Guided extracellular matrix formation from fibroblast cells cultured on bio-inspired configurable multiscale substrata.

Engineering complex extracellular matrix (ECM) is an important challenge for cell and tissue engineering applications as well as for understanding fundamental cell biology. We developed the methodology for fabrication of precisely controllable multiscale hierarchical structures using capillary force lithography in combination with original wrinkling technique for the generation of well-defined native ECM-like platforms by culturing fibroblast cells on the multiscale substrata [1]. This paper provides information on detailed characteristics of polyethylene glycol-diacrylate multiscale substrata. In addition, a possible model for guided extracellular matrix formation from fibroblast cells cultured on bio-inspired configurable multiscale substrata is proposed.

Bio-inspired configurable multiscale extracellular matrix-like structures for functional alignment and guided orientation of cells.

Inspired by the hierarchically organized protein fibers in extracellular matrix (ECM) as well as the physiological importance of multiscale topography, we developed a simple but robust method for the design and manipulation of precisely controllable multiscale hierarchical structures using capillary force lithography in combination with an original wrinkling technique. In this study, based on our proposed fabrication technology, we approached a conceptual platform that can mimic the hierarchically multiscale topographical and orientation cues of the ECM for controlling cell structure and function. We patterned the polyurethane acrylate-based nanotopography with various orientations on the microgrooves, which could provide multiscale topography signals of ECM to control single and multicellular morphology and orientation with precision. Using our platforms, we found that the structures and orientations of fibroblast cells were greatly influenced by the nanotopography, rather than the microtopography. We also proposed a new approach that enables the generation of native ECM having nanofibers in specific three-dimensional (3D) configurations by culturing fibroblast cells on the multiscale substrata. We suggest that our methodology could be used as efficient strategies for the design and manipulation of various functional platforms, including well-defined 3D tissue structures for advanced regenerative medicine applications.

In situ realization of asymmetric ratchet structures within microchannels by directionally guided light transmission and their directional flow behavior.

An asymmetric ratchet structure within microchannels is demonstrated by directionally guided light transmission for controlled liquid flow. A direct and facile method is presented to realize programmed asymmetric structures, which control the fluid direction and speed.

Pitch-tunable size reduction patterning with a temperature-memory polymer.

A scalable and pitch-tunable size reduction patterning method is introduced by exploiting the temperature memory effect of shape memory polymer and replica molding of UV-curable materials.

Enhanced skin adhesive patch with modulus-tunable composite micropillars.

Modulus-tunable composite micropillars are presented by combining replica molding and selective inking for skin adhesive patch in "ubiquitous"-health diagnostic devices. Inspired from hierarchical hairs in the gecko's toe pad, a simple method is presented to form composite polydimethylsiloxane (PDMS) micropillars that are highly adhesive (∼1.8 N cm(-2) ) and mechanically robust (∼30 cycles).

One-step process for superhydrophobic metallic surfaces by wire electrical discharge machining.

We present a direct one-step method to fabricate dual-scale superhydrophobic metallic surfaces using wire electrical discharge machining (WEDM). A dual-scale structure was spontaneously formed by the nature of exfoliation characteristic of Al 7075 alloy surface during WEDM process. A primary microscale sinusoidal pattern was formed via a programmed WEDM process, with the wavelength in the range of 200 to 500 µm. Notably, a secondary roughness in the form of microcraters (average roughness, Ra: 4.16 to 0.41 µm) was generated during the exfoliation process without additional chemical treatment. The low surface energy of Al 7075 alloy (γ = 30.65 mJ/m(2)) together with the presence of dual-scale structures appears to contribute to the observed superhydrophobicity with a static contact angle of 156° and a hysteresis less than 3°. To explain the wetting characteristics on dual-scale structures, we used a simple theoretical model. It was found that Cassie state is likely to present on the secondary roughness in all fabricated surfaces. On the other hand, either Wenzel or Cassie state can present on the primary roughness depending on the characteristic length of sinusoidal pattern. In an optimal condition of the serial cutting steps with applied powers of ∼30 and ∼8 kW, respectively, a stable, superhydrophobic metallic surface was created with a sinusoidal pattern of 500 µm wavelength.

Pitch reduction lithography by pressure-assisted selective wetting and thermal reflow.

