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Terms modified by PDMS Selected AbstractsDevelopment of micropost force sensor array with culture experiments for determination of cell traction forcesCYTOSKELETON, Issue 7 2007Bin Li Abstract Cell traction forces (CTFs) are critical for cell motility and cell shape maintenance. As such, they play a fundamental role in many biological processes such as angiogenesis, embryogenesis, inflammation, and wound healing. To determine CTFs at the sub-cellular level with high sensitivity, we have developed high density micropost force sensor array (MFSA), which consists of an array of vertically standing poly(dimethylsiloxane) (PDMS) microposts, 2 ,m in diameter and 6 ,m in height, with a center-to-center distance of 4 ,m. In combination with new image analysis algorithms, the MFSA can achieve a spatial resolution of 40 nm and a force sensitivity of 0.5 nN. Culture experiments with various types of cells showed that this MFSA technology can effectively determine CTFs of cells with different sizes and traction force magnitudes. Cell Motil. Cytoskeleton 2007. © 2007 Wiley-Liss, Inc. [source] Toner and paper-based fabrication techniques for microfluidic applicationsELECTROPHORESIS, Issue 15 2010Wendell Karlos Tomazelli Coltro Abstract The interest in low-cost microfluidic platforms as well as emerging microfabrication techniques has increased considerably over the last years. Toner- and paper-based techniques have appeared as two of the most promising platforms for the production of disposable devices for on-chip applications. This review focuses on recent advances in the fabrication techniques and in the analytical/bioanalytical applications of toner and paper-based devices. The discussion is divided in two parts dealing with (i) toner and (ii) paper devices. Examples of miniaturized devices fabricated by using direct-printing or toner transfer masking in polyester-toner, glass, PDMS as well as conductive platforms as recordable compact disks and printed circuit board are presented. The construction and the use of paper-based devices for off-site diagnosis and bioassays are also described to cover this emerging platform for low-cost diagnostics. [source] Dynamic coating of SU-8 microfluidic chips with phospholipid disksELECTROPHORESIS, Issue 15 2010Tiina Sikanen Abstract In this work, PEG-stabilized phosphatidylcholine lipid aggregates (disks), mimicking mammalian cell membranes, were introduced as a new biofouling resistant coating for SU-8 polymer microchannels. A rapid and simple method was developed for immobilization of PEGylated phosphatidylcholine disks in microchannels. Microfluidic chips made from SU-8, PDMS, or glass were dynamically coated with the PEGylated disks followed by characterization of their surface chemistry before and after coating. On the basis of the observed changes in EOF and nonspecific protein adsorption, the affinity of the PEGylated disks was shown to be particularly strong toward SU-8. The PEG-lipid coating enabled permanent change in EOF in SU-8 microchannels with an initial value of 4.5×10,8,m2,V,1,s,1, decreasing to 2.1×10,8,m2,V,1,s,1 (immediately after modification), and, eventually, to 1.5×10,8,m2,V,1,s,1 (7 days after modification) for 9,mM sodium borate (pH 10.5) as BGE. As determined by the Wilhelmy plate measurements and microchip-CE analysis of BSA, the PEG-lipid coating also enabled efficient biofouling shield against protein adsorption, similar to that of low amounts of SDS (3.5,mM) or Tween-20 (80,,M) as buffer additives. These results suggest that dynamically attached PEG-lipid aggregates provide stable, biomimicking surface modification that efficiently reduces biofouling on SU-8. [source] Multiple-point electrochemical detection for a dual-channel hybrid PDMS-glass microchip electrophoresis deviceELECTROPHORESIS, Issue 19 2009Mario Castaño-Álvarez Abstract A new PDMS-based dual-channel MCE with multiple-point amperometric detection has been evaluated. Electrophoresis has been optimised in a single-channel device. Pretreatment with 0.1,M NaOH is very important for increasing and stabilising the EOF. The precision is adequate for a day's work in terms of both peak current and migration time. The RSD of the peak current for five successive signals was 1.9, 2.4 and 3.1% for dopamine, p- aminophenol and hydroquinone. RSD for the migration time was always less than 1.3%, which demonstrates the stability of the EOF and the possibility of running multiple experiments in the same microchip. The adequate inter-microchip precision as well as the rapid and simple manufacturing procedure indicates the disposable nature of the PDMS microchips. A dual-channel device with very simple multiple-point amperometric detection is proposed here. Elasticity of the PDMS allows removing the polymer slightly and aligning gold wires working electrodes. Injection can be performed from each of the sample reservoirs or from both simultaneously. The distance between the separation channels is critical