Surface determinants of neuronal survival and growth on self-assembled monolayers in culture

Mimicking the Tendon Microenvironment to Enhance Skeletal Muscle Adhesion and Longevity in a Functional Microcantilever Platform

Microcantilever platforms are functional models for studying skeletal muscle force dynamics in vitro. However, the contractile force generated by the myotubes can cause them to detach from the cantilevers, especially during long-term experiments, thus impeding the chronic investigations of skeletal muscles for drug efficacy and toxicity. To improve the integration of myotubes with microcantilevers, we drew inspiration from the elastomeric proteins, elastin and resilin, that are present in the animal and insect worlds, respectively. The spring action of these proteins plays a critical role in force dampening in vivo. In animals, elastin is present in the collagenous matrix of the tendon which is the attachment point of muscles to bones. The tendon microenvironment consists of elastin, collagen, and an aqueous jelly-like mass of proteoglycans. In an attempt to mimic this tendon microenvironment, elastin, collagen, heparan sulfate proteoglycan, and hyaluronic acid were deposited on a positively charged silane substrate. This enabled the long-term survival of mechanically active myotubes on glass and silicon microcantilevers for over 28 days. The skeletal muscle cultures were derived from both primary and induced pluripotent stem cell (iPSC)-derived human skeletal muscles. Both types of myoblasts formed myotubes which survived for five weeks. Primary skeletal muscles and iPSC-derived skeletal muscles also showed a similar trend in fatigue index values. Upon integration with the microcantilever system, the primary muscle and iPSC-derived myotubes were tested successively over a one month period, thus paving the way for long-term chronic experiments on these systems for both drug efficacy and toxicity studies.

Silicon Carbide Technology for Advanced Human Healthcare Applications

Silicon carbide (SiC) is a highly robust semiconductor material that has the potential to revolutionize implantable medical devices for human healthcare, such as biosensors and neuro-implants, to enable advanced biomedical therapeutic applications for humans. SiC is both bio and hemocompatible, and is already commercially used for long-term human in vivo applications ranging from heart stent coatings and dental implants to short-term diagnostic applications involving neural implants and sensors. One challenge facing the medical community today is the lack of biocompatible materials which are inherently smart or, in other words, capable of electronic functionality. Such devices are currently implemented using silicon technology, which either has to be hermetically sealed so it does not directly interact with biological tissue or has a short lifetime due to instabilities in vivo. Long-term, permanently implanted devices such as glucose sensors, neural interfaces, smart bone and organ implants, etc., require a more robust material that does not degrade over time and is not recognized and rejected as a foreign object by the inflammatory response. SiC has displayed these exceptional material properties, which opens up a whole new host of applications and allows for the development of many advanced biomedical devices never before possible for long-term use in vivo. This paper is a review of the state-of-the art and discusses cutting-edge device applications where SiC medical devices are poised to translate to the commercial marketplace.

Long-term adherence of human brain cells in vitro is enhanced by charged amine-based plasma polymer coatings

Advances in cellular reprogramming have radically increased the use of patient-derived cells for neurological research in vitro. However, adherence of human neurons on tissue cultureware is unreliable over the extended periods required for electrophysiological maturation. Adherence issues are particularly prominent for transferable glass coverslips, hindering imaging and electrophysiological assays. Here, we assessed thin-film plasma polymer treatments, polymeric factors, and extracellular matrix coatings for extending the adherence of human neuronal cultures on glass. We find that positive-charged, amine-based plasma polymers improve the adherence of a range of human brain cells. Diaminopropane (DAP) treatment with laminin-based coating optimally supports long-term maturation of fundamental ion channel properties and synaptic activity of human neurons. As proof of concept, we demonstrated that DAP-treated glass is ideal for live imaging, patch-clamping, and optogenetics. A DAP-treated glass surface reduces the technical variability of human neuronal models and enhances electrophysiological maturation, allowing more reliable discoveries of treatments for neurological and psychiatric disorders.

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DAP-coated glass optimally supports long-term adhesion of human brain cells in vitro

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DAP-coated glass coverslips or plates are optimal for patch-clamping, live imaging, and optogenetic applications in vitro

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DAP coating combined with laminin reduces experimental loss due to cell detachment in long-term in vitro studies

Negatively-charged supported lipid bilayers regulate neuronal adhesion and outgrowth

Primary cortical neurons were cultured on negatively charged supported lipid bilayers (SLBs). Such membranes demonstrated the potential effect of negative charges on neuronal growth and neurite branching and elongation.

Myelination and Node of Ranvier Formation in a Human Motoneuron-Schwann Cell Serum-Free Coculture

Myelination and node of Ranvier formation play an important role in the rapid conduction of nerve impulses, referred to as saltatory conduction, along axons in the peripheral nervous system. We report a human-human myelination model using human primary Schwann cells (SCs) and human-induced pluripotent stem-cell-derived motoneurons utilizing a serum-free medium supplemented with ascorbate to induce myelination, where 41.6% of SCs expressed the master transcription factor for myelination, early growth response protein 2. After 30 days in coculture, myelin segments were visualized using immunocytochemistry for myelin basic protein surrounding neurofilament-stained motor neuron axons, which was confirmed via 3D confocal Raman microscopy, a viable alternative for transmission electron microscopy analysis. The myelination efficiency was 65%, and clusters of voltage-gated sodium channels and the paranodal protein contactin-associated protein 1 indicated node of Ranvier formation. This model has applications to study remyelination and demyelinating diseases, including Charcot-Marie Tooth disorder, Guillian-Barre syndrome, and anti-myelin-associated glycoprotein peripheral neuropathy.

