Patterning axonal guidance molecules using a novel strategy for microcontact printing

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.

Numerical and experimental study of critical roof collapse conditions in soft lithography

One of the major issues during soft lithographic processes is that, if the pressing force on the stamp becomes too high, the stamp may erroneously come into contact with the substrate in zones where contact is not intended. This decreases the patterning accuracy and may lead to badly or nonperforming electronic devices and is therefore undesired. Design rules, available at an early stage in the design phase, are desired to speed-up the development of this technique. Ultimately, these rules should give an indication of the critical pressure that can safely be applied on the stamp thereby avoiding unwanted contact between the stamp and the substrate. To obtain these critical pressures, numerical analyses of the deformation behavior of two characteristic configurations in the microstructured surface pattern of the rubber stamp are performed. The deformation behavior of the rubber is modeled according to a Gaussian and a non-Gaussian approach, leading to a neo-Hookean and Arruda-Boyce constitutive model, respectively. Besides these material nonlinearities, geometrical nonlinearities are taken into account as well. The calculated pressure at which undesired contact takes place (the roof collapse pressure) is compared to experimentally obtained values for two particular types of structures, and the results are in agreement within the error margins of the experiments and those ensuing from the assumptions of the numerical simulations.

Microgrooved fibrillar collagen membranes as scaffolds for cell support and alignment

For several years, microgrooved substrates have been evaluated as a means to orient cells in engineered tissues. Recently, we fabricated thin (0.1-5.3 microm) planar and tubular collagen membranes (CMs) from air-dried hydrogels of native, fibrillar type I collagen (Vernon et al., Biomaterials 2004;26:1109-17). The CMs were strong, stable, and permeable and, hence, of potential use as scaffolds for tissue engineering. In the present study, planar CMs supported a robust attachment, spreading, and proliferation of human dermal fibroblasts (HDFs) and human umbilical artery smooth muscle cells (HUASMCs). Collagen hydrogels were air-dried onto microgrooved templates and subsequently removed in the form of grooved CMs with the potential to align cells. The grooved CMs were highly effective at inducing HDFs and HUASMCs to elongate and align, as revealed by scanning electron microscopy and by assays of f-actin and nuclear orientation. Alignment of cells was maintained at high cell densities. CMs with grooves of substantially different widths and depths were similarly effective in causing cell alignment; however, cells aligned poorly on CMs that had grooves less than 1 microm in depth. Grooved CMs with the capability to align cells might be of considerable use in the fabrication of tissue substitutes.

Synaptic plasticity in micropatterned neuronal networks

Synaptic plasticity is thought to be of central importance for information processing by the nervous system. Additionally, specific neuronal connectivity patterns in the brain are implicated to play a role in the perception, processing and storage of incoming signals. Experimental control over connectivity within functional neuronal networks is therefore a promising approach in research on signal transduction and processing by the nervous system. A cell culture system is presented that allows experimental determination of neuronal connectivity patterns in an in vitro network. Rat embryonic cortical neurons were grown on patterns of extracellular matrix proteins applied to polystyrene substrates by microcontact printing. Cells comply well with the pattern and form synaptic connections along the experimentally defined pathways. Chemical synapses identified by double patch-clamp measurement showed paired pulse depression as well as frequency-dependent depression in response to trains of stimuli. This type of short-term plasticity has similarly been reported by others in brain slices. Thus, the system reproduces features central for neuronal information processing while the architecture of the network is experimentally manipulable. The ability to tailor the geometry of functional neuronal networks offers a valuable tool both for fundamental questions in neuroscientific research and a wide range of biotechnological applications.

Gentle cell trapping and release on a microfluidic chip by in situ alginate hydrogel formation

Microfluidic devices are increasingly used to perform biological experiments on a single-cell basis. However, long-term stability of cell positions is still an issue. A novel biocompatible method for cell entrapment and release on a microchip is presented. It is based on the controlled formation of an alginate hydrogel by bringing two laminar flows of alginate and calcium ions in the range of 2 mM to 40 mM into contact. The resulting growth of a gel bar is used to enclose and immobilize yeast cells. Adding ethylenediaminetetraacetic acid (EDTA) to the alginate solution allows for control of the hydrogel growth, and by varying the ratio of Ca(2+) to EDTA concentrations gel growth or gel shrinkage can be induced at will. Trapped cells are released during shrinkage of the gel. The trapping efficiency for different cell speeds is investigated and the properties of gel growth are discussed using a diffusion model. Precise positioning of a single cell is demonstrated. The technique presented allows not only the reversible immobilization of cells under gentle conditions but also offers the potential of long-term cell cultures as shown by on-chip incubation of yeast cells. The procedure may provide a simple and fully biocompatible technique for a multitude of innovative experiments on cells in microsystems.

Micropatterning of cells using modulated magnetic fields

A new technique of cell micropatterning was presented. Mouse osteoblast cells (MC3T3-E1) were seeded on a substrate whose surface was exposed to a periodically modulated magnetic field (a line pattern with a 200- or 600-microm pitch) produced by a field modulator inserted into a homogeneous magnetic field of 1 T generated by an electromagnet. The cells were trapped consistent with the line profile of the modulated field. The trapping efficiency was enhanced by adding Mn(II)EDTA (paramagnetic) to the cultivation medium. The cells were subsequently incubated in the magnetic field. The same technique was applied to whole blood to pattern red blood cells.

Three-Dimensional BioAssembly Tool for Generating Viable Tissue-Engineered Constructs

The primary emphasis of tissue engineering is the design and fabrication of constructs for the replacement of nonfunctional tissue. Because tissue represents a highly organized interplay of cells and extracellular matrix, the fabrication of replacement tissue should mimic this spatial organization. This report details studies evaluating the use of a three-dimensional, direct-write cell deposition system to construct spatially organized viable structures. A direct-write bioassembly system was designed and fabricated to permit layer-by-layer placement of cells and extracellular matrix on a variety of material substrates. Human fibroblasts suspended in polyoxyethylene/polyoxypropylene were coextruded through a positive displacement pen delivery onto a polystyrene slide. After deposition, approximately 60% of the fibroblasts remained viable. Bovine aortic endothelial cells (BAECs) suspended in soluble collagen type I were coextruded via microdispense pen delivery onto the hydrophilic side of flat sheets of polyethylene terephthalate. After deposition with a 25-gauge tip, approximately 86% of the BAECs were viable. When maintained in culture for up to 35 days, the constructs remained viable and maintained their original spatial organization. These results indicate the potential for utilizing a direct-write, three-dimensional bioassembly tool to create viable, patterned tissue-engineered constructs.