PDMS mold

One channel is made by KOH etching (in the framework of the above-mentioned technology steps), the other by a molding process using an PDMS mold and an epoxy cast. 

In this method, NWs can be aligned by passing a suspension of NWs through microfluidic channel structures, for example, formed between a poly(dimethylsiloxane) (PDMS) mold 49 and a flat substrate (Fig. 11.3a). Images of NWs assembled on substrate surfaces (Fig. 11.3b) within micro-fluidic flows demonstrate that virtually all NWs are aligned along the flow direction. This alignment readily extends over hundreds of micrometers, and... 

The basic procedure for creating addressed aqueous compartments above individual bilayers is outline in Figure 6.6. In the first step, a lithographically patterned PDMS mold is brought into direct contact with a planar supported lipid bilayer containing covalently attached ligands, to create hermetically sealed compartments by microcontact displacement... 

Some streptavidin was observed to adsorb to the walls of the PDMS mold. This process could be suppressed by preadsorbing bovine serum albumin. 

FIGURE 2.23 Scheme for fabrication of plastic microdevices from silicon master using an intermediate soft mold, (a) Silicon structures are fabricated using conventional photolithography and reactive ion etching, (b) PDMS is cured in situ over the silicon master, (c) Polystyrene is hot embossed onto the PDMS mold or polymerized in situ from partially polymerized styrene, (d) Polystyrene replica is separated from the mold [85]. Reprinted with permission from Springer Science and Business Media. 

In MIMIC, a PDMS mold is brought into contact with a rigid support, forming microchannels between the substrate and the recessed regions of the PDMS mold as shown in Figure 5.5.28. The fluid, placed at the end of mold, hlls the channels of the mold by capillary action. The material is then cross-linked, crystallized, or... 

FIGURE 5.5.28 Schematic of MIMIC. At least one end of the PDMS stamp is cut off to create entrances to the microchannels. The PDMS mold is then placed on a support to form the microchannels. When a precursor or a prepolymer solution is placed at one end, capillary action spontaneously fills the channels with the solution. After curing, the PDMS stamp is removed, leaving behind solid polymer features on the substrate. (From E. Kim et ah, J. Am. Chem. Soc., 118, 5722, 1996.)... 

Fig. 2. Outline of steps involved in the generation ot the silicon-wafer master mold and fabrication of microfluidic devices. Photolithography techniques are used to generate a silicon-water master mold patterned with the negative image of the desired microtluidic pattern. A PDMS mold is made trom the silicon-water mask and irreversibly bonded to a glass slide to generate a microtluidic tlow cell.

Soft lithography includes a collection of lithographic methods in which a soft mold or template is used to create patterned structures in the subjeeted materials. These methods offer attractive solutions for producing well-ordered CP nanowires. For example, Beh et al have developed a micromolding in capillaries (MIMIC) process in which a poly(dimethylsiloxane) (PDMS) mold with embedded ehannels can be used for the... 

The principles of capillary force lithography [72,73] and a representative pattern of poly(ferrocenylmethylphenylsilane) (PFMPS) stripes on Si obtained by this technique, are shown in Fig. 8. A PDMS mold was placed in contact with a thin PFMPS film (thickness 27 nm) and, subsequently, the temperature was raised above the Tg (74 °C) of the polymer. The polymer, initially confined in a thin film, is squeezed out from areas of contact between stamp and substrate. It diffuses into the grooves where structures are formed along the vertical walls of the stamp due to capillary rise. Polymer structmes, which are approximately 110 nm high and 500 nm wide, were fabricated. Section analysis of the AFM height images revealed a meniscus of the capillary rise (note the different scales for the vertical and horizontal directions). The structmes were developed by CF4/O2-RIE. After resist removal, a patterned substrate as shown earUer in Fig. 2 was obtained. 

There are also a number of other molding techniques to pattern polymers on substrates. One technique is capillary force lithography (CFL), which is a technique in which a patterned PDMS mold is placed on a layer of polymer that is either noncross-linked or heated above its melting point. In CFL, surface tension directs the movement of the polymer melt into the void spaces of the PDMS mold. This process can be merged with different types of polymers to enable cell and protein deposition on substrates. 

Curing agent and prepolymer are mixed together (1 10 wt/wt) and placed in a desiccator for 45 min. The mixture is then poured over a SU-8-2100 (MicroChem Corp., Newton, MA) master in a tissue culture dish which contains the positive relief of the microchannel design. The PDMS mold is cured for 2.5 h at 80 °C on a programmable hotplate. 

Each PDMS mold is then treated with a plasma cleaner for 20 s and placed on a number 1 24 mm X 50 mm glass coversUp. 

Multiphenotype cell arrays have been created by capturing cells in a connected network of reversibly sealed microfluidic channels [8]. Elastomeric PDMS molds can be reversibly sealed on a surface to sequentially deliver fluids or cell suspensions to specific locations on a substrate. Khademhosseini et al. [8] have used this technique to capture and immobilize embryonic stem cells in low-shear-stress microwells within microfluidic channels. Orthogonal alignment of a secondary array of channels was then used to perfuse the cell patterns with media. 

Micromolding in capillaries (MIMIC) is another nonphotolithographic technique developed by Whitesides and co-workers [76-79] for generating patterned microstructures of organic polymers on the surfaces of solid substrates. In this technique, a PDMS mold having a patterned relief structure on its surface is prepared using... 

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