Orientation of cell adhesion and growth on patterned heterogeneous polystyrene surface

Cell Patterning Technology on Polymethyl Methacrylate through Controlled Physicochemical and Biochemical Functionalization

In recent years, innovative cell-based biosensing systems have been developed, showing impact in healthcare and life science research. Now, there is a need to design mass-production processes to enable their commercialization and reach society. However, current protocols for their fabrication employ materials that are not optimal for industrial production, and their preparation requires several chemical coating steps, resulting in cumbersome protocols. We have developed a simplified two-step method for generating controlled cell patterns on PMMA, a durable and transparent material frequently employed in the mass manufacturing of microfluidic devices. It involves air plasma and microcontact printing. This approach allows the formation of well-defined cell arrays on PMMA without the need for blocking agents to define the patterns. Patterns of various adherent cell types in dozens of individual cell cultures, allowing the regulation of cell-material and cell-cell interactions, were developed. These cell patterns were integrated into a microfluidic device, and their viability for more than 20 h under controlled flow conditions was demonstrated. This work demonstrated the potential to adapt polymeric cytophobic materials to simple fabrication protocols of cell-based microsystems, leveraging the possibilities for commercialization.

Pyro-Electrification of Freestanding Polymer Sheets: A New Tool for Cation-Free Manipulation of Cell Adhesion in vitro

Localized electric fields have become, in recent years, a source of inspiration to researchers and laboratories thanks to a huge amount of applications derived from it, including positioning of microparticles as building blocks for electrical, optical, and magnetic devices. The possibility of producing polymeric materials with surface charge thus opens new perspectives for applications where process simplicity and cost-effectiveness of flexible electronics are of fundamental importance. In particular, the influence of surface charges is widely studied and is a critical issue especially when new materials and functional technologies are introduced. Here, we report a voltage-free pyro-electrification (PE) process able to induce a permanent dipole orientation into polymer sheets under both mono- and bipolar distribution. The technique makes use of the pyroelectric effect for generating electric potentials on the order of kilovolts by an easy-to-accomplish thermal treatment of ferroelectric lithium niobate (LN) crystals. The PE allows us to avoid the expensive and time-consuming fabrication of high-power electrical circuits, as occurs in traditional generator-based techniques. Since the technique is fully compatible with spin-coating-based procedures, the pyro-electrified polymer sheets are easily peeled off the surface of the LN crystal after PE completion, thus providing highly stable and freestanding charged sheets. We show the reliability of the technique for different polymers and for different applications ranging from live cell patterning to biofilm formation tests for bacteria linked to food-processing environments.

The Evolution of Polystyrene as a Cell Culture Material

Polystyrene (PS) has brought in vitro cell culture from its humble beginnings to the modern era, propelling dozens of research fields along the way. This review discusses the development of the material, fabrication, and treatment approaches to create the culture material. However, native PS surfaces poorly facilitate cell adhesion and growth in vitro. To overcome this, liquid surface deposition, energetic plasma activation, and emerging functionalization methods transform the surface chemistry. This review seeks to highlight the many potential applications of the first widely accepted polymer growth surface. Although the majority of in vitro research occurs on two-dimensional surfaces, the importance of three-dimensional (3D) culture models cannot be overlooked. The methods to transition PS to specialized 3D culture surfaces are also reviewed. Specifically, casting, electrospinning, 3D printing, and microcarrier approaches to shift PS to a 3D culture surface are highlighted. The breadth of applications of the material makes it impossible to highlight every use, but the aim remains to demonstrate the versatility and potential as both a general and custom cell culture surface. The review concludes with emerging scaffolding approaches and, based on the findings, presents our insights on the future steps for PS as a tissue culture platform.

Bipolar Patterning of Polymer Membranes by Pyroelectrification

Polymer freestanding membranes with permanent bipolar patterns are fabricated by "pyroelectrification". The thermal stimulation of periodically poled lithium niobate (PPLN) crystals simultaneously generates the pyroelectric effect, the glass transition of the polymer, and therefore the periodic electric poling of the polymer. The reliability of these membranes is demonstrated for applications under both dry and wet conditions, including cell patterning.

