Micro-stamped surfaces for the patterned growth of neural stem cells

Flexibility of in vitro cortical circuits influences resilience from microtrauma

Background

Small clusters comprising hundreds to thousands of neurons are an important level of brain architecture that correlates single neuronal properties to fulfill brain function, but the specific mechanisms through which this scaling occurs are not well understood. In this study, we developed an in vitro experimental platform of small neuronal circuits (islands) to probe the importance of structural properties for their development, physiology, and response to microtrauma.

Methods

Primary cortical neurons were plated on a substrate patterned to promote attachment in clusters of hundreds of cells (islands), transduced with GCaMP6f, allowed to mature until 10-13 days in vitro (DIV), and monitored with Ca²⁺ as a non-invasive proxy for electrical activity. We adjusted two structural factors-island size and cellular density-to evaluate their role in guiding spontaneous activity and network formation in neuronal islands.

Results

We found cellular density, but not island size, regulates of circuit activity and network function in this system. Low cellular density islands can achieve many states of activity, while high cellular density biases islands towards a limited regime characterized by low rates of activity and high synchronization, a property we summarized as "flexibility." The injury severity required for an island to lose activity in 50% of its population was significantly higher in low-density, high flexibility islands.

Conclusion

Together, these studies demonstrate flexible living cortical circuits are more resilient to microtrauma, providing the first evidence that initial circuit state may be a key factor to consider when evaluating the consequences of trauma to the cortex.

Micro-patterned cell populations as advanced pharmaceutical drugs with precise functional control

Human cells are both advanced pharmaceutical drugs and 'drug deliverers'. However, functional control prior to or after cell implantation remains challenging. Micro-patterning cells through geometrically defined adhesion sites allows controlling morphogenesis, polarity, cellular mechanics, proliferation, migration, differentiation, stemness, cell-cell interactions, collective cell behavior, and likely immuno-modulatory properties. Consequently, generating micro-patterned therapeutic cells is a promising idea that has not yet been realized and few if any steps have been undertaken in this direction. This review highlights potential therapeutic applications, summarizes comprehensively the many cell functions that have been successfully controlled through micro-patterning, details the established micro-pattern designs, introduces the available fabrication technologies to the non-specialized reader, and suggests a quality evaluation score. Such a broad review is not yet available but would facilitate the manufacturing of therapeutically patterned cell populations using micro-patterned cell-instructive biomaterials for improved functional control as drug delivery systems in the context of cells as pharmaceutical products.

Biomaterials patterning regulates neural stem cells fate and behavior: The interface of biology and material science

The combination of nanotechnology and stem cell biology is one of the most promising advances in the field of regenerative medicine. This novel combination has widely been utilized in vitro settings in an attempt to develop efficient therapeutic strategies to overcome the limited capacity of the central nervous system (CNS) in replacing degenerating neural cells with functionally normal cells after the onset of acute and chronic neurological disorders. Importantly, biomaterials, not only, enhance the endogenous CNS neurogenesis and plasticity, but also, could provide a desirable supportive microenvironment to harness the full potential of the in vitro expanded neural stem cells (NSCs) for regenerative purposes. Here, first, we discuss how the physical and biochemical properties of biomaterials, such as their stiffness and elasticity, could influence the behavior of NSCs. Then, since the NSCs niche or microenvironment is of fundamental importance in controlling the dynamic destiny of NSCs such as their quiescent and proliferative states, topographical effects of surface diversity in biomaterials, that is, the micro-and nano-patterned surfaces will be discussed in detail. Finally, the influence of biomaterials as artificial microenvironments on the behavior of NSCs through the specific mechanotransduction signaling pathway mediated by focal adhesion formation will be reviewed.

