Rapid, low-cost patterning of microstructures in polydimethylsiloxane via mask-less laser-machining

Summary form only given. Polydimethylsiloxane (PDMS), due to its unique characteristics including biocompatibility, possibility to be flexibly moulded into the desired shape, optical transparency, and its low-cost provides a valuable advantage as a building material for the fabrication of microfluidics-based lab-on-chip devices and micro-contact printing [1, 2] moulds that allow parallel deposition of various materials on a target surface. A range of methodologies such as wet chemical etching, dry plasma etching, decal transfer microlithography, and bond-detach method have been utilised for creating patterns in PDMS. However, one of the most commonly used approaches for the prototyping of PDMS for such applications is soft-lithography. This involves the use of a clean-room based UV-lithography step that uses expensive custom-designed masks for the fabrication of a master-mould with structures that are then duplicated via stamping of this master to produce a secondary-mould in PDMS, which is then used for micro-contact printing applications. Even though this lithographic procedure can routinely produce high-resolution micron-scale structures, the procedure is time-consuming and expensive. Instead, for the production of the master, we propose as a cheap alternative to expensive UV-lithography, a mask-less laser-based procedure which does not rely on cleanroom access. Similar to the soft-lithographic procedure, the process is two-step and allows the creation of high-quality sub-micron to millimetre-scale features, in a wide range of materials, with the added advantage of being able to fabricate complex and differently-shaped structures adjacent to each other, in either a sequential or a single-step. This laser-based method (Fig.1) has been used to create two-dimensional surface relief patterns in a master-mould for replication into PDMS and subsequent contact-printing.