If there is one material that has enabled microfluidic research in academia, poly(dimethylsiloxane) (PDMS) is surely it. PDMS is cheap and easy to prototype with, and its elastomeric properties have led to complicated structures (e.g. valving) in microfluidic channels. Although it is great for rapid prototyping, there is often a disconnect between the prototype and high throughput manufacturing due to a lack of scalable production methods. Researchers at VTT-Technical Research Centre of Finland and the University of California Berkeley have recently reported a roll-to-roll method for fabricating PDMS microfluidic chips.
In roll-to-roll (R2R) processing—common to the paper industry—long sheets of materials are continuously processed, feeding through rollers and modules with different functionalities. To form R2R microfluidic devices, PDMS was applied to an aluminized paper substrate and then embossed by a heated nickel imprinting cylinder which also cured the PDMS. The devices had good reproducibility and channel depths around 100 µm were achieved. Replication from the nickel master was automated and performed at high throughput of 1.5 m/min. Olli-Heikki Huttunen, one of the authors on the paper, said that “although the process required a lot of fine tuning, it was surprisingly simple.” Like other high-throughput manufacturing techniques (e.g. injection moulding), the nickel tool is quite expensive, but these costs can be overcome by the volume of production.
As a proof-of-principle application, the authors demonstrated nucleic acid detection by loop-mediated isothermal amplification (LAMP). Reagents were spotted and dried in the microchannels using a roll-to-roll compatible dispensing machine, and PDMS lids with vias for fluidic and vacuum connections were formed by a roll-to-roll process (though vias were manually punched) and then bonded manually. Huttunen said that the next steps are to figure out how to manufacture the entire device roll-to-roll, but that it should not be too challenging.
Using aluminized paper as the base substrate for the devices offered a couple advantages. One is that the aluminium dramatically reduced the paper’s autofluorescence. Another advantage was the aluminum reflected back both excitation and emission light, resulting in stronger signals. Results from the test could be read within 20 minutes, suggesting that these devices would be useful for low-cost point-of-care testing.
The challenge for the future, says corresponding author Luke Lee, will be “to learn what the new rules of thinking and design are for roll-to-roll microfluidics in order to solve the problem of mass production in integrated molecular diagnostics for all.” This is an exciting new prospect for both PDMS and the microfluidics community.
To read the full paper for free*, click the link below:
*article free to read from 06/06/2018 – 06/07/2018
Darius Rackus (Right) is a postdoctoral researcher at the University of Toronto working in the Wheeler Lab. His research interests are in combining sensors with digital microfluidics for healthcare applications.