Silicones for Microfluidic Systems

Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Lodz, Poland 

Keywords PDMS, microfluidics, surface modification, hydrophobic recovery, soft lithography, repHca molding 

Microfluidic devices contain systems of miniaturized channels with cross-sectional dimensions of 10-100 pm [1]. Manipulation of Hquids and gases in such mini-devices has many advantages over conventional systems. The benefits include efficiency and reduced consumption of reagents and analytes. 

The material used for microfluidics should be appropriate for fabrication of such micrometer-scale features and should allow for integration of functional components. Early microfluidic systems were fabricated by photolithography and etching of silicon and glass [2], which have desirable surface characteristics but also some serious Hmitations. Polymers can replace these materials in microfluidic technologies, as they involve much simpler and less expensive microfabrication procedures [2-6]. Polyfdimethylsiloxane) (PDMS) seems to be one of the most suitable materials for microfluidic appHcations [ 1,7j. It exhibits a range of unique properties  

Atul Tiwari and Mark D. Soucek (eds.) Concise Encyclopedia of High Performance Silicones. (371-380) 2014 Scrivener Publishing LLC 

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The optical properties of borosilicate glasses are important if the glasses are to be used to encapsulate silicon chips or for microfluidic systems, e.g. the customer wants to observe chemical reactions or in case of DNA the fluorescent radiation. For such applications the glass has to be transparent in the visible. 

Silicon is undoubtedly the material which has been most often applied for microfluidic applications, especially in the field of analysis systems. Detailed information has also been obtained for a number of microreactor components and some of them are already commercially available. Even more striking, first experiments with integrated systems have been reported by DuPont [8]. However, silicon components did not find a broad use in industrial applications, especially in the field of synthetic chemistry. For this purpose, future developments have to address a broader variety of components than those mentioned above, including e.g. heat exchangers, extractors and others, and the feasibility of the fabrication of integrated systems has to be demonstrated in more detail. 

Martinoia, S., Bove, M., Tedeso, M., Margesin, B., Grattarola, M., A simple microfluidic system for patterning populations of neurons on silicon microma-chined substrates. J. Neurol. Methods 1999, 87, 35—44. 

Solvent-resistant polymers are attractive for a variety of microanalytical applications. For chemical sensing, solvent-resistant polymers are important as supports for deposition of solvent-based polymeric sensing formulations.1 Otherwise, a solvent that is used for the preparation of the sensor formulation can attack a plastic substrate of choice forcing the use of either less attractive substrate materials or the use of a complicated sensor-assembly process.2 3 Solvent-resistant polymers also attract interest for microfluidic applications as an alternative to glass and silicon.43 Examples of solvent-resistant polymeric microfluidic systems include those for organic-phase synthesis,6 polymer synthesis,7 studies of polymeric and colloidal... 

It is known that glass cannot be anodicafly bonded to glass. However, research has found that this can be realized by depositing an intermediate layer. The intermediate layer can be polysilicon, amorphous silicmi, silicon nitride, or silicon carbide [9]. This has opened an easy route to constmct glass-based microfluidic systems which are widely used for capillary electrophoresis. Other investigations into anodic braiding have... 

The anisotropic wet etching of silicon is a unique fabrication process in the MEMS field. The need to develop new processes to fabricate functional 3D microstructures in various materials is urgent for progress in microfluidic systems, microsensors, micro-actuators, and microinstrumentation. At present, to integrate surface micromachined devices and standard IC devices with bulk micromachined structures to demonstrate a new functional MEMS application is still a challenge for researchers who work in this field. The cooperation of multidisciplinary researchers will be required to develop miniature systems with the most appropriate building philosophy and the best operation performance. 

Most of the aforementioned work describes short-term assays that were largely independent of ceU response to the microfluidic environment. A thorough investigation of a channel microfluidic system for long-term experiments was performed by Davidssmi et al. [5] using luciferase (an enzyme that catalyzes biolumines-cent reactions) reporter gene activity in the cell line HFFll. Cells were immobilized on silicon chips at 37 °C (Fig. la), incubated in CO2-independent cell media, and monitored for up to... 

Verpoorte et al. produced one of the first microfluidic systems based on stacked silicon modules with polymer gaskets forming interfacial layers [5]. Since then, many other researchers have successfully utilized this concept for the assembly of even more complex microfluidic devices and systems. 

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