Polarity Induced in Human Stem Cell Derived Motoneurons on Patterned Self-Assembled Monolayers

The control of polarized human neurite/axon development at the single neuron level is critical in geographically directing signal propagation in engineered neural networks, for both in vitro and in vivo applications. While there is an increasing need to exert control over axonal growth for the successful development and establishment of integrative and functional in vitro systems, controlled, polarized distribution of either human-derived neurons or motoneurons in vitro has yet to be reported. In this study, we established the polarized distribution of stem cell derived human motoneurons, using a patterned surface, and maintained the cells in a serum-free system. A surface pattern with defined polarity was developed using self-assembled monolayers (SAMs). A cell permissive SAM, DETA (trimethoxysilyl propyldiethylenetri-amine), combined with photolithography and a nonpermissive fluorinated silane, 13F (tridecafluoro-1,1,2,2-tetrahydroctyl-1-dimethylchloro-silane), generated a surface where neurons only adhered to the designed attachment sites and did so with preferred orientation. In addition, 75% of the cells attached to the patterns were motoneurons compared to their percentage in the standard unpatterned surface which was used as a control condition (20%), demonstrating the preference of these human motoneurons in adhering to the patterns. The ability to dictate the distribution and polarity of human motoneurons will be essential to the engineering of human-based functional in vitro systems in which the control of signal propagation is necessary but more importantly for cell implantation studies. Such systems will greatly benefit the study of motor function as well as aid the development of high-throughput systems for drug screening and test beds for use in preclinical studies related to conditions such as spinal cord injury, ALS, and muscular dystrophy.

Temporal Characterization of Neuronal Migration Behavior on Chemically Patterned Neuronal Circuits in a Defined in Vitro Environment

Directed control of neuronal migration, facilitating the correct spatial positioning of neurons, is crucial to the development of a functional nervous system. An understanding of neuronal migration and positioning on patterned surfaces in vitro would also be beneficial for investigators seeking to design culture platforms capable of mimicking the complex functional architectures of neuronal tissues for drug development as well as basic biomedical research applications. This study used coplanar self-assembled monolayer patterns of cytophilic, N-1[3-(trimethoxysilyly)propyl] diethylenetriamine (DETA) and cytophobic, tridecafluoro-1,1,2,2-tetrahydrooctyl-1-trichlorosilane (13F) to assess the migratory behavior and physiological characteristics of cultured neurons. Analysis of time-lapse microscopy data revealed a dynamic procedure underlying the controlled migration of neurons, in response to extrinsic geometric and chemical cues, to promote the formation of distinct two-neuron circuits. Immunocytochemical characterization of the neurons highlights the organization of actin filaments (phalloidin) and microtubules (β-tubulin) at each migration stage. These data have applications in the development of precise artificial neuronal networks and provide a platform for investigating neuronal migration as well as neurite identification in differentiating cultured neurons. Importantly, the cytoskeletal arrangement of these cells identifies a specific mode of neuronal migration on these in vitro surfaces characterized by a single process determining the direction of cell migration and mimicking somal translocation behavior in vivo. Such information provides valuable additional insight into the mechanisms controlling neuronal development and maturation in vitro and validates the biochemical mechanisms underlying this behavior as representative of neuronal positioning phenomena in vivo.

Accelerated Development of Hippocampal Neurons and Limited Adhesion of Astrocytes on Negatively Charged Surfaces

This work examines the development of primary neurons and astrocytes on thoroughly controlled functional groups. Negatively charged surfaces presenting carboxylate (COO^-) or sulfonate (SO₃^-) groups prove beneficial to neuronal behavior, in spite of their supposed repulsive electrostatic interactions with cellular membranes. The adhesion and survival of primary hippocampal neurons on negatively charged surfaces are comparable to or slightly better than those on positively charged (poly-d-lysine-coated) surfaces, and neuritogenesis and neurite outgrowth are accelerated on COO^- and SO₃^- surfaces. Moreover, such favorable influences of the negatively charged surfaces are only seen in neurons but not for astrocytes. Our results indicate that the in vitro developmental behavior of primary hippocampal neurons is sophisticatedly modulated by angstrom-sized differences in chemical structure or the charge density of the surface. We believe that this work provides new implications for understanding neuron-material interfaces as well as for establishing new ways to fabricate neuro-active surfaces.

Self-contained, low-cost Body-on-a-Chip systems for drug development

Integrated multi-organ microphysiological systems are an evolving tool for preclinical evaluation of the potential toxicity and efficacy of drug candidates. Such systems, also known as Body-on-a-Chip devices, have a great potential to increase the successful conversion of drug candidates entering clinical trials into approved drugs. Systems, to be attractive for commercial adoption, need to be inexpensive, easy to operate, and give reproducible results. Further, the ability to measure functional responses, such as electrical activity, force generation, and barrier integrity of organ surrogates, enhances the ability to monitor response to drugs. The ability to operate a system for significant periods of time (up to 28 d) will provide potential to estimate chronic as well as acute responses of the human body. Here we review progress towards a self-contained low-cost microphysiological system with functional measurements of physiological responses. Impact statement Multi-organ microphysiological systems are promising devices to improve the drug development process. The development of a pumpless system represents the ability to build multi-organ systems that are of low cost, high reliability, and self-contained. These features, coupled with the ability to measure electrical and mechanical response in addition to chemical or metabolic changes, provides an attractive system for incorporation into the drug development process. This will be the most complete review of the pumpless platform with recirculation yet written.

The structural development of primary cultured hippocampal neurons on a graphene substrate

The potential of graphene-based nanomaterials as a neural interfacing material for neural repair and regeneration remains poorly understood. In the present study, the response to the graphene substrate by neurons was determined in a hippocampal culture model. The results revealed the growth and maturation of hippocampal cultures on graphene substrates were significantly improved compared to the commercial control. In details, graphene promoted growth cone growth and microtubule formation inside filopodia 24h after seeding as evidenced by a higher average number of filopodia emerging from growth cones, a longer average length of filopodia, and a larger growth cone area. Graphene also significantly boosted neurite sprouting and outgrowth. The dendritic length, the number of branch points, and the dendritic complex index were significantly improved on the graphene substrate during culture. Moreover, the spine density was enhanced and the maturation of dendritic spines from thin to stubby spines was significantly promoted on graphene at 21 days after seeding. Lastly, graphene significantly elevated the synapse density and synaptic activity in the hippocampal cultures. The present study highlights graphene's potential as a neural interfacing material for neural repair and regeneration and sheds light on the future biomedical applications of graphene-based nanomaterials.