Adsorption of a PEO-PPO-PEO triblock copolymer on metal oxide surfaces with a view to reducing protein adsorption and further biofouling

Abstract Biomolecule adsorption is the first stage of biofouling. The aim of this work was to reduce the adsorption of proteins on stainless steel (SS) and titanium surfaces by modifying them with a poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO)-PEO triblock copolymer. Anchoring of the central PPO block of the copolymer is known to be favoured by hydrophobic interaction with the substratum. Therefore, the surfaces of metal oxides were first modified by self-assembly of octadecylphosphonic acid. PEO-PPO-PEO preadsorbed on the hydrophobized surfaces of titanium or SS was shown to prevent the adsorption of bovine serum albumin (BSA), fibrinogen and cytochrome C, as monitored by quartz crystal microbalance (QCM). Moreover, X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry were used to characterize the surfaces of the SS and titanium after competitive adsorption of PEO-PPO-PEO and BSA. The results show that the adsorption of BSA is well prevented on hydrophobized surfaces, in contrast to the surfaces of native metal oxides.

High fidelity neuronal networks formed by plasma masking with a bilayer membrane: analysis of neurodegenerative and neuroprotective processes

Spatially defined neuronal networks have great potential to be used in a wide spectrum of neurobiology assays. We present an original technique for the precise and reproducible formation of neuronal networks. A PDMS membrane comprising through-holes aligned with interconnecting microchannels was used during oxygen plasma etching to dry mask a protein rejecting poly(ethylene glycol) (PEG) adlayer. Patterns were faithfully replicated to produce an oxidized interconnected array pattern which supported protein adsorption. Differentiated human SH-SY5Y neuron-like cells adhered to the array nodes with the micron-scale interconnecting tracks guiding neurite outgrowth to produce neuronal connections and establish a network. A 2.0 μm track width was optimal for high-level network formation and node compliance. These spatially standardized neuronal networks were used to analyse the dynamics of acrylamide-induced neurite degeneration and the protective effects of co-treatment with calpeptin or brain derived neurotrophic factor (BDNF).

Surface chemical patterning for long-term single-cell culture

Surface chemical patterning of polystyrene (PS) dishes for long-term single-cell culture was accomplished by oxygen plasma treatment through the windows of a polydimethylsiloxane membrane mask that produced hydrophilic areas of different shapes and sizes, followed by overnight incubation with either Pluronic F108 solution or a mixture of Pluronic F108 solution and fibronectin. Selective cell attachment on pattern areas of PS dishes was investigated in light of cell seeding experiments and X-ray photoelectron spectroscopy measurements. Activation of the hydrophilic areas of patterned PS surfaces by serum proteins in the culture medium was conducive to cell attachment on the pattern areas of dishes incubated with only Pluronic solution. Preferential adsorption of fibronectin on hydrophilic pattern areas enhanced selective cell attachment on patterned dishes incubated with a mixture of Pluronic solution and fibronectin. Cell-culture experiments demonstrated an effect of surface patterning on both cell and nucleus shape and confirmed the long-term (>2 weeks) stability of the produced single-cell patterns in serum medium.

Patterning of polystyrene by scanning electrochemical microscopy. Biological applications to cell adhesion

Polystyrene surfaces may be patterned by Ag(II), NO(3)(•), and OH(•) electrogenerated at the tip of a scanning electrochemical microscope. These electrogenerated reagents lead to local surface oxidation of the polymer. The most efficient surface treatment is obtained with Ag(II). The patterns are evidenced by XPS and IR and also by the surface wettability contrast between the hydrophobic virgin surface and the hydrophilic pattern. Such Ag(II) treatment of a polystyrene Petri dish generates discriminative surfaces able to promote or disfavor the adhesion of proteins and also the adhesion and growth of adherent cells. The process is also successfully applied to a cyclo-olefin copolymer and should be suitable to pattern any hydrogenated polymer.

