Fabrication of suspended electrokinetic microchannels from directly written sacrificial polymer fibers (original) (raw)
Related papers
2006
validate this procedure as a viable methodology for the construction of 3-D microchannels. Figure 1. Stylus-draw method of creating PMMA fibers. FABRICATION Initially, fibers were drawn from reservoirs of solvated poly-methyl methacrylate (PMMA) (MicroChem) using a tungsten stylus (tip radius = 20 nm) to create a filament of solution between the two reservoirs (Fig. 1). As the solvent (chlorobenzene) evaporates, surface tension forces cause the filament to thin, resulting in the formation of a cylindrical polymer fiber with a nearly uniform cross-section Precise positioning of the fibers was accomplished by controlling the stylus with a programmable, custom-made ultra-high-precision micromilling machine (MMM) (Dover Instruments, Inc.) [3]. An alternative, direct-write, method of fiber drawing was also developed. This new technique involved loading a glass capillary (1-mm I.D.) with solvated PMMA and utilizing it to both deposit the reservoirs and draw the fibers, eliminating the need for the low-precision, manual reservoir deposition in the method previously described (Fig. 2). Manipulation of the direct-write capillary process was also controlled with the MMM, enabling nanoscale positioning resolution. Channels were fabricated by coating the PMMA fibers with a layer of borosilicate glass (BSG) followed by Parylene®. BSG was deposited via RF sputtering (Technics 4604) to a thickness of 25 nm to establish a hydrophilic interior channel wall. A 10 µm Parylene® layer (SCS Parylene Deposition System 2010) was included to provide structural reinforcement for the fragile BSG thin wall. 500 µm-diameter holes were drilled into the coated and dried PMMA reservoirs to provide access to the PMMA and completed channels. The entire platform was submerged in acetone
Fabrication of Microchannels Using Polynorbornene Photosensitive Sacrificial Materials
Journal of The Electrochemical Society, 2003
A processing method has been demonstrated for the fabrication of microchannels using photosensitive polynorbornene copolymer based sacrificial materials. The channel geometric patterns of sacrificial polymer were made via photolithography. The sacrificial polymer patterns were encapsulated with a dielectric medium and then thermally decomposed to form air channels. For the thermal decomposition of sacrificial polymer, the heating program was determined on the basis of the kinetic model obtained from thermogravimetric analysis to maintain the decomposition at a constant rate. The results indicate that a properly selected heating program can avoid the deformation in the channel structure; at the same conditions, a large-size channel is more easily deformed than a small one. The tapered-structure microchannels were also produced using a gray-scale mask. The result shows that a suitably low contrast for the photosensitive sacrificial material can lead to smooth and tapered microchannels.
Direct Write Fabrication of Polymer Fibers for Microscale Applications
2008 17th Biennial University/Government/Industry Micro/Nano Symposium, 2008
Polymer fibers have been produced for decades using a variety of methods including wet spinning, dry spinning, melt spinning, and electrospinning. The first three of these processes involve extruding a solvated or melted polymer through an orifice plate to produce a polymer filament which is then dried and collected on a take-up wheel. Electrospinning utilizes a strong electric field to propel a thin jet of solvated polymer into a nanofibrous mat. Of these techniques, only electrospinning facilitates the production of fibers with micro-/ nanoscale diameters and none of these methods enable production of suspended fibers that are precisely oriented between two discrete points in 3D [1].
Electrokinetic Velocity Characterization of Microparticles in Glass Microchannels
The 2008 Annual …, 2008
Insulator-based dielectrophoresis (iDEP) is an efficient technique with great potential for miniaturization. It has been applied successfully for the manipulation and concentration of a wide array of particles, including bioparticles such as macromolecules and microorganisms. When iDEP is applied employing DC electric fields, other electrokinetic transport mechanisms are present: electrophoresis and electroosmotic flow. In order to achieve dielectrophoretic trapping of bioparticles, dielectrophoresis has to overcome electrokinetics (electroosmosis and electrophoresis). Therefore, to improve and optimize iDEP-based separations, it is necessary to characterize these electrokinetic mechanisms under the operating conditions employed for dielectrophoretic separations. The main objective of this work was to identify the operating conditions that will benefit dielectrophoretic trapping and concentration of particles when electrokinetics is present.
Handling of Polymer Particles in Microchannels
Chemical Engineering & Technology, 2010
This paper deals with solid-liquid operations in microchannels. Continuous operations on solids (modification of frequency, change of solvent, encapsulation) in order to handle polymer particles in microchannels are described in terms of the limits of operating conditions and their possible applications. A methodology to design and implement operations on polymer particles is presented here. It is applied for the generation of onion-like structures. A microdevice completely built with Plexiglas plates and fused silica capillaries is used. The device includes droplet generation, polymerization and microparticle flow manipulation. The particles manipulated are in the range of 70 to 200 microns with a very low index of polydispersity.
