentiation in 3-D. Having properties similar to those of wt-PC12 and an ability to grow and differentiate in 3-D structures, these highly visualized GFP-expressing PC12 cells may serve as an ideal model for investigating various aspects of differentiation to serve in neural engineering.

Analysis of the sensitivity and frequency characteristics of coplanar electrical cell-substrate impedance sensors

A PDMS-glass based micro-device was designed and fabricated with 12 coplanar impedance sensors integrated for electrical cell-substrate impedance sensing (ECIS). The sensitivity and frequency characteristics of the sensors were investigated both theoretically (equivalent circuit model) and experimentally for the commonly used micro-electrode dimension scale (20-80 microm). The experimental results matched well with the theoretical model analysis and revealed that, within this micro-electrode dimension scale, as the electrode width decreased or as the total electrode length decreased the sensitivity of sensor increased over the whole sensing frequency range, whilst electrode to electrode distance had no influence on sensitivity. Through our frequency characteristics analysis, the whole frequency range could be divided into four parts. New functions describing the dominant components in each frequency range were defined and validated experimentally, and could be used to explain the phenomenon of an ECIS sensing frequency window. The contribution to the impedance measurement of cells growing on the edges of the electrodes was determined for the first time. Finally, novel proposals for ECIS sensor design and ECIS measurements were presented.

Microelectrode array biochip: tool for in vitro drug screening based on the detection of a drug effect on dopamine release from PC12 cells

Novel, yet simple detection techniques of drug effect, including the effect of a vesicular monoamine transporter inhibitor (reserpine), a dopamine precursor (L-dopa), and a dopamine transporter inhibitor (nomifensine), on dopamine release from dopaminergic PC12 cells were developed based on a microelectrode array (MEA) biochip. Upon multi-injections of KCl solution into the culture of PC12 cells attached on a MEA biochip, the K+-stimulated dopamine release was temporally and amperometrically recorded by biochip microelectrodes. Two parameters in the recorded amperometric spectra were defined in this study: the peak current of the first KCl injection (Max1), and the steady current after the fourth KCl injection (St4). Statistically significant effects of L-dopa and reserpine were demonstrated by comparing both Max1 and St4 of the second detections in drugs with those of the control without drug treatment. The values of both Max1 and St4 in the first detections were normalized as 1. In contrast, the statistically significant effect of nomifensine was detected by comparing the ratios of St4 to Max1 in the first detections in drug with those of the control. The reason for using different analytical methods for measurements between L-dopa/reserpine and nomifensine lies in the different mechanisms of action on PC12 cells among these drugs. The novel analytical methods developed use the same detection setup and parameters, and the data analysis for the effect of drugs becomes simple. The methods hence may provide a high-throughput in vitro drug screening approach for dopamine-related psychiatric disorders.

Improving neuron-to-electrode surface attachment via alkanethiol self-assembly: an alternating current impedance study

In this work, the omega-amine alkanethiols, cysteamine (CA) and 11-amino-1-undecanethiol (11-AUT), were chemisorbed as self-assembled monolayers (SAMs) onto 250-microm gold microelectrodes that were microlithographically fabricated within eight-well cell culture plates and investigated as a means to improve neuron-to-electrode surface attachment (NESA). Dynamic contact angle (DCA) measurements showed similar advancing, theta(a) (69 degrees and 65 degrees ), but contrasting receding contact angles, theta(r) (9 and 30 degrees ) for CA- and 11-AUT-SAMs, respectively. The corresponding hysteresis (Deltatheta(ar) = 60 and 35 degrees, respectively) indicates the CA-SAM displays greater amphiphilic character than the 11-AUT-SAM. A portion of the greater Deltatheta(ar) for CA-SAMs may arise from surface heterogeneity, as compared to sputter-deposited gold and 11-AUT-SAMs. Tapping mode atomic force microscopy (AFM) confirmed a 6% increase (CA-SAM) and a 22% decrease (11-AUT-SAM) in surface roughness when compared to clean but unmodified, sputter-deposited gold. The extracellular matrix cell adhesion proteins, collagen, fibronectin, and laminin, were covalently coupled to the aminoalkanethiol-decorated gold electrodes via acid-amine heterobifunctional cross-linking. Using fluorescein isothiocyanate-tagged laminin, confocal fluorescence microscopy of both CA- and 11-AUT-SAM-modified and unmodified gold microelectrodes confirmed coupling of the protein to the electrode and was readily distinguishable from nonspecifically adsorbed protein. DCA measurements of laminin physisorbed directly onto gold or covalently immobilized via CA- or 11-AUT-SAM had similar advancing (ca. 63-65 degrees ) and receding (ca. 7-9 degrees ) contact angles. Tapping mode AFM of these protein-bearing surfaces likewise showed dimerized protein aggregates of similar surface roughness. PC-12 cells cultured to confluence on both unmodified and SAM-modified, protein-derivatized gold microelectrodes were examined by alternating current impedance (50 mV p-t-p at 4 kHz). CA- and 11-AUT-SAM-modified surfaces when serving as a foundation or covalently immobilized adhesion proteins produced highly stable and reproducible temporal impedance responses. On the basis of the magnitude and the reproducibility of the impedance responses, the CA-SAM-modified surfaces were identified as being best suited for optimal neuron-to-electrode contact with laminin. Laminin performed best when compared to collagen and fibronectin. Covalent immobilization of the adhesion-promoting proteins results in enhanced NESA by tightly anchoring cells to the electrode.