Soft lithography based on photolithography and two-photon polymerization

Over the past decades, soft lithography has greatly facilitated the development of microfluidics due to its simplicity and cost-effectiveness. Besides, numerous fabrication techniques such as multi-layer photolithography, stereolithography and other methods have been developed to fabricate moulds with complex 3D structures nowadays. But these methods are usually not beneficial for microfluidic applications either because of low resolution or sophisticated fabrication procedures. Besides, high-resolution methods such as two-photon lithography, electron-beam lithography, and focused ion beam are often restricted by fabrication speed and total fabricated volume. Nonetheless, the region of interest in typical microfluidic devices is usually very small while the rest of the structure does not require complex 3D fabrication methods. Herein, conventional photolithography and two-photon polymerization are combined for the first time to form a simple hybrid approach in fabricating master moulds for soft lithography. It not only benefits from convenience of photolithography, but also gives rise to complex 3D structures with high resolution based on two-photon polymerization. In this paper, various tests have been conducted to further study its performance, and a passive micromixer has been created as a demonstration for microfluidic applications.