Bioengineering of the Human Neural Stem Cell Niche: A Regulatory Environment for Cell Fate and Potential Target for Neurotoxicity

Human neural stem/progenitor cells of the developing and adult organisms are surrounded by the microenvironment, so-called neurogenic niche. The developmental processes of stem cells, such as survival, proliferation, differentiation, and fate decisions, are controlled by the mutual interactions between cells and the niche components. Such interactions are tissue specific and determined by the biochemical and biophysical properties of the niche constituencies and the presence of other cell types. This dynamic approach of the stem cell niche, when translated into in vitro settings, requires building up "biomimetic" microenvironments resembling natural conditions, where the stem/progenitor cell is provided with diverse extracellular signals exerted by soluble and structural cues, mimicking those found in vivo. The neural stem cell niche is characterized by a unique composition of soluble components including neurotransmitters and trophic factors as well as insoluble extracellular matrix proteins and proteoglycans. Biotechnological innovations provide tools such as a new generation of tunable biomaterials capable of releasing specific signals in a spatially and temporally controlled manner, thus creating in vitro nature-like conditions and, when combined with stem cell-derived tissue specific progenitors, producing differentiated neuronal tissue structures. In addition, substantial progress has been made on the protocols to obtain stem cell-derived cell aggregates such as neurospheres and self-assembled organoids.In this chapter, we have assessed the application of bioengineered human neural stem cell microenvironments to produce in vitro models of different levels of biological complexity for the efficient control of stem cell fate. Examples of biomaterial-supported two-dimensional and three-dimensional (2D and 3D) complex culture systems that provide artificial neural stem cell niches are discussed in the context of their application for basic research and neurotoxicity testing.

Microenvironments to study migration and somal translocation in cortical neurons

Migrating post-mitotic neurons of the developing cerebral cortex undergo terminal somal translocation (ST) when they reach their final destination in the cortical plate. This process is crucial for proper cortical layering and its perturbation can lead to brain dysfunction. Here we present a reductionist biomaterials platform that faithfully supports and controls the distinct phases of terminal ST in vitro. We developed microenvironments with different adhesive molecules to support neuronal attachment, neurite extension, and migration in distinct manners. Efficient ST occurred when the leading process of migratory neurons crossed from low-to high-adhesive areas on a substrate, promoting spreading of the leading growth cone. Our results indicate that elementary adhesive cell-substrate interactions strongly influence migratory behavior and the final positioning of neurons during their developmental journey. This in vitro model allows advanced experimentation to reveal the microenvironmental requirements underlying cortical layer development and disorders.

Current Understanding of the Pathways Involved in Adult Stem and Progenitor Cell Migration for Tissue Homeostasis and Repair

With the advancements in the field of adult stem and progenitor cells grows the recognition that the motility of primitive cells is a pivotal aspect of their functionality. There is accumulating evidence that the recruitment of tissue-resident and circulating cells is critical for organ homeostasis and effective injury responses, whereas the pathobiology of degenerative diseases, neoplasm and aging, might be rooted in the altered ability of immature cells to migrate. Furthermore, understanding the biological machinery determining the translocation patterns of tissue progenitors is of great relevance for the emerging methodologies for cell-based therapies and regenerative medicine. The present article provides an overview of studies addressing the physiological significance and diverse modes of stem and progenitor cell trafficking in adult mammalian organs, discusses the major microenvironmental cues regulating cell migration, and describes the implementation of live imaging approaches for the exploration of stem cell movement in tissues and the factors dictating the motility of endogenous and transplanted cells with regenerative potential.

Multiplex cell microarrays for high-throughput screening

Microarray technology was developed in the early 1990s to measure the transcription levels of thousands of genes in parallel. The basic premise of high-density arraying has since been expanded to create cell microarrays. Cells on chip are powerful experimental tools for high-throughput and multiplex screening of samples or cellular functions. Miniaturization increases assay throughput while reducing both reagent consumption and cell population heterogeneity effect, making these systems attractive for a wide range of assays, from drug discovery to toxicology, stem cell research and therapy. It is usual to functionalize the surface of a substrate to design cell microarrays. One form of cell microarrays, the transfected cell microarray, wherein plasmid DNA or siRNA spotted on the surface of a substrate is reverse-transfected locally into adherent cells, has become a standard tool for parallel cell-based analysis. With the advent of technology, cells can also be directly spotted onto functionalized surfaces using robotic fluid-dispensing devices or printed directly on bio-ink material. We are providing herein an overview of the latest developments in optical cell microarrays allowing high-throughput and high-content analysis.

