Replicating Nanoscale Microfluidic Arrays with LEGO

Have you ever wondered what the behavior of particles, cells and molecules is like in a nanoscale environment? Have you ever thought of using microfluidic arrays (lab-on-a-chip devices used to sort tiny samples by physical composition) made out of LEGO pieces to recreate microscopic activity? Sure you have. We all have. I know I have.

In reality, we haven't. Which makes it that much more creative and just damn cool that someone did.

Assistant professors of chemical and biomolecular engineering at John Hopkins University Whiting School of Engineering, Joelle Frechette and German Drazer wanted to research how particles flow through microfludic arrays. The only problem is, it's a bit hard to see what's happening at the micro cellular level, much less perform a controlled experiment.

With the concept of dimensional analysis (where something is studied at a different scale keeping the governing principles) in mind, the team filled an aquarium with glycerol and arranged the LEGO pieces on a LEGO board. They stacked the pegs two high (see picture) and arranged them in rows and columns on the board to create a lattice of obstacles. A Plexiglass sheet was attached to the LEGO board to improve stiffness and then pressed up against the wall of the tank. Tracking the experiment with a camera, graduate students dropped in stainless steel & plastic balls of varying sizes to replicate the particles on a nanoscale level.

Using the same graduate students (Manuel Balvin and Tara Iracki, and undergraduate Eunkyung Sohn) the balls were dropped one by one into the tank. The students progressively rotated the LEGO array, altering the forcing angle. By doing this, they were able to determine that the path of the balls as particles were deterministic and could be predicted with relative precision.

"Our experiment shows that if you know one single parameter—a measure of the asymmetry in the motion of a particle around a single obstacle—you can predict the path that particles will follow in a microfluidic array at any forcing angle, simply by doing geometry." Drazer said.

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This fun result, the balls moving in the same direction no matter the different forcing angle is called phase locking. The researchers believe that even if the experiment were scaled down to the nanosize level, the results would be similar.

"There are forces present between a particle and an obstacle when they get really close to each other which are present whether the system is at the micro- or nanoscale or as large as the LEGO board," Frechette said. "In this separation method, the periodic arrangement of the obstacles allows the small effect of these forces to accumulate, and amplify, which we suspect is the mechanism for particle separation."

As a follow up, I spoke (via the magic of the internetwebs) with Joelle Frechette about why they chose to use LEGO bricks instead of any other material and how you - yes, you sitting at home - can replicate this very experiment.

I understand that the concept of dimensional analysis led you to build the array on a scale that you can measure, but what exactly led you to build it out of LEGO and not say, plastic sheeting and PVC?

Using LEGO make for simple and cheap experiments that can be easily reproduced in any laboratories or classrooms. Most importantly, it also makes the arrays reconfigurable (i.e. it's easy to change the spacing and the lattice of the arrays or the shape of the obstacles without having to machine a new set up). Finally, LEGO are well machined with a high tolerance.

Do you think that using the LEGO bricks instead of other materials skewed the results in any way? Based on things like the density of the bricks or any other factors?

I don't think so. The roughness (even if small) of the lego pegs and the lego board should, in principle, limit how close the particles and obstacles can get from each other. This is something we actually try to capture with the impact parameter in our model. The density of the legos themselves is not really a relevant parameter in our experiments because they are attached to the lego board (they are not falling in the tank). On the other hand, we've explored the effect of changing the density of the particles (by comparing steel vs plastic particles). We observed that the density of the particles influence their motion, which we believe is an indication that the dynamic of the system is irreversible.

Can you theorize as to what would happen if there are multiple particles at play in the array, wouldn't that change the behavior of a single particle?

We have not yet performed these experiments. We analyze the separation principle in the dilute limit (i.e. we do not include interactions between particles, we only look at interactions between a particle and obstacles). The non-dilute limit is an interesting case that we hope to investigate in the future. I would not be surprised if the trajectories change in the case where the concentration of particles is large but how exactly I am not sure.

What do you think is the best way for someone who is not a biomolecular scientist to duplicate this experiment?

All you need is a large LEGO board with small lego pegs (1x1 or 2x2 should do). You also need a tank that is tall and narrow with enough room so that the board can be rotated while staying in the tank. Once the pegs are on the board you put the board inside the tank against the wall, fill the tank with liquid and you can start dropping balls (plastic or metals) in the fluid and look at the trajectory taken by particles of different sizes for different angles of the board. The choice of the fluid is important because you want the particles to fall slowly (to stay in the laminar flow regime). We opted for glycerol, but any other viscous fluid should work. Interesting features to observe are the migration angle of the particles with respect to the angle of the board, you will see that for certain board angles the migration angle is not the same for all the particle sizes. Also, another feature that many students do not expect to see at first is the fact that the particles' trajectory goes around a peg as it falls, which is quite different than what one would observe in air.

Want to learn more?

German Drazer's Lab website

Joelle Frechette Lab website

Institute for NanoBioTechnology