Schwann cell response to micropatterned laminin surfaces

Scalable fabrication, compartmentalization and applications of living microtissues

Living microtissues are used in a multitude of applications as they more closely resemble native tissue physiology, as compared to 2D cultures. Microtissues are typically composed of a combination of cells and materials in varying combinations, which are dictated by the applications' design requirements. Their applications range wide, from fundamental biological research such as differentiation studies to industrial applications such as cruelty-free meat production. However, their translation to industrial and clinical settings has been hindered due to the lack of scalability of microtissue production techniques. Continuous microfluidic processes provide an opportunity to overcome this limitation as they offer higher throughput production rates as compared to traditional batch techniques, while maintaining reproducible control over microtissue composition and size. In this review, we provide a comprehensive overview of the current approaches to engineer microtissues with a focus on the advantages of, and need for, the use of continuous processes to produce microtissues in large quantities. Finally, an outlook is provided that outlines the required developments to enable large-scale microtissue fabrication using continuous processes.

Photofabricated Gelatin-Based Nerve Conduits: Nerve Tissue Regeneration Potentials

There is a strong demand for development of nerve guide conduit with prompt nerve regeneration potential for injury-induced nerve defect. Prior to study on nerve tissue engineering using Schwann cells or nerve stem cells, the effectiveness of photofabricated scaffolds based on photocurable gelatin was examined. This study describes the evaluation of in vivo nerve tissue regeneration potentials of three custom-designed and -fabricated prostheses (inner diameter, 1.2 mm; outer diameter, 2.4 mm; wall thickness, 0.60 mm; and length, 15 mm) made of photocured gelatin: a plain photocured gelatin tube (model I), a photocured gelatin tube packed with bioactive substances (laminin, fibronectin, and nerve growth factor) coimmobilized in a photocured gelatin rod (model II), and a photocured gelatin tube packed with bioactive substances coimmobilized in multifilament fibers (model III). These prostheses were implanted between the proximal and distal stumps 10 mm of the dissected right sciatic nerve of 70 adult male Lewis rats for up to 1 year. The highest regenerative potentials were found using the model III prosthesis, followed by the model II prosthesis. Markedly retarded neural regeneration was observed using the model I prosthesis. These were evaluated from the viewpoints of functional recovery, electrophysiological responses, and tissue morphological regeneration. The significance of the synergistic cooperative functions of multifilaments, which serve as a platform that provides contact guidance to direct longitudinal cell movement and tissue ingrowth and as a cell adhesive matrix with high surface area, and immobilized bioactive substances, which enhance nerve regeneration via biological stimulation, is discussed.

Neuropeptide expression and morphometric differences in crushed alveolar inferior nerve of rats: Effects of photobiomodulation

Inferior alveolar nerve (IAN) injuries may occur during various dental routine procedures, especially in the removal of impacted lower third molars, and nerve recovery in these cases is a great challenge in dentistry. Here, the IAN crush injury model was used to assess the efficacy of photobiomodulation (PBM) in the recovery of the IAN in rats following crushing injury (a partial lesion). Rats were divided into four experimental groups: without any procedure, IAN crush injury, and IAN crush injury with PBM and sham group with PBM. Treatment was started 2 days after surgery, above the site of injury, and was performed every other day, totaling 10 sessions. Rats were irradiated with GaAs Laser (Gallium Arsenide, Laserpulse, Ibramed Brazil) emitting a wavelength of 904 nm, an output power of 70 mWpk, beam spot size at target ∼0.1 cm², a frequency of 9500 Hz, a pulse time 60 ns, and an energy density of 6 J/cm². Nerve recovery was investigated by measuring the morphometric data of the IAN using TEM and by the expression of laminin, neurofilaments (NFs), and myelin protein zero (MPZ) using Western blot analysis. We found that IAN-injured rats which received PBM had a significant improvement of IAN morphometry when compared to IAN-injured rats without PBM. In parallel, all MPZ, laminin, and NFs exhibited a decrease after PBM. The results of this study indicate that the correlation between the peripheral nerve ultrastructure and the associated protein expression shows the beneficial effects of PBM.

A facile construction of gradient micro-patterned OCP coatings on medical titanium for high throughput evaluation of biocompatibility

A facile construction of gradient micro-patterned octacalcium phosphate (OCP) coatings on titanium was developed for high-throughput screening of biocompatibility and bioactivity.

