Chemical valve electrically activated

Figure 16 is a schematic representation of an electrically activated chemical valve membrane whose pore size expands and contracts reversibly in response to an electrical stimulus. When the chemomechanical contraction is developed iso-metrically, i.e., keeping the membrane dimensions constant, the contractile stress... 

Figure 16 also shows the effect of a chemomechanical contraction of the PVA-PPA membrane on water permeation when 6.5 V DC was applied in alternate on and off cycles [46]. It can be seen that the chemical valve membrane can increase and decrease the water permeability many times on electrical stimulation. Water permeability increased in proportion to the DC current. This makes it possible to use the membrane as a permeation-selective membrane continuously separating solute mixtures with different molecular sizes. This type of electrically activated chemical valve membrane exhibited long-term stability. 

Fig. 30. Apparatus for the electro-activated chemical valve membrane and change of the water permeability by alternative on and off of an electric field Electric field 2.6 V/cm. The membrane was prepared by polymerization of AMPS in the presence of a porous (average pore size 8 pm) polyfvinyl alcohol) sheet...

Microfluidic Control Sequential and combinatorial delivery of signals to cells or tissue in microfluidic devices can be accomplished by using built-in control systems. Several microfluidic tools including valves, pumps, mixers, fluidic oscillators, fluidic diodes, etc. have been developed to accomplish fluidic control in these devices. These components can either be passive or active. Examples of passive elements include one-way valves (flap, ball) and hydrophobic patohes which take advantage of the interactiOTi between the chemical surface properties of the substrate and Uquid. Active elements, on the other hand, typically require some type of actuation mechanism. Several mechanisms for force transduction in microfluidic devices include mechanical, thermal, electrical, magnetic, and chemical actuation systems as well as the use of biological transducers. There has been a significant amount of work in this area that has been presented in a review by Erickson and Li [5]. 

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