Ink-jet printing for micropattern generation of laminin for neuronal adhesion

A versatile method for dynamically controlled patterning of small populations of epithelial cells on substrates via non-contact piezoelectric inkjet printing

Intercellular interactions play a central role at the tissue and whole organism level modulating key cellular functions in normal and disease states. Studies of cell-cell communications are challenging due to ensemble averaging effects brought about by intrinsic heterogeneity in cellular function which requires such studies to be conducted with small populations of cells. Most of the current methods for producing and studying such small cell populations are complex to implement and require skilled personnel limiting their widespread utility in biomedical research labs. We present a simple and rapid method to produce small populations with varying size of epithelial cells (10-50 cells/population) with high-throughput (~ 1 population/second) on flat surfaces via patterning of extracellular matrix (ECM) proteins and random seeding of cells. We demonstrate that despite inherent limitations of non-contact, drop-on-demand piezoelectric inkjet printing for protein patterning, varying mixtures of ECM proteins can be deposited with high reproducibility and level of control on glass substrates using a set of dynamically adjustable optimized deposition parameters. We demonstrate high consistency for the number of cells per population (~1 cell standard error of mean), the population's size (~0.2 coefficient of variation) and shape, as well as accurate spatial placement of and distance between colonies of a panel of metaplastic and dysplastic esophageal epithelial cells with differing adhesion and motility characteristics. The number of cells per colony, colony size and shape can be varied by dynamically varying the amount of ECM proteins deposited per spatial location and the number of spatial locations on the substrate. The method is applicable to a broad range of biological and biomedical studies including cell-cell communications, cellular microenvironment, migration, and stimulus response.

Spatial regulation of controlled bioactive factor delivery for bone tissue engineering

Limitations of current treatment options for critical size bone defects create a significant clinical need for tissue engineered bone strategies. This review describes how control over the spatiotemporal delivery of growth factors, nucleic acids, and drugs and small molecules may aid in recapitulating signals present in bone development and healing, regenerating interfaces of bone with other connective tissues, and enhancing vascularization of tissue engineered bone. State-of-the-art technologies used to create spatially controlled patterns of bioactive factors on the surfaces of materials, to build up 3D materials with patterns of signal presentation within their bulk, and to pattern bioactive factor delivery after scaffold fabrication are presented, highlighting their applications in bone tissue engineering. As these techniques improve in areas such as spatial resolution and speed of patterning, they will continue to grow in value as model systems for understanding cell responses to spatially regulated bioactive factor signal presentation in vitro, and as strategies to investigate the capacity of the defined spatial arrangement of these signals to drive bone regeneration in vivo.

Investigating axonal guidance with microdevice-based approaches

The precise wiring of the nervous system relies on processes by which axons navigate in a complex environment and are guided by a concerted action of attractive and repulsive factors to reach their target. Investigating these guidance processes depends critically on our ability to control in space and time the microenvironment of neurons. The implementation of microfabrication techniques in cell biology now enables a precise control of the extracellular physical and chemical environment of cultured cells. However, microtechnology is only beginning to be applied in the field of axon guidance due to specific requirements of neuronal cultures. Here we review microdevices specifically designed to study axonal guidance and compare them with the conventional assays used to probe gradient sensing in cell biology. We also discuss how innovative microdevice-based approaches will enable the investigation of important systems-level questions on the gradient sensing properties of nerve cells, such as the sensitivity and robustness in the detection of directional signals or the combinatorial response to multiple cues.