We report on a new pitch reduction lithographic technique by utilizing pressure-assisted selective wetting and thermal reflow. The primary line-and-space pattern of low molecular weight polystyrene (PS) (Mw=17,300) was formed by solvent-assisted capillary force lithography (CFL), on which a diluted photoresist (PR) solution was selectively filled into the spaces by the application of a slight pressure (200 g cm(-2)). Subsequent removal of the PS pattern by toluene and ashing process led to a line pattern with approximately 50% pitch reduction. It was observed that the size reduction and space to width ratios were controllable by changing PR concentration and ashing time.

Shape-controllable microlens arrays via direct transfer of photocurable polymer droplets.

A simple method is presented to form an array of shape-controllable microlenses by partial photocuring of an UV-curable polymer and direct transfer. Using the transferred lens array, nanoscale metal patterns as small as 130-nm gaps are detected under an optical microscope with a distinguishable resolution.

Arrays of Lucius microprisms for directional allocation of light and autostereoscopic three-dimensional displays.

Directional and asymmetric properties are attractive features in nature that have proven useful for directional wetting, directional flow of liquids and artificial dry adhesion. Here we demonstrate that an optically asymmetric structure can be exploited to guide light with directionality. The Lucius prism array presented here has two distinct properties: the directional transmission of light and the disproportionation of light intensity. These allow the illumination of objects only in desired directions. Set up as an array, the Lucius prism can function as an autostereoscopic three-dimensional display.

Anisotropic adhesion properties of triangular-tip-shaped micropillars.

Directional dry adhesive microstructures consisting of high-density triangular-tip-shaped micropillars are described. The wide-tip structures allow for unique directional shear adhesion properties with respect to the peeling direction, along with relatively high normal adhesion.

Mold design rules for residual layer-free patterning in thermal imprint lithography.

We present the mold design rules for assuring residual layer-free patterning in thermal imprint processes. Using simple relations for mass balance, structural stability, and work of adhesion, we derive the conditions with respect to the given single or multigeometrical feature of the mold, which are compared with simple thermal imprint experiments using soft imprint molds. Our analysis could serve as a guideline for designing the optimum mold geometry and selecting mold material in residual layer-free thermal imprint processes.

High-throughput single-cell quantification using simple microwell-based cell docking and programmable time-course live-cell imaging.

Extracting single-cell information during cellular responses to external signals in a high-throughput manner is an essential step for quantitative single-cell analyses. Here, we have developed a simple yet robust microfluidic platform for measuring time-course single-cell response on a large scale. Our method combines a simple microwell-based cell docking process inside a patterned microfluidic channel, with programmable time-course live-cell imaging and software-aided fluorescent image processing. The budding yeast, Saccharomyces cerevisiae (S. cerevisiae), cells were individually captured in microwells by multiple sweeping processes, in which a cell-containing solution plug was actively migrating back and forth several times by a finger-pressure induced receding meniscus. To optimize cell docking efficiency while minimizing unnecessary flooding in subsequent steps, circular microwells of various channel dimensions (4-24 µm diameter, 8 µm depth) along with different densities of cell solution (1.5-6.0 × 10(9) cells per mL) were tested. It was found that the microwells of 8 µm diameter and 8 µm depth allowed for an optimal docking efficiency (>90%) without notable flooding issues. For quantitative single-cell analysis, time-course (time interval 15 minute, for 2 hours) fluorescent images of the cells stimulated by mating pheromone were captured using computerized fluorescence microscope and the captured images were processed using a commercially available image processing software. Here, real-time cellular responses of the mating MAPK pathway were monitored at various concentrations (1 nM-100 µM) of mating pheromone at single-cell resolution, revealing that individual cells in the population showed non-uniform signaling response kinetics.

Use of directly molded poly(methyl methacrylate) channels for microfluidic applications.

A direct molding method for creating a homogeneous, polymer microfluidic channel is presented. By utilizing capillary rise and subsequent absorption of poly(methyl methacrylate) (PMMA) solution into a solvent-permeable poly(dimethyl siloxane) (PDMS) mold, various circular or elliptic polymer microchannels were fabricated without channel bonding and additional surface modification processes. In addition, the channel diameter was tunable from several micrometres to several hundreds of micrometres by controlling concentration and initial amount of polymer solution for a given PDMS mold geometry. The molded PMMA channels were used for two applications: blocking absorption of Rhodamine B dye and constructing artificial endothelial cell-cultured capillaries. It was observed that the molded PMMA channels effectively prevented absorption and diffusion of Rhodamine molecules over 5 h time span, demonstrating approximately 40 times higher blocking efficiency as compared to porous PDMS channels. Also, calf pulmonary artery endothelial cells (CPAEs) adhered, spread, and proliferated uniformly within the molded microchannels to form near confluency within 3 days and remained viable at day 6 without notable cell death, suggesting high biocompatibility and possibility for emulating in vivo-like three-dimensional architecture of blood vessels.

