Photopolymerization of acrylic oligomers and photolithographic processes for the fabrication of microfluidic devices

Microfluidic analytical devices, also referred to as Lab-On-a-Chips (LOCs), represent an emerging technology with a great potential in chemistry, biochemistry and analytical life science.1-3 Scaling down chemical and analytical reactions to a microscopic size can offer many advantages,4 such as low reagents consumption, rapid analysis, easy operation, and increased reproducibility, selectivity and efficiency; moreover the involved costs are reduced and the performance improved.5,6 Microfluidic devices are used for transporting and manipulating small amounts of fluids and/or biological samples through microchannels and allow the integration of various chemical and biochemical processes into fast and automated microflow systems.7,8

In recent years polymers have assumed a leading role in the fabrication of microfluidic devices. In particular, polydimethylsiloxane (PDMS) has rapidly become a reference material for different applications, thanks to simpler and less expensive fabrication procedures as well as its interesting properties (optical transparency, durability, low cost, biocompatibility, non-toxicity and stability over a wide temperature range).9-11 However, extensive application of PDMS in the fields of chemistry and life science is limited due to its low chemical resistance. Its incompatibility with many solvents and reagents causes swelling and chemical etching, effects that are even more pronounced in microscale channels due to the high surface to volume ratio. These drawbacks lead to clogging of microchannels, device damaging and delamination, contamination of reactions and assays.12,13

A tremendous benefit could therefore come from the development of polymeric devices that offer the same advantages of PDMS with the additional feature of high solvent resistance. Photocurable polymers can be interesting alternatives for the fabrication of microfluidic devices both for chemical and biological applications. In fact final properties can be tuned selecting the appropriate monomers, and moreover photocurable macromers behave as the so called “negative photoresist” commonly used in photolithography. For devices fabrication they can be processed by direct photopolymerization through photomasks, obtaining defined 3D patterns in one step without using any mould.14,15 Therefore this technique it is very competitive if compared to hot embossing, injection moulding, soft lithography, etc: these technologies usually require several steps, special equipment and sometimes stringent conditions, and are not very suitable for research or prototyping,16 when different chip designs may need to be prepared in a short sequence.

This work is made of two parts. In the first one, we study highly fluorinated and siloxane-based UV curable acrylic polymers demonstrating that they are suitable for the fabrication of LOCs. In

the second part we describe the production