Orientation of human osteoblasts on hydroxyapatite-based microchannels

The effect of calcium phosphate-based microchannels on the growth and orientation of human osteoblast cells is investigated in this study. As substrates, hydroxyapatite-based microchannels with high contouring accuracy were fabricated by a novel micro-moulding technique. Microchannels obtained by this method featured widths ranging from 16.0±0.7 to 76.6±1.4 μm and depths from 7.9±0.8 to 15.5±1.3 μm. Surface and contour characterization was carried out using X-ray diffraction analysis, scanning electron microscopy imaging and 3D-confocal profilometry. Cell activity and alignment on microchannels with different widths were determined after 1 and 3 days by photometric spectroscopy and fluorescence microscopic imaging and statistically analysed by Tukey's multiple comparison test. On days 1 and 3 for microchannels of width 16 and 30 μm, 70-80% of the osteoblasts oriented within an angular range of 0-15° relative to the microchannel direction. Interestingly, only 20% of the cells grew inside the microchannels for channel widths of 16 and 30 μm. Substrates with channel widths of 45, 65 and 76 μm allowed ∼40% of the cells to grow inside. The depth of the microchannel showed hardly any significant impact. All micropatterned surfaces provoked a good cell attachment, as flat and spread cell morphologies with lamellipodiae and filopodiae could already be observed after 1 day. The effect of the microchannels on osteoblast activity was determined using the colorimetric WST-1 assay. In addition, the cell differentiation was assessed by collagen type I staining. The cell activity obtained by WST-1 assay differed insignificantly for all micropatterned samples of various widths and depths. The assessment of collagen type I yielded the same amounts for all micropatterned samples after 1, 3 and 7 days. In summary, the microchannel width of HA-based patterns has a distinct effect on the directed growth of human osteoblast cells, allowing novel design strategies for surfaces such as dental implants.

Fabrication and characterization of cytocompatible polypyrrole films inkjet printed from nanoformulations cytocompatible, inkjet-printed polypyrrole films

Inkjet printed polypyrrole (PPy) films with good uniformity and conductivity are fabricated from a stable, printable PPy nanodispersion, and the cytocompatability of these platforms is demonstrated using PC12 cells. This novel approach to fabricating PPy electrodes and films for tissue engineering and cell stimulation is particularly useful where microstructures are required.

Electrospray deposited fibronectin retains the ability to promote cell adhesion

Scaffolds for tissue engineering require the correct biochemical cues if the seeded cells are to migrate into the scaffold and proliferate. For complex tissues this would require precise patterning of the scaffold structure with the particular biochemical cue required at each location on the scaffold. Electrospray enables the deposition of a wide number of biomolecules onto surfaces and can be used for precise patterning. We assessed the functionality of a key cell-adhesion molecule, fibronectin, after depositing it onto a surface using the electrospray technique. The addition of polypropylene glycol allowed a stable spray to be obtained from solutions with a range of fibronectin concentrations. Immunoassay tests showed that the amount of fibronectin retained on the surface was proportional to that sprayed from the solution. Increasing the surface density of fibronectin deposited onto silicon surfaces enhanced fibroblast attachment. The fibronectin thus appears to have retained its cell attachment functionality after undergoing the electrospray process. Since recent advances allow electrospray to pattern material from solution with micrometre accuracy this may allow materials to be biologically functionalized on a similar scale.

Inkjet printing of laminin gradient to investigate endothelial cellular alignment

To investigate the influence of the protein surface-density gradient on endothelial cell alignment, a novel approach for the fabrication of a laminin gradient on gold-coated substrates has been developed in this study. Our approach involves programmed inkjet printing of an alkanethiol (11-mercaptoundecanoic acid, C(10)COOH, MUA) gradient onto gold-coated substrates, followed by backfilling with 11-mercapto-1-undecanol (C(11)OH, MUD). The -COOH moieties were activated and then covalently linked with laminin. This treatment led to a surface-density gradient of laminin. Contact angle measurement, X-ray photoelectron spectroscopy (XPS) and fluorescence microscopy were employed to characterize the self-assembled monolayers (SAMs) and protein gradient, respectively. Results proved the feasibility of the fabrication of a protein gradient by using the inkjet printing technique. The self-assembled monolayer gradients displayed a high packing density, as indicated by dynamic contact angle measurement. More importantly, the gradient slope was easily tunable over a significant distance from 20 to 30 mm. The laminin gradient was clearly visible by fluorescence microscopy observation. Endothelial cells cultured on the surface-density gradient of laminin demonstrated a strong alignment tendency in parallel to the gradient. The higher the laminin density the more cells were observed. The result indicates that cell attachment is dependent on the surface density of laminin. This work broadens our methodology to investigate chemical stimuli-induced cell directional alignment. It is potentially important for understanding cell alignment/ingrowth behavior for angiogenesis and implant technology including tissue-engineered structures.

