In the past years, polymers have become increasingly popular, and are now the most used materials for making microfluidic devices. Compared to inorganic materials, polymers enable low-cost manufacturing, provided a sufficient number of devices is produced. High quality polymers with a wide range of properties are available, and advances have been made in microfabrication technologies for polymers. Therefore, it is predicted that the use of polymers will keep increasing. Due to its ease of fabrication, the elastomer poly(dimethylsiloxane) (PDMS) has been the most popular polymer in academic research. However, for industrial manufacturing thermoplastics such as cyclic olefin (co)polymer (COP, COC), polycarbonate (PC) and poly(methyl methacrylate) (PMMA) are much more suitable.
In contrast to glass, most polymers used for fabricating microfluidic devices are hydrophobic, which impedes filling of channels by capillary flow. Moreover, proteins and other biomolecules tend to adsorb to the hydrophobic polymers, leading to issues in biological applications. Both problems can be overcome by applying a nanocoating that has both hydrophilic and antifouling properties.
The possibility to create patterned nanocoatings by local surface modification yields local control of the wettability and/or antifouling properties, which enables advanced functionalities such as control of liquid flow (see example 1) or the generation of double emulsions in a single microfluidic chip (see example 2). In the R&D project Coat PoCKET, a microfluidic chip with advanced functionalities enabled by patterned nanocoatings is being developed.