ToF-SIMS analysis of a polymer microarray composed of poly(meth)acrylates with C6 derivative pendant groups

Surface analysis plays a key role in understanding the function of materials, particularly in biological environments. Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) provides highly surface sensitive chemical information that can readily be acquired over large areas and has, thus, become an important surface analysis tool. However, the information‐rich nature of ToF‐SIMS complicates the interpretation and comparison of spectra, particularly in cases where multicomponent samples are being assessed. In this study, a method is presented to assess the chemical variance across 16 poly(meth)acrylates. Materials are selected to contain C₆ pendant groups, and ten replicates of each are printed as a polymer microarray. SIMS spectra are acquired for each material with the most intense and unique ions assessed for each material to identify the predominant and distinctive fragmentation pathways within the materials studied. Differentiating acrylate/methacrylate pairs is readily achieved using secondary ions derived from both the polymer backbone and pendant groups. Principal component analysis (PCA) is performed on the SIMS spectra of the 16 polymers, whereby the resulting principal components are able to distinguish phenyl from benzyl groups, mono‐functional from multi‐functional monomers and acrylates from methacrylates. The principal components are applied to copolymer series to assess the predictive capabilities of the PCA. Beyond being able to predict the copolymer ratio, in some cases, the SIMS analysis is able to provide insight into the molecular sequence of a copolymer. The insight gained in this study will be beneficial for developing structure–function relationships based upon ToF‐SIMS data of polymer libraries. © 2016 The Authors Surface and Interface Analysis Published by John Wiley & Sons Ltd.

Synaptic connectivity in engineered neuronal networks

We have developed a method to organize cells in dissociated cultures using engineered chemical clues on a culture surface and determined their connectivity patterns. Although almost all elements of the synaptic transmission machinery can be studied separately in single cell models in dissociated cultures, the complex physiological interactions between these elements are usually lost. Thus, factors affecting synaptic transmission are generally studied in organotypic cultures, brain slices, or in vivo where the cellular architecture generally remains intact. However, by utilizing engineered neuronal networks complex phenomenon such as synaptic transmission or synaptic plasticity can be studied in a simple, functional, cell culture-based system. We have utilized self-assembled monolayers and photolithography to create the surface templates. Embryonic hippocampal cells, plated on the resultant patterns in serum-free medium, followed the surface clues and formed the engineered neuronal networks. Basic whole-cell patch-clamp electrophysiology was applied to characterize the synaptic connectivity in these engineered two-cell networks. The same technology has been used to pattern other cell types such as cardiomyocytes or skeletal muscle fibers.

Utilization of microscale silicon cantilevers to assess cellular contractile function in vitro

The development of more predictive and biologically relevant in vitro assays is predicated on the advancement of versatile cell culture systems which facilitate the functional assessment of the seeded cells. To that end, microscale cantilever technology offers a platform with which to measure the contractile functionality of a range of cell types, including skeletal, cardiac, and smooth muscle cells, through assessment of contraction induced substrate bending. Application of multiplexed cantilever arrays provides the means to develop moderate to high-throughput protocols for assessing drug efficacy and toxicity, disease phenotype and progression, as well as neuromuscular and other cell-cell interactions. This manuscript provides the details for fabricating reliable cantilever arrays for this purpose, and the methods required to successfully culture cells on these surfaces. Further description is provided on the steps necessary to perform functional analysis of contractile cell types maintained on such arrays using a novel laser and photo-detector system. The representative data provided highlights the precision and reproducible nature of the analysis of contractile function possible using this system, as well as the wide range of studies to which such technology can be applied. Successful widespread adoption of this system could provide investigators with the means to perform rapid, low cost functional studies in vitro, leading to more accurate predictions of tissue performance, disease development and response to novel therapeutic treatment.

A phenotypic culture system for the molecular analysis of CNS myelination in the spinal cord

Studies of central nervous system myelination lack defined in vitro models which would effectively dissect molecular mechanisms of myelination that contain cells of the correct phenotype. Here we describe a co-culture of purified motoneurons and oligodendrocyte progenitor cells, isolated from rat embryonic spinal cord using a combination of immunopanning techniques. This model illustrates differentiation of oligodendrocyte progenitors into fully functional mature oligodendrocytes that myelinate axons. It also illustrates a contribution of axons to the rate of oligodendrocyte maturation and myelin gene expression. The defined conditions used allow molecular analysis of distinct stages of myelination and precise manipulation of inductive cues affecting axonal-oligodendrocyte interactions. This phenotypic in vitro myelination model can provide valuable insight into our understanding of demyelinating disorders, such as multiple sclerosis and traumatic diseases such as spinal cord injury where demyelination represents a contributing factor to the pathology of the disorder.

Two cell circuits of oriented adult hippocampal neurons on self-assembled monolayers for use in the study of neuronal communication in a defined system

In this study, we demonstrate the directed formation of small circuits of electrically active, synaptically connected neurons derived from the hippocampus of adult rats through the use of engineered chemically modified culture surfaces that orient the polarity of the neuronal processes. Although synaptogenesis, synaptic communication, synaptic plasticity, and brain disease pathophysiology can be studied using brain slice or dissociated embryonic neuronal culture systems, the complex elements found in neuronal synapses makes specific studies difficult in these random cultures. The study of synaptic transmission in mature adult neurons and factors affecting synaptic transmission are generally studied in organotypic cultures, in brain slices, or in vivo. However, engineered neuronal networks would allow these studies to be performed instead on simple functional neuronal circuits derived from adult brain tissue. Photolithographic patterned self-assembled monolayers (SAMs) were used to create the two-cell "bidirectional polarity" circuit patterns. This pattern consisted of a cell permissive SAM, N-1[3-(trimethoxysilyl)propyl] diethylenetriamine (DETA), and was composed of two 25 μm somal adhesion sites connected with 5 μm lines acting as surface cues for guided axonal and dendritic regeneration. Surrounding the DETA pattern was a background of a non-cell-permissive poly(ethylene glycol) (PEG) SAM. Adult hippocampal neurons were first cultured on coverslips coated with DETA monolayers and were later passaged onto the PEG-DETA bidirectional polarity patterns in serum-free medium. These neurons followed surface cues, attaching and regenerating only along the DETA substrate to form small engineered neuronal circuits. These circuits were stable for more than 21 days in vitro (DIV), during which synaptic connectivity was evaluated using basic electrophysiological methods.