for obtaining adequate signals as well as the introduction of a high-voltage electrode in the buffer reservoir. Simultaneous measurement of the same analytes in both channels is possible by applying the same potential. Moreover, since no cross-separation is produced, different analytes or samples can be simultaneously measured. [source] Enhancement of electrokinetically driven microfluidic T-mixer using frequency modulated electric field and channel geometry effectsELECTROPHORESIS, Issue 18 2009Deguang Yan Abstract This study reports improved electrokinetically driven microfluidic T-mixers to enhance their mixing efficiency. Enhancement of electrokinetic microfluidic T-mixers is achieved using (i) an active approach of utilizing a pulsating EOF, and (ii) a passive approach of using the channel geometry effect with patterned blocks. PDMS-based electrokinetic T-mixers of different designs were fabricated. Experimental measurements were carried out using Rhodamine B to examine the mixing performance and the micro-particle image velocimetry technique to characterize the electrokinetic flow velocity field. Scaling analysis provides an effective frequency range of applied AC electric field. Results show that for a T-mixer of 10,mm mixing length, utilizing frequency modulated electric field and channel geometry effects can increase the mixing efficiency from 50 to 90%. In addition, numerical simulations were performed to analyze the mixing process in the electrokinetic T-mixers with various designs. The simulation results were compared with the experimental data, and reasonable agreement was found. [source] A microfabricated CE chip for DNA pre-concentration and separation utilizing a normally closed valveELECTROPHORESIS, Issue 18 2009Chen-Hua Kuo Abstract A simple, sequential DNA pre-concentration and separation method by using a micro-CE chip integrated with a normally closed valve, which is activated by pneumatic suction, has been developed. The CE chip is fabricated using PDMS. A surface treatment technique for coating a polymer bilayer with an anionic charge is applied to modify the surface of the microchannel. A normally closed valve with anionic surface charges forms a nanoscale channel that only allows the passage of electric current but traps the DNA samples so that they are pre-concentrated. After the pre-concentration step, a pneumatic suction force is applied to the normally closed valve. This presses down the valve membrane, which reconnects the channels. The DNA samples are then moved into a separation channel for further separation and analysis. Successful DNA pre-concentration and separation has been achieved. Fluorescent intensity at the pre-concentration area is increased by approximately 3570 times within 1.9,min of operation. The signals from the separation of ,X174 DNA/HaeIII markers are enhanced approximately 41 times after 100,s of pre-concentration time, as compared with the results using a traditional cross-shaped micro-CE chip. These results clearly demonstrate that successful DNA pre-concentration for signal enhancement and separation analysis can be performed by using this new micro-CE chip. [source] Integration of continuous-flow sampling with microchip electrophoresis using poly(dimethylsiloxane)-based valves in a reversibly sealed deviceELECTROPHORESIS, Issue 14 2007Michelle W. Li Abstract Here we describe a reversibly sealed microchip device that incorporates poly(dimethylsiloxane) (PDMS)-based valves for the rapid injection of analytes from a continuously flowing stream into a channel network for analysis with microchip electrophoresis. The microchip was reversibly sealed to a PDMS-coated glass substrate and microbore tubing was used for the introduction of gas and fluids to the microchip device. Two pneumatic valves were incorporated into the design and actuated on the order of hundreds of milliseconds, allowing analyte from a continuously flowing sampling stream to be injected into an electrophoresis separation channel. The device was characterized in terms of the valve actuation time and pushback voltage. It was also found that the addition of sodium dodecyl sulfate (SDS) to the buffer system greatly increased the reproducibility of the injection scheme and enabled the analysis of amino acids derivatized with naphthalene-2,3-dicarboxaldehyde/cyanide. Results from continuous injections of a 0.39,nL fluorescein plug into the optimized system showed that the injection process was reproducible (RSD of 0.7%, n,=,10). Studies also showed that the device was capable of monitoring off-chip changes in concentration with a device lag time of 90,s. Finally, the ability of the device to rapidly monitor on-chip concentration changes was demonstrated by continually sampling from an analyte plug that was derivatized upstream from the electrophoresis/continuous flow interface. A reversibly sealed device of this type will be useful for the continuous monitoring and analysis of processes that occur either off-chip (such as microdialysis