Effects of parylene-C photooxidation on serum-assisted glial and neuronal patterning

The increasing use of patterned neural networks in multielectrode arrays and similar devices drives the constant development and evaluation of new biomaterials. Recently, we presented a promising technique to guide neurons and glia reliably and effectively. Parylene-C, a common hydrophobic polymer, was photolithographically patterned on silicon oxide (SiO(2)) and subsequently activated via immersion in serum. In this article, we explore the effects of ultraviolet (UV)-induced oxidation on parylene's ability to pattern neurons and glia. We exposed parylene-C stripe patterns to increasing levels of UV radiation and found a dose-dependent reduction in the total mass of patterned cells, as well as a gradual loss of glial and neuronal conformity to the patterns. In contrast, nonirradiated patterns had superior patterning results and increased presence of cells. The reduced cell adhesion and patterning after the formation of aldehyde and carboxyl groups on UV-radiated parylene-C supports our hypothesis that cell adhesion and growth on parylene is facilitated by hydrophobic adsorption of serum proteins. We conclude that unlike other cell patterning schemes, our technique does not rely on photooxidation of the polymer. Nonetheless, the precise control of oxygenated groups on parylene could pave the way for the differential binding of proteins and other molecules on the surface, aiding in the adhesion of alternative cell types. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.

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

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

Extensive adipogenic and osteogenic differentiation of patterned human mesenchymal stem cells in a microfluidic device

Microtechnology offers great prospects for cellular research by enabling controlled experimental conditions that cannot be achieved by traditional methods. This study demonstrates the use of a microfluidic platform for long-term cultivation (3 weeks) of human mesenchymal stem-like cells (MSCs), a cell population of high interest for tissue engineering. The typical high motility of the MSCs required a strategy for preventing cells from inhabiting the feeding channels and thus interfere with a steady perfusion of medium to the cell cultivation chamber. Hence, a straightforward and long-term patterning method was developed and implemented for reliable cell positioning within the device. This method was based on the modification of a polystyrene substrate into cell supportive and non-supportive regions by the use of selective oxygen plasma treatment and the triblock copolymer Pluronic. Also, a novel and size-effective "flip-chip" set-up for operating the devices was invented. Successful and reproducible adipogenic and osteogenic differentiation of MSCs in the device was demonstrated, verifying that an adequate long-term microfluidic cultivation environment was obtained. Strengths of the experimental protocol include ease of fabrication and maintenance (gravity driven), good cell performance (viability/differentiation), as well as the possibility of exposing the culture to heterogeneous laminar flow for experimental purposes.

Plasma stencilling methods for cell patterning

In this paper we describe plasma stencilling techniques for patterning 10 mammalian cell lines on hydrophobic and cell repellent poly(dimethylsiloxane) (PDMS), methylated glass and bacterial grade polystyrene surfaces. An air plasma produced with a Tesla generator operating at atmospheric pressure was used with microengineered stencils for patterned surface oxidation, selectively transforming the surface to a hydrophilic state to enable cell adhesion and growth. Plasma stencilling obviates the need for directly patterning cell adhesion molecules. Instead, during cell culture, adhesion proteins from the media assemble in a bioactive form on the hydrophilic regions. Critically, the removal of protein patterning prior to cell culture provides the option to also use PDMS-PDMS plasma bonding to incorporate cell patterns within microfluidic systems. Linear patterns were generated using PDMS microchannel stencils, and polyimide stencils with through holes were used for the production of cellular arrays. For the production of smaller cellular arrays, a novel microcapillary-based dielectric barrier discharge system was developed. A numerical method to characterise the cell patterns is also introduced and was used to demonstrate that plasma stencilling is highly effective, with complete patterns confined during long term cell culture (>10 days). In summary, plasma stencilling is simple, rapid, inexpensive, reproducible and a potentially universal cell line patterning capability.

Determination of cross-link density in ion-irradiated polystyrene surfaces from rippling

The irradiation of polymer surfaces with ion beams leads to pronounced chemical and physical modifications when the ions are scattered at the atoms in the polymer chain. In this way, different products of decomposition occur. Here we show that by changing the ion fluence and the mass of the ion the local mechanical properties as Young's modulus of a polystyrene surface layer can be tailored. By annealing prestretched irradiated PS near the glass transition, surface rippling occurs in the irradiated areas only, which can be described with an elastic model. The moduli obtained from rippling periodicities and elastic model assumptions are in the range between 8 and 800 MPa at the glass transition and characterize the irradiated PS as rubberlike. From these values the network density and the molar mass of entanglement are quantified. The obtained network density equals the density of hydrogen vacancies generated through the scattered ions, as confirmed by simulations of the atomic scattering and displacement processes. The obtained molar mass of entanglement reveals that the PS locally was densely cross-linked. Our results show that even for nondiscrete layered polymer systems relevant polymer parameters can be derived from the well-known surface rippling without the need for costly chemical analysis.