Surface-printed microdot array chips coupled with matrix-assisted laser desorption/ionization mass spectrometry for high-throughput single-cell patterning and phospholipid analysis

RATIONALE

Single-cell analysis is very important in several research fields for the heterogeneity of individual cells, which has been well accepted. However, restricted by the size and low content of a single cell, current studies have encountered challenges in high-throughput, high-space resolution and sensitivity, and multicomponent analysis. A methodology of a surface-printed microdot array chip coupled with matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) is presented in this study for high-throughput single-cell patterning and phospholipid analysis.

METHODS

The poly-L-lysine (PLL) used as ink molecule was printed on an oxygen plasma processed indium tin oxide (ITO)-coated glass slide to form a microdot array by micro-contact printing technology. The cell array was then formed on the PLL microarray through electrostatic adsorption force. 9-Aminoacridine (9-AA) matrix was applied on the cell array before it was analyzed by MALDI-TOF MS. MALDI mass spectrometry imaging (MALDI-MSI) was then used for high-throughput, quick measurement, and multicomponent analysis of the cell array.

RESULTS

The single-cell capture efficiency of the cell array formed on the PLL microarray was about 40%. Twelve phospholipids were detected at the single-cell level, and the structures were further confirmed by MS/MS. The MALDI-MSI of selected ions showed a conformity with the cell array. The relative signal intensity data of selected ions were extracted from every pixel in the image within several minutes. The heterogeneity between individual cells was revealed from the relative signal intensity of phospholipids in 1-3 cells.

CONCLUSIONS

Compared to the existing related approaches, high-throughput, quick measurement, and multicomponent single-cell analysis have been realized by our method. Through different ink molecules used for micro-contact printing, the established platform could have the potential to capture and analyze specific cells. Copyright © 2016 John Wiley & Sons, Ltd.

Hierarchical Patterning of Cells with a Microeraser and Electrospun Nanofibers

For tissue engineering applications, it is important to develop fabrication strategies for building models with controlled cell distributions in defined structures. Here, a simple, flexible approach (named the μ-eraser strategy) is developed to construct multicell micropatterns. This approach involves pressing a poly(dimethylsiloxane) stamp to erase cells growing on substrates, and seeding other types of cells. The pressing/seeding process can be conducted in any designed pattern at desired time point. In a proof of concept, multicell micropatterns of human lung adenocarcinoma epithelial A549 cells, murine fibroblast (FB) cells and murine osteoblast (OB) cells are achieved on Petri dishes and electrospun sheets. Besides forming multicell micropatterns, the cell orientation can be regulated by microstripes and alignment of nanofibers. On Petri dishes and random fiber sheets, FB and OB cells align along microstripes, while A549 cells do not. However, when growing on aligned fiber sheets, no matter whether solo-cultured or co-cultured, all cells in micropatterns orient along the fibers. Based on this technique, a platform is built up to investigate rates of cell migration and interinvasion under solo-culture and co-culture systems. It is believed that this μ-eraser strategy has promise for biological, pharmaceutical, and biomedical applications.

Effects of ECM protein micropatterns on the migration and differentiation of adult neural stem cells

The migration and differentiation of adult neural stem cells (aNSCs) are believed to be strongly influenced by the spatial distribution of extracellular matrix (ECM) proteins in the stem cell niche. In vitro culture platform, which involves the specific spatial distribution of ECM protein, could offer novel tools for better understanding of aNSC behavior in the spatial pattern of ECM proteins. In this work, we applied soft-lithographic technique to design simple and reproducible laminin (LN)-polylysine cell culture substrates and investigated how aNSCs respond to the various spatial distribution of laminin, one of ECM proteins enriched in the aNSC niche. We found that aNSC preferred to migrate and attach to LN stripes, and aNSC-derived neurons and astrocytes showed significant difference in motility towards LN stripes. By changing the spacing of LN stripes, we were able to control the alignment of neurons and astrocytes. To the best of our knowledge, this is the first time to investigate the differential cellular responses of aNSCs on ECM protein (LN) and cell adhesive synthetic polymer (PDL) using surface micropatterns. Our findings would provide a deeper understanding in astrocyte-neuron interactions as well as ECM-stem cell interactions.

