Fidelity of micropatterned cell cultures

Engineered Hydrogels for Brain Tumor Culture and Therapy

Brain tumors' severity ranges from benign to highly aggressive and invasive. Bioengineering tools can assist in understanding the pathophysiology of these tumors from outside the body and facilitate development of suitable antitumoral treatments. Here, we first describe the physiology and cellular composition of brain tumors. Then, we discuss the development of three-dimensional tissue models utilizing brain tumor cells. In particular, we highlight the role of hydrogels in providing a biomimetic support for the cells to grow into defined structures. Microscale technologies, such as electrospinning and bioprinting, and advanced cellular models aim to mimic the extracellular matrix and natural cellular localization in engineered tumor tissues. Lastly, we review current applications and prospects of hydrogels for therapeutic purposes, such as drug delivery and co-administration with other therapies. Through further development, hydrogels can serve as a reliable option for in vitro modeling and treatment of brain tumors for translational medicine.

Cell patterning via linker-free protein functionalization of an organic conducting polymer (polypyrrole) electrode

The interaction of proteins and cells with polymers is critical to their use in scientific and medical applications. In this study, plasma immersion ion implantation (PIII) was used to modify the surface of the conducting polymer, polypyrrole, which possesses electrical properties. PIII treatment enabled persistent, covalent binding of the cell adhesive protein, tropoelastin, without employing chemical linking molecules. In contrast tropoelastin was readily eluted from the untreated surface. Through this differential persistence of binding, surface bound tropoelastin supported cell adhesion and spreading on the PIII treated but not the untreated polypyrrole surface. The application of a steel shadow mask during PIII treatment allowed for spatial definition of tropoelastin exclusively to PIII treated regions. The general applicability of this approach to other extracellular matrix proteins was illustrated using collagen I, which displayed similar results to tropoelastin but required extended washing conditions. This approach allowed fine patterning of cell adhesion and spreading to tropoelastin and collagen, specifically on PIII treated polypyrrole regions. We therefore present a methodology to alter the functionality of polypyrrole surfaces, generating surfaces that can spatially control cellular interactions through protein functionalization with the potential for electrical stimulation.

Simple benchtop patterning of hydrogel grids for living cell microarrays

A living cell microarray consists of an orderly arrangement of cells attached to a solid support such as a glass microscope slide. The chief difficulty of obtaining such arrays is the fabrication of substrates patterned with micro-wells, adhesive spots, or other features to guide orderly cell attachment. Here we report a novel method using woven Nylon mesh to micropattern three-dimensional alginate hydrogel grids on glass slides. The Nylon mesh is both inexpensive and off-the-shelf. By using Nylon mesh we have eliminated any need for lithography, clean room equipment, and microarray printers to generate microarray patterns; thus, this technique can be easily adopted by biological research labs that may lack microfabrication expertise and facilities. We have demonstrated that glass slides micropatterned with hydrogel grids guide the orderly attachment of single fibroblast cells and Schwann cell clusters in microarrays. The fibroblast arrays consisted of 70 microm square compartments at a density of 21,000 compartments per cm(2). The Schwann cell arrays consisted of 100 microm square compartments at a density of 6000 per cm(2). This patterning technique addresses the need for a simple, inexpensive, benchtop method for micro-patterning glass slides and obtaining living cell microarrays.

Three-dimensional pattering of poly (ethylene Glycol) hydrogels through surface-initiated photopolymerization

Photopolymerizable hydrogels have been investigated extensively for biomedical applications, specifically in the area of tissue engineering. While fabrication approaches have shown promise in designing hydrogel scaffolds that guide cell function, the ability to spatially control localization in three-dimensions has been limited. We have developed a method for generating two-dimensional and three-dimensional (3D) patterns within multilayered poly(ethylene glycol) diacrylate (PEG-DA) hydrogels. Covalently attached hydrogel layers are formed using precursor solutions with a 10:1 mole ratio of PEG-DA to PEG-aminoacrylate (Acr-PEG-NH2). Upon illumination of the precursor with visible light (wavelength = 514 nm), a hydrogel layer forms with pendant amine groups induced by the presence of Acr-PEG-NH2 macromer. Pendant amine groups are further functionalized with free carboxyl groups present on the visible light photoinitiator eosin, allowing for the formation of subsequent hydrogel layers. Using noncontact photolithography, the prepolymer solution is polymerized through a photomask, resulting in hydrogel structures with distinct pattern formation in each layer. Unreacted regions immobilized with eosin can be subsequently filled with a different PEG hydrogel. The technique presented shows a great potential for tissue engineering applications, for biosensors, and in the formation of cell and protein patterning for biotechnology.

