Modification of Bulk PDMS

Nanomaterials (carbon nanotubes (CNT) [115-118], carbon black [119], metal nanoparticles [120,121]) can be incorporated in PDMS to improve its performance in microfluidics and impart superior thermal and electrical conductivity [115, 120] or mechanical flexibility [115]. Other polymers can be admixed as additives into siloxane prepolymer formulation and cured together during the molding step [122]. Microfluidic devices with integrated components (pumps, valves, heaters, sensors, sorters) made of nanocomposite materials exhibit better performance not only as adjustable conductive zones, but also allow for adhesion and immobilization of bioparticles. 

Medium flow in microfluidic channels can be moderated using electrokinetic or hydrodynamic (pressure-driven) controls [123]. Electrokinetic control (electrophoresis or 

Microfluidic pumps, switches and valves are used to manipulate fluid flow in microchannels (flow regulation, switching, sealing) [124, 125]. The fluid displacement inside chips can also be actuated with stimuli-responsive hydrogels [126, 127]. Mechanical means of flow control are also possible. For example, a pneumatically actuated elastomeric switch works by applying external pressure across the contact area of two crossing channels situated in two different layers [13]. Thermally formed microbubbles [128] and magnetic valves [129] can also be used for flow control. 

Electronic systems can be incorporated into microdevices using electrode-patterned substrates sealed onto PDMS molds [143]. They are fabricated with conventional lithography or sputtering and lift-off techniques. Electrodes can be deposited directly on PDMS molds using molten solder [44,144], metal ion implantation [145], conducting composites (carbon paste filling) [146] or single-walled carbon nanotubes embedded in PDMS surface [147]. Optical components (fibers, filters, photodiodes). 

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