Portable Micropatterns of Neuronal Cells Supported by Thin Hydrogel Films

A grid micropattern of neuronal cells was formed on a free-standing collagen film (35 μm thickness) by directing migration and extension of neurons along a Matrigel pattern previously prepared on the film by the microcontact printing method. The neurons migrated to reach the nodes on the grid pattern and extended neurites to bridge cell bodies at the nodes. The resulting neuronal micropattern on the collagen film containing culture medium can be handled and deformed with tweezers with maintenance of physiological activity of the neurons, as examined by response of cytosolic Ca²⁺ concentration to a dose of bradykinin. This portability is the unique advantage of the present system that will open novel possibility of cellular engineering including the on-demand combination with analytical devices. The repetitive lamination of the film on a microelectrode chip was demonstrated for local electrical stimulation of a specific part of the grid micropattern of neurons, showing Ca²⁺ wave propagation along the neurites. The molecular permeability is the further advantage of the free-standing hydrogel substrate, which allows external supply of nutrients and dosing with chemical stimulants through the film even under rolled and laminated conditions.

Material and mechanical factors: new strategy in cellular neurogenesis

Since damaged neural circuits are not generally self-recovered, developing methods to stimulate neurogenesis is critically required. Most studies have examined the effects of soluble pharmacological factors on the cellular neurogenesis. On the other hand, it is now recognized that the other extracellular factors, including material and mechanical cues, also have a strong potential to induce cellular neurogenesis. This article will review recent data on the material (chemical patterning, micro/nano-topography, carbon nanotube, graphene) and mechanical (static cue from substrate stiffness, dynamic cue from stretch and flow shear) stimulations of cellular neurogenesis. These approaches may provide new neural regenerative medicine protocols. Scaffolding material templates capable of triggering cellular neurogenesis can be explored in the presence of neurogenesis-stimulatory mechanical environments, and also with conventional soluble factors, to enhance axonal growth and neural network formation in neural tissue engineering.

The effects of confinement on neuronal growth cone morphology and velocity

Optimizing growth cone guidance through the use of patterned substrates is important for designing regenerative substrates to aid in recovery from neuronal injury. Using laser ablation, we designed micron-scale patterns capable of confining dissociated mouse cerebellar granule neuron growth cones to channels of different widths ranging from 1.5 to 12 μm. Growth cone dynamics in these channels were observed using time-lapse microscopy. Growth cone area was decreased in channels between 1.5 and 6 μm as compared to that in 12 μm and unpatterned substrates. Growth cone aspect ratio was also affected as narrower channels forced growth cones into a narrow, elongated shape. There was no difference in the overall rate of growth cone advance in uniform channels between 1.5 and 12 μm as compared to growth on unpatterned substrates. The percentage of time growth cones advanced, paused, and retracted was also similar. However, growth cones did respond to changes in confinement: growth cones in narrow lanes rapidly sped up when encountering a wide region and then slowed down as they entered another narrow region. Our results suggest that the rate of neurite extension is not affected by the degree of confinement, but does respond to changes in confinement.

Cellphone camera imaging of a periodically patterned chip as a potential method for point-of-care diagnostics

In this study, we demonstrate that a disposable chip periodically patterned with suitable ligands, an ordinary cellphone camera, and a simple pattern recognition software, can potentially be used for quantitative diagnostics. A key factor in this demonstration is the design of a calibration grid around the chip that, through a contrast transfer process, enables reliable analysis of the images collected under variable ambient lighting conditions. After exposure to a dispersion of amine terminated silica beads used as analyte mimicking pathogens, an epoxy-terminated glass substrate microcontact printed with octadecyltrichlorosilane (250 μm periodicity) developed a characteristic pattern of beads which could be easily imaged with a cellphone camera of 3.2 MP pixels. A simple pattern recognition algorithm using fast Fourier transform produced a quantitative estimate of the analyte concentration present in the test solution. In this method importantly, neither the chip fabrication process nor the fill-factor of the periodic pattern need be perfect to arrive at a conclusive diagnosis. The method suggests a viable platform that may potentially find use in fault-tolerant and robust point-of-care diagnostic applications.