Myelination and node of Ranvier formation on sensory neurons in a defined in vitro system

One of the most important developmental modifications of the nervous system is Schwann cell myelination of axons. Schwann cells ensheath axons to create myelin segments to provide protection to the axon as well as increase the conduction of action potentials. In vitro neuronal systems provide a unique modality to study a variety of factors influencing myelination as well as diseases associated with myelin sheath degradation. This work details the development of a patterned in vitro myelinating dorsal root ganglion culture. This defined system utilized a serum-free medium in combination with a patterned substrate, utilizing the cytophobic and cytophilic molecules (poly)ethylene glycol (PEG) and N-1[3 (trimethoxysilyl) propyl] diethylenetriamine (DETA), respectively. Directional outgrowth of the neurites and subsequent myelination was controlled by surface modifications, and conformity to the pattern was measured over the duration of the experiments. The myelinated segments and nodal proteins were visualized and quantified using confocal microscopy. This tissue-engineered system provides a highly controlled, reproducible model for studying Schwann cell interactions with sensory neurons, as well as the myelination process, and its effect on neuronal plasticity and peripheral nerve regeneration. It is also compatible for use in bio-hybrid constructs to reproduce the stretch reflex arc on a chip because the media combination used is the same that we have used previously for motoneurons, muscle, and for neuromuscular junction (NMJ) formation. This work could have application for the study of demyelinating diseases such as diabetes induced peripheral neuropathy and could rapidly translate to a role in the discovery of drugs promoting enhanced peripheral nervous system (PNS) remyelination.

Control of cell adhesion and neurite outgrowth by patterned gold nanoparticles with tunable attractive or repulsive surface properties

Guiding of neuronal cells on surfaces is required for the investigation of fundamental aspects of neurobiology, for tissue engineering, and for numerous bioelectronic applications. A modular method to establish nanostructured chemical templates for local deposition of gold nanoparticles is presented. A process comprising nanoimprint lithography, silanization, lift-off, and gold nanoparticle immobilization is used to fabricate the particle patterns. The chemical composition of the surface can be modified by in situ adsorption of cell-binding ligands to locally addressed particles. The versatility of this approach is demonstrated by inverting the binding affinity between rat cortical neurons and nanopatterned surfaces via wet-chemical means and thereby reversing the pattern of guided neurons.

Synthesis, copolymerization and peptide-modification of carboxylic acid-functionalized 3,4-ethylenedioxythiophene (EDOTacid) for neural electrode interfaces

BACKGROUND

Conjugated polymers have been developed as effective materials for interfacing prosthetic device electrodes with neural tissue. Recent focus has been on the development of conjugated polymers that contain biological components in order to improve the tissue response upon implantation of these electrodes.

METHODS

Carboxylic acid-functionalized 3,4-ethylenedioxythiophene (EDOTacid) monomer was synthesized in order to covalently bind peptides to the surface of conjugated polymer films. EDOTacid was copolymerized with EDOT monomer to form stable, electrically conductive copolymer films referred to as PEDOT-PEDOTacid. The peptide GGGGRGDS was bound to PEDOT-PEDOTacid to create peptide functionalized PEDOT films.

RESULTS

The PEDOT-PEDOTacid-peptide films increased the adhesion of primary rat motor neurons between 3 and 9 times higher than controls, thus demonstrating that the peptide maintained its biological activity.

CONCLUSIONS

The EDOT-acid monomer can be used to create functionalized PEDOT-PEDOTacid copolymer films that can have controlled bioactivity.

GENERAL SIGNIFICANCE

PEDOT-PEDOTacid-peptide films have the potential to control the behavior of neurons and vastly improve the performance of implanted electrodes. This article is part of a Special Issue entitled Organic Bioelectronics-Novel Applications in Biomedicine.

Tissue engineering the monosynaptic circuit of the stretch reflex arc with co-culture of embryonic motoneurons and proprioceptive sensory neurons

The sensory circuit of the stretch reflex arc is composed of intrafusal muscle fibers and their innervating proprioceptive neurons that convert mechanical information regarding muscle length and tension into action potentials that synapse onto the homonymous motoneurons in the ventral spinal cord which innervate the extrafusal fibers of the same muscle. To date, the in vitro synaptic connection between proprioceptive sensory neurons and spinal motoneurons has not been demonstrated. A functional in vitro system demonstrating this connection would enable the understanding of feedback by the integration of sensory input into the spinal reflex arc. Here we report a co-culture of rat embryonic motoneurons and proprioceptive sensory neurons from dorsal root ganglia (DRG) in a defined serum-free medium on a synthetic silane substrate (DETA). Furthermore, we have demonstrated functional synapse formation in the co-culture by immunocytochemistry and electrophysiological analysis. This work will be valuable for enabling in vitro model systems for the study of spinal motor control and related pathologies such as spinal cord injury, muscular dystrophy and spasticity by improving our understanding of the integration of the mechanosensitive feedback mechanism.

Small Molecule Induction of Human Umbilical Stem Cells into MBP-positive Oligodendrocytes in a Defined Three-Dimensional Environment

Stem cells from umbilical cord would be a favorable alternative to embryonic stem cells for therapeutic applications. In this study, human multipotent progenitor cells (MLPCs) from umbilical cord were differentiated into oligodendrocytes by exposure to a range of microenvironmental chemical and physical cues. Chemical cues were represented by a novel defined differentiation medium containing the neurotransmitter norepinephrine (NE). In traditional 2 dimensional (2D) conditions, the MLPCs differentiated into oligodendrocyte precursors, but did not progress further. However, in a 3 dimensional (3D) environment, the MLPCs differentiated into committed oligodendrocytes that expressed MBP. The apparent method of interaction of NE in stimulating the differentiation process was identified to occur through the adenergic pathway while all prior differentiation methods have used other routes. This novel method of obtaining functional human oligodendrocytes from MLPCs would eliminate many of the difficulties associated with their differentiation from embryonic stem cells.

Decellularized porcine brain matrix for cell culture and tissue engineering scaffolds

The extracellular matrix (ECM) plays important roles in influencing cellular behavior such as attachment, differentiation, and proliferation. However, in conventional culture and tissue engineering strategies, single proteins are frequently utilized, which do not mimic the complex extracellular microenvironment seen in vivo. In this study we report a method to decellularize brain tissue using detergents. This decellularized brain matrix is rich in glycosaminoglycans and contains collagen I, collagen III, collagen IV, collagen V, collagen VI, perlecan, and laminin. By further processing the material into a liquid form, the brain matrix can be used as a cell culture coating. Neurons derived from human induced pluripotent stem cells plated on the brain matrix express neuronal markers and assume neuronal morphology. Additionally, the same material can potentially be used as a scaffold for tissue engineering as it reassembles upon injection in vivo to form a gel. Thus, our work demonstrates the ability to use decellularized brain ECM for cell culture and tissue engineering applications.