Antifouling properties of poly(methyl methacrylate) films grafted with poly(ethylene glycol) monoacrylate immersed in seawater

Biofouling of all structures immersed in seawater constitutes an important problem, and many strategies are currently being developed to tackle it. In this context, our previous work shows that poly(ethylene glycol) monoacrylate (PEGA) macromonomer grafted on preoxidized poly(methyl methacrylate) (PMMAox) films exhibits an excellent repellency against the bovine serum albumin used as a model protein. This study aims to evaluate the following: (1) the prevention of a marine extract material adsorption by the modified surfaces and (2) the antifouling property of the PEGA-g-PMMAox substrates when immersed in natural seawater during two seasons (season 1: end of April-beginning of May 2007, and season 2: end of October-beginning of November 2007). The antifouling performances of the PEGA-g-PMMAox films are investigated for different PEG chain lengths and macromonomer concentrations into the PEGA-based coatings. These two parameters are followed as a function of the immersion time, which evolves up to 14 days. The influence of the PEGA layer on marine compounds (proteins and phospholipids) adsorption is evidenced by time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). It was found that the antifouling efficiency of the PEGA-grafted surfaces increases with both PEGA concentration and PEG chain length.

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.

Orientation and confinement of cells on chemically patterned polystyrene surfaces

UV/ozone oxidation was combined with a photomasking technique to produce adjacent regions of different chemistry on polystyrene (PS) surfaces. The surface chemistry and topography were studied using AFM, XPS and contact angle measurements. The physicochemical patterns were visualised by the condensation of water vapour upon the surfaces and by the differential attachment of Chinese hamster ovarian (CHO) cells. The orientation of CHO cells on 55 and 125 microm wide oxidised PS strips were measured and found to be highly dependent on the width of the oxidised feature. CHO cells in relatively close proximity to a linear polar/non-polar border showed significant axial alignment along the border. CHO cells can also be confined to specific regions of the polymer surface. Cells attached to larger areas (75 microm x 75 microm) were found to have a smaller average cell size than cells attached to the smaller (56 microm x 56 microm) areas.

Surface immobilized protein multilayers for cell seeding

Multilayer assemblies containing various cell-adhesive proteins such as gelatin, collagen IV, and laminin or polycations polylysine and poly(ethyleneimine) were immobilized on the polystyrene surface using the layer-by-layer technique based on hydrophobic and electrostatic interactions between oppositely charged macromolecules. The formation and stability of the assemblies and the adsorption of proteins from a serum containing cell-cultivation media onto their surfaces were observed in real time by Fourier transform infrared multiple internal reflection spectroscopy. The adhesion and growth of mouse embryonic stem cells line D3 were tested in polystyrene culture dishes coated with the assemblies. The cells were seeded in complete serum-containing media or in serum-free media and in the presence (non-differentiated) and/or absence (differentiated) of leukemia inhibitory factor. Proteins from serum-containing cell-cultivation media adsorbed rapidly onto positively charged surfaces. The cells grew best on surfaces coated with gelatin and collagen IV assemblies. There were no significant differences in the growth of the non-differentiated and differentiated cells in complete serum-containing media. When seeded in serum-free media, non-differentiated cells grew better than the differentiated ones. Particularly, polycation surfaces treated with glutaraldehyde promoted the growth of the non-differentiated cells and hindered the growth of the differentiated cells. The layer-by-layer deposition appears to be a practicable technique by which scaffolds for tissue engineering can be coated with biomolecular assemblies tailored to specific cells and applications.