Enhanced Schwann cell attachment and alignment using one-pot "dual click" GRGDS and YIGSR derivatized nanofibers

Using metal-free click chemistry and oxime condensation methodologies, GRGDS and YIGSR peptides were coupled to random and aligned degradable nanofiber networks postelectrospinning in a one-pot reaction. The bound peptides are bioactive, as demonstrated by Schwann cell attachment and proliferation, and the inclusion of YIGSR with GRGDS alters the expression of the receptor for YIGSR. Additionally, aligned nanofibers act as a potential guidance cue by increasing the aspect ratio and aligning the actin filaments, which suggest that peptide-functionalized scaffolds would be useful to direct SCs for peripheral nerve regeneration.

Rat sciatic nerve reconstruction across a 30 mm defect bridged by an oriented porous PHBV tube with Schwann cell as artificial nerve graft

An oriented poly(3-hydroxybutyrate-co-3-hydroxyvalerate) nerve conduit has been used to evaluate its efficiency based on the promotion of peripheral nerve regeneration in rats. The oriented porous micropatterned artificial nerve conduit was designed onto the micropatterned silicon wafers, and then their surfaces were modified with oxygen plasma to increase cell adhesion. The designed conduits were investigated by cell culture analyses with Schwann cells (SCs). The conduits were implanted into a 30 mm gap in sciatic nerves of rats. Four months after surgery, the regenerated nerves were monitored and evaluated by macroscopic assessments and histology and behavioral analyses. Results of cellular analyses showed suitable properties of designed conduit for nerve regeneration. The results demonstrated that in the polymeric graft with SCs, the rat sciatic nerve trunk had been reconstructed with restoration of nerve continuity and formatted nerve fibers with myelination. Histological results demonstrated the presence of Schwann and glial cells in regenerated nerves. Functional recovery such as walking, swimming, and recovery of nociceptive function was illustrated for all the grafts especially conduits with SCs. This study proves the feasibility of the artificial nerve graft filled with SCs for peripheral nerve regeneration by bridging a longer defect in an animal model.

Cell patterning with a heptagon acoustic tweezer--application in neurite guidance

Accurate control over positioning of cells is a highly desirable feature in tissue engineering applications since it allows, for example, population of substrates in a controlled fashion, rather than relying on random seeding. Current methods to achieve a differential distribution of cells mostly use passive patterning methods to change chemical, mechanical or topographic properties of surfaces, making areas differentially permissive to the adhesion of cells. However, these methods have no ad hoc control over the actual deposition of cells. Direct patterning methods like bioprinting offer good control over cell position, but require sophisticated instrumentation and are often cost- and time-intensive. Here, we present a novel electronically controlled method of generating dynamic cell patterns by acoustic trapping of cells at a user-determined position, with a heptagonal acoustic tweezer device. We demonstrate the capability of the device to create complex patterns of cells using the device's ability to re-position acoustic traps by using a phase shift in the acoustic wave, and by switching the configuration of active piezoelectric transducers. Furthermore, we show that by arranging Schwann cells from neonatal rats in a linear pattern we are able to create Bands of Büngner-like structures on a non-structured surface and demonstrate that these features are able to guide neurite outgrowth from neonatal rat dorsal root ganglia.

One-step generation of engineered drug-laden poly(lactic-co-glycolic acid) micropatterned with Teflon chips for potential application in tendon restoration

Regulating cellular behaviors such as cellular spatial arrangement and cellular phenotype is critical for managing tissue microstructure and biological function for engineered tissue regeneration. We herein pattern drug-laden poly(lactic-co-glycolic acid) (PLGA) into grooves using novel Teflon stamps (that possess excellent properties of resistance to harsh organic solvents and molecular adsorption) for engineered tendon-repair therapeutics. The drug release and biological properties of melatonin-laden PLGA grooved micropatterns are investigated. The results reveal that fibroblasts cultured on the melatonin-laden PLGA groove micropatterns not only display significant cell alignment that mimics the cell behavior in native tendon, but also promote the secretion of a major extracellular matrix in tendon, type I collagen, indicating great potential for the engineering of functional tendon regeneration.