Interplay between long- and short-range interactions drives neuritogenesis on stiff surfaces

Substrate factors such as surface energy distribution can affect cell functions, such as neuronal differentiation of PC12 cells. However, the surface effects that trigger such cell responses need to be clarified and analyzed. Here we show that the total surface tension is not a critical parameter. Self-assembled monolayers of alkylsiloxanes on glass were used as culture substrates. By changing the nanoscale structure and ordering of the monolayer, we designed surfaces with a range of dispersive (γ(d) ) and nondispersive (γ(nd) ) potentials, but with a similar value for total free-energy (50 ≤ γ(d) + γ(nd) ≤ 55 mN m⁻¹). When seeded on surfaces displaying γ(d) /γ(nd) ≤ 3.7, PC12 cells underwent low level of neuritogenesis. On surfaces exhibiting γ(d) /γ(nd) ≥ 5.4, neurite outgrowth was greatly enhanced and apparent by only 24 h of culture in absence of nerve growth-factor treatment. These data indicate how the spatial distribution of surface potentials may control neuritogenesis, thus providing a new criterion to address nerve regeneration issues on rigid biocompatible surfaces.

Neuromuscular junction formation between human stem cell-derived motoneurons and human skeletal muscle in a defined system

Functional in vitro models composed of human cells will constitute an important platform in the next generation of system biology and drug discovery. This study reports a novel human-based in vitro Neuromuscular Junction (NMJ) system developed in a defined serum-free medium and on a patternable non-biological surface. The motoneurons and skeletal muscles were derived from fetal spinal stem cells and skeletal muscle stem cells. The motoneurons and skeletal myotubes were completely differentiated in the co-culture based on morphological analysis and electrophysiology. NMJ formation was demonstrated by phase contrast microscopy, immunocytochemistry and the observation of motoneuron-induced muscle contractions utilizing time-lapse recordings and their subsequent quenching by d-Tubocurarine. Generally, functional human based systems would eliminate the issue of species variability during the drug development process and its derivation from stem cells bypasses the restrictions inherent with utilization of primary human tissue. This defined human-based NMJ system is one of the first steps in creating functional in vitro systems and will play an important role in understanding NMJ development, in developing high information content drug screens and as test beds in preclinical studies for spinal or muscular diseases/injuries such as muscular dystrophy, Amyotrophic lateral sclerosis and spinal cord repair.

Controlling neurite outgrowth with patterned substrates

In vivo, neurons form neurites, one of which develops into the axon while others become dendrites. While this neuritogenesis process is well programmed in vivo, there are limited methods to control the number and location of neurite extension in vitro. Here we report a method to control neuritogenesis by confining neurons in specific regions using cell resistant poly(oligoethyleneglycol methacrylate-co-methacrylic acid (OEGMA-co-MA)) or poly(ethyleneglycol-block-lactic acid) PEG-PLA. Line patterned substrates reduce multiple extension of neurites and stimulate bi-directional neurite budding for PC12 and cortical neurons. PC12 cells on 20 and 30 μm line patterns extended one neurite in each direction along the line pattern while cortical neuron on 20 and 30 μm line patterns extended one or two neurites in each direction along the line pattern. Statistical analysis of neurite lengths revealed that PC12 cells and cortical neurons on line patterns extend longer neurites. The ability to guide formation of neurites on patterned substrates is useful for generating neural networks and promoting neurite elongation.

Direct patterning of coplanar polyethylene glycol alkylsilane monolayers by deep-ultraviolet photolithography as a general method for high fidelity, long-term cell patterning and culture

This manuscript details a general method for patterning coplanar alkylsilane monolayers using deep-ultraviolet photolithography that has broad application for high fidelity patterning of cells of varying phenotype in long-term cultures. A polyethylene glycol monolayer was formed on a silica substrate and then patterned using 193 nm light from an ArF excimer laser. The regions of photoablation were then rederivatized with (3-trimethoxysilyl propyl) diethyltriamine (DETA), yielding high contrast cytophilic islands that promoted cell adhesion and growth. Rat hippocampal neurons, motoneurons, and myoblasts were then cultured in a defined, serum-free medium on the patterned surfaces for periods in excess of 40 days. This approach has been shown to be useful as a general method for the long-term culture of multiple cell types in highly defined spatial patterns and can be used for supporting complex cocultures for creating in vitro models for biological systems.

Tissue engineering the mechanosensory circuit of the stretch reflex arc: sensory neuron innervation of intrafusal muscle fibers

The sensory circuit of the stretch reflex arc, composed of specialized intrafusal muscle fibers and type Ia proprioceptive sensory neurons, converts mechanical information regarding muscle length and stretch to electrical action potentials and relays them to the central nervous system. Utilizing a non-biological substrate, surface patterning photolithography and a serum-free medium formulation a co-culture system was developed that facilitated functional interactions between intrafusal muscle fibers and sensory neurons. The presence of annulospiral wrappings (ASWs) and flower-spray endings (FSEs), both physiologically relevant morphologies in sensory neuron-intrafusal fiber interactions, were demonstrated and quantified using immunocytochemistry. Furthermore, two proposed components of the mammalian mechanosensory transduction system, BNaC1 and PICK1, were both identified at the ASWs and FSEs. To verify functionality of the mechanoreceptor elements the system was integrated with a MEMS cantilever device, and Ca(2+) currents were imaged along the length of an axon innervating an intrafusal fiber when stretched by cantilever deflection. This system provides a platform for examining the role of this mechanosensory complex in the pathology of myotonic and muscular dystrophies, peripheral neuropathy, and spasticity inducing diseases like Parkinson's. These studies will also assist in engineering fine motor control for prosthetic devices by improving our understanding of mechanosensitive feedback.