Directional Neurite Outgrowth Is Enhanced by Engineered Meningeal Cell-Coated Substrates

After injury to the CNS, the anatomical organization of the tissue is disrupted, posing a barrier to the regeneration of axons. Meningeal cells, a central participant in the CNS tissue response to injury, migrate into the core of the wound site in an unorganized fashion and deposit a disorganized extracellular matrix (ECM) that produces a nonpermissive environment. Previous work in our laboratory has shown that the presentation of nanometer-scale topographic cues to these cells influences their morphological, cytoskeletal, and secreted ECM alignment. In the present study, we provided similar environmental cues to meningeal cells and examined the ability of the composite construct to influence dorsal root ganglion regeneration in vitro. When grown on control surfaces of meningeal cells lacking underlying topographic cues, there was no bias in neurite outgrowth. In contrast, when grown on monolayers of meningeal cells with underlying nanometer-scale topography, neurite outgrowth length was greater and was directed parallel to the underlying surface topography even though there exists an intervening meningeal cell layer. The observed outgrowth was significantly longer than on laminin-coated surfaces, which are considered to be the optimal substrata for promoting outgrowth of dorsal root ganglion neurons in culture. These results suggest that the nanometer-level surface finish of an implanted biomaterial may be used to organize the encapsulation tissue that accompanies the implantation of materials into the CNS. It furthermore suggests a simple approach for improving bridging materials for repair of nerve tracts or for affecting cellular organization at a device-tissue interface.

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.

Expression of a functional Fas death receptor by human foetal motoneurons

The expression of the apoptosis inducer Fas (CD95/APO-1) surface receptor by human foetal neurons was investigated in vitro and ex vivo. Immunofluorescence studies of brain and spinal cord cells in primary cultures and of cryosections obtained from 9- and 10-week-old human foetuses, respectively, showed that all Fas-expressing cells were motoneurons (5.3 and 4.2% of the neurons in brain or spinal cord cultures, respectively) on the basis of morphology, reactivity with the monoclonal antibody SMI-32, a mostly motoneuronal marker and acetylcholine esterase expression. Fas was undetectable on the other cell types in culture. The ability of Fas to induce apoptosis of cultured cells from both tissues was determined by using the terminal transferase (TdT)-mediated dUTP nick-end labelling (TUNEL) method combined with the same double-staining procedure. Under basal culture conditions, about 9% of cells, all glial fibrillary acidic protein-expressing astrocytes, were apoptotic. After a 48-h incubation with Fas ligand, mean 28.5% of brain motoneurons and 29.4% of spinal motoneurons underwent apoptosis, with an inhibition by Z-IETD-FMK, a caspase-8 inhibitor. Hence, Fas appears to be functional through a caspase-8-dependent pathway in a subpopulation of human foetal motoneurons.

Photolithographically defined deposition of attachment factors as a versatile method for patterning the growth of different cell types in culture

Spatially defined growth of cells in culture is a useful model for studies ranging from the characterization of cellular motility to the analysis of network behaviour in structurally defined ensembles of excitable cells. Current methodological approaches for obtaining patterned growth include sophisticated modifications of surface chemistry, stamping techniques and microfluidics. The implementation of most of these techniques requires the availability of highly specialized apparatus and some of the methods are specific for certain cell types and/or substrate materials. The goal of the present study was to develop a cell-patterning technique that can be implemented by any laboratory working with cell culture and that is highly adaptable in terms of cell types and substrate materials. The method is based on a photolithographic process that permits the patterned deposition of attachment factors of choice on surfaces previously coated with agar with a spatial resolution (maximal deviation from a straight line) of +/-3 micro m. Because agar efficiently prevents cell adhesion, patterned growth obtained with this technique displays virtually no off-pattern cell attachment. The method permitted the patterning of cardiomyocytes, fibroblasts and HeLa cells on either glass substrates or polymer-coated materials with a spatial resolution of a few micrometers.

The effect of surface wettability on induction and growth of neurites from the PC-12 cell on a polymer surface

Surface properties of polymeric devices that are used to regenerate nervous damage are a point to be considered for axon regeneration in nerve system. In our previous studies, we prepared a wettability gradient on polyethylene (PE) surfaces using a corona discharge treatment from a knife-type electrode whose power increases gradually along the sample length. The PE surfaces were oxidized gradually with increasing power. The effect of surface wettability on the different types of cells has an important role for cell adhesion and proliferation. The purpose of this study is to investigate neurite formation on polymer surfaces with different wettability. Induction and growth of neurites from the rat pheochromocytoma (PC-12) cells attached on the polymer surfaces with different hydrophilicity were investigated using the wettability gradient PE surfaces prepared by a corona discharge treatment. Neurites were investigated for number and length of neurites in terms of surface wettability. It was observed that neurite formation of PC-12 cells was increased more onto the positions with moderate hydrophilicity of the wettability gradient surface than onto the more hydrophobic or hydrophilic positions. From those results, it could be assumed that initial adhesion of PC-12 cells was caused by more calf serum (CS) protein than nerve growth factor (NGF), whereas the neurite formation of PC-12 cells was caused by more NGF than CS protein. It follows from what has been said thus far that PC-12 cells are a differentiated neuronal phenotype with a long neurite at around the position 2.5 cm (water contact angle of about 55 deg). In conclusion, surface wettability plays an important role for neurite formation on the polymer surfaces for axon regeneration.