Inducing functional radial glia-like progenitors from cortical astrocyte cultures using micropatterned PMMA

Radial glia cells (RGC) are multipotent progenitors that generate neurons and glia during CNS development, and which also served as substrate for neuronal migration. After a lesion, reactive glia are the main contributor to CNS regenerative blockage, although some reactive astrocytes are also able to de-differentiate in situ into radial glia-like cells (RGLC), providing beneficial effects in terms of CNS recovery. Thus, the identification of substrate properties that potentiate the ability of astrocytes to transform into RGLC in response to a lesion might help in the development of implantable devices that improve endogenous CNS regeneration. Here we demonstrate that functional RGLC can be induced from in vitro matured astrocytes by using a precisely-sized micropatterned PMMA grooved scaffold, without added soluble or substrate adsorbed biochemical factors. RGLC were extremely organized and aligned on 2 μm line patterned PMMA and, like their embryonic counterparts, express nestin, the neuron-glial progenitor marker Pax6, and also proliferate, generate different intermediate progenitors and support and direct axonal growth and neuronal migration. Our results suggest that the introduction of line patterns in the size range of the RGC processes in implantable scaffolds might mimic the topography of the embryonic neural stem cell niche, driving endogenous astrocytes into an RGLC phenotype, and thus favoring the regenerative response in situ.

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.

Engineered in vitro/in silico models to examine neurite target preference

Research on spinal cord injury (SCI) repair focuses on developing mechanisms to allow neurites to grow past an injury site. In this article, we observe that numerous divergent paths (i.e., spinal roots) are present along the spinal column, and hence guidance strategies must be devised to ensure that regrowing neurites reach viable targets. Therefore, we have engineered an in vitro micropatterned model in which cultured E7 dorsal root ganglia (DRG) explants may enter alternate pathways (?roots?) along a branching micropattern. Alongside this in vitro model, we have developed an in silico simulation that we validate by comparison with independent experiments. We find in both in silico and in vitro models that the probability of a neurite entering a given root decreases exponentially with respect to the number of roots away from the DRG; consequently, the likelihood of neurites reaching a distant root can be vanishingly small. This result represents a starting point for future strategies to optimize the likelihood that neurites will reach appropriate targets in the regenerating nervous system, and provides a new computational tool to evaluate the feasibility and expected success of neurite guidance in complex geometries.

Carbon nanotubes in neural interfacing applications

Carbon nanotubes (CNT) are remarkable materials with a simple and inert molecular structure that gives rise to a range of potentially valuable physical and electronic properties, including high aspect ratio, high mechanical strength and excellent electrical conductivity. This review summarizes recent research on the application of CNT-based materials to study and control cells of the nervous system. It includes the use of CNT as cell culture substrates, to create patterned surfaces and to study cell-matrix interactions. It also summarizes recent investigations of CNT toxicity, particularly as related to neural cells. The application of CNT-based materials to directing the differentiation of progenitor and stem cells toward neural lineages is also discussed. The emphasis is on how CNT surface chemistry and nanotopography can be altered, and how such changes can affect neural cell function. This knowledge can be applied to creating improved neural interfaces and devices, as well as providing new approaches to neural tissue engineering and regeneration.

Spatial control of cell adhesion and patterning through mussel-inspired surface modification by polydopamine

The spatial control and patterning of mammalian cells were achieved by using the universal adhesive property of mussel-inspired polydopamine (PDA). The self-polymerization of dopamine, a small molecule inspired by the DOPA motif of mussel foot proteins, resulted in the formation of a PDA adlayer when aqueous dopamine solution was continuously injected into poly(dimethylsiloxane) microchannels. We found that various cells (fibrosarcoma HT1080, mouse preosteoblast MC3T3-E1, and mouse fibroblast NIH-3T3) predominantly adhered to PDA-modified regions, maintaining their normal morphologies. The cells aligned in the direction of striped PDA patterns, and this tendency was not limited by the type of cell line. Because PDA modification does not require complex chemical reactions and is applicable to any type of material, it enables cell patterning in a simple and versatile manner as opposed to conventional methods based on the immobilization of adhesive proteins. The PDA-based method of cell patterning should be useful in many biomaterial research areas such as the fabrication of tissue engineering scaffolds, cell-based devices for drug screening, and the fundamental study of cell-material interactions.

