Hamming-distance-based valve-switching optimization for control-layer multiplexing in flow-based microfluidic biochips

Flow-based microfluidic biochips have progressed significantly in the past decade. Thanks to innovations in multilayer soft lithography (MSL) fabrication technology, the integration of thousands of microvalves along with large-scale networks of microchannels on a chip has been enabled. This progress has even been compared to the evolution of VLSI circuits following Moore's Law. In flow-based microfluidic biochips, microvalves are critical components to control the fluidic transportation for complex operations. To activate the open/close states of a microvalve, off-chip control pins are required. Due to the tremendous increase of the number of microvalves, a software-programmable microfluidic platform has been proposed to reduce the number of off-chip control pins, which integrates a microfluidic multiplexer on a separate control layer to control the array of microvalves. The multiplexer needs to be switched when the states of microvalves are changed between every two adjacent time slots. High switching frequency will make the multiplexer vulnerable and decrease the chip's reliability. We observe that different switching orders of microvalves lead to different switching frequencies of a multiplexer. Based on this observation, this paper proposes the first Hamming-distance-based switching order optimization method for microvalves to enhance the reliability of the multiplexer. Experimental results show that our method can significantly reduce the switching frequency of multiplexer, and the solution is very close to the theoretical optimal lower bound.