Site-specific differentiation of neural stem cell regulated by micropatterned multicomponent interfaces

Stem cell microenvironments are enriched by signals from a variety of components, which cooperate spatially and temporally to regulate cellular function. In vitro recapitulating such complexity in a well-controlled manner is elusive. Here, a platform for patterning multiple bio-active proteins on a single substrate is developed and optimized, and is used it to study the cooperative involvement of cell-matrix interaction and cell-cell signaling in regulating neural stem cell (NSC) function. An affinity-capturing-based multi-step microcontact printing is used to pattern, extracellular matrix proteins, and cell-cell signaling ligands, as intersecting lines on a nonadhesive background. Such design provides spatial segregation of signals from different extrinsic components, while allowing cell traffic between them during their proliferation and differentiation processes. Rat embryonic neural stem cells are cultured and characterized on the multicomponent substrates patterned with different combinations of fibronectin, N-cadherin, and Jagged1 proteins and allow to proliferate and differentiate over long term. It is found that local presentation of Notch signaling ligand (Jagged1) or cell adhesion molecule (N-cadherin) effectively modulate the balance between cell-cell and cell-matrix interaction, and significantly change the overall spatial remodeling of NSC differentiation. This platform provides an unambiguous approach to study the spatial and temporal cooperative involvement of different extrinsic components in regulating stem cell behavior. It is also readily expandable for inclusion of extra components and applicable to use with other types of cells, which provide a powerful tool for basic study of cell-material interaction or advanced tissue-interface engineering.

Micropatterning neuronal networks

A simple and effective method for patterning primary neuronal networks and circuits.

Mechanoregulation of stem cell fate via micro-/nano-scale manipulation for regenerative medicine

Recent developments in the field of mechanobiology have renewed the call for a better understanding of the role of mechanical forces as potent regulators and indicators of stem cell fate. Although it is well established that mechanical forces play a crucial role in guiding tissue development, little is known about how submicroscopic biomechanical forces can influence key stem cell behaviors. This review will detail the use of micro-/nano-technologies that are advancing our current understanding of stem cell mechanobiology, and mechanoregulation of stem cell fate using engineered surface topographies and small-scale patterning techniques. The involvement of focal adhesions and the cytoskeleton systems as a common biophysical impetus through which these mechanical signals are transduced via distinct signaling pathways will also be discussed. These insights are envisioned to provide the basis for the rational design of future biocompatible materials and may inspire alternative drug-free therapeutic strategies to manage diseased sites via biomechanical management.

Developmental stage dependent neural stem cells sensitivity to methylmercury chloride on different biofunctional surfaces

Sensitivity of neural stem cells viability, proliferation and differentiation upon exposure to methylmercury chloride (MeHgCl) was investigated on different types of biofunctional surfaces. Patterns of biodomains created by microprinting/microspotting of poly-l-lysine or extracellular matrix proteins (fibronectin and vitronectin) allowed for non-specific electrostatic or specific, receptor mediated interactions, respectively, between stem cells and the surface. The neural stem cell line HUCB-NSC has been previously shown to be susceptible to MeHgCl in developmentally dependent manner. Here we demonstrated that developmental sensitivity of HUCB-NSC to MeHgCl depends upon the type of adhesive biomolecules and the geometry of biodomains. Proliferation of HUCB-NSC was diminished in time and MeHgCl concentration dependent manner. In addition, the response to MeHgCl was found to be cell-type dependent. Undifferentiated cells were the most sensitive independently of the type of bioactive domain. Significant decrease of GFAP+ cells was detected among cells growing on poly-l-lysine, while on fibronectin and vitronectin, this effect was observed only in the highest (1μM) concentration of MeHgCl. β-Tubulin III expressing cells were most sensitive on fibronectin domains. In addition, limited bioactive domains to μm in size, as compared to non-patterned larger area of the same adhesive substrate, exerted protective role. Thus, the surface area and type of cell/biofunctional surface interaction exerted significant influence on developmental stage and cell-type specific response of HUCB-NSC to MeHgCl.