Patterning of diverse mammalian cell types in serum free medium with photoablation

Integration of living cells with novel microdevices requires the development of innovative technologies for manipulating cells. Chemical surface patterning has been proven as an effective method to control the attachment and growth of diverse cell populations. Patterning polyelectrolyte multilayers through the combination of layer-by-layer self-assembly technique and photolithography offer a simple, versatile, and silicon compatible approach that overcomes chemical surface patterning limitations, such as short-term stability and low-protein adsorption resistance. In this study, direct photolithographic patterning of two types of multilayers, PAA (poly acrylic acid)/PAAm (poly acryl amide) and PAA/PAH (poly allyl amine hydrochloride), were developed to pattern mammalian neuronal, skeletal, and cardiac muscle cells. For all studied cell types, PAA/PAAm multilayers behaved as a cytophobic surface, completely preventing cell attachment. In contrast, PAA/PAH multilayers have shown a cell-selective behavior, promoting the attachment and growth of neuronal cells (embryonic rat hippocampal and NG108-15 cells) to a greater extent, while providing little attachment for neonatal rat cardiac and skeletal muscle cells (C2C12 cell line). PAA/PAAm multilayer cellular patterns have also shown a remarkable protein adsorption resistance. Protein adsorption protocols commonly used for surface treatment in cell culture did not compromise the cell attachment inhibiting feature of the PAA/PAAm multilayer patterns. The combination of polyelectrolyte multilayer patterns with different adsorbed proteins could expand the applicability of this technology to cell types that require specific proteins either on the surface or in the medium for attachment or differentiation, and could not be patterned using the traditional methods.

Surface topography induces 3D self-orientation of cells and extracellular matrix resulting in improved tissue function

The organization of cells and extracellular matrix (ECM) in native tissues plays a crucial role in their functionality. However, in tissue engineering, cells and ECM are randomly distributed within a scaffold. Thus, the production of engineered-tissue with complex 3D organization remains a challenge. In the present study, we used contact guidance to control the interactions between the material topography, the cells and the ECM for three different tissues, namely vascular media, corneal stroma and dermal tissue. Using a specific surface topography on an elastomeric material, we observed the orientation of a first cell layer along the patterns in the material. Orientation of the first cell layer translates into a physical cue that induces the second cell layer to follow a physiologically consistent orientation mimicking the structure of the native tissue. Furthermore, secreted ECM followed cell orientation in every layer, resulting in an oriented self-assembled tissue sheet. These self-assembled tissue sheets were then used to create 3 different structured engineered-tissue: cornea, vascular media and dermis. We showed that functionality of such structured engineered-tissue was increased when compared to the same non-structured tissue. Dermal tissues were used as a negative control in response to surface topography since native dermal fibroblasts are not preferentially oriented in vivo. Non-structured surfaces were also used to produce randomly oriented tissue sheets to evaluate the impact of tissue orientation on functional output. This novel approach for the production of more complex 3D tissues would be useful for clinical purposes and for in vitro physiological tissue model to better understand long standing questions in biology.

Simple and versatile methods for the fabrication of arrays of live mammalian cells

Single-step methods for the generation of patterned surfaces on hydrogels are presented. Poly(vinyl alcohol) films covalently bonded on glass cover slips and commercially available hydrogel-coated polystyrene plates were used as cell-repellent surfaces. Cell-adhesive domains were created by spotting dilute solutions of sodium hypochlorite onto the surfaces. Alternatively, domains supporting cell attachment were created by exposure to UV light from a xenon excimer lamp, employing a contact mask. Rat skeletal myoblast cells, HEK 293 human embryonic kidney cells and Caco-2 colon carcinoma cells adhered and spread exclusively on modified areas. The surfaces are durable for weeks under cell culture conditions and re-usable after removal of the cells by trypsin treatment. Arrays of adhesive spots seeded with cells at a low density permitted dynamic monitoring of cell proliferation. Selected colonies can be harvested from the surfaces by means of local trypsination. Thus, these techniques may provide useful tools for the isolation of clonal cell populations. Additionally, we demonstrate the possibility of surface-mediated gene delivery from the micro patterns. We show that DNA, complexed with a lipid reagent, can be adsorbed on modified poly(vinyl alcohol) coatings, resulting in spatially controlled adhesion and reverse transfection of HEK 293 cells.

Spatial patterns of protein expression in focal infections of human cytomegalovirus

Human cytomegalovirus (HCMV) is a medically significant human pathogen that infects a wide range of cell and tissue types. During infection, HCMV activates a variety of signal transduction pathways that induce profound changes in cellular processes and dramatically affect cellular gene expression patterns. To better define how these virus-host interactions affect the local microenvironment and influence the spatial and temporal spread of HCMV, we initiated HCMV focal infections on normal human dermal fibroblast monolayers and monitored viral gene expression patterns and infection spread over 45 days. To establish baseline temporal measurements of HCMV infection and spread in cell monolayers, we characterized the influence of three experimental variables on viral gene expression: cell plating density, the presence of serum, and neutralization of cellular antiviral responses with an antibody against interferon-beta. We found that high cell plating density or the inclusion of serum correlated with enhanced HCMV infection spread. Dramatic differences in the expression pattern of the viral immediate early 2 (IE2) gene were observed under these conditions as compared to low plating density or the absence of serum. In the latter case round, uniform foci were observed with a clear wave of IE2 expression visible in advance of a late stage viral protein, envelope glycoprotein B. By contrast, larger irregular foci with arms of IE2 expression were observed in the presence of serum. Addition of the antibody had little effect on the rate of spread, which is consistent with the knowledge that HCMV represses antiviral responses during infection. This experimental system provides a useful means to visualize and quantify complex virus-host interactions.