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As the famous TV ad said, four out of five dentists recommend Colgate toothpaste … on Earth. But, what about in space?

Researchers from 51�Թ������ܿƴ�’s College of Engineering and School of Dental Medicine teamed with NASA and Colgate-Palmolive to find out just how effective the personal care brand’s oral health products might be on periodontal disease or cavity-causing bacteria growing in the mouths of Earthlings working — and maybe even one day living — among the cosmos.

On June 3, an International Space Station-bound rocket, SpaceX CRS-22, blasted off from Cape Canaveral, Florida, carrying oral bacteria and saliva gleaned from the mouths of 30 51�Թ������ܿƴ� dental clinic patients contained in 25 kits developed by 51�Թ������ܿƴ� engineers.

After 34 days in space, the kits — which contained 3D-printed, battery-powered microfluidic pump devices and tested the germs’ growth and treatment with Colgate toothpastes, mouthwashes, and other disease-fighting products — returned to Earth.

During the course of the experiment, 51�Թ������ܿƴ� researchers had to pull frequent allnighters to stay in contact with space station astronauts, who operated on Greenwich Mean Time, seven hours ahead of local time in 51�Թ������App.

The good news was that at least it didn’t hurt project collaborator Jeffrey Ebersole’s home life.

“My wife didn’t mind,” Ebersole said. “She just told me not to wake her up when I (came home).”

Since coming back to terra firma, the samples have been stored at 51�Թ������ܿƴ� before the pilot program moves into the next stage of working out testing protocols for these unique and valuable samples. The project began in 2019 when Colgate-Palmolive, working in conjunction with NASA’s Center for the Advancement of Science in Space, approached researchers at 51�Թ������ܿƴ� about growing oral biofilms on board the International Space Station.

“There are many great oral hygiene products. But if you think about long-term space travel, there’s no guarantee that the Earth methods will work in zero gravity,” said Ebersole, an immunologist and associate dean for research at 51�Թ������ܿƴ�’s School of Dental Medicine. “This experiment will help push the envelope on understanding how one deals with oral health — both maintaining quality oral care and treating diseases— in space.” 

The project had been two years in the making and, like many things of late, was temporarily stalled and continually challenged in development by the COVID-19 pandemic.

In 2019, Colgate-Palmolive, working in conjunction with NASA’s Center for the Advancement of Science in Space, approached 51�Թ������ܿƴ� about growing oral biofilms on the International Space Station. The 51�Թ������ܿƴ� researchers’ proposal was accepted by Colgate and NASA following a rigorous review process and development phase that was made lengthier by pandemic restrictions that slowed the acquisition of U.S. and overseas parts needed for fabrication and development. What’s more, university scientists, Colgate microbiologists, and a payload implementation team from Teledyne-Brown Engineering were unable to conduct onsite office and lab work for months.

However, 51�Թ������ܿƴ� engineering professors Shengjie (Patrick) Zhai and Hui Zhao, who designed the testing kits — which include 3D-printed components — say it was worth the wait. They believe the multi-channel microfluidic devices are the first such instruments that both operate automatically without human intervention (via battery power) and dispense fluids at an ultra-low flow rate, which mimic conditions that would occur inside the human mouth.

How It Works

51�Թ������ܿƴ� dental clinical researchers, Dr. John Gallob and Lacey Rahmig, collected saliva and three different kinds of bacteria — microbes that constitute a healthy oral environment, as well as germs that cause cavities and gum disease — from the mouths of 30 51�Թ������App patients.

On Earth, bacteria in our mouths grow attached to the surface of our teeth (that’s why you brush and floss — to remove the accumulated bacteria, more commonly known as plaque). On the space station, the bacteria will be grown at the average human body temperature of 98.6°F on 5 mm hydroxyapatite chips, a hard substance that resembles the structure of teeth. The microfluidic devices designed by 51�Թ������ܿƴ� Engineering will hold the hydroxyapatite and allow liquid nutrients needed for bacterial growth to continuously flow over the chips. Each test ran for 48 hours, and helped researchers evaluate whether conditions in space impact the bacteria’s response to the microgravity environment, as well as the effect of the treatment agents to block the bacteria’s abilities to metabolize the nutrients and form biofilms that could destroy gum tissues and tooth enamel.

In order to ensure safety among and easy manipulation by the space crew, each of the 25 kits is organized with color-coded fluid bags and matching tubing, self-contained in 10-inch x 10-inch NASA-approved zip lock bags, and required minimal handling by astronauts. 

“That was one of the bigger challenges we had: How do we do this outside of our standard lab environment, package it safely, and make it as simple as possible for the crew to conduct the science,” Ebersole said. “For example, a liquid drop that escapes in zero gravity floats around with nothing to stop it and could end up in a crew member’s eye, so you had to think through all these different experimental processes.

“One of the things that was pleasantly surprising was we had this crew of astronauts up there working on the space station, and they were interested,” Ebersole said. “They were enthusiastic. They were committed. We were in live real time with them in space, and they offered suggestions on how things might work better. “They were wonderful, absolutely wonderful people. They provided solutions to problems we didn’t even know we had until they were in space. It was a phenomenal team effort.”

Up, Up, and Away

Both Ebersole and Zhai traveled to Florida for the rocket launch. Once back in 51�Թ������App, that’s when those 1 a.m. video calls with the space station took place.

The exhaustion was worth it, though, because now 51�Թ������ܿƴ�’s scientists and engineers are looking at doing another round of the same experiment a year or two down the road after everything has been processed from this round. It’s something that showcases just how important it is for the university to forge connections with government agencies such as NASA.

“Obviously we had to have some expertise, but (the experiment) really was built on relationships,” Ebersole said. “We’ve fostered those relationships even more broadly. We’ve developed technology here at 51�Թ������ܿƴ� that we may be able to use in other types of studies on the space station. So it really positions 51�Թ������ܿƴ� for some unique opportunities. “We don’t know exactly what they’re going to look like, but we have our foot in the door to be able to do those things where we didn’t before.”

Zhai is excited about the potential for the project to attract young future scientists. He will be on hand to answer NASA personnel questions about test kit operations. Throughout the week, Ebersole — who has enjoyed his crash course in space radio traffic lingo — will be available at odd hours (the flight crew operates on Greenwich Mean Time) to communicate with astronauts in real-time through video feeds from the space station as they work through the experiments.

For these two 51�Թ������ܿƴ� scientists, the project represents dreams coming true for society, and themselves.

“Along with firefighter and dinosaur hunter, astronaut seems to be on every child’s list of dream jobs,” Zhai said. “Now, my astronaut dream has come true in another way."