Biology on a chip: microfabrication for studying the behavior of cultured cells

The ability to culture cells in vitro has revolutionized hypothesis testing in basic cell and molecular biology research and has become a standard methodology in drug screening and toxicology assays. However, the traditional cell culture methodology--consisting essentially of the immersion of a large population of cells in a homogeneous fluid medium--has become increasingly limiting, both from a fundamental point of view (cells in vivo are surrounded by complex spatiotemporal microenvironments) and from a practical perspective (scaling up the number of fluid handling steps and cell manipulations for high-throughput studies in vitro is prohibitively expensive). Microfabrication technologies have enabled researchers to design, with micrometer control, the biochemical composition and topology of the substrate, the medium composition, as well as the type of neighboring cells surrounding the microenvironment of the cell. In addition, microtechnology is conceptually well suited for the development of fast, low-cost in vitro systems that allow for high-throughput culturing and analysis of cells under large numbers of conditions. Here we review a variety of applications of microfabrication in cell culture studies, with an emphasis on the biology of various cell types.

Controlling the lateral distribution and alignment of human gingival fibroblasts by micropatterned polysaccharide surfaces

Adhesion and alignment of primary human gingival fibroblast to Petri dishes were controlled by proper modification of the surface chemistry of the solid substrate. In particular, air plasma (glow-discharge) treatment, coupled to a masking technique, was used to pattern cell-adhesive areas on a cell-adhesion-resistant alginate coated surface. Fibroblasts were successfully confined to the air plasma-treated areas, which show a much greater growth rate and cell density as compared to the original alginate coated surface. Beside the implications for the study of the mechanisms of bio-adhesion at hydrophilic surfaces, these systems can be of interest for a number of applications in dental surgery and materials.

Adhesion and proliferation of rat vascular smooth muscle cells (VSMC) on polyethylene implanted with O+ and C+ ions

Polyethylene was implanted with 30-keV oxygen (PE/O+) or 23-keV carbon ions (PE/C+) at 10(13) to 5 x 10(15) ions cm(-2) doses in order to improve the adhesion of vascular smooth muscle cell (VSMC) to the polymer surface in vitro because of its oxidation and carbon-enrichment. The concentration of -CO- groups in the PE/O+ and PE/C+ samples increased only up to doses of 3 x 10(14) and 10(15) ions cm(-2), respectively, and then declined. At the same time, the concentration of these groups, measured at a dose of 3 x 10(14) ions cm(-2), was higher in PE/O+ than in PE/C+ samples. Similarly, the number of initially-adhering rat VSMC (24 h after seeding) increased only up to a dose of 3 x 10(13) and 10(15) ions cm(-2) on PE/O+ and PE/C+ samples, respectively. In addition, between doses of 10(13) and 10(14) ions cm(-2), this number was about two to three times higher on PE/O+ samples. On the other hand, the surface wettability increased proportionally to the implanted ion dose, especially above a dose of 10(14) ions cm(-2). Thus, the number of initially-adhered cells appeared to be positively correlated with the amount of the oxygen group present at the polymer surface rather than with the surface wettability. The higher cell adhesion was accompanied by adsorption of fluorescent dye-conjugated collagen IV in larger amounts. The highest numbers of initially-adhered cells were usually associated with the lowest rates of subsequent proliferation (measured by the doubling time, BrdU labelling and M

Surface characterization of poly(methyl methacrylate) microgrooved for contact guidance of mammalian cells

