Fabrication of molds for PDMS microfluidic devices by laser swelling of PMMA

The volume increase experienced by Polymethylmethacrylate (PMMA), a common thermoplastic material, when subjected to a fast heating-cooling cycle by the action of an ultraviolet laser beam has been investigated in this work. The effects of laser power, focusing, writing speed, cooling and number of exposures on the dimensions of ridges formed by surface swelling were quantified. The biggest swellings, having near Gaussian cross-sectional shapes, were obtained by performing laser treatments with the polymer immersed in water. The laser swelling technique was applied to the fabrication of molds for microfluidic chips made from Polydimethylsiloxane (PDMS) and the results of the study are discussed within this framework. The method allows the rapid fabrication of molds with a very smooth finish, providing dimensional accuracy appropriate for replication of complex PDMS microfluidic devices. Swelling of polymers upon the action of a laser allows "direct drawing" of molds for PDMS microfluidic devices having very smooth surfaces and variable channel depths.