sampling) or on-chip from other integrated functions. [source] Viability study of HL60 cells in contact with commonly used microchip materialsELECTROPHORESIS, Issue 24 2006Floor Wolbers Abstract This paper presents a study in which different commonly used microchip materials (silicon oxide, borosilicate glass, and PDMS) were analyzed for their effect on human promyelocytic leukemic (HL60) cells. Copper-coated silicon was analyzed for its toxicity and therefore served as a positive control. With quantitative PCR, the expression of the proliferation marker Cyclin D1 and the apoptosis marker tissue transglutaminase were measured. Flow cytometry was used to analyze the distribution through the different phases of the cell cycle (propidium iodide, PI) and the apoptotic cascade (Annexin V in combination with PI). All microchip materials, with the exception of Cu, appeared to be suitable for HL60 cells, showing a ratio apoptosis/proliferation (Rap) comparable to materials used in conventional cell culture (polystyrene). These results were confirmed with cell cycle analysis and apoptosis studies. Precoating the microchip material surfaces with serum favor the proliferation, as demonstrated by a lower Rap as compared to uncoated surfaces. The Cu-coated surface appeared to be toxic for HL60 cells, showing over 90% decreased viability within 24,h. From these results, it can be concluded that the chosen protocol is suitable for selection of the cell culture material, and that the most commonly used microchip materials are compatible with HL60 culturing. [source] Electrokinetic-driven microfluidic system in poly(dimethylsiloxane) for mass spectrometry detection integrating sample injection, capillary electrophoresis, and electrospray emitter on-chipELECTROPHORESIS, Issue 24 2005Sara Thorslund Abstract A novel microsystem device in poly(dimethylsiloxane) (PDMS) for MS detection is presented. The microchip integrates sample injection, capillary electrophoretic separation, and electrospray emitter in a single substrate, and all modules are fabricated in the PDMS bulk material. The injection and separation flow is driven electrokinetically and the total amount of external equipment needed consists of a three-channel high-voltage power supply. The instant switching between sample injection and separation is performed through a series of low-cost relays, limiting the separation field strength to a maximum of 270,V/cm. We show that this set-up is sufficient to accomplish electrospray MS analysis and, to a moderate extent, microchip separation of standard peptides. A new method of instant in-channel oxidation makes it possible to overcome the problem of irreversibly bonded PDMS channels that have recovered their hydrophobic properties over time. The fast method turns the channel surfaces hydrophilic and less prone to nonspecific analyte adsorption, yielding better separation efficiencies and higher apparent peptide mobilities. [source] A polymeric master replication technology for mass fabrication of poly(dimethylsiloxane) microfluidic devicesELECTROPHORESIS, Issue 9 2005Hai-Fang Li Abstract A protocol of producing multiple polymeric masters from an original glass master mold has been developed, which enables the production of multiple poly(dimethylsiloxane) (PDMS)-based microfluidic devices in a low-cost and efficient manner. Standard wet-etching techniques were used to fabricate an original glass master with negative features, from which more than 50 polymethylmethacrylate (PMMA) positive replica masters were rapidly created using the thermal printing technique. The time to replicate each PMMA master was as short as 20 min. The PMMA replica masters have excellent structural features and could be used to cast PDMS devices for many times. An integration geometry designed for laser-induced fluorescence (LIF) detection, which contains normal deep microfluidic channels and a much deeper optical fiber channel, was successfully transferred into PDMS devices. The positive relief on seven PMMA replica masters is replicated with regard to the negative original glass master, with a depth average variation of 0.89% for 26 ,m deep microfluidic channels and 1.16% for the 90 ,m deep fiber channel. The imprinted positive relief in PMMA from master-to-master is reproducible with relative standard deviations (RSDs) of 1.06% for the maximum width and 0.46% for depth in terms of the separation channel. The PDMS devices fabricated from the PMMA replica masters were characterized and applied to the separation of a fluorescein isothiocyanate (FITC)-labeled epinephrine sample. [source] Multilayer poly(vinyl alcohol)-adsorbed coating on poly(dimethylsiloxane) microfluidic chips for biopolymer separationELECTROPHORESIS, Issue 1 2005Dapeng Wu Abstract A poly(dimethylsiloxane) (PDMS) microfluidic chip surface was modified by multilayer-adsorbed and heat-immobilized poly(vinyl alcohol) (PVA) after oxygen plasma treatment. The reflection absorption infrared spectrum (RAIRS) showed that 88% hydrolyzed PVA