Coexpression of glutamate vesicular transporter (VGLUT1) and choline acetyltransferase (ChAT) proteins in fetal rat hippocampal neurons in culture

A very small population of choline acetyltransferase (ChAT) immunoreactive cells is observed in all layers of the adult hippocampus. This is the intrinsic source of the hippocampal cholinergic innervation, in addition to the well-established septo-hippocampal cholinergic projection. This study aimed at quantifying and identifying the origin of this small population of ChAT-immunoreactive cells in the hippocampus at early developmental stages, by culturing the fetal hippocampal neurons in serum-free culture and on a patternable, synthetic silane substrate N-1 [3-(trimethoxysilyl) propyl] diethylenetriamine. Using this method, a large proportion of glutamatergic (glutamate vesicular transporter, VGLUT1-immunoreactive) neurons, a small fraction of GABAergic (GABA-immunoreactive) neurons, and a large proportion of cholinergic (ChAT-immunoreactive) neurons were observed in the culture. Interestingly, most of the glutamatergic neurons that expressed glutamate vesicular transporter (VGLUT1) also co-expressed ChAT proteins. On the contrary, when the cultures were double-stained with GABA and ChAT, colocalization was not observed. Neonatal and adult rat hippocampal neurons were also cultured to verify whether these more mature neurons also co-express VGLUT1 and ChAT proteins in culture. Colocalization of VGLUT1 and ChAT in these relatively more mature neurons was not observed. One possible explanation for this observation is that the neurons have the ability to synthesize multiple neurotransmitters at a very early stage of development and then with time follows a complex, combinatorial strategy of electrochemical coding to determine their final fate.

Patterning N-type and S-type neuroblastoma cells with Pluronic F108 and ECM proteins

Influencing cell shape using micropatterned substrates affects cell behaviors, such as proliferation and apoptosis. Cell shape may also affect these behaviors in human neuroblastoma (NBL) cancer, but to date, no substrate design has effectively patterned multiple clinically important human NBL lines. In this study, we investigated whether Pluronic F108 was an effective antiadhesive coating for human NBL cells and whether it would localize three NBL lines to adhesive regions of tissue culture plastic or collagen I on substrate patterns. The adhesion and patterning of an S-type line, SH-EP, and two N-type lines, SH-SY5Y and IMR-32, were tested. In adhesion assays, F108 deterred NBL adhesion equally as well as two antiadhesive organofunctional silanes and far better than bovine serum albumin. Patterned stripes of F108 restricted all three human NBL lines to adhesive stripes of tissue culture plastic. We then investigated four schemes of applying collagen and F108 to different regions of a substrate. Contact with collagen obliterates the ability of F108 to deter NBL adhesion, limiting how both materials can be applied to substrates to produce high fidelity NBL patterning. This patterned substrate design should facilitate investigations of the role of cell shape in NBL cell behavior.

Addition of glutamate to serum-free culture promotes recovery of electrical activity in adult hippocampal neurons in vitro

A long-term cell culture system utilizing normal adult hippocampal neurons would represent an important tool that could be useful in research on the mature brain, neurological disorders and age-related neurological diseases. Historically, in vitro neuronal systems are derived from embryonic rather than mature brain tissue, a practice predicated upon difficulties in supporting regeneration, functional recovery and long-term survival of adult neurons in vitro. A few studies have shown that neurons derived from the hippocampal tissue of adult rats can survive and regenerate in vitro under serum-free conditions. However, while the adult neurons regenerated morphologically under these conditions, both the electrical activity characteristic of in vivo neurons as well as long-term neuronal survival was not consistently recovered in vitro. In this study, we report on the development of a defined culture system with the ability to support functional recovery and long-term survival of adult rat hippocampal neurons. In this system, the cell-adhesive substrate, N-1 [3-(trimethoxysilyl) propyl]-diethylenetriamine, supported neuronal attachment, regeneration, and long-term survival of adult neurons for more than 80 days in vitro. Additionally, the excitatory neurotransmitter glutamate, applied at 25muM for 1-7 days after morphological neuronal regeneration in vitro, enabled full recovery of neuronal electrical activity. This low concentration of glutamate promoted the recovery of neuronal electrical activity but with minimal excitotoxicity. These improvements allowed electrically active adult neurons to survive in vitro for several months, providing a stable test-bed for the long-term study of regeneration in adult-derived neuronal systems, especially for traumatic brain injury (TBI).

Designing Neural Networks in Culture: Experiments are described for controlled growth, of nerve cells taken from rats, in predesigned geometrical patterns on laboratory culture dishes

Technology has advanced to where it is possible to design and grow-with predefined geometry and surprisingly good fidelity-living networks of neurons in culture dishes. Here we overview the elements of design, emphasizing the lithographic techniques that alter the cell culture surface which in turn influences the attachment and growth of the neural networks. Advanced capability in this area makes it possible to design networks of desired complexity. Other issues addressed include the influence of glial cells and media on activity and the potential for extending the designs into three dimensions. Investigators are advancing the art and science of analyzing and controlling through stimulation the function of the neural networks, including the ability to take advantage of their geometric form in order to influence functional properties.

Surface plasmon resonance imaging of polymer microarrays to study protein-polymer interactions in high throughput

Polymer microarrays provide a high-throughput format in which to assess biointerfacial interactions. This endeavor greatly assists with the development of advanced biomaterials. In order to increase the scope of this platform technology, the development of analytical tools that are compatible with the microarray format and are capable of analyzing biomolecular interactions in high throughput is needed. Here, we show that surface plasmon resonance imaging (SPRi) is such a tool. SPRi enables spatially resolved, surface sensitive, label free, real-time analysis of multiple surface-biomolecular interactions in parallel. In order to demonstrate this, we first printed phenylazide-modified polymers onto a slide coated with a low fouling base polymer. UV irradiation of the slide resulted in the cross-linking of the printed polymer spots to the surface. SPRi was then employed to study the adsorption and desorption of bovine serum albumin, collagen, and fibronectin to these adhesive microarray spots. The spots were also incubated with an adherent cell line, enabling insight into the underlying mechanisms of cell attachment to the polymers studied. For the system analyzed here, electrostatic interactions were shown to dominate cell attachment.

Influence of surface energy distribution on neuritogenesis

PC12 cells are a useful model to study neuronal differentiation, as they can undergo terminal differentiation, typically when treated with nerve growth factor (NGF). In this study we investigated the influence of surface energy distribution on PC12 cell differentiation, by atomic force microscopy (AFM) and immunofluorescence. Glass surfaces were modified by chemisorption: an aminosilane, n-[3-(trimethoxysilyl)propyl]ethylendiamine (C(8)H(22)N(2)O(3)Si; EDA), was grafted by polycondensation. AFM analysis of substrate topography showed the presence of aggregates suggesting that the adsorption is heterogeneous, and generates local gradients in energy of adhesion. PC12 cells cultured on these modified glass surfaces developed neurites in absence of NGF treatment. In contrast, PC12 cells did not grow neurites when cultured in the absence of NGF on a relatively smooth surface such as poly-L-lysine substrate, where amine distribution is rather homogeneous. These results suggest that surface energy distribution, through cell-substrate interactions, triggers mechanisms that will drive PC12 cells to differentiate and to initiate neuritogenesis. We were able to create a controlled physical nano-structuration with local variations in surface energy that allowed the study of these parameters on neuritogenesis.