Novel thin-walled nerve conduit with microgrooved surface patterns for enhanced peripheral nerve repair

Randomly aligned nerve cells in vitro on conventional culture substrata do not represent the complex neuronal network in vivo and neurites growing in uncontrolled manner may form neuroma. It is of great importance to mimic the organised growth pattern of nerve cells in the study of peripheral nerve repair. The aim of this work was to modify and optimize the photolithographic technique in creating a reusable template in the form of a silicon wafer that could be used to produce contact guidance on biodegradable polymer surface for the orientated growth of nerve cells. Micro-grooves (approximately 3 μm in depth) were etched into the silicon template using KOH at increased temperature. The originality of this work lies in the low cost and high efficiency method in producing microgrooves on the surface of biodegradable ultra-thin polymer substrates (50-100 μm), which can be readily rolled up to form clinically implantable nerve conduits. The design of a pattern with small ridge width (i.e., 5 μm) and bigger groove width (i.e., 20 μm) favored the alignment of cells along the grooves rather than on the ridges of the patterns, which minimized the effect of cross growing of neurites between adjacent grooves. Effectively, enhanced nerve regeneration could be anticipated from these patterned conduits.

Fasciculation and defasciculation of neurite bundles on micropatterned substrates

We describe experiments of fasciculation, i.e., bundling, of chick sensory neurites on 2D striped substrates. By Fourier decomposition, we separate left-going and right-going neurite components from in vitro images, and we find first that neurite bundles orient toward preferred angles with respect to the stripe direction, and second that in vitro bundles travel in leftward and rightward directions nearly uninterrupted by crossings of bundles traveling in the opposing direction. We explore mechanisms that lead to these behaviors, and summarize implications for future models for neurite outgrowth and guidance.

Microtopographically patterned surfaces promote the alignment of tenocytes and extracellular collagen

This paper investigates the role of microtopographical features on the cytomorphology, alignment, proliferation and gene expression of tenocytes. We made use of simple microfabrication approaches to create surfaces patterned with topographical features suitable for in vitro studies of tenocytes. These surfaces were composed of glass substrates patterned with polymeric ridges spaced from 50 to 250 microm apart. Our studies demonstrate that the microgrooves differentially impact tenocyte shape, alignment and matrix organization along the direction of grooves. Groove widths significantly influenced cellular alignment, with 50 microm grooved patterns affecting alignment most substantially. Polarized light microscopy demonstrated that mature collagen fibers were denser and more oriented within 50 microm patterns. None of the patterns had a significant effect on the expression of genes linked to proliferation or extracellular matrix synthesis, although time in culture profoundly influenced both gene groups. COMP mRNA expression was moderately increased in tenocytes seeded onto 250 microm grooves, but there was no overall beneficial phenotypic effect of aligned growth. The results of this study indicate that microtopography affects cell density and alignment of tenocytes and leads to the deposition of an aligned collagen matrix, but does not significantly impact matrix gene expression or cell phenotype. These outcomes provide insights into the biology of tendon regeneration, thus providing guidance in the design of clinical procedures for tendon repair.

Optimization by Response Surface Methodology of Confluent and Aligned Cellular Monolayers for Nerve Guidance

Anisotropic tissue structures provide guidance for navigating neurons in vitro and in vivo. Here we optimized the generation of comparable anisotropic monolayers of astrocytes, endothelial cells, and Schwann cells as a first step toward determining which properties of anisotropic cells are sufficient for nerve guidance. The statistical experimental design method Design of Experiments and the experimental analysis method Response Surface Methodology were applied to improve efficiency and utility. Factors investigated included dimensions of microcontact printed protein patterns, cell density, and culture duration. Protein patterning spacing had the strongest influence. When cells initially aligned at borders and proliferated to fill in spaces, space between stripes was most effective when it was comparable to cell size. Maximizing the area of adhesive molecule coverage was also important for confluence of these types of cells. When cells adhered and aligned over the width of a stripe and broadened to fill spaces, space width about half the cell width was most effective. These findings suggest that if the mechanism of alignment, alignment at borders or over the width of the stripe, is predetermined and the cell size determined, the optimal size of the micropatterning for aligned monolayers of other cell types can be predicted. This study also demonstrates the effective use of DOE and RSM to probe cellular responses to various and multiple factors toward determination of optimal conditions for a desired cellular response.

