Combined topographical and chemical micropatterns for templating neuronal networks

Regulatory Effects of Gradient Microtopographies on Synapse Formation and Neurite Growth in Hippocampal Neurons

Among approaches aiming toward functional nervous system restoration, those implementing microfabrication techniques allow the manufacture of platforms with distinct geometry where neurons can develop and be guided to form patterned connections in vitro. The interplay between neuronal development and the microenvironment, shaped by the physical limitations, remains largely unknown. Therefore, it is crucial to have an efficient way to quantify neuronal morphological changes induced by physical or contact guidance of the microenvironment. In this study, we first devise and assess a method to prepare anisotropic, gradient poly(dimethylsiloxane) micro-ridge/groove arrays featuring variable local pattern width. We then demonstrate the ability of this single substrate to simultaneously profile the morphologcial and synaptic connectivity changes of primary cultured hippocampal neurons reacting to variable physical conditons, throughout neurodevelopment, in vitro. The gradient microtopography enhanced adhesion within microgrooves, increasing soma density with decreasing pattern width. Decreasing pattern width also reduced dendritic arborization and increased preferential axon growth. Finally, decreasing pattern geometry inhibited presynaptic puncta architecture. Collectively, a method to examine structural development and connectivity in response to physical stimuli is established, and potentially provides insight into microfabricated geometries which promote neural regeneration and repair.

Combinatorial effect of plasma treatment, fiber alignment and fiber scale of poly (ε-caprolactone)/collagen multiscale fibers in inducing tenogenesis in non-tenogenic media

Tendon being a hypocellular, low vascularized tissue often requires assistance for restoration after complete tear. Tendon tissue engineering aims in the development of suitable scaffold that could support the regeneration of tendon after damage. The success of such scaffolds is dependent on its integration with the native tissue which in turn is influenced by the cell-material interaction. In this work aligned poly(ε-caprolactone)/collagen (PCL/collagen) multiscale fibers were developed and plasma treatment using argon, nitrogen and its combination was accessed for inducing tenogenic differentiation in mesenchymal stem cells. The developed fibers mimicked tendon extracellular matrix (ECM) which upon plasma treatment maintained moderate hydrophilicity. Oxygen and nitrogen containing groups were observed to be incorporated after argon and nitrogen treatment respectively. Statistically significant (p < 0.001) enhancement was observed in average and root mean square (RMS) roughness after plasma treatment with the maximum in argon treated fibers. Vitronectin was competitively (statistically significant, p < 0.05) adsorbed after argon and combination treatment whereas nitrogen treatment led to the competitive adsorption of fibronectin (statistically significant, p < 0.05). Human mesenchymal stem cells (hMSCs) showed enhanced proliferation and attachment on plasma treated fibers. Increased porosity due to the presence of sacrificial collagen nanofibers improved cell infiltration which was further enhanced upon plasma treatment. RhoA activation was observed (statistically significant, p < 0.05) on aligned PCL/collagen multiscale fibers and PCL microfibers, which proved its impact on tenogenic differentiation. Further enhancement in rhoA expression was observed on argon (p < 0.01) and combination plasma (p < 0.05) treated fibers. Tenogenic differentiation of hMSCs was enhanced (statistically significant) on argon plasma treated aligned fibers which was confirmed by the expression of scleraxis, mohawk (early markers) and tenomodulin (late marker) at protein level and mohawk, collagen I, collagen III (early markers), thrombospondin 4 and tenascin C (late markers) at gene level. Thus argon plasma treatment on aligned fibers is an effective method to induce tenogenesis even in non-tenogenic media.

A neuronal wiring platform through microridges for rationally engineered neural circuits

Precisely engineered neuronal circuits are promising for both fundamental research and clinical applications. However, randomly plating thousands of cells during neural network fabrication remains a major technical obstacle, which often results in a loss of tracking in neurons' identities. In this work, we demonstrated an accurate and unique neural wiring technique, mimicking neurons' natural affinity to microfibers. SU-8 microridges, imitating lie-down microfibers, were photolithographically patterned and then selectively coated with poly-l-lysine. We accurately plated Aplysia californica neurons onto designated locations. Plated neurons were immobilized by circular microfences. Furthermore, neurites regrew effectively along the microridges in vitro and reached adjacent neurons without undesirable crosstalks. Functional chemical synapses also formed between accurately wired neurons, enabling two-way transmission of electrical signals. Finally, we fabricated microridges on a microelectrode array. Neuronal spikes, stimulation-evoked synaptic activity, and putative synaptic adaption between connected neurons were observed. This biomimetic platform is simple to fabricate and effective with neurite pathfinding. Therefore, it can serve as a powerful tool for fabricating neuronal circuits with rational design, organized cellular communications, and fast prototyping.

