Development and study of hydrogel-based microvalves for lab-on-a-chip systems

Stimuli-responsive hydrogels such as poly(N-isopropylacrylamdie) (PNIPAAm) are excellent materials for microvalves due to their biocompatibility and high energy conversion efficiency. Hydrogel-based microvalves are simple to fabricate and operate compared to other actuation schemes. While many other hydrogel-based valves have been developed by other researchers, the valves presented here differ in the use of polymers as the basis for all microvalve components for increased flexibility. This work presents the design, fabrication and characterization of a hydrogel-based plug-type microvalve and a hydrogel-based microvalve diaphragm actuator. The two designs for the valve actuation scheme are presented: 1) a microvalve diaphragm actuator; and 2) a hydrogel plug actuator. The diaphragm actuator can be fabricated employing traditional soft lithography processes for fabrication of all components, including the nanocomposite polymer (NCP) heater element, the hydrogel reservoir, and the deflecting polymer membrane. The actuation is provided by the hydrogel-actuated diaphragm deflection, with the application of heat opening a normally closed microvalve via de-swelling. The hydrogel plug element can be patterned and inserted into the structure as a fluidic control component within a microfluidic channel. The swelling and shrinking of the hydrogel plug in the microchannel results in closing and opening of the valve within 20 seconds.