Monolithic valves for microfluidic chips based on thermoresponsive polymer gels

Abstract

The direct preparation of thermoresponsive monolithic copolymers by photopatterning of a liquid phase consisting of an aqueous solution of N-isopropylacrylamide, N-ethylacrylamide, N,N'-methylenebisacrylamide, and 4,4'-azobis(4-cyanovaleric acid) has been studied and the products used as valves within the channels of microfluidic devices. The volume change associated with the polymer phase transition at its lower critical solution temperature (LCST) leads to the rapid swelling and the deswelling of the 2.5% cross-linked monolithic gel thus enabling the polymer to close or open the channel and to function as a nonmechanically actuated valve. The LCST at which the valve switches was easily adjusted within a range of 35 degrees C-74 degrees C by varying the proportions of the monovinyl monomers in the polymerization mixture. The closed valve holds pressures of up to 18 MPa without noticeable dislocation, structural damage, or leakage. In contrast, following deswelling by raising the temperature above LCST the valve offers no appreciable flow resistance since its large, micrometer-size pores are open. Laser-triggered photobleaching of a fluorescent dye contained in the liquid phase enabled monitoring of flow through the device and determination of the times required to open and close the valve. The valves are characterized by very fast actuation times in a range of 1-4 s depending on the type of device. No changes in performance were observed even after repeated open-close cycling of the valves.

Monolithic porous polymer stationary phases in polyimide chips for the fast high-performance liquid chromatography separation of proteins and peptides

“…Numerous functional modules for different applications in microfluidic formats, such as pre-concentration and solid-phase extraction (SPE) [39,40], micro reactors [36,41], mixers [42], stationary phases [29] and valves [43] have already been reported.…”

Thermally-actuated, phase change flow control for microfluidic systems

“…Not surprisingly, a considerable effort has been invested in the development of microvalves. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] While many of these microvalves are miniaturized versions of their macro, conventional counterparts, some of them are based on unconventional concepts ranging from elastomer, 9,10 hydrogel, 11,12 paraffin, 13,14 and ice valves [15][16][17][18] to colloid valves manipulated by magnetic 8 and electromagnetic 7 fields.…”

Light-Stimulated Hydrogels with Incorporated Graphene Oxide as Actuator Material for Flow Control in Microfluidic Applications

“…Because of the large number of possible functionalities such as detection, mixing and separation of analytes, drug release and flow control, etc., LoC systems have to comprise a variety of different elements including electronic, mechanical and fluidic units [2,3]. Actuators such as valves are essential for the flow control within those microfluidic systems.…”