Hybrid Interfaces Made of Nanotubes and Backbone-Altered Dipeptides Tune Neuronal Network Architecture

Peptides constituted of backbone homologated α-amino acids combined with carbon materials offer interesting possibilities in the modulation of cellular functions. In this work, we have prepared diphenylalanine β- and γ-peptides and conjugated them to carbon nanotubes (CNTs). These hybrids were able to self-assemble into fibrillar dendritic structures enabling the growth of primary hippocampal cells and the modulation of their neuronal functions. In particular, following the deposition of the different nanomaterials on glass substrates, we have evaluated their effects on circuit function and geometry. The geometrical restrictions due to CNT nucleated nodes allowed growth of neuronal networks with control over network geometry, and exploring its functional impact. In diverse applications from basic neuroscience, the presence of CNT nodes may be exploited in brain interfaces able to convey highly localized electrical stimuli.

In-mold patterning and actionable axo-somatic compartmentalization for on-chip neuron culture

Oriented neuronal networks with controlled connectivity are required for many applications ranging from studies of neurodegeneration to neuronal computation. To build such networks in vitro, an efficient, directed and long lasting guidance of axons toward their target is a pre-requisite. The best guidance achieved so far, however, relies on confining axons in enclosed microchannels, making them poorly accessible for further investigation. Here we describe a method providing accessible and highly regular arrays of axons, emanating from somas positioned in distinct compartments. This method combines the use of a novel removable partition, allowing soma positioning outside of the axon guidance patterns, and in-mold patterning (iMP), a hybrid method combining chemical and mechanical cell positioning clues applied here for the first time to neurons. The axon guidance efficiency of iMP is compared to that of conventional patterning methods, e.g. micro-contact printing (chemical constraints by a poly-l-lysine motif) and micro-grooves (physical constraints by homogeneously coated microstructures), using guiding tracks of different widths and spacing. We show that iMP provides a gain of 10 to 100 in axon confinement efficiency on the tracks, yielding mm-long, highly regular, and fully accessible on-chip axon arrays. iMP also allows well-defined axon guidance from small populations of several neurons confined at predefined positions in μm-sized wells. iMP will thus open new routes for the construction of complex and accurately controlled neuronal networks.

Cell microenvironment engineering and monitoring for tissue engineering and regenerative medicine: the recent advances

In tissue engineering and regenerative medicine, the conditions in the immediate vicinity of the cells have a direct effect on cells' behaviour and subsequently on clinical outcomes. Physical, chemical, and biological control of cell microenvironment are of crucial importance for the ability to direct and control cell behaviour in 3-dimensional tissue engineering scaffolds spatially and temporally. In this review, we will focus on the different aspects of cell microenvironment such as surface micro-, nanotopography, extracellular matrix composition and distribution, controlled release of soluble factors, and mechanical stress/strain conditions and how these aspects and their interactions can be used to achieve a higher degree of control over cellular activities. The effect of these parameters on the cellular behaviour within tissue engineering context is discussed and how these parameters are used to develop engineered tissues is elaborated. Also, recent techniques developed for the monitoring of the cell microenvironment in vitro and in vivo are reviewed, together with recent tissue engineering applications where the control of cell microenvironment has been exploited. Cell microenvironment engineering and monitoring are crucial parts of tissue engineering efforts and systems which utilize different components of the cell microenvironment simultaneously can provide more functional engineered tissues in the near future.

Surface engineering of synthetic polymer materials for tissue engineering and regenerative medicine applications

When using polymer materials as scaffolds for tissue engineering or regenerative medicine applications the initial, and often lasting, interaction between cells and the material areviasurfaces.

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.

A simplified micropatterning method for straight-line neurite extension of cultured hippocampal neurons

We report a simplified micropatterning method for the straight-line extension of the neurites of cultured neurons. We prepared a poly-D-lysine (PDL)-patterned surface using a polydimethylsiloxane microfluidic stamp. Hippocampal neurons were cultured on the PDL-bound substrate with the stamp removed, allowing for conventional cell seeding and detailed optical observation without fluorescent label. Cultured neurons elongated neurites along straight lines at the single-cell level and displayed spontaneous firing as detected by time-lapse imaging and Ca(2+) imaging.