adsorbed more strongly than 100% hydrolyzed one on the oxygen plasma-pretreated PDMS surface, and they all had little adsorption on original PDMS surface. Repeating the coating procedure three times was found to produce the most robust and effective coating. PVA coating converted the original PDMS surface from a hydrophobic one into a hydrophilic surface, and suppressed electroosmotic flow (EOF) in the range of pH 3,11. More than 1 000,000 plates/m and baseline resolution were obtained for separation of fluorescently labeled basic proteins (lysozyme, ribonuclease B). Fluorescently labeled acidic proteins (bovine serum albumin, ,-lactoglobulin) and fragments of dsDNA ,X174 RF/HaeIII were also separated satisfactorily in the three-layer 88% PVA-coated PDMS microchip. Good separation of basic proteins was obtained for about 70 consecutive runs. [source] Direct electrochemical detection of glucose in human plasma on capillary electrophoresis microchipsELECTROPHORESIS, Issue 21-22 2004Yan Du Abstract We developed an electrochemical detector on a hybrid chip for the determination of glucose in human plasma. The microchip system described in this paper consists of a poly(dimethylsiloxane) (PDMS) layer containing separation and injection channels and an electrode plate. The copper microelectrode is fabricated by selective electroless deposition. The fabrication of the decoupler is performed by platinum electrochemical deposition on the metal film formed by electroless deposition. Factors influencing the performance, including detection potential, separation field strength, and buffer concentration, were studied. The electrodes exhibited good stability and durability in the analytical procedures. Under optimized detection conditions, glucose responded linearly from 10 ,M to 1 mM. Finally, glucose in human plasma from three healthy individuals and two diabetics was successfully determined, giving a good prospect for a new clinical diagnostic instrument. [source] Electroosmotic flow in a poly(dimethylsiloxane) channel does not depend on percent curing agentELECTROPHORESIS, Issue 7-8 2004Aaron R. Wheeler Abstract Poly(dimethylsiloxane) (PDMS) microfluidic devices were prepared from different ratios of "curing agent" (which contains silicon hydride groups) to "base" (which contains vinyl-terminated noncross-linked PDMS), to determine the effect of this ratio on electroosmotic flow (EOF). In fabricating devices for this purpose, a novel method for permanently enclosing PDMS channels was developed. As a supplement to the microfluidic method, the inner walls of capillaries were coated with PDMS formed from varying ratios of curing agent to base. EOF was found to be constant for PDMS formed with each ratio, which implies that the negative surface charges do not arise from chemical species present only in the base or the curing agent. [source] Poly(dimethylsiloxane)-based microfluidic device with electrospray ionization-mass spectrometry interface for protein identificationELECTROPHORESIS, Issue 21 2003Wang-Chou Sung Abstract An easy method to fabricate poly(dimethylsiloxane) (PDMS)-based microfluidic chips for protein identification by tandem mass spectrometry is presented. This microchip has typical electrophoretic microchannels, a flow-through sampling inlet, and a sheathless nanoelectrospray ionization (ESI) interface. The surface of the microchannel was modified with 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and the generated electroosmotic flow under acidic buffer condition used for the separation was found to be more stable compared to that generated by the microchannel without modification. The feasibility of the device for flow-through sampling, separation, and ESI-MS/MS analysis was demonstrated by the analysis of a standard mixture composed of three tryptic peptides. Results show that four peaks corresponding to three peptide standards and acetylated products of the standard peptide were well resolved and the deduced sequences were consistent with those expected. Furthermore, the compatibility of this device with other miniaturized devices to integrate the whole process was also explored by connecting a miniaturized enzymatic digestion cartridge and a desalting cartridge in series to the sampling inlet of the microchip for the identification of a model protein, ,-casein. [source] Field testing of equilibrium passive samplers to determine freely dissolved native polycyclic aromatic hydrocarbon concentrationsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2008Gerard Cornelissen Abstract Equilibrium passive samplers are promising tools to determine freely dissolved aqueous concentrations (CW,free) of hydrophobic organic compounds. Their use in the field, however, remains a challenge. In the present study on native polycyclic aromatic hydrocarbons (PAHs) in Oslo Harbor, Norway, two different passive sampler materials, polyoxymethylene (POM; thickness, 55 ,m [POM-55] and 500 ,m [POM-500]) and polydimethylsiloxane (PDMS; thickness, 200 ,m), were used