Effect of functionalized micropatterned PLGA on guided neurite growth

When coaptation is not possible in the repair of nerve injuries, a bridge of biomaterial scaffold provides a structural support for neuronal cell growth and guides nerve regeneration. Poly(lactide-co-glycolide) (PLGA) scaffolds have been widely investigated for neural tissue engineering applications. In order to investigate guided neurite growth, we have fabricated micropatterns on PLGA films using laser ablation methods. The micropatterned PLGA films were coated with collagen type I or laminin peptide (PPFLMLLKGSTR) to promote axon growth. Micropatterned PLGA films provide a guidance effect on both early stage neurite outgrowth and elongation. Small (5 microm) grooves showed more statistically significant parallel neurite growth compared with larger size grooves (10 microm). Micropatterned PLGA films coated with laminin peptide showed more parallel neurite growth compared with those coated with collagen type I. Primary neurite number and total neurite length per cell decreased on micropatterned PLGA films compared with the controls. Neurites showed a preference for growth in the microgrooves rather than on the spaces. This study indicates that surface micropatterned structures with conjugated functional molecules can be used to guide neurite growth.

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.

Aligned electrospun nanofibers specify the direction of dorsal root ganglia neurite growth

Nerve injury, a significant cause of disability, may be treated more effectively using nerve guidance channels containing longitudinally aligned fibers. Aligned, electrospun nanofibers direct the neurite growth of immortalized neural stem cells, demonstrating potential for directing regenerating neurites. However, no study of neurite guidance on these fibers has yet been performed with primary neurons. Here, we examined neurites from dorsal root ganglia explants on electrospun poly-L-lactate nanofibers of high, intermediate, and random alignment. On aligned fibers, neurites grew radially outward from the ganglia and turned to follow the fibers upon contact. Neurite guidance was robust, with neurites never leaving the fibers to grow on the surrounding cover slip. To compare the alignment of neurites to that of the nanofiber substrates, Fourier methods were used to quantify the alignment. Neurite alignment, however striking, was inferior to fiber alignment on all but the randomly aligned fibers. Neurites on highly aligned substrates were 20 and 16% longer than neurites on random and intermediate fibers, respectively. Schwann cells on fibers assumed a very narrow morphology compared to those on the surrounding coverslip. The robust neurite guidance demonstrated here is a significant step toward the use of aligned, electrospun nanofibers for nerve regeneration. (c) 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007.

The effect of the alignment of electrospun fibrous scaffolds on Schwann cell maturation

Peripheral nerve regeneration can be enhanced by the stimulation of formation of bands of Büngner prior to implantation. Aligned electrospun poly(epsilon-caprolactone) (PCL) fibers were fabricated to test their potential to provide contact guidance to human Schwann cells. After 7 days of culture, cell cytoskeleton and nuclei were observed to align and elongate along the fiber axes, emulating the structure of bands of Büngner. Microarray analysis revealed a general down-regulation in expression of neurotrophin and neurotrophic receptors in aligned cells as compared to cells seeded on two-dimensional PCL film. Real-time-PCR analyses confirmed the up-regulation of early myelination marker, myelin-associated glycoprotein (MAG), and the down-regulation of NCAM-1, a marker of immature Schwann cells. Similar gene expression changes were also observed on cells cultured on randomly oriented PCL electrospun fibers. However, up-regulation of the myelin-specific gene, P0, was observed only on aligned electrospun fibers, suggesting the propensity of aligned fibers in promoting Schwann cell maturation.

Optimal Micropattern Dimensions Enhance Neurite Outgrowth Rates, Lengths, and Orientations

Micropattern dimensions can significantly influence neurite outgrowth orientation, rate, and length. Laminin micropatterns of various widths from 10 to 50 microm at 10 microm intervals separated by 40 microm spaces were generated on poly(methyl methacrylate) surfaces using microscale plasma-initiated patterning (microPIP). Dissociated dorsal root ganglion (DRG) neurons were seeded on the micropatterned surfaces and cultured for 24 h in serum-free media. Neurite outgrowth numbers, lengths, rates, and orientations were measured on all micropatterned substrates. The results indicated that the dimension of the laminin pattern influenced the neurite outgrowth length, rate, and orientation, but not the numbers of neurite outgrowth. Neurons on more than 30 microm wide laminin pattern showed faster neurite outgrowth compared to other dimensions, and relatively low orientation at 50 microm pattern dimensions. Neurites at 40 microm laminin pattern widths demonstrated the fastest outgrowth rates and were highly oriented. The 40 microm laminin dimension is wide enough to provide sufficient laminin amounts for neuron growth and narrow enough to efficiently guide neurites. Based on these results, adhesive protein micropatterns of 40 microm dimensions are recommended when investigating DRG neurons.