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.

Highly ordered large-scale neuronal networks of individual cells - toward single cell to 3D nanowire intracellular interfaces

The use of artificial, prepatterned neuronal networks in vitro is a promising approach for studying the development and dynamics of small neural systems in order to understand the basic functionality of neurons and later on of the brain. The present work presents a high fidelity and robust procedure for controlling neuronal growth on substrates such as silicon wafers and glass, enabling us to obtain mature and durable neural networks of individual cells at designed geometries. It offers several advantages compared to other related techniques that have been reported in recent years mainly because of its high yield and reproducibility. The procedure is based on surface chemistry that allows the formation of functional, tailormade neural architectures with a micrometer high-resolution partition, that has the ability to promote or repel cells attachment. The main achievements of this work are deemed to be the creation of a large scale neuronal network at low density down to individual cells, that develop intact typical neurites and synapses without any glia-supportive cells straight from the plating stage and with a relatively long term survival rate, up to 4 weeks. An important application of this method is its use on 3D nanopillars and 3D nanowire-device arrays, enabling not only the cell bodies, but also their neurites to be positioned directly on electrical devices and grow with registration to the recording elements underneath.

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.

Cell patterning using a template of microstructured organosilane layer fabricated by vacuum ultraviolet light lithography

Micropatterning techniques have become increasingly important in cellular biology. Cell patterning is achieved by various methods. Photolithography is one of the most popular methods, and several light sources (e.g., excimer lasers and mercury lamps) are used for that purpose. Vacuum ultraviolet (VUV) light that can be produced by an excimer lamp is advantageous for fabricating material patterns, since it can decompose organic materials directly and efficiently without photoresist or photosensitive materials. Despite the advantages, applications of VUV light to pattern biological materials are few. We have investigated cell patterning by using a template of a microstructured organosilane layer fabricated by VUV lithography. We first made a template of a microstructured organosilane layer by VUV lithography. Cell adhesive materials (poly(d-lysine) and polyethyleneimine) were chemically immobilized on the organosilane template, producing a cell adhesive material pattern. Primary rat cardiac and neuronal cells were successfully patterned by culturing them on the pattern substrate. Long-term culturing was attained for up to two weeks for cardiac cells and two months for cortex cells. We have discussed the reproducibility of cell patterning and made suggestions to improve it.

MALDI mass spectrometry imaging of neuronal cell cultures

Mass spectrometry imaging (MSI) provides the ability to detect and identify a broad range of analytes and their spatial distributions from a variety of sample types, including tissue sections. Here we describe an approach for probing neuropeptides from sparse cell cultures using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MSI--at single cell spatial resolution-in both MS and tandem MS modes. Cultures of Aplysia californica neurons are grown on an array of glass beads embedded in a stretchable layer of Parafilm M. As the membrane is stretched, the beads/neurons are separated physically and the separated beads/neurons analyzed via MALDI TOF MS. Compared with direct MS imaging of samples, the stretching procedure enhances analyte extraction and incorporation into the MALDI matrix, with negligible analyte spread between separated beads. MALDI tandem MSI using the stretched imaging approach yields localization maps of both parent and fragment ions from Aplysia pedal peptide, thereby confirming peptide identification. This methodology represents a flexible platform for MSI investigation of a variety of cell cultures, including functioning neuronal networks.

Electrically controlled drug release from nanostructured polypyrrole coated on titanium

Previous studies have demonstrated that multi-walled carbon nanotubes grown out of anodized nanotubular titanium (MWNT-Ti) can be used as a sensing electrode for various biomedical applications; such sensors detected the redox reactions of certain molecules, specifically proteins deposited by osteoblasts during extracellular matrix bone formation. Since it is known that polypyrrole (PPy) can release drugs upon electrical stimulation, in this study antibiotics (penicillin/streptomycin, P/S) or an anti-inflammatory drug (dexamethasone, Dex), termed PPy[P/S] or PPy[Dex], respectively, were electrodeposited in PPy on titanium. The objective of the present study was to determine if such drugs can be released from PPy on demand and (by applying a voltage) control cellular behavior important for orthopedic applications. Results showed that PPy films possessed nanometer-scale roughness as analyzed by atomic force microscopy. X-ray photoelectron spectroscopy confirmed the presence of P/S and Dex encapsulated within the PPy films. Results from cyclic voltammetry showed that 80% of the drugs were released on demand when sweep voltages were applied for five cycles at a scan rate of 0.1 V s(-1). Furthermore, osteoblast (bone-forming cells) and fibroblast (fibrous tissue-forming cells) adhesion were determined on the PPy films. Results showed that PPy[Dex] enhanced osteoblast adhesion after 4 h of culture compared to plain Ti. PPy-Ti (with or without anionic drug doping) inhibited fibroblast adhesion compared to plain Ti. These in vitro results confirmed that electrodeposited PPy[P/S] and PPy[Dex] can release drugs on demand to potentially fight bacterial infection, reduce inflammation, promote bone growth or reduce fibroblast functions, further implicating the use of such materials as implant sensors.