to determine in the laboratory CW,free in sediment pore water (CPW,free), and the suitability of five passive samplers for determination of CW,free in overlying surface water was tested under field conditions. For laboratory determinations of CPW,free, both POM-55 and PDMS turned out to be suitable. In the field, the shortest equilibrium times (approximately one month) were observed for POM-55 and PDMS (thickness, 28 ,m) coatings on solid-phase microextraction fibers, with PDMS tubing as a good alternative. Low-density polyethylene (thickness, 100 ,m) and POM-500 did not reach equilibrium within 119 d in the field. Realistic values were obtained for dissolved organic carbon,water partition coefficients in the field (approximately one log unit under log KOW), which strengthened the conclusion that equilibrium was established in field-exposed passive samplers. At all four stations, chemical activity ratios between pore water and overlying water were greater than one for all PAHs, indicating that the sediment was a PAH diffusion source and that sediment remediation may be an appropriate treatment for PAH contamination in Oslo Harbor. [source] Adhesion Characteristics of PDMS Surfaces During Repeated Pull-Off Force Measurements,ADVANCED ENGINEERING MATERIALS, Issue 5 2010Elmar Kroner Abstract To mimic the adhesive effects of gecko toes, artificial surfaces have been manufactured recently using polydimethylsiloxanes (PDMS). However, the effects of repeated contacts on the adhesive properties remain largely unexplored. In this paper we report on the effect of repeated pull-off force measurements on the adhesion behavior of PDMS (polymer kit Sylgard 184, Dow Corning) tested with a borosilicate glass probe. A decrease in pull-off force with increase in number of test cycles is found until a plateau is reached. The initial value and the rate of change in pull-off force strongly depend on the sample preparation procedure, including curing time and cross-linking. It is proposed that the behavior is due to steady coverage of the probe with free oligomers. The results are crucial for developing reusable, durable, and residue-free bioinspired adhesives. [source] High Breakdown Field Dielectric Elastomer Actuators Using Encapsulated Polyaniline as High Dielectric Constant FillerADVANCED FUNCTIONAL MATERIALS, Issue 19 2010Martin Molberg Abstract A novel method allowing rapid production of reliable composites with increased dielectric constant and high dielectric strength for dielectric elastomer actuators (DEA) is reported. The promising approach using composites of conductive particles and insulating polymers generally suffers from low breakdown fields when applied to DEA devices. The present publication shows how to overcome this deficiency by using conductive polyaniline (PANI) particles encapsulated into an insulating polymer shell prior to dispersion. PANI particles are encapsulated using miniemulsion polymerization (MP) of divinylbenzene (DVB). The encapsulation process is scaled up to approximately 20 g particles per batch. The resulting particles are used as high dielectric constant (,,) fillers. Composites in a polydimethylsiloxane (PDMS) matrix are prepared and the resulting films characterized by dielectric spectroscopy and tensile tests, and evaluated in electromechanical actuators. The composite films show a more than threefold increase in ,,, breakdown field strengths above 50 V ,m,1, and increased strain at break. These novel materials allow tuning the actuation strain or stress output and have potential as materials for energy harvesting. [source] Nanopatterning by an Integrated Process Combining Capillary Force Lithography and Microcontact PrintingADVANCED FUNCTIONAL MATERIALS, Issue 4 2010Xuexin Duan Abstract A novel nanopatterning process was developed by combining capillary force lithography (CFL) and microcontact printing (µCP). Flat polydimethylsiloxane (PDMS) was used as the substrate in CFL, and after chemical functionalization, as the stamp in µCP, which increased the resolution of both methods. The polymer patterns, produced by CFL on a thin polymer film on the flat PDMS substrate, acted as a mask to oxidize the uncovered regions of the PDMS. The chemical patterns were subsequently formed by gas phase evaporation of a fluorinated silane. After removal of the polymer, these stamps were used to transfer thiol inks to a gold substrate by µCP. Gold patterns at a scale of less than 100,nm were successfully replicated by these chemically patterned flat PDMS stamps. [source] Silicon Microstructures: Detachment Lithography of Photosensitive Polymers: A Route to Fabricating Three-Dimensional Structures (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 2 2010Mater. The scanning electron microscope image featured on the front cover shows a three-dimensional polydimethylsiloxane (PDMS) molded film bonded on a glass rod. Multilevel silicon structures used to mold the PDMS film were fabricated from successive steps of detachment lithography of photoresist