If you just landed on Softbites for the first time, you probably have not had the chance to read our previous posts about microfluidics (like this one, or that one, and more). If this field of science is foreign to you, all you need to know is that it studies how fluids flow at really small scales (typically tens to hundreds of micrometers). For instance, you can quickly generate tiny droplets of a solution, turning each droplet into an individual “reactor”. Or you can create microenvironments with precisely controlled chemical concentrations to grow cells in different conditions.
In addition to being a thriving field of research, I think microfluidics is simply beautiful! I have spent hours looking at the Softbites website’s banner, a movie of droplets that was shot by the Lutetium project. You can imagine my excitement when I registered to the annual MRSEC microfluidics summer course 2019 at Brandeis University. This summer course was run by four talented grad students from the Fraden lab and the Rogers lab: Ali Aghvami, Alex Hensley, Marilena Moustaka and Zahra Zarei. These labs are part of the MRSEC program at Brandeis, an important place in the New England soft matter community. Therefore, I think it was the perfect place to get started with microfluidics!
Figure 1. Me, trying to pour some resin on a silicon wafer (left). A drop maker setup (middle). A gradient maker chip, with a defect leading to a non-stable gradient (right).
Over five days, we learned the basics of one of the standard methods for making microfluidic channels, called soft lithography. The rationale is to make a mold using a UV-light sensitive resin. A 2D pattern can then be polymerized in the resin by shining UV-light through a mask. Whatever the UV light hits gets hard, while the rest of the resin stays soft. The soft resin is washed away leaving only the hard, UV-treated resin behind in the shape of the mask. The mold will finally be used to imprint the design in a soft transparent material called PDMS (a very nice video from the Lutetium project explains all this process). We experimented with this fabrication during three main sessions:
- We drew our 2D design using a drawing software
- We fabricated our mold in a clean room so no dust ruined our tiny features
- We cast the PDMS on the mold and sealed the device with a glass slide
We were taught each of these steps through a combination of lectures and hands-on sessions. You can see a droplet maker and a gradient making device that we made in Figure 1.
In addition to learning how to make these routinely used PDMS-based devices, we were also introduced to another technique used in the Fraden lab. This technique, which was recently published (2017), uses a thermoplastic (a plastic that melts at moderate temperatures) as the main device material. This thermoplastic can be cast onto a PDMS mold by means of a thermopress (as shown in Figure 2). Unlike PDMS, thermoplastic is not permeable to water and organic solvent, and is stiffer. If the permeability of PDMS is a limitation for your microfluidics application, thermoplastic might be the way to go!
Figure 2. Ali Aghvami placing thermoplastic chips onto the PDMS mold (left). Close-up on the thermoplastic in the thermopress before being cast (middle). The final device (right), from Aghvami et al. 2017.
This week-long course introduced us to both classical microfluidics techniques that are routinely used in labs and some more advanced ones. More importantly, our instructors dedicated important time to discuss our personal projects with us. We even had a consulting session with Seth Fraden! I strongly encourage anyone to attend the next editions of this course. Each year, the dates and the call for applications are released in spring, so don’t miss out!