Nanoscale surfacing for regenerative medicine

Cells in most tissues reside in microenvironment surrounded with specific three-dimensional features. The extracellular matrix or substratum with which cells interact often includes topography at the nanoscale. For example, the basement membrane of many tissues displays features of pores, fibers and ridges in the nanometer range. The nanoscale topography has significant effects on cellular behavior. Knowledge of the cell-substratum interactions is crucial to the understanding of many fundamental biological questions and to regenerative medicine. Rapid advances in nanotechnology enable cellular study on engineered nanoscale surfaces. Recent findings underscore the phenomenon that mammalian cells do respond to nanosized features on a synthetic surface. This review covers the commonly used techniques of engineering nanoscale surface and the techniques which have not been adapted but are of great potential in regenerative medicine, surveys the applications of nanoscale surface in regenerative medicine including vascular, bone, neural and stem cell tissue engineering, and discusses the possible mechanisms of cellular responses to nanoscale surface. A better understanding of the interactions between cells and nanoscale surfacing will help advance the field of regenerative medicine.

Design and Implementation of Functional Nanoelectronic Interfaces With Biomolecules, Cells, and Tissue Using Nanowire Device Arrays

Nanowire FETs (NWFETs) are promising building blocks for nanoscale bioelectronic interfaces with cells and tissue since they are known to exhibit exquisite sensitivity in the context of chemical and biological detection, and have the potential to form strongly coupled interfaces with cell membranes. We present a general scheme that can be used to assemble NWs with rationally designed composition and geometry on either planar inorganic or biocompatible flexible plastic surfaces. We demonstrate that these devices can be used to measure signals from neurons, cardiomyocytes, and heart tissue. Reported signals are in millivolts range, which are equal to or substantially greater than those recorded with either planar FETs or multielectrode arrays, and demonstrate one unique advantage of NW-based devices. Basic studies showing the effect of device sensitivity and cell/substrate junction quality on signal magnitude are presented. Finally, our demonstrated ability to design high-density arrays of NWFETs enables us to map signal at the subcellular level, a functionality not enabled by conventional microfabricated devices. These advances could have broad applications in high-throughput drug assays, fundamental biophysical studies of cellular function, and development of powerful prosthetics.

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

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

Length-scale mediated adhesion and directed growth of neural cells by surface-patterned poly(ethylene glycol) hydrogels

We engineered surfaces that permit the adhesion and directed growth of neuronal cell processes but that prevent the adhesion of astrocytes. This effect was achieved based on the spatial distribution of sub-micron-sized cell-repulsive poly(ethylene glycol) [PEG] hydrogels patterned on an otherwise cell-adhesive substrate. Patterns were identified that promoted cellular responses ranging from complete non-attachment, selective attachment, and directed growth at both cellular and subcellular length scales. At the highest patterning density where the individual hydrogels almost overlapped, there was no cellular adhesion. As the spacing between individual hydrogels was increased, patterns were identified where neurites could grow on the adhesive surface between hydrogels while astrocytes were unable to adhere. Patterns such as lines or arrays were identified that could direct the growth of these subcellular neuronal processes. At higher hydrogel spacings, both neurons and astrocytes adhered and grew in a manner approaching that of unpatterned control surfaces. Patterned lines could once again direct growth at cellular length scales. Significantly, we have demonstrated that the patterning of sub-micron/nano scale cell-repulsive features at microscale lengths on an otherwise cell-adhesive surface can differently control the adhesion and growth of cells and cell processes based on the difference in their characteristic sizes. This concept could potentially be applied to an implantable nerve-guidance device that would selectively enable regrowing axons to bridge a spinal-cord injury without interference from the glial scar.