Microfluidic chips are powerful tools for biochemical experiments. High speed and precise flow control can be achieved by using microvalves on a chip. Several types of microvalves that can be integrated into a microfluidic chip have been reported. Among them, gel microvalves have certain advantages over other valves because of their soft structure, which will contribute to prevent mechanical damage the cells passing though the valve. Here we use Bioresist, a photoprocessable thermoresponsive gel, as a key component of the microvalve. Since Bioresist is photopatternable, we can create any arbitrary 2D shape from the thermoresponsive gel using photolithography. Moreover, Bioresist has the unique feature of a phase transition around 30°C, and swells and shrinks repeatedly with temperature change. By integrating the patterned thermoresponsive gel with a microheater, we developed a gel actuator and designed a gel-valve. The gel-valve has the advantages of a simple actuation mechanism: high leakage pressure, high speed actuation and low power consumption. The valve is biocompatible and easily integrated into a chip by using conventional photolithography. Using this valve, we achieved on-chip flow control, and applied it to cell sorting on a chip.
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