Inducing neurite outgrowth by mechanical cell stretch

Establishing extracellular milieus to stimulate neuronal regeneration is a critical need in neuronal tissue engineering. Many studies have used a soluble factor (such as nerve growth factor or retinoic acid [RA]), micropatterned substrate, and electrical stimulation to induce enhanced neurogenesis in neuronal precursor cells. However, little attention has been paid to mechanical stimulation because neuronal cells are not generally recognized as being mechanically functional, a characteristic of mechanoresponsive cells such as osteoblasts, chondrocytes, and muscle cells. In this study, we performed proof-of-concept experiments to demonstrate the potential anabolic effects of mechanical stretch to enhance cellular neurogenesis. We cultured human neuroblastoma (SH-SY5Y) cells on collagen-coated membrane and applied 10% equibiaxial dynamic stretch (0.25 Hz, 120 min/d for 7 days) using a Flexcell device. Interestingly, cell stretch alone, even without a soluble neurogenic stimulatory factor (RA), produced significantly more and longer neurites than the non-RA-treated, static control. Specific neuronal differentiation and cytoskeletal markers (e.g., microtubule-associated protein 2 and neurofilament light chain) displayed compatible variations with respect to stretch stimulation.

Biomimetic polymer brushes containing tethered acetylcholine analogs for protein and hippocampal neuronal cell patterning

This paper describes a method to control neuronal cell adhesion and differentiation with both chemical and topographic cues by using a spatially defined polymer brush pattern. First, biomimetic methacrylate polymer brushes containing tethered neurotransmitter acetylcholine functionalities in the form of dimethylaminoethyl methacrylate or free hydroxyl-terminated poly(ethylene glycol) units were prepared using the "grown from" method through surface-initiated atom transfer radical polymerization reactions. The surface properties of the resulting brushes were thoroughly characterized with various techniques and hippocampal neuronal cell culture on the brush surfaces exhibit cell viability and differentiation comparable to, or even better than, those on commonly used poly-l-lysine coated glass coverslips. The polymer brushes were then patterned via UV photolithography techniques to provide specially designed surface features with different sizes (varying from 2 to 200 μm) and orientations (horizontal and vertical). Protein absorption experiments and hippocampal neuronal cell culture tests on the brush patterns showed that both protein and neurons can adhere to the patterns and therefore be guided by such patterns. These results also demonstrate that, because of their unique chemical composition and well-defined nature, the developed polymer brushes may find many potential applications in cell-material interactions studies and neural tissue engineering.

Micropatterning-retinoic acid co-control of neuronal cell morphology and neurite outgrowth

Creating physical-biochemical superposed microenvironments optimal for stimulating neurite outgrowth would be beneficial for neuronal regenerative medicine. We investigated potential co-regulatory effects of cell micropatterning and retinoic acid (RA) soluble factor on neuronal cell morphology and neurite outgrowth. Human neuroblastoma (SH-SY5Y) cell patterning sensitivity could be enhanced by poly-L-lysine-g-polyethylene glycol cell-repellent back-filling, enabling cell confinement in lanes as narrow as 5 μm. Cells patterned on narrow (5 and 10 μm) lanes showed preferred nucleus orientation following the patterning direction. These cells also showed high nucleus aspect ratio but constrained nucleus spreading. On the other hand, cells on wide (20 μm and above) lanes showed random nucleus orientation and cell and nucleus sizes similar to those on unpatterned controls. All these changes were generally maintained with or without RA. Confining cells on narrow (5 and 10 μm) lanes, even without RA, significantly enhanced neurite extension relative to unpatterned control, which was further stimulated by RA. Interestingly, cell patterning on 5 and 10 μm lanes without RA produced longer neurites relative to the RA treatment alone case. Our data on the potential interplay between microscale physical cell confinement and RA-soluble stimulation may provide a new, integrative insight on how to trigger neurite/axon formation for neuronal regenerative medicine.

Surface coating as a key parameter in engineering neuronal network structures in vitro

By quantitatively comparing a variety of macromolecular surface coating agents, we discovered that surface coating strongly modulates the adhesion and morphogenesis of primary hippocampal neurons and serves as a switch of somata clustering and neurite fasciculation in vitro. The kinetics of neuronal adhesion on poly-lysine-coated surfaces is much faster than that on laminin and Matrigel-coated surfaces, and the distribution of adhesion is more homogenous on poly-lysine. Matrigel and laminin, on the other hand, facilitate neuritogenesis more than poly-lysine does. Eventually, on Matrigel-coated surfaces of self-assembled monolayers, neurons tend to undergo somata clustering and neurite fasciculation. By replacing coating proteins with cerebral astrocytes, and patterning neurons on astrocytes through self-assembled monolayers, microfluidics and micro-contact printing, we found that astrocyte promotes soma adhesion and astrocyte processes guide neurites. There, astrocytes could be a versatile substrate in engineering neuronal networks in vitro. Besides, quantitative measurements of cellular responses on various coatings would be valuable information for the neurobiology community in the choice of the most appropriate coating strategy.