Microcontact printing of laminin on oxygen plasma activated substrates for the alignment and growth of Schwann cells

Microenvironment mimicking biological situation is a vital issue in tissue regeneration. With much progress being made, one of the major challenges remains to develop a convenient method to fabricate the scaffold microenvironment suitable for cell attachment and proliferation. This article demonstrates the efficacy of microcontact printed laminin, an extracellular matrix protein, on three different oxygen plasma treatment substrates-tissue culture polystyrene, poly(methyl methacrylate) films, and chitosan films-for alignment and growth of the Schwann cells in in vitro culturing. Replica molding of polydimethylsiloxane elastomeric stamps, fabricated from patterned SU-8 structure on silicon master, was used to print laminin on the three substrates. Pattern and growth of Schwann cells for low (10(3) cells/cm(2)) and increased cell density (2 x 10(4) cells/cm(2)) on the varied substrates with and without microcontact printed laminin were characterized. Results of in vitro cell culture of Schwann cells showed a high degree of cell orientation on the laminin-micropatterned substrates for both cell densities. However, different cell seeding densities will strongly impact the morphology and orientation of Schwann cells. Microcontact printing proves to be a convenient means to pattern cell-recognition molecules on scaffold for cell-guilded growth in tissue regeneration.

Neurite guidance on protein micropatterns generated by a piezoelectric microdispenser

In this study, we developed a microdispenser technique in order to create protein patterns for guidance of neurites from cultured adult mouse dorsal root ganglia (DRG). The microdispenser is a micromachined silicon device that ejects 100 picolitre droplets and has the ability to position the droplets with a precision of 6-8 microm. Laminin and bovine serum albumin (BSA) was used to create adhesive and non-adhesive protein lines on polystyrene surfaces (cell culture dishes). Whole-mounted DRGs were then positioned close to the patterns and neurite outgrowth was monitored. The neurites preferred to grow on laminin lines as compared to the unpatterned plastic. When patterns were made from BSA the neurites preferred to grow in between the lines on the unpatterned plastic surface. We conclude that microdispensing can be used for guidance of sensory neurites. The advantages of microdispensing is that it is fast, flexible, allows deposition of different protein concentrations and enables patterning on delicate surfaces due to its non-contact mode of operation. It is conceivable that microdispensing can be utilized for the creation of protein patterns for guiding neurites to obtain in vitro neural networks, in tissue engineering or rapid screening for guiding proteins.

Combining cell therapy and nanotechnology

Cell transplantation to treat diseases characterised by tissue and cell dysfunction, ranging from diabetes to spinal cord injury, has made great strides preclinically and towards clinical efficacy. In order to enhance clinical outcomes, research needs to continue in areas including the development of a universal cell source that can be differentiated into specific cellular phenotypes, methods to protect the transplanted allogeneic or xenogeneic cells from rejection by the host immune system, techniques to enhance cellular integration of the transplant within the host tissue, strategies for in vivo detection and monitoring of the cellular implants, and new techniques to deliver genes to cells without eliciting a host immune response. Overcoming these obstacles will be of considerable benefit, as it allows understanding, visualising and controlling cellular interactions at a submicron level. Nanotechnology is a multidisciplinary field that allows us to manipulate materials, tissues, cells and DNA at the level of and within the individual cell. As such, nanotechnology may be well suited to optimise the generally encouraging results already achieved in cell transplantation. This review presents some of the ways that nanotechnology can directly contribute to cell transplantation.

Fabrication of semipermeable hollow fiber membranes with highly aligned texture for nerve guidance

In order to improve the guidance potential of a nerve entubulation bridging device, highly aligned textures were formed on the inner surface of semipermeable hollow fiber membranes (HFMs) during the wet phase inversion process. By precisely controlling the fabrication parameters, such as polymer solution flow rate, coagulant solution flow rate, and the air-gap distance, also called drop height, different-sized aligned grooves can be fabricated on the inner surface of HFMs. Preliminary studies using in vitro dorsal root ganglion (DRG) regeneration assay showed that both the alignment and outgrowth rate of regenerating axons increased significantly on HFMs with aligned textures compared to those on HFMs with a smooth inner surface. Studies in progress are evaluating axonal outgrowth and regeneration using in vivo sciatic-nerve and spinal-cord-injury models.