Excimer laser channel creation in polyethersulfone hollow fibers for compartmentalized in vitro neuronal cell culture scaffolds

Hollow fiber scaffolds that compartmentalize axonal processes from their cell bodies can enable neuronal cultures with directed neurite outgrowth within a three-dimensional (3-D) space for controlling neuronal cell networking in vitro. Controllable 3-D neuronal networks in vitro could provide tools for studying neurobiological events. In order to create such a scaffold, polyethersulfone (PES) microporous hollow fibers were ablated with a KrF excimer laser to generate specifically designed channels for directing neurite outgrowth into the luminal compartments of the fibers. Excimer laser modification is demonstrated as a reproducible method to generate 5microm diameter channels within PES hollow fiber walls that allow compartmentalization of neuronal cell bodies from their axons. Laser modification of counterpart flat sheet PES membranes with peak surface fluences of 1.2Jcm(-2) results in increased hydrophobicity and laminin adsorption on the surface compared with the unmodified PES surface. This is correlated to enhanced PC12 cell adhesion with increasing fluence onto laser-modified PES membrane surfaces coated with laminin when compared with unmodified surfaces. Adult rat neural progenitor cells differentiated on PES fibers with laser-created channels resulted in spontaneous cell process growth into the channels of the scaffold wall while preventing entrance of cell bodies. Therefore, laser-modified PES fibers serve as scaffolds with channels conducive to directing neuronal cell process growth. These hollow fiber scaffolds can potentially be used in combination with perfusion and oxygenation hollow fiber membrane sets to construct a hollow fiber-based 3-D bioreactor for controlling and studying in vitro neuronal networking in three dimensions between compartmentalized cultures.

Mammalian cell-seeded hydrogel microarrays printed via dip-pin technology

Although significant advances have been made in the development of DNA and protein microarrays, less effort has been put toward developing mammalian cell microarrays. Such cellular microarrays may be useful in examining the effects of biological or chemical agents on cells, particularly in drug development and toxicological applications. Here, mammalian cell-seeded hydrogel microarrays were created using two different commercial microarrayers, with four different pin types. Human dermal fibroblasts were used here as a model cell type, seeded within polyethylene glycol-based hydrogels similar to those under investigation as tissue engineering scaffolds, which serve as synthetic extracellular matrices for the cells. Spot sizes of the hydrogels were found to vary with pin type. Multiple touches on a slide following a single dip in the reservoir print solution led to decreasing spot size with each touch; therefore, subsequent microarrays were printed with single touches after a dip. Individual pins of the same type and tip diameter had significantly different spot sizes, likely due to wear of the pins at the tip. However, there was high run-to-run reproducibility between subsequent microarrays. Cell viability varied with pin type, and the number of cells per spot varied with cell density in the print solution, as expected.

Novel surface patterning approaches for tissue engineering and their effect on cell behavior

Methods for the creation of specially designed surfaces for use in the preparation of tailor-made tissue constructs with the ultimate aim of tissue engineering are reviewed here. Fundamental aspects of cell adhesion, proliferation and differentiation and the parameters involved in these processes are discussed. A survey of recent micro- and nano-technological methods for creating physical and chemical cues on tissue engineering carriers is presented. This overview is supported with data from the literature on various applications of different cells on materials with widely differing chemistries and physical properties. Interactions between different cell types and micro- and nano-fabricated substrates are summarized.

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.

Nanoliter-scale reactor arrays for biochemical sensing

A general approach is described for array-based biochemical sensing that uses contact-free dispersal of compounds into addressable microfabricated reactors. The arrays are composed of 1 to 100 nL volume open reactors that have been microfabricated on quartz substrates using lithography. The open architecture of these reactors allows them to be addressed in parallel or individually with an ink-jet arrayer that is capable of distributing 0.004 to 1 nL volumes of reagents. A seven-step biochemical assay has been conducted on a small array of reactors to demonstrate how they can be integrated with an ink-jet arrayer and optical detector. This nanoreactor assay format appears to overcome several limitations that chip-based microarray technology currently imposes on protein assays: the arrays can be created in a manner that does not expose the biochemical reagents to osmotic stress, independent reactions can be conducted in individual reactors, and the conditions in all of the reactors (e.g., concentration and pH) can be rapidly scanned. We believe that these nanoreactor arrays will be useful for biochemical sensing that involves delicate proteins and protein assemblies.

Electrohydrodynamic jetting of mouse neuronal cells

CAD (Cath.a-differentiated) cells, a mouse neuronal cell line, were subjected to electrohydrodynamic jetting at a field strength of 0.47-0.67 kV/mm, corresponding to an applied voltage of 7-10 kV. After jetting, the cells appeared normal and continued to divide at rates similar to those shown by control samples. Jetted cells, when placed in serum-free medium, underwent differentiation that was sustained for at least 1 month. Some of the droplets produced by jetting contained only a few cells. These results indicate that the process of jetting does not significantly perturb neuronal cells and that this novel approach might in the future be a useful way to deposit small numbers of living nerve cells on to surfaces.