Modeling neural differentiation on micropatterned substrates coated with neural matrix components

Topographical and biochemical characteristics of the substrate are critical for neuronal differentiation including axonal outgrowth and regeneration of neural circuits in vivo. Contact stimuli and signaling molecules allow neurons to develop and stabilize synaptic contacts. Here we present the development, characterization and functional validation of a new polymeric support able to induce neuronal differentiation in both PC12 cell line and adult primary skin-derived precursor cells (SKPs) in vitro. By combining a photolithographic technique with use of neural extracellular matrix (ECM) as a substrate, a biocompatible and efficient microenvironment for neuronal differentiation was developed.

Adaptation of high-throughput screening in drug discovery-toxicological screening tests

High-throughput screening (HTS) is one of the newest techniques used in drug design and may be applied in biological and chemical sciences. This method, due to utilization of robots, detectors and software that regulate the whole process, enables a series of analyses of chemical compounds to be conducted in a short time and the affinity of biological structures which is often related to toxicity to be defined. Since 2008 we have implemented the automation of this technique and as a consequence, the possibility to examine 100,000 compounds per day. The HTS method is more frequently utilized in conjunction with analytical techniques such as NMR or coupled methods e.g., LC-MS/MS. Series of studies enable the establishment of the rate of affinity for targets or the level of toxicity. Moreover, researches are conducted concerning conjugation of nanoparticles with drugs and the determination of the toxicity of such structures. For these purposes there are frequently used cell lines. Due to the miniaturization of all systems, it is possible to examine the compound's toxicity having only 1-3 mg of this compound. Determination of cytotoxicity in this way leads to a significant decrease in the expenditure and to a reduction in the length of the study.

High fidelity neuronal networks formed by plasma masking with a bilayer membrane: analysis of neurodegenerative and neuroprotective processes

Spatially defined neuronal networks have great potential to be used in a wide spectrum of neurobiology assays. We present an original technique for the precise and reproducible formation of neuronal networks. A PDMS membrane comprising through-holes aligned with interconnecting microchannels was used during oxygen plasma etching to dry mask a protein rejecting poly(ethylene glycol) (PEG) adlayer. Patterns were faithfully replicated to produce an oxidized interconnected array pattern which supported protein adsorption. Differentiated human SH-SY5Y neuron-like cells adhered to the array nodes with the micron-scale interconnecting tracks guiding neurite outgrowth to produce neuronal connections and establish a network. A 2.0 μm track width was optimal for high-level network formation and node compliance. These spatially standardized neuronal networks were used to analyse the dynamics of acrylamide-induced neurite degeneration and the protective effects of co-treatment with calpeptin or brain derived neurotrophic factor (BDNF).

Micro- and nanoengineering approaches to control stem cell-biomaterial interactions

As our population ages, there is a greater need for a suitable supply of engineered tissues to address a range of debilitating ailments. Stem cell based therapies are envisioned to meet this emerging need. Despite significant progress in controlling stem cell differentiation, it is still difficult to engineer human tissue constructs for transplantation. Recent advances in micro- and nanofabrication techniques have enabled the design of more biomimetic biomaterials that may be used to direct the fate of stem cells. These biomaterials could have a significant impact on the next generation of stem cell based therapies. Here, we highlight the recent progress made by micro- and nanoengineering techniques in the biomaterials field in the context of directing stem cell differentiation. Particular attention is given to the effect of surface topography, chemistry, mechanics and micro- and nanopatterns on the differentiation of embryonic, mesenchymal and neural stem cells.

Photo-responsive polymer with erasable and reconfigurable micro- and nano-patterns: an in vitro study for neuron guidance

The interaction of cells with nanoscale topography has proven to be an important modality in controlling cell responses. Topographic parameters on material surfaces play a role in cell growth. We have synthesized a new bio compatible polymer containing photoswitching molecules. Stripepatterned (groove/ridge pattern) were patterned and erased with ease on this bio azopolymer with two different set-ups: one with the projection of an optical interference pattern and the other one by molecular self-organization with one single laser beam. These two set-ups allow the re-writing of pattern after erasing and its inscription in vitro. PC12 cells were cultured on the bio-photoswitching patterned polymer and compared with PC12 cells growing on a well know substrate: poly-L-lysine. This result is of interest for facilitating contact guidance and designing reconfigurable scaffold for neural network formation in vitro.

