How science sprung from the depths of the disposable baby diaper

Courtesy McGovern Institute for Brain Research/MIT

For a parent, the diaper has a short life and a simple mission. Once removed from the baby’s bottom and disposed of in the diaper pail, the typical diaper has served its purpose. But it turns out all this time, it contained the source of an important new technology. From the depths of the disposable baby diaper has emerged a new technique to see tiny details under the microscope.

For hundreds of years, the microscope has allowed scientists to study cells that are invisible to the naked eye. The concept is fairly simple: Drop the cells onto a glass slide beneath a glass lens. Shine a light under the slide. The lens magnifies the light, along with the image on the slide. A 21st century electron microscopes push that magnification to a nanometer scale. But for all the advances of the past 300 years, there’s one problem, says Ed Boyden, an associate professor at the McGovern Institute for Brain Research at MIT.

“All of these existing microscopy methods are limited. They can’t take a three dimensional image of a large sample with nanoscale precision,” Boyden says, something neuroscientists need to understand how neurons and circuits in the brain work.

Boyden and his team at MIT came up with an idea: what if they made the sample itself bigger?

They were half-joking, Boyden says, but after a few months they started looking into research from a late-MIT professor on materials that expand rapidly. After trial and error, they found the best material for the job was sodium polyacrylate, which is very similar to the material that makes disposable diapers so absorbent.

“Expansion microscopy is not a new microscope. It’s a series of steps we apply to the sample to physically magnify it,” says Fei Chen, a research assistant in Boyden’s lab.

It’s like building a sponge inside the tissue, Boyden says. Tiny molecules of acrylate are added to the tissue, linking to each other like cars on a train. Add water and the material expands, bringing the tissue around it for the ride, he says.

In their studies, the tissue increased 100 times in volume, or about five-fold larger, Boyden says. Their results are published today in the journal Science.

Boyden thinks this technology will be useful in many areas of nanobiology because it allows scientists to see three dimensional tissue with nanoscale precision. For neuroscientists, that means they can navigate brain circuits.

“It’s incredible. For hundreds of years we’ve used the lens to magnify things, and now we can make it bigger. Now you can see tiny structures with your own eyes,” he says.

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