films, which are patterned with lithography and reactive ion etching, as reported by J. Yeom and M. A. Shannon on page 289. The smallest feature on the pyramid is 2 µm in diameter. [source] Detachment Lithography of Photosensitive Polymers: A Route to Fabricating Three-Dimensional StructuresADVANCED FUNCTIONAL MATERIALS, Issue 2 2010Junghoon Yeom Abstract A technique to create arrays of micrometer-sized patterns of photosensitive polymers on the surface of elastomeric stamps and to transfer these patterns to planar and nonplanar substrates is presented. The photosensitive polymers are initially patterned through detachment lithography (DL), which utilizes the difference in adhesion forces to induce the mechanical failure in the film along the edges of the protruded parts of the mold. A polydimethylsiloxane (PDMS) stamp with a kinetically and thermally adjustable adhesion and conformal contact can transfer the detached patterns to etched or curved substrates, as well as planar ones. These printed patterns remain photochemically active for further modification via photolithography, and/or can serve as resists for subsequent etching or deposition, such that photolithography can be used on highly nonconformal and nonplanar surfaces. Various 3D structures fabricated using the process have potential applications in MEMS (micro-electromechanical systems) sensors/actuators, optical devices, and microfluidics. [source] Solvent-Resistant PDMS Microfluidic Devices with Hybrid Inorganic/Organic Polymer CoatingsADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Bo-Yeol Kim Abstract This study presents a method for the fabrication of solvent-resistant poly(dimethylsiloxane) (PDMS) microfluidic devices by coating the microfluidic channel with a hybrid inorganic/organic polymer (HR4). This modification dramatically increases the resistance of PDMS microfluidic channels to various solvents, because it leads to a significant reduction in the rate of solvent absorption and consequent swelling. The compatibility of modified PDMS with a wide range of solvents is investigated by evaluating the swelling ratio measured through weight changes in a standard block. The HR4-modified PDMS microfluidic device can be applied to the formation of water-in-oil (W/O) and oil-in-water (O/W) emulsions. The generation of organic solvent droplets with high monodispersity in the microfluidic device without swelling problems is demonstrated. The advantage of this proposed method is that it can be used to rapidly fabricate microfluidic devices using the bulk properties of PDMS, while also increasing their resistance to various organic solvents. This high compatibility with a variety of solvents of HR4-modified PDMS can expand the application of microfluidic systems to many research fields. [source] Reversibly Deformable and Mechanically Tunable Fluidic AntennasADVANCED FUNCTIONAL MATERIALS, Issue 22 2009Ju-Hee So Abstract This paper describes the fabrication and characterization of fluidic dipole antennas that are reconfigurable, reversibly deformable, and mechanically tunable. The antennas consist of a fluid metal alloy injected into microfluidic channels comprising a silicone elastomer. By employing soft lithographic, rapid prototyping methods, the fluidic antennas are easier to fabricate than conventional copper antennas. The fluidic dipole radiates with ,90% efficiency over a broad frequency range (1910,1990,MHz), which is equivalent to the expected efficiency for a similar dipole with solid metallic elements such as copper. The metal, eutectic gallium indium (EGaIn), is a low-viscosity liquid at room temperature and possesses a thin oxide skin that provides mechanical stability to the fluid within the elastomeric channels. Because the conductive element of the antenna is a fluid, the mechanical properties and shape of the antenna are defined by the elastomeric channels, which are composed of polydimethylsiloxane (PDMS). The antennas can withstand mechanical deformation (stretching, bending, rolling, and twisting) and return to their original state after removal of an applied stress. The ability of the fluid metal to flow during deformation of the PDMS ensures electrical continuity. The shape and thus, the function of the antenna, is reconfigurable. The resonant frequency can be tuned mechanically by elongating the antenna via stretching without any hysteresis during strain relaxation, and the measured resonant frequency as a function of strain shows excellent agreement (±0.1,0.3% error) with that predicted by theoretical finite element modeling. The antennas are therefore sensors of strain. The fluid metal also facilitates self-healing in response to sharp cuts through the antenna. [source] Fabrication of Flexible Binary Amplitude Masks for Patterning on Highly Curved SurfacesADVANCED FUNCTIONAL MATERIALS, Issue 20 2009Audrey M. Bowen Abstract This paper describes soft lithography methods that expand current fabrication capabilities by enabling high-throughput patterning on nonplanar