Filtration & fl uid control The Bristol team’s microfluidic mould-manufacturing process


Robert Hughes’ team from the University of Bristol has developed a low-cost and open-source process for manufacturing microfl uidic devices using 3D-printed interconnecting microchannel scaffolds. The basic process is as follows: 1. Use open-source software to design microchannel module. 2. Print the microchannel scaffolds. 3. Assemble the interconnecting channels on glass substrate. 4. Bond channels to substrate using heat. 5. Rapidly cool on metal plate. 6. Peel mould from substrate slide.


In fact, photolithography is so expensive that his research grant wouldn’t stretch to it. Instead, he set his sights on 3D printing. “I had a small amount of money, but I wasn’t willing to spend it on something


I couldn’t then adapt,” he says. His ultimate aim was to produce microfluidic devices that could be cheaply manufactured and deployed from anywhere, from schools to research facilities in developing countries. He needed to devise a way of making LOC devices as cheaply as possible. The Bristol team is not the first research group to explore 3D printing for microfluidic channels. Other scientists have trialled additive manufacturing for LOC chip devices and come up against a range of limitations. In 2016, a team from the University of Seattle found that 3D-printed parts could not be arbitrarily joined at the channel intersections. They also discovered that 3D printing resulted in weak seals between the device’s layers. What’s more, the size of the extruded material was often larger than channel diameters typically required in microfluidic point- of-care tests.


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“Another problem with 3D printing is that you get lots of ridges as you lay down each filament,” says Hughes. “So, it ends up being a very rough surface, which means that when you come to add the PDMS to make the chips themselves, it’s very hard to stick it to the glass.” The roughness can also lead to contamination and fouling of the channels, meaning they wouldn’t be able to be reused.


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Another dimension Hughes, along with researchers Harry Felton and Andrea Diaz Gaxiola, was determined to find a 3D-printing technique that was fit for purpose. Together they developed a more accessible way to manufacture microfluidic chips using a desktop material extrusion (MEX) 3D printer. They shunned expensive equipment and instead employed an Ultimaker 3 Extended machine (a standard commercially available unit) with a 0.4mm nozzle. They also set about developing open-source software that would allow any user to replicate the process. Their findings are detailed in the journal PLOS ONE. After much trial and error, the team found a process they were satisfied with. First, they 3D print interconnecting microchannel scaffolds directly on to a build plate (the flat surface that 3D-printed objects will stick to during printing). The channels are then mounted on 1mm-thick glass microscope


96 Medical Device Developments / www.nsmedicaldevices.com


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