Stem cells in toxicology: fundamental biology and practical considerations

This "Commentary" has examined the use of human stem cells for detection of toxicities of physical, chemical, and biological toxins/toxicants in response to the challenge posed by the NRC Report, "Toxicity Testing in the 21st Century: A vision and Strategy." Before widespread application of the use of human embryonic, pluripotent, "iPS," or adult stem cells be considered, the basic characterization of stem cell biology should be undertaken. Because no in vitro system can mimic all factors that influence cells in vivo (individual genetic, gender, developmental, immunological and diurnal states; niche conditions; complex intercellular interactions between stem, progenitor, terminal differentiated cells, and the signaling from extracellular matrices, oxygen tensions, etc.), attempts should be made to use both embryonic and adult stem cells, grown in three dimension under "niche-like" conditions. Because many toxins and toxicants work by "epigenetic" mechanisms and that epigenetic mechanisms play important roles in regulating gene expression and in the pathogenesis of many human diseases, epigenetic toxicity must be incorporated in toxicity testing. Because modulation of gap junctional intercellular communication by epigenetic agents plays a major role in homeostatic regulation of both stem and progenitor cells in normal tissues, the modulation of this biological process by both endogenous and endogenous chemicals should be incorporated as an end point to monitor for potential toxicities or chemo-preventive attributes. In addition, modulation of quantity, as well as the quality, of stem cells should be considered as potential source of a chemical's toxic potential in affecting any stem cell-based pathology, such as cancer.

The network formation assay: a spatially standardized neurite outgrowth analytical display for neurotoxicity screening

We present a rapid, reproducible and sensitive neurotoxicity testing platform that combines the benefits of neurite outgrowth analysis with cell patterning. This approach involves patterning neuronal cells within a hexagonal array to standardize the distance between neighbouring cellular nodes, and thereby standardize the length of the neurite interconnections. This feature coupled with defined assay coordinates provides a streamlined display for rapid and sensitive analysis. We have termed this the network formation assay (NFA). To demonstrate the assay we have used a novel cell patterning technique involving thin film poly(dimethylsiloxane) (PDMS) microcontact printing. Differentiated human SH-SY5Y neuroblastoma cells colonized the array with high efficiency, reliably producing pattern occupancies above 70%. The neuronal array surface supported neurite outgrowth, resulting in the formation of an interconnected neuronal network. Exposure to acrylamide, a neurotoxic reference compound, inhibited network formation. A dose-response curve from the NFA was used to determine a 20% network inhibition (NI(20)) value of 260 microM. This concentration was approximately 10-fold lower than the value produced by a routine cell viability assay, and demonstrates that the NFA can distinguish network formation inhibitory effects from gross cytotoxic effects. Inhibition of the mitogen-activated protein kinase (MAPK) ERK1/2 and phosphoinositide-3-kinase (PI-3K) signaling pathways also produced a dose-dependent reduction in network formation at non-cytotoxic concentrations. To further refine the assay a simulation was developed to manage the impact of pattern occupancy variations on network formation probability. Together these developments and demonstrations highlight the potential of the NFA to meet the demands of high-throughput applications in neurotoxicology and neurodevelopmental biology.

Grading the commercial optical biosensor literature-Class of 2008: 'The Mighty Binders'

Optical biosensor technology continues to be the method of choice for label-free, real-time interaction analysis. But when it comes to improving the quality of the biosensor literature, education should be fundamental. Of the 1413 articles published in 2008, less than 30% would pass the requirements for high-school chemistry. To teach by example, we spotlight 10 papers that illustrate how to implement the technology properly. Then we grade every paper published in 2008 on a scale from A to F and outline what features make a biosensor article fabulous, middling or abysmal. To help improve the quality of published data, we focus on a few experimental, analysis and presentation mistakes that are alarmingly common. With the literature as a guide, we want to ensure that no user is left behind.