Connectivity patterns in neuronal networks of experimentally defined geometry

Experimental control over the position and connectivity pattern of neurons on a surface is of central interest for applications in biotechnology, such as cell-based biosensors and tissue engineering. By restricting neuronal networks to a simple grid pattern, a drastic reduction of network complexity can be achieved relative to networks on homogeneous substrates. Therefore, patterned neuronal networks are also a valuable tool in research on neuronal signal transduction. Microcontact printing has emerged as a simple and efficient method for surface patterning to direct cellular attachment. Although the formation of synaptic contacts in networks of rat cortical cells on such surfaces has been demonstrated, evidence of more complex circuits has been lacking. Triple patch-clamp measurements were performed to analyze connectivity in neuronal networks complying with a grid-shaped micropattern. Cells adhered stringently to the pattern and interconnected to a range of different types of circuits: linear connections, feedback loops, as well as branching and converging pathways. We conclude that in spite of the severe geometric restrictions, a complex repertoire of different connectivity patterns can form along the provided pathways. At the same time, network complexity is kept low enough to allow the study of these patterns at the resolution of single cell-cell contacts.

Neurite Outgrowth Is Directed by Schwann Cell Alignment in the Absence of Other Guidance Cues

Schwann cells enhance axonal regeneration following nerve injury in vivo and provide a favorable substrate for neurite outgrowth in vitro. However, much remains unknown about the nature of interactions that occur between Schwann cells and growing neurites. In this paper, we describe direct evidence of the ability of Schwann cell alignment alone to direct neurite outgrowth. Previously, we reported that laminin micro-patterns can be used to align Schwann cells and thus create oriented Schwann cell monolayers. In the current study, dissociated rat spinal neurons were seeded onto oriented Schwann cell monolayers, whose alignment provided the only directional cue for growing neurites, and neurite alignment with the underlying Schwann cells was analyzed. The orientation of neurite outgrowth mimicked that of the Schwann cells. Associations observed between neurites and Schwann cells suggest that Schwann cells may guide neurite outgrowth through both topographical and molecular mechanisms. This work demonstrates that Schwann cell alignment can direct neurite outgrowth in the absence of other directional cues, and provides a new method for examining neuronal-Schwann cell interactions in vitro.

Oriented Schwann cell growth on microgrooved surfaces

Silicon wafers bearing microgrooved surfaces with various groove width, spacing, and depth were fabricated using microlithography. The orientation of rat Schwann cells along the direction of the grooves was measured at 24 h after seeding the cells. When the width/spacing of the grooves was fixed at 10/10 microm, the mean percentage of aligned cells was 12% for grooves of 0.5 microm depth, 15% for those of 1 microm depth, and 26% for those of 1.5 microm depth (P < 0.05). When the depth of grooves was fixed at 1.5 microm, the mean percentage of aligned cells increased from 26% for width/spacing 10/10 microm, to 33% for 10/20 microm or 20/10 microm, and up to 41% for 20/20 microm (P < 0.05). On the surface with grooves of width/spacing/depth = 20/20/1.5 microm and modified by laminin, the alignment at 24 h approached 60%, versus 51% for collagen-coated surface and 41% for uncoated surface (P < 0.05). At 48 h after seeding, about 66% of the cells were aligned on the above laminin-modified surface. The groove depth influenced orientation of Schwann cells significantly. The cell alignment on 20/20/3 microm microgrooved poly(D,L-lactide-co-glycolide) 90:10 (PLGA) surfaces transferred from silicon reached 72% at 48 h and 92% at 72 h (P < 0.05). Coating this surface with laminin enhanced cell alignment only in short term (67% vs. 62% at 24 h, P < 0.05). The cell alignment guided by surface microgrooves was time dependent.

Patterning of a Random Copolymer of Poly[lactide-co-glycotide-co-(ɛ-caprolactone)] by UV Embossing for Tissue Engineering