High-resolution patterns of grooves have been made in poly(methyl methacrylate) films, PMMA, by an electron-beam microlithographic process. The surface of films processed over a large width was characterized in terms of chemical composition (X-ray photoelectron spectroscopy (XPS). time of flight secondary ion mass spectroscopy), wettability (sessile drop) and topography (atomic force microscopy). Collagen adsorption was also studied (radiocounting, XPS) as such or in competition with Pluronic F68. The chemical alteration of the surface induced by the electron-beam irradiation disappeared after the dissolution involved in the development process. W138 human fibroblasts cultivated on microgrooved substrata (grooves 1 microm deep and 0.5-10 microm wide) showed a strong orientation parallel to the grooves. The contact guidance is induced by the topography of the surface and not by the alternation of zones with different physico-chemical properties. It may be explained in terms of probability of successful substratum contact by cell protrusions.

Effects of Serum on the Kinetics of CHO Attachment to Ultraviolet-Ozone Modified Polystyrene Surfaces

Attachment kinetics of Chinese hamster ovarian (CHO) cells were investigated on ultraviolet-ozone oxidized polystyrene (UVO-PS) dishes in the presence and absence of serum. The surface chemistry of UVO-PS has been extensively characterized. Although cells attached rapidly to the oxidized dishes with serum present it was found that serum actually inhibits the rate of attachment. Spreading of attached cells was favored by the presence of serum. It is suggested that the increased quantity of hydrophilic carboxyl groups on longer exposed UVO-PS leads to a change in the protein layer adsorbed from serum and also a higher affinity of the surface for extracellular proteins secreted by the attached cells. The UVO-PS surfaces present a new way of producing tissue culture grade polystyrene (TCPS) in a highly controllable method, which would ensure greater consistency in TCPS surfaces. Copyright 2001 Academic Press.

Low concentrations of fibrinogen increase cell migration speed on fibronectin/fibrinogen composite cables

Optimal cell migration rate in a given direction (velocity) is a function of speed and directional persistence. Migration speed has been reported to be a function of adhesion strength such that optimal cell migration occurs where the cell is able to form enough stable attachments for good traction while allowing attachments at the trailing end to be broken during locomotion. This is particularly important in peripheral nerve regeneration where rapid Schwann cell recruitment across the injury site will lead to better functional recovery and reduced end organ atrophy. The aim here was to investigate the effects of changing adhesion properties of Fn materials by adding fibrinogen in order to design an optimal material for repair processes. Cell migration on Fn/Fg-cables increased with increasing content of %Fg to a peak cell migration velocity (Schwann cells) of 49 microm/h, at 50% Fg. Further increases in Fg content hindered cell migration. Vinculin-rich attachment plaques were reduced in a dose-dependent manner as the content of %Fg was increased whilst cells at the optimum Fg proportion for cell migration were moderately well spread. These results support the idea that optimum cell migration rates occur at intermediate attachment conditions, in this case at 50% Fg. These results show that incorporation of Fg into Fn-based materials will enhance the speed of Schwann cell migration and this would be likely to improve peripheral nerve regeneration. Indeed, directionally aligned Fn-based materials can now be engineered to give optimal cell velocity during repair cell recruitment in a range of tissue repair or tissue engineering applications.

Fibronectin-pluronic coadsorption on a polystyrene surface with increasing hydrophobicity: relationship to cell adhesion

Recently, patterned polystyrene surfaces containing hydrophobic (PS) and more hydrophilic (PSox) areas have been shown to be capable of directing cellular growth, which is mainly due to the competitive adsorption of adhesive and antiadhesive molecules. In this article, the competitive adsorption between a pluronic surfactant and fibronectin was studied on homogeneous PS or PSox substrates conditioned with mixtures containing increasing concentrations of one of the two molecules. Radiolabeling and X-ray photoelectron spectroscopy techniques showed that fibronectin adsorption increased on both surfaces if the fibronectin concentrations increased in the conditioning mixture. In contrast, fibronectin adsorption decreased on PSox and did not occur on PS surfaces when pluronic concentrations increased in the coating mixture. A comparison of these data with pheochromocytoma and Schwann cells cultured on patterned surfaces showed that the direction of cell growth on PSox areas depended first on the relative concentrations of the two components in the mixtures, and second, on their ratio; the best concentration ratio probably depends on the cell's ability to recondition its support.