Rapid and low cost replication of complex microfluidic structures with PDMS double casting technology

In this paper, a new method for fast and precise replication of high-aspect-ratio microfluidic structures is reported. First, SU-8 microfluidic structures on the master mold were replicated into Polydimethylsiloxane (PDMS), which served as an intermediate, negative mold, by a conventional soft lithography process. The PDMS negative mold was then treated by wetting its surface with a diluted aqueous solution of a hydrophilic polymer, hydroxypropylmethylcellulose and rinsed with deionized water. Last, the negative mold was used in yet another PDMS molding process to produce a PDMS replica of the microfluidic structures (the hydrofocusing unit for a micro-cytometer) with the same structures as the master mold. Experimental results showed that microstructures with high-aspect-ratio could be consistently replicated with high fidelity. This technique can not only greatly simplify the design and fabrication of master molds, but also protect the expensive and fragile original master mold. The process does not require sophisticated equipment and is well suited for the replication of precision master structures in bulk quantities at low cost.