Node of Ranvier formation on motoneurons in vitro

One of the most significant interactions between Schwann cells and neurons is myelin sheath formation. Myelination is a vertebrate adaptation that enables rapid conduction of action potentials without a commensurate increase in axon diameter. In vitro neuronal systems provide a unique modality to study both factors influencing myelination and diseases associated with myelination. Currently, no in vitro system for motoneuron myelination by Schwann cells has been demonstrated. This work details the myelination of motoneuron axons by Schwann cells, with complete Node of Ranvier formation, in a defined in vitro culture system. This defined system utilizes a novel serum-free medium in combination with the non-biological substrate, N-1[3 (trimethoxysilyl) propyl] diethylenetriamine (DETA). The myelinated segments and nodal proteins were visualized and quantified using confocal microscopy. This defined system provides a highly controlled, reproducible model for studying Schwann cell interactions with motoneurons as well as the myelination process and its effect on neuronal plasticity. Furthermore, an in vitro system that would allow studies of motoneuron myelination would be beneficial for understanding peripheral demyelinating neuropathies such as diabetes induced peripheral neuropathy and could lead to a better understanding of CNS demyelinating diseases like multiple sclerosis, as well as neuromuscular junction maturation and maintenance.

Growth cone 3-D morphology is modified by distinct micropatterned adhesion substrates

The development, connectivity, and structural plasticity of neuronal networks largely depend on the directional growth of axonal growth cones (GCs). The morphology and 3-D profile of axons and GCs of primary hippocampal neurons, grown onto glass surfaces coated with poly-D-lysine (PDL) and micropatterned with stripes of the adhesion molecule L1 by using the indirect microcontact printing, were investigated. Neurons were fixed at early stages (one to seven days) of in vitro development prior to synapse formation, and analyzed by fluorescence and atomic force microscopy. The latter technique allowed us to investigate the 3-D morphology of the GCs, and detect their morphological rearrangements during axon outgrowth and during contact with the underlying substrate. We found that axons decreased their height-to-width ratio over development in culture, and that this value became particularly low when the axon and the GC proceeded onto a surface containing attracting cues such as L1 with respect to GCs growing onto a nonspecific adhesion substrate such as PDL. Along with this shape change of the axons, GCs lying onto L1 tracks displayed a flattened shape, ideal for sensing and progression, whereas GCs onto areas of nonspecific adhesion displayed more prominent shapes and steeper edges.

Tissue engineering intrafusal fibers: dose- and time-dependent differentiation of nuclear bag fibers in a defined in vitro system using neuregulin 1-beta-1

While much is known about muscle spindle structure, innervation and function, relatively few factors have been identified that regulate intrafusal fiber differentiation and spindle development. Identification of these factors will be a crucial step in tissue engineering functional muscle systems. In this study, we investigated the role of the growth factor, neuregulin 1-beta-1 (Nrg 1-beta-1) EGF, for its ability to influence myotube fate specification in a defined culture system utilizing the non-biological substrate N-1[3-(trimethoxysilyl)propyl]-diethylenetriamine (DETA). Based on morphological and immunocytochemical criteria, Nrg 1-beta-1 treatment of developing myotubes increases the ratio of nuclear bag fibers to total myotubes from 0.019 to 0.100, approximately a five-fold increase. The myotube cultures were evaluated for expression of the intrafusal fiber-specific alpha cardiac-like myosin heavy chain and for the expression of the non-specific slow myosin heavy chain. Additionally, the expression of ErbB2 receptors on all myotubes was observed, while phosphorylated ErbB2 receptors were only observed in Nrg 1-beta-1-treated intrafusal fibers. After Nrg 1-beta-1 treatment, we were able to observe the expression of the intrafusal fiber-specific transcription factor Egr3 only in fibers exhibiting the nuclear bag phenotype. Finally, nuclear bag fibers were characterized electrophysiologically for the first time in vitro. This data shows conclusively, in a serum-free system, that Nrg 1-beta-1 is necessary to drive specification of forming myotubes to the nuclear bag phenotype.

Transferring complementary target DNA from aqueous solutions onto solid surfaces by using affinity microcontact printing

In this paper, we report a method of transferring complementary target DNA from an aqueous solution onto a solid surface by using affinity microcontact printing. In this approach, the probe DNA is first immobilized on the surface of an aminated poly(dimethylsiloxane) (PDMS) stamp. After a complementary target DNA hybridizes with the probe DNA on the stamp surface, the PDMS stamp is printed on an aminated glass slide. By using fluorescent microscopy, we show that only complementary target DNA, but not noncomplementary DNA, can be captured onto the surface of the stamp and then transferred to the aminated glass slide. The transfer of DNA can be attributed to the stronger electrostatic attraction between DNA and amine groups compared to the hydrogen bonds between the hybridized DNA molecules. We also investigate several factors that may influence the transfer of DNA, such as the surface density of amine groups, hybridization conditions, and contamination from unreacted PDMS monomers.

Embryonic motoneuron-skeletal muscle co-culture in a defined system

This paper describes a significant biotechnological advancement by creating a minimalist serum-free defined system to co-culture rat mammalian nerve and muscle cells in order to form functional neuromuscular junctions. To date, all the known in vitro nerve and muscle co-culture models use serum containing media; and while functional neuromuscular junctions (NMJ) are described, they failed to detail or quantify the minimum factors needed to recreate the NMJ in vitro. In this work, we demonstrate the development of a defined motoneuron and muscle co-culture system resulting in the formation of NMJs including: 1) a new culture technique, 2) a novel serum-free medium formulation and 3) a synthetic self-assembled monolayer (SAM) substrate N-1 [3-(trimethoxysilyl) propyl] diethylenetriamine (DETA). We characterized the culture by morphology, immunocytochemistry, electrophysiology and videography. This model system provides a better understanding of the minimal growth factor and substrate interactions necessary for NMJ formation and provides a basic system that can be utilized for nerve-muscle tissue engineering, regenerative medicine and development of limb prosthetics.

