Portia Tieze: Conducting scientific research from home in the event of a pandemic

The question she is addressing this summer is how microscopic swimmers – bacteria, sperm and other microorganisms – can move around. Large-scale creatures like fish and humans are able to easily swim in water and similar liquids. But imagine if this water looked more like maple syrup. Plowing it wouldn’t be that easy, and that’s the situation microorganisms are in.

One of Tieze’s swimmers walks through a tub of corn syrup.

On a microscopic scale, viscous forces are much greater, but microorganisms are able to move with apparent ease. Understanding how they do it could shed light on everything from the spread of infections throughout the body to the design of tiny swimming robots.

“My specialty is fluid mechanics and I’m interested in how fluid properties affect swimming behavior,” said Zenit, who oversees Tieze’s work via Zoom videoconferencing and worked with her on the setup. appropriate equipment. “It’s hard to work with real bacteria because they’re so small. So we cheat. We scale everything and increase the viscosity of the fluid accordingly. We now have a model where we can modify different parameters of the experience to determine which ones are important. “

For his experiments, Tieze made pill-sized plastic swimmers, each fitted with a rare earth magnet. The swimmers are placed in a small vat of viscous fluid, in this case corn syrup. The vessel is surrounded by a Helmholtz coil – a pair of strong electromagnets that create a magnetic field. Switching the orientation of the magnetic field back and forth causes magnetic swimmers to move in a way that mimics micro-scale swimming. The oscilloscope measures the amount of current flowing through the coils, which reveals the forces involved in the swimming motion.

Much of the work Tieze has done to date has been to set up the device, prepare the swimmers, and get the entire setup to work properly. It has sometimes been a challenge to do this remotely rather than in the lab, say Tieze and Zenit. But they make it work.

Image of an oscilloscope
An oscilloscope measures the forces exerted by little swimmers.

“We kind of became Zoom experts,” said Zenit. “Sometimes Portia uses both her computer and her phone on Zoom so that we can talk and see what she’s doing up close. It was pretty fun, actually.

With the fully functional setup, Tieze can perform a variety of swimming experiences. For example, she can modify swimmers’ tail attributes to unravel how length, thickness, and stiffness affect swimming forces. The results could reveal fundamental new knowledge about micro-scale swimming. The work could also earn Tieze’s authorship on a peer-reviewed journal article – a major boon for any undergraduate researcher considering graduate school.

Tieze says the project was full of little reminders of why she fell in love with science in the first place. She had to use precise calculations, for example, to design the neutral buoyancy swimmers – able to be suspended in liquid without sinking or floating upwards.

“It’s one of my favorite things in physics,” said Tieze, who focuses in mechanical engineering. “You do the math, follow what he tells you to do – and it actually works! “

“Working with Professor Zenit this summer reaffirmed what I first understood to be the beauty of science,” she added. “With a little math and a little creativity, we have the power to ask and seek answers to any question imaginable. “

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About Donald P. Hooten

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