Meet the Researchers: Chase Brisbois

Chase Brisbois is a graduate student specializing in computational soft matter in the laboratory of CBES deputy director Monica Olvera de la Cruz. In this Q&A, Brisbois describes his early love of science and plants as well as his research on using magnetic fields to control microswimmers.

What sparked your interest in science in general, and what led you to explore a path in nanoscience and materials science in particular?

My mother gave me this book a really long time ago and I don’t know what was on any other pages, but I remember this page that described how atoms bond. It was basically explaining general chemistry, where they had a Bohr model of the atom and they taught about octet rules and how different gases are composed.

I remember loving that page and it just struck a chord with me that the whole world is made up of a handful of types of atoms, and they’re all just bonded in different ways. I think that was the first point in my life where I thought I wanted to be a scientist.

Growing up, I had pretty broad scientific interests and ultimately the multidisciplinary nature of materials science is what appealed to me.

How would you describe your current CBES research interests to a non-scientist?

I’m interested in how I can use magnetic fields to manipulate small machines to move through fluids. Small “swimmers” have trouble moving through water — it’s like they’re trying to swim through molasses because they’re so much weaker than the surrounding fluid. It’s easy for humans to go through water, but it’s difficult to travel through water for something that’s really, really small.

This creates an interesting situation because microswimmers don’t enjoy the luxury of inertia, meaning that if they stop swimming they stop moving immediately. So, if it pushes its fin to the left, it’ll move a little bit, but then if it pushes it back to the right, it will undo everything it just did and end up in the same place. You need a different way of swimming that doesn’t undo itself, and bacteria and different small organisms do this by creating continuously spinning helical tails or by producing waves that only travel in one direction.

What I’m trying to do is induce this kind of swimming into a small swimmer by using magnetic fields.

What potential applications would it have if you are able to improve the swimming capability of these materials?

When people talk about microswimmers, they usually talk about two things. Sometimes they talk about catalysis, where you can mount some kind of catalyst on a microswimmer and trigger a chemical reaction through diffusion. If you have something that can swim, it can stir up your “pot” and your reaction can proceed in a faster manner.

People also discuss microswimmers in terms of medicine. You can have swimmers that move around in the fluid of your eye and perform surgeries. Because I’m working with nanoparticles and the swimmers I’m simulating are so much smaller, it’s not unreasonable to think that these swimmers could swim inside of cells. Cells are actually quite large compared to the materials that I’m talking about so I think the most ambitious application would be to add swimmers inside of living cells. This could be used, for example, to facilitate site-specific drug delivery or intracellular mechanical manipulation.

How did you get involved in performing the computational side of this research?

I was an experimentalist all the way up until grad school, but I realized that computational methods and simulations are only going to become more important in the future. 

I wasn’t a very good programmer and I wanted to learn how to be a computational materials scientist, but I still consider myself an experimentalist, too. If I were to start a lab in the future, I think I would include both the experimental and theoretical aspects of the work.

What attracted you to the Olvera de la Cruz group?

It was a combination of two things: It was apparent that she was going to give me intellectual freedom, and I found the work exciting. 

She’s known for electrostatics and soft materials, and I knew that I wanted to work with soft matter. Even within the field of soft matter, her lab seemed like it was working at a bunch of different interfaces: there were polymers but also self-assembling systems and magnetic filaments. All these different aspects appealed to me. 

Can you tell me about the two CBES-supported papers you’ve already published and what the findings were of each of those projects?

Of course. The paper we published in 2019 in PNAS was basically an extension of work from a previous grad student in the group, Joshua Dempster. We extended his superparamagnetic filament work into a second dimension — we went from a filament to a membrane.

What we wanted to know was how a magnetic field buckles a magnetoelastic membrane, or a membrane that is elastic in response to magnetic fields. We wanted to know how this happened and whether it could be used for anything, and what we saw is that there is this competition between the bending and stretching of the membrane. In other words, the magnetic field transmits forces and torques that drive the membrane to expand, contract or twist in different ways. We identified critical field values that will cause this buckling to happen, and we also observed spontaneous symmetry breaking that is induced with a certain field strength.

We also observed regimes where multiple membrane configurations are observed due to hysteresis in the membrane buckling response. The hope is that these insights into different buckling mechanisms — the spontaneous symmetry breaking and these different field thresholds — will provide the basis in developing microswimmers or other microactuators.

For the paper with Chad Mirkin’s group in Advanced Materials, I used theory and computer simulations to explain the phenomena that they observed. The goal of that project was to use magnetic fields to create high-aspect ratio colloidal crystals, but it goes much deeper than that because magnetic fields can be used to alter the crystal morphology itself.

The magnetic coupling between colloids depends on field strength, and controls how readily they will assemble due to magnetic attraction. But unless the magnetic field is very strong, the colloids will first assemble into a cluster due to the DNA-hybridization interactions. As the cluster grows, its effective magnetic coupling will increase as well and eventually cause the larger clusters to assemble due to their magnetic interactions. I showed that by changing the initial magnetic coupling between colloids, you can control the cluster size at which magnetic assembly will occur, which in turn affects the colloidal crystal morphology.

I saw on your CV that you’ve volunteered at dozens of events related to gardening and sustainability. Is there a tie-in there with your research interests in energy science?

It’s a bit of a coincidence, to be honest. I’ve loved plants since I was a little kid and I just think plants are so cool.

If I wasn’t doing what I’m doing right now, I’d be studying plants. I think their immunology is cool as well as the structures they form and their survivability. My mother had this aloe plant that she forgot about in her laundry room for three years. She started watering it, putting it by the window, and it’s doing fine now.

When I came to Northwestern I joined Plant-It Purple, which is the graduate student club that runs the garden in the middle of Tech Institute. We plant new things and we educate people about doing their own gardens and the way different plants grow. I think the sustainability piece grew out of my initial interest in plants, because then you can teach people about how to compost and the importance of keeping and preserving native wildlife and plants.