Auto-catalytic ceria nanoparticles offer neuroprotection to adult rat spinal cord neurons

This paper describes the evaluation of the auto-catalytic anti-oxidant behavior and biocompatibility of cerium oxide nanoparticles for applications in spinal cord repair and other diseases of the central nervous system. The application of a single dose of nano-ceria at a nano-molar concentration is biocompatible, regenerative and provides a significant neuroprotective effect on adult rat spinal cord neurons. Retention of neuronal function is demonstrated from electrophysiological recordings and the possibility of its application to prevent ischemic insult is suggested from an oxidative injury assay. A mechanism is proposed to explain the auto-catalytic properties of these nanoparticles.

Synaptic connectivity in engineered neuronal networks

In this study, we have demonstrated a method to organize cells in dissociated cultures using engineered chemical clues on the culture surface and determined their connectivity patterns. Although almost all elements of the synaptic transmission machinery between neurons or between neurons and muscle fibers can be studied separately in single-cell models in dissociated cultures, the difficulty of clarifying the complex interactions between these elements makes random cultures not particularly suitable for specific studies. Factors affecting synaptic transmission are generally studied in organotypic cultures, brain slices, or in vivo where the cellular architecture generally remains intact. However, by utilizing engineered neuronal networks, complex phenomenon such as synaptic transmission can be studied in a simple, functional, cell culture-based system. We have utilized self-assembled monolayers (SAMs) and photolithography to create the surface templates. Embryonic hippocampal cells, plated on the resultant patterns in serum-free medium, followed the surface clues and formed the engineered neuronal networks. Basic electrophysiological methods were applied to characterize the synaptic connectivity in these engineered two-cell networks.

Modified aminosilane substrates to evaluate osteoblast attachment, growth, and gene expression in vitro

Bone cell-substrate interactions are important to understand in the design, selection, and surface modification of bone implants. To gain insight into such interactions, substrates designed with surface species approximating the physiological environment of bone matrix were studied. Osteoblasts (Ob) grown on three such surfaces were used to evaluate cell-substrate effects on attachment, growth, and gene expression as compared with controls. Initial surface preparation consisted of coating glass slides with aminopropyltriethoxy silane (APTES), after which the coated slides were modified with collagen-rich extracellular matrix components obtained from normally mineralizing avian tendon: the tripeptide arginine-glycine-aspartic acid (arg-gly-asp), or a precipitate formed from a metastable solution containing inorganic ions normally found in blood (simulated body fluid). Each of the modified substrates, as well as the nonmodified (APTES) control, provided distinctly different physical (evidenced by differences in rms roughness) and chemical surfaces for seeding primary osteoblasts obtained from 14-day-old normal embryonic chickens. Cell responses to each of the substrates were evaluated over a 21-day period in terms of Ob growth and growth rate, alkaline phosphatase (ALP) activity, and gene expression of type I collagen (COL I), osteopontin (OPN), osteocalcin (OC), and bone sialoprotein (BSP). From these preliminary experiments, indications are that cell attachment and growth in this study possibly are independent processes, an assumption that compels the need for further studies. Collagen-rich matrix-modified substrates had a distinct advantage over others when cell growth rate, ALP activity, and gene expression were considered; cells on these substrates exhibited increased ALP activity and enhanced expression of BSP, OPN, and OC when compared with those of cells on APTES controls or other modified substrates. These results indicate that matrix-modified substrates such as those used in this study provide favorable templates for tissue generation, suggesting their potential in the design of surfaces for bone implants.

Synthesis of cell-adhesive dextran hydrogels and macroporous scaffolds

Dextran hydrogels have been previously investigated as drug delivery vehicles and more recently as macroporous scaffolds; however, the non-cell-adhesive nature of dextran has limited its utility for tissue engineering. To overcome this limitation, macroporous scaffolds of methacrylated dextran (Dex-MA) copolymerized with aminoethyl methacrylate (AEMA) were synthesized, thereby introducing primary amine groups for covalent immobilization of extracellular-matrix-derived peptides. The amino group density for hydrogels copolymerized with 0.5 wt% AEMA was found to be 36.1+/-0.4 micromol/cm(3) by elemental analysis. To further enhance cellular interaction, poly(Dex-MA-co-AEMA) hydrogels were modified with either CRGDS or a mixture of CDPGYIGSR and CQAASIKVAV (1:1, v/v) using sulfo-(N-maleimidomethyl)cyclohexane-1-carboxylate (sulfo-SMCC). The immobilized peptide concentration was determined using amino acid analysis at: 2.6+/-0.9 micromol/cm(3) for CRGDS-derived hydrogels and 2.2+/-0.3 micromol/cm(3) plus 1.9+/-0.2 micromol/cm(3) for CDPGYIGSR plus CQAASIKVAV-derived hydrogels, respectively. Cellular interactions of primary embryonic chick dorsal root ganglia (DRGs) were compared on the hydrogels. Cell adhesion and neurite outgrowth on poly(Dex-MA) increased with copolymerization of AEMA and further improved with peptide modification and significantly for CDPGYIGSR/CQAASIKVAV-derived poly(Dex-MA-co-AEMA) hydrogels. Moreover, DRGs penetrated within the first 600 microm of the scaffolds, thereby demonstrating the potential of this scaffold for guided cell and axonal regeneration in vivo.

A defined system to allow skeletal muscle differentiation and subsequent integration with silicon microstructures

This work documents the development of an in vitro cell culture model consisting of a novel serum-free medium and a non-biological growth substrate, N-1[3 (trimethoxysilyl) propyl] diethylenetriamine (DETA), to enable functional myotube integration with cantilevers fabricated using MEMS technology. This newly developed, defined in vitro model was used to study the differentiation of fetal rat skeletal muscle and it promoted the formation of myotubes from the dissociated rat fetal muscle cells. The myotubes were characterized by morphological analysis, immunocytochemistry and electrophysiology. Further, it was demonstrated that when the dissociated muscle cells were plated on fabricated microcantilevers, the muscle cells aligned along the major axis of the cantilever and formed robust myotubes. This novel system could not only find applications in skeletal muscle differentiation and biocompatibility studies but also in bioartificial muscle engineering, hybrid actuation system development, biorobotics and for a better understanding of myopathies and neuromuscular disorders.