The random copolymer, poly[lactide-co-glycotide-co-(epsilon-caprolactone)] (PLGACL) diacrylate was prepared by ring-opening polymerization of L-lactide, glycolide, and epsilon-caprolactone initiated with tetra(ethylene glycol). The diacrylated polymers were extensively characterized. With a UV embossing method, these copolymers were successfully fabricated into microchannels separated by microwalls with a high aspect (height/width) ratio. The PLGACL network films showed good cytocompatibility. Varieties of microstructures were fabricated, such as 10 x 40 x 60, 10 x 80 x 60, 25 x 40 x 60, or 25 x 80 x 60 microm(3) structures (microwall width x microchannel width x microwall height). The results demonstrated that smooth muscle cells (SMCs) can grow not only on the microchannel surfaces but also on the surfaces of the microwall and sidewall. The SMCs aligned along the 25 microm wide microwall with an elongated morphology and proliferated very slowly in comparison to those on the smooth surface with a longer cell-culture term. Few cells could attach and spread on the surface of the 40 microm wide microchannel, while the cells flourished on the 80 microm, or more than 80 microm, wide microchannel with a spindle morphology. The biophysical mechanism mediated by the micropattern geometry is discussed. Overall, the present micropattern, consisting of biodegradable and cytocompatible PLGACL, provides a promising scaffold for tissue engineering.

Permeable guidance channels containing microfilament scaffolds enhance axon growth and maturation

Successful peripheral nerve regeneration is still limited in artificial conduits, especially for long lesion gaps. In this study, porous poly(L-lactide-co-DL-lactide, 75:25) (PLA) conduits were manufactured with 16 poly(L-lactide) (PLLA) microfilaments aligned inside the lumen. Fourteen and 18 mm lesion gaps were created in a rat sciatic nerve lesion model. To evaluate the combined effect of permeable PLA conduits and microfilament bundles on axon growth, four types of implants were tested for each lesion gap: PLA conduits with 16 filaments; PLA conduits without filaments; silicone conduits with 16 filaments; and silicone conduits without filaments. Ten weeks following implantation, regeneration within the distal nerve was compared between corresponding groups. Antibodies against the markers S100, calcitonin gene related peptide (CGRP), RMDO95, and P0 were used to identify Schwann cells, unmyelinated axons, myelinated axons, and myelin, respectively. Results demonstrated that the filament scaffold enhanced tissue cable formation and Schwann cell migration in all groups. The filament scaffold enhanced axonal regeneration toward the distal stump, especially across long lesion gaps, but significance was only achieved with PLA conduits. When compared to corresponding silicone conduits, permeable PLA conduits enhanced myelinated axon regeneration across both lesion gaps and achieved significance only in combination with filament scaffolds. Myelin staining indicated PLA conduits supported axon myelination with better myelin quantity and quality when compared to silicone conduits.

Alteration of human neuroblastoma cell morphology and neurite extension with micropatterns

The spatial orientation of nerve cells plays a pivotal role in nerve regeneration. Here we report a new method for regulating neuronal cell morphology and guiding neurite extension on standard tissue culture dishes. Random copolymers of oligoethyleneglycol methacrylate and methacrylic acid [poly(OEGMA-co-MA)], microcontact printed on standard tissue culture dishes, resist cell attachment and remain intact in serum-containing medium for up to 2 weeks. Cell viability assay of SH-SY5Y cells demonstrated that poly(OEGMA-co-MA) on the substrate or in solution has no cytotoxic effect. When retinoic acid was added to SH-SY5Y cells, they extended neurites along the line patterns that are significantly longer than cells cultured on non-patterned culture dishes. The ability to guide neurite extension with micrometer precision is valuable for guiding directional growth of neurites and path finding of regenerating nerves.

Micropatterned polymer substrates control alignment of proliferating Schwann cells to direct neuronal regeneration

Microcontact printed polymeric substrates were evaluated for their ability to control Schwann cell attachment and direct proliferation, as Schwann cell guidance is a crucial factor in directing peripheral nerve regeneration. Elastomeric stamps of poly(dimethylsiloxane) were "inked" with laminin, a permissive protein for Schwann cell adhesion, and stamped onto poly(methyl methacrylate) substrates to create patterns of lines and intervals varying from 10 to 50 microm wide. Schwann cells were seeded onto the substrates in serum-free media. After 4h, media was replaced with serum-containing growth media and changed daily thereafter. The addition of growth media to stimulate proliferation initially caused some loss in cell orientation relative to the laminin pattern, but when monolayer formation was complete, a high degree of cell orientation was observed. As both cell-cell contacts and surface coverage were maximized, the Schwann cells achieved an even higher order of orientation than observed during the early stages of proliferation. Significantly, smaller pattern widths increased the degree of orientation, regardless of interval width. Our results indicate that patterned polymeric substrates may enhance peripheral nerve regeneration by creating a highly ordered Schwann cell matrix for guidance of neurons.