Surface engineering approaches to micropattern surfaces for cell-based assays

The ability to produce patterns of single or multiple cells through precise surface engineering of cell culture substrates has promoted the development of cellular bioassays that provide entirely new insights into the factors that control cell adhesion to material surfaces, cell proliferation, differentiation and molecular signaling pathways. The ability to control shape and spreading of attached cells and cell-cell contacts through the form and dimension of the cell-adhesive patches with high precision is important. Commitment of stem cells to different specific lineages depends strongly on cell shape, implying that controlled microenvironments through engineered surfaces may not only be a valuable approach towards fundamental cell-biological studies, but also of great importance for the design of cell culture substrates for tissue engineering. Furthermore, cell patterning is an important tool for organizing cells on transducers for cell-based sensing and cell-based drug discovery concepts. From a material engineering standpoint, patterning approaches have greatly profited by combining microfabrication technologies, such as photolithography, with biochemical functionalization to present to the cells biological cues in spatially controlled regions where the background is rendered non-adhesive ("non-fouling") by suitable chemical modification. The focus of this review is on the surface engineering aspects of biologically motivated micropatterning of two-dimensional (flat) surfaces with the aim to provide an introductory overview and critical assessment of the many techniques described in the literature. In particular, the importance of non-fouling surface chemistries, the combination of hard and soft lithography with molecular assembly techniques as well as a number of less well known, but useful patterning approaches, including direct cell writing, are discussed.

Photo-chemically patterned polymer surfaces for controlled PC-12 adhesion and neurite guidance

The in vitro assembling of cellular networks offering control over cell positions and connectivities by patterned culture substrates is a valuable tool for neuroscience research and other applications in cell biology. We developed a versatile technique based on polymer surface modification which allows the patterning of different cell lines for advanced tissue engineering, among them are Pheochromocytoma cells (PC-12). In contrast to other techniques applied for surface patterning, the presented photo patterning by deep UV irradiation is applicable to the widely used cell culture substrate material polystyrene (PS) and should be easily performed in most laboratories. Irradiation of polystyrene with UV radiation of lambda = 185 nm yields mainly carboxyl groups at the polymer surface which can be used to control the spontaneous competitive protein adsorption from serum containing culture media [Welle A, Gottwald E. UV-based patterning of polymeric substrates for cell culture applications. Biomed. Microdev. 2002;4:33-41] or to serve as defined coupling sites for controlled protein/peptide immobilization. Extending our previous studies on patterning hepatoma cells and fibroblasts via spatially defined plasma protein adsorption, we here describe an advanced application to produce patterns of cell repellent albumin domains and cell attractive laminin regions for the patterning of Pheochromocytoma cells.

A fast flexible ink-jet printing method for patterning dissociated neurons in culture

We present a new technique that uses a custom-built ink-jet printer to fabricate precise micropatterns of cell adhesion materials for neural cell culture. Other work in neural cell patterning has employed photolithography or "soft lithographic" techniques such as micro-stamping, but such approaches are limited by their use of an un-alterable master pattern such as a mask or stamp master and can be resource-intensive. In contrast, ink-jet printing, used in low-cost desktop printers, patterns material by depositing microscopic droplets under robotic control in a programmable and inexpensive manner. We report the use of ink-jet printing to fabricate neuron-adhesive patterns such as islands and other shapes using poly(ethylene) glycol as the cell-repulsive material and a collagen/poly-D-lysine (PDL) mixture as the cell-adhesive material. We show that dissociated rat hippocampal neurons and glia grown at low densities on such patterns retain strong pattern adherence for over 25 days. The patterned neurons are comparable to control, un-patterned cells in electrophysiological properties and in immunocytochemical measurements of synaptic density and inhibitory cell distributions. We suggest that an inexpensive desktop printer may be an accessible tool for making micro-island cultures and other basic patterns. We also suggest that ink-jet printing may be extended to a range of developmental neuroscience studies, given its ability to more easily layer materials, build substrate-bound gradients, construct out-of-plane structure, and deposit sources of diffusible factors.