substrates. These techniques exploit optically dense elastomeric mask elements embedded in a transparent poly(dimethylsiloxane) (PDMS) matrix by vacuum-assisted microfluidic patterning, UV,ozone-mediated irreversible sealing, and chemical etching. These protocols provide highly flexible photomasks exhibiting either positive- or negative-image contrasts, which serve as amplitude masks for large-area photolithographic patterning on a variety of curved (and planar) surfaces. When patterning on cylindrical surfaces, the developed masks do not experience significant pattern distortions. For substrates with 3D curvatures/geometries, however, the PDMS mask must undergo relatively large strains in order to make conformal contact. The new methods described in this report provide planar masks that can be patterned to compliantly compensate for both the displacements and distortions of features that result from stretching the mask to span the 3D geometry. To demonstrate this, a distortion-corrected grid pattern mask was fabricated and used in conjunction with a homemade inflation device to pattern an electrode mesh on a glass hemisphere with predictable registration and distortion compensation. The showcased mask fabrication processes are compatible with a broad range of substrates, illustrating the potential for development of complex lithographic patterns for a variety of applications in the realm of curved electronics (i.e., synthetic retinal implants and curved LED arrays) and wide field-of-view optics. [source] Mechanical Gradient Cues for Guided Cell Motility and Control of Cell Behavior on Uniform SubstratesADVANCED FUNCTIONAL MATERIALS, Issue 18 2009Barbara Cortese Abstract A novel method for the fabrication and the use of simple uniform poly(dimethylsiloxane) PDMS substrates for controlling cell motility by a mechanical gradient is reported. The substrate is fabricated in PDMS using soft lithography and consists of a soft membrane suspended on top of a patterned PDMS substrate. The difference in the gradient stiffness is related to the underlying pattern. It is shown experimentally that these uniform substrates can modulate the response of cell motility, thus enabling patterning on the surfaces with precise cell motility. Because of the uniformity of the substrate, cells can spread equally and a directional movement to stiffer regions is clearly observed. Varying the geometry underlying the membrane, cell patterning and movement can be quantitatively characterized. This procedure is capable of controlling cell motility with high fidelity over large substrate areas. The most significant advance embodied in this method is that it offers the use of mechanical features to control cell adhesion and not topographical or chemical variations, which has not been reported so far. This modulation of the response of cell motility will be useful for the design and fabrication of advanced planar and 3D biological assemblies suitable for applications in the field of biotechnology and for tissue-engineering purposes. [source] Fabrication of Ordered Nanostructured Arrays Using Poly(dimethylsiloxane) Replica Molds Based on Three-Dimensional Colloidal CrystalsADVANCED FUNCTIONAL MATERIALS, Issue 10 2009Hong Kyoon Choi Abstract Hexagonally arrayed structures of colloidal crystals with uniform surface are a good candidate for master molds to be used in soft lithography. Here, the fabrication of periodically arrayed nanostructures using poly(dimethylsiloxane) (PDMS) molds based on three-dimensionally (3D) ordered colloidal crystals is reported. A robust, high-quality 3D colloidal-crystal master molds is prepared using the colloidal suspension containing a water-soluble polymer. The surface patterns of the 3D colloidal crystals can then be transferred onto a polymer film via soft lithography, by means of the replication of the surface pattern with PDMS. Various hexagonally arrayed nanostructure patterns can be fabricated, including close-packed and non-close-packed 2D arrays and honeycomb structures by the structural modification of the 3D colloidal-crystal templates. The replicated hexagonally arrayed structures can also be used as templates for producing colloidal crystals with 2D superlattices. [source] Generation of Monodisperse Inorganic,Organic Janus Microspheres in a Microfluidic DeviceADVANCED FUNCTIONAL MATERIALS, Issue 10 2009Naveen Prasad Abstract This study presents a simple synthetic approach for the in situ preparation of monodisperse hybrid Janus microspheres (HJM) having organic and inorganic parts in a PDMS-based microfluidic device. Based on the mechanism of shear-force-driven break-off, merged droplets of two photocurable oligomer solutions having distinctive properties are generated into an immiscible continuous phase. Functionalized perfluoropolyether (PFPE) as the organic phase and hydrolytic allylhydridopolycarbosilane (AHPCS) as the inorganic phase are used for the generation in aqueous medium of HJM with well-defined morphology and high monodispersity (average diameter of 162,µm and a 3.5% coefficient of variation). The size and shape of the HJM is controlled by varying the flow rate of the disperse and continuous phases. The HJM have two distinctive regions: a hydrophobic hemisphere (PFPE) having a smooth surface and a relatively hydrophilic region (AHPCS) with a rough, porous surface. In addition, pyrolysis and subsequent oxidation of these HJM convert them into SiC-based ceramic hemispheres through the removal of the organic portion and etching off the silica shell. The selective incorporation of magnetic nanoparticles into the inorganic part shows the feasibility of the forced assembly of HJM in an applied magnetic field. [source] Metal Ion Implantation for the Fabrication of Stretchable Electrodes on ElastomersADVANCED FUNCTIONAL MATERIALS, Issue 3 2009Samuel Rosset Abstract Here, the use of low-energy metal ion implantation by filtered cathodic vacuum arc to create highly deformable electrodes on polydimethylsiloxane (PDMS) membranes is reported. Implantation leads to the creation of nanometer-size clusters in the first 50,nm below the surface. When the elastomer is stretched, these small clusters can move relative to one another, maintaining electrical conduction at strains of up to 175%. Sheet resistance versus ion dose, resistance versus strain, time stability of the resistance, and the impact of implantation on the elastomer's Young's modulus are investigated for gold, palladium, and titanium implantations. Of the three tested metals, gold has the best performance, combining low and stable surface resistance, very high strain capabilities before loss of electrical conduction, and low impact on the Young's modulus of the PDMS membrane. These electrodes are cyclically strained to 30% for more than 105 cycles and remain conductive. In contrast, sputtered or evaporate metals films cease to conduct at strains of order 3%. Additionally, metal ion implantation allows for creating semi-transparent electrodes. The optical transmission through 25-µm-thick PDMS membranes decreases from 90% to 60% for Pd implantations at doses used to make stretchable electrodes. The implantation technique presented here allows the rapid production of reliable stretchable electrodes for a number of applications, including dielectric elastomer actuators and foldable or rollable electronics. [source] Cover Picture: Highly Fluorescent Poly(dimethylsiloxane) for On-Chip Temperature Measurements (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 2 2009Mater. Highly fluorescent poly(dimethylsiloxane) (PDMS) doped with ZnO quantum dots (QDs) is conveniently generated and used directly for whole-chip temperature measurements, as described by Hongkai Wu and co-workers on page 324. A model is also given to elucidate the temperature sensitivity and extremely high stability of this material by studying the bonding between the QDs and the PDMS. [source] Highly Fluorescent Poly(dimethylsiloxane) for On-Chip Temperature MeasurementsADVANCED FUNCTIONAL MATERIALS, Issue 2 2009Jianhua Zhou Abstract This work describes a convenient method to generate a poly(dimethylsiloxane) (PDMS) composite containing ZnO quantum dots (QDs) for whole-chip temperature measurements. This composite is highly fluorescent and very sensitive to temperature changes (0.4,nm,°C,1, compared to 0.1,nm,°C,1 in commonly used CdSe QDs). It also shows extremely high fluorescent stability under various conditions over long time without phase separation or fluorescent changes. Both merits make this composite an ideal material for sensing temperature changes on microfluidic chips. The bonding between the QDs and PDMS is studied by comparing PDMS composites with ZnO QDs of different sizes, and a model is given to elucidate the high stability of this composite. [source] Simple Patterning via Adhesion between a Buffered-Oxide Etchant-Treated PDMS Stamp and a SiO2 Substrate,ADVANCED FUNCTIONAL MATERIALS, Issue 13 2007Y.-K. Kim Abstract A very simple polydimethylsiloxane (PDMS) pattern-transfer method is devised, called buffered-oxide etchant (BOE) printing. The mechanism of pattern transfer is investigated, by considering the strong adhesion between the BOE-treated PDMS and the SiO2 substrate. PDMS patterns from a few micrometers to sub-micrometer size are transferred to the SiO2 substrate by just pressing a stamp that has been immersed in BOE solution for a few minutes. The patterned PDMS layers work as perfect physical and chemical passivation layers in the fabrication of metal electrodes and V2O5 nanowire channels, respectively. Interestingly, a second stamping of the BOE-treated PDMS on the SiO2 substrate pre-patterned with metal as well as PDMS results in a selective transfer of the PDMS patterns only to the bare SiO2. In this way, the fabrication of a device structure consisting of two Au electrodes and V2O5 nanowire network channels is possible; non-ohmic semiconducting I,V characteristics, which can be modeled by serially connected percolation, are observed. [source] |