Measurement of pull-off force on imprinted nanopatterns in an inert liquid.

We report on the measurement of the pull-off force on nanoscale patterns that are formed by thermal nanoimprint lithography (t-NIL). Various patterns with feature sizes in the range of 50-900 nm were fabricated on silicon substrates using a rigiflex polymeric mold of ultraviolet curable polyurethane acrylate (PUA, Young's modulus approximately 1 GPa) or perfluoropolyether (PFPE, Young's modulus approximately 10.5 MPa) and a resist layer of polystyrene (PS) of three different molecular weights (M(w) = 18,100, 211,600 and 2043,000). The pull-off force was measured in non-polar, non-reactive perfluorodecalin (PFD) solvent between a sharp atomic force microscopy (AFM) tip and an imprinted pattern. Our experimental data demonstrated that the measured pull-off forces were in good agreement with a simple adhesion model based on Lifshitz theory. Also, the force on the pressed region (valley) is higher than that on the cavity region (hill), with the ratio (hill/valley) decreasing with the decrease of pattern size and the increase of molecular weight. The confinement effects were more pronounced for smaller patterns (<300 nm) and higher molecular weights (M(w) = 211,600 and 2043,000) presumably due to sluggish movement of polymer chains into nano-cavities. Finally, the experimental observations were compared with molecular dynamic simulations based on a simplified amorphous polyethylene model.

Face selection in one-step bending of Janus nanopillars.

We introduce a one-step procedure of bending nanopillars, which simply involves oblique metal deposition at a tilted angle of 45 degrees on the pillars by thermal evaporation. The face selection in the bending procedure was determined by the nature of residual stress generated in the metal film during evaporation. If the stress was tensile as with many metals (sigma(f) > 0), the Janus nanopillars were bent toward the metal face; if the residual stress was compressive as in the case of Al (sigma(f) < 0), they were bent toward the polymer face. It has also been demonstrated that groups of Janus nanopillars could be bent in different directions on the same substrate with the aid of a shadow-mask deposition. The degree of bending increased with the decrease in pillar diameter in the range of 360-800 nm for a fixed height of 1 microm.

An optimal micropatterned end-effecter for enhancing frictional force on large intestinal surface.

We present a simple surface modification method for enhancing the frictional properties on soft, viscoelastic tissue of large intestine by integrating micropatterned structures with controlled shape and geometry. The micropatterned end-effecter (EE) was fabricated onto micromachined EE body (20 mm long, 2 mm diameter cylinders) in the forms of line, box, pyramid, and bottle shape by utilizing capillary molding technique with UV-curable poly(urethane acrylate) (PUA) polymer. To evaluate the frictional behavior of micropatterned EE, we employed a biotribotester, for easy loading and test of a biological organ specimen. It was found that the frictional properties of micropatterned EE are heavily dependent upon the shape of microstructure. The patterned EE with parallel lines (to the direction of locomotion) showed better frictional performance (average frictional coefficient approximately 1.53 and maximum approximately 3.98) compared with other micropatterned EEs (average frictional coefficient 0.72-0.94 and maximum 1.78-2.49) and nonpatterned EE (average frictional coefficient approximately 0.58 and maximum approximately 1.51). In addition, various geometric parameters (e.g., height, width, and space) as well as operating conditions (e.g., contact load and sliding speed) were systematically investigated for probing optimal anchoring function of the parallel line patterned EE.

Self-modulating polymer resist patterns in pressure-assisted capillary force lithography.

We present pressure-assisted capillary force lithography (CFL) to generate self-modulating polymer resist patterns without residual layers and film instability. The method utilizes roof collapse of a patterned, deformable poly(dimethyl siloxane) (PDMS) mold that is placed on a thermoplastic polymer film with a constant external pressure (approximately 4 bars) and the resulting shape-variable capillary filling of a polymer melt into the reduced void space. A constraint on the coated polymer layer thickness was derived in order to ensure that there is no residual layer left after patterning and at the same time that film stability is guaranteed without film dewetting within the cavity. In addition, the height of a polymer pattern at the center of the filled void was estimated as a function of initial polymer layer thickness based on the assumption of the hemispherical shape of a meniscus and full capillary rise, which agrees well with the experimental data.