Hydrodynamic microfabrication via “on the fly” photopolymerization of microscale fibers and tubes
Lab Chip, 2004
A microfluidic apparatus capable of creating continuous microscale cylindrical polymeric structures has been developed. This system is able to produce microstructures (e.g. fibers, tubes) by employing 3D multiple stream laminar flow and ''on the fly'' in-situ photopolymerization. The details of the fabrication process and the characterization of the produced microfibers are described. The apparatus is constructed by merging pulled glass pipettes with PDMS molding technology and used to manufacture the fibers and tubes. By controlling the sample and sheath volume flow rates, the dimensions of the microstructures produced can be altered without re-tooling. The fiber properties including elasticity, stimuli responsiveness, and biosensing are characterized. Responsive woven fabric and biosensing fibers are demonstrated. The fabrication process is simple, cost effective and flexible in materials, geometries, and scales.
Electrokinetic characterization of poly (dimethylsiloxane) microchannels
…, 2003
This paper characterizes the basic electrokinetic phenomena occurring within native poly(dimethylsiloxane) (PDMS) microchannels. Using simple buffers and current measurements, current density and electroosmosis data were determined in trapezoidal, reversibly sealed PDMS/PDMS and hybrid PDMS/glass channels with a cross-sectional area of 1035.5 mm 2 and about 6 cm length. This data was then compared to that obtained in an air-thermostated 50 mm inner diameter (1963.5 mm 2 cross-sectional area) fused-silica (FS) capillary of 70 cm length. Having a pH 7.8 buffer with an ionic strength (I) of 90 mM, Ohms's law was observed in the microchannels with electric field strengths of up to about 420 V/cm, which is about twice as high as for the FS capillary. The electroosmotic mobility (m EO ) in PDMS and FS is shown to exhibit the same general dependences on I and pH. For all configurations tested, the experimentally determined m EO values were found to correlate well with the relationship m EO = a 1 b log(I), where a and b are coefficients that are determined via nonlinear regression analysis. Electroosmotic fluid pumping in native PDMS also follows a pH dependence that can be estimated with a model based upon the ionization of silanol. Compared to FS, however, the magnitude of the electroosmotic flow in native PDMS is 50-70% smaller over the entire pH range and is difficult to maintain at acidic pH values. Thus, the origin of the negative charge at the inner wall of PDMS, glass, and FS appears to be similar but the density is lower for PDMS than for glass and FS.
Surface Textured Polymer Fibers for Microfluidics
Advanced Functional Materials, 2014
This article introduces surface textured polymer fibers as a new platform for the fabrication of affordable microfluidic devices. Fibers are produced tens of meters‐long at a time and comprise 20 continuous and ordered channels (equilateral triangle grooves with side lengths as small as 30 micrometers) on their surfaces. Extreme anisotropic spreading behavior due to capillary action along the grooves of fibers is observed after surface modification with polydopamine (PDA). These flexible fibers can be fixed on any surface—independent of its material and shape—to form three‐dimensional arrays, which spontaneously spread liquid on predefined paths without the need for external pumps or actuators. Surface textured fibers offer high‐throughput fabrication of complex open microfluidic channel geometries, which is challenging to achieve using current photolithography‐based techniques. Several microfluidic systems are designed and prepared on either planar or 3D surfaces to demonstrate out...
The effect of varying pH on electrokinetically driven flow has been investigated by an optical measurement system using fluorescent submicron particles. The objectives of the present study are to establish quantitative measurements of electroosmotic velocity and zeta-potential, and to apply a spatially averaged time-resolved particle tracking velocimetry (SAT-PTV) technique to particle stacking affected by pH gradient. SAT-PTV can detect an unsteady microchannel flow, eliminating the errors associated with Brownian motion without losing temporal resolution. A flow is driven by the electric field in a T-shaped microchannel that is comprised of a poly(dimethylsiloxane) (PDMS) chip and a fused silica cover glass. 500 nm diameter particles were included in buffer solutions. Electroosmotic velocity was obtained by subtracting particle electrophoretic velocity from the observed particle velocity, and the zeta-potential of particles and each wall was calculated by using electrophoretic and electroosmotic velocities, respectively. With increasing pH, electroosmotic velocity and the zeta-potential of glass and PDMS surface was increased due to deprotonation at each surface.