RODNEY PRIESTLEY, XIAOHUI XU - PROFESSOR, POSTDOCTORAL RESEARCHER, PRINCETON UNIVERSITY

More than 800 million people worldwide lack access to safe drinking water. Over half the U.S. population drinks from water with detectable lead levels, studies suggest. And even as the pandemic reminded us of the importance of frequent handwashing with soap and water, three in 10 people around the globe can't do that in their own homes. The World Health Organization and UNICEF warn that these numbers are likely to get worse in the next decade unless societies create and improve water infrastructure—a vast and expensive proposition. A new tool for meeting this challenge has emerged from the laboratory of Princeton University chemical engineers Rodney Priestley and Xiaohui Xu. They have created a material that removes impurities in drinking water, requires no additional energy source beyond sunshine and is potentially cheap to manufacture.

The two engineers stumbled on their new approach while working on a project to make artificial skin to help heal wounds. Skin typically acts as a selective shield—keeping pathogens out of the body, while still permitting water to pass through it. To make artificial skin, they created a hydrogel (a complex polymer that will not dissolve in water) with a molecular structure that would permit the passage of water and block contaminants. As they developed and tested this material, Xu realized the hydrogel might potentially have another application: water purification. That spurred a new project, in which the two researchers modified their hydrogel in a few key ways so it would not only filter impurities, but actively draw water in as well.

They designed their hydrogel so that it acts as a heat-sensitive sponge. At room temperature, compounds in the hydrogel attract water molecules. When heated, the molecular structure changes and the gel releases water. "Inside it is highly porous so it can store the water," explains Xiaohui Xu. "When you heat it, the volume of the material will shrink [and] all of the water inside will be released."

Then they covered the layer of spongy hydrogel with different polymer that acts as a filter. As the sponge draws in the water, the outer layer keeps impurities from entering. These layers sandwiched together form a thin, sheetlike "membrane." In their testing to date, they've found the combined layers can block problem particles like lead and nitrates from agricultural run-off. "It effectively just sucks in all of the pure water while leaving out all of the contaminants," Priestley explains.

Priestley and Xu's invention has many advantages over water purification systems already in use by NGOs. It needs no power source—no electricity to run a pump—other than sunshine, which makes it easier to deploy. And the membrane is potentially cheaper to produce than conventional filters and can be manufactured without using harsh chemical solvents. "We just realized there was a huge opportunity in this space to try and do this in a sustainable manner," Priestley says.

Michael Brown, CEO of AquaPao, the company developing and commercializing this technology, notes that the material can be used not only for filtering water but for collecting drinkable water from the atmosphere. "If you put the membrane outside, it will start attracting water at a pretty significant rate," he notes.

Before the invention is ready for prime time, Priestley and Xu still need to investigate how durable the membrane is. And like other water filters and purifiers, it's not 100 percent effective at removing all contaminants—it's unlikely, for instance, to provide an efficient solution for desalinating salt water.

Still, Priestley adds, having a system that treats water for many different types of impurities could put their material ahead of many other approaches: "We have shown the ability to purify many different types of impurities—heavy metals like lead, small molecules, organic matter like microbes and yeast and oil contaminants. If it turns out that it's a membrane that can really purify 20 different impurities as opposed to just one targeted impurity, I think that would also set it apart." —Daisy Yuhas

ROBERT MONTGOMERY - DIRECTOR, NYU LANGONE TRANSPLANT INSTITUTE

Three years ago, doctors told Dr. Montgomery, who has a rare, progressive disease of the heart muscle, that he needed a transplant. He joined more than 106,800 Americans in organ-transplant purgatory, waiting for a donor organ—a wait 17 people fail to outlast each day. "This paradigm just isn't working," he says. "We need a renewable, unlimited source of organs."

Dr. Montgomery has devoted much of his 20-plus years as a transplant surgeon to that end. He pioneered the use of organs from donors infected with hepatitis C and performed the first "domino paired donation," which combines two or more donors and recipients in a kidney swap. In September, he and his team succeeded in transplanting a genetically-engineered pig kidney into a human body (since it was a test case, the recipient was a patient who had lost brain function). The body did not reject the kidney, and over a 54-hour test run, the pig organ performed like a normal human kidney. He expects a similar procedure to be performed on a live patient in the next year or so. Montgomery is optimistic that within a decade, pig organs will be a viable option for those on dialysis or in need of a kidney transplant—and eventually hearts, lungs and other organs. —Kerri Anne Renzulli

MIMI AUNG — FORMER PROJECT MANAGER, NASA'S JET PROPULSION LABORATORY

MiMi Aung has had a very good year. On April 19, the six-year project she led to get a helicopter to fly in the thin atmosphere of Mars finally reached fruition: The extraterrestrial aircraft Ingenuity took off from the planet's surface for a 39-second flight. It has since made 15 more trips to gather data and photos and help guide the Perseverance rover.

This first-of-a-kind venture had many challenges to overcome: the thinness of the planet's atmosphere, which is less than one percent the density of Earth's, the intense cold of Mars and the seven-month voyage through space to get there. Also, the communications delay between Earth and Mars meant that the helicopter largely had to pilot itself. Aung recently moved on to a new challenge: building a network of satellites for broadband internet connection in her new job at Amazon's Project Kuiper. Her former team of engineers and scientists at NASA will carry on creating Ingenuity's successors—larger aircraft capable of carrying rock samples. —K.R.

RADHIKA NAGPAL — COMPUTER SCIENTIST, WYSS INSTITUTE FOR BIOLOGICALLY INSPIRED ENGINEERING AT HARVARD UNIVERSITY

If Harvard researcher Radhika Nagpal has her way, thousands of tiny robots will soon work together cleaning up chemical spills, building dams and inspecting bridges. "We are really on the cusp of a revolution in robotics," she says.

Nagpal and her team create robots that mimic real-life organisms, self-organizing and collaborating to complete complex tasks beyond what any individual robot can do. Their role, as she sees it, is to free up humans from "the 3Ds:" tasks that are dirty, dull or dangerous.

Her team's first project was inspired by termites. A thousand-robot army, the Kilobots, are now being used in labs around the world for research and education. In 2021, her lab built underwater robots, the BlueSwarm, that act like a school of fish, complete with intricate migration patterns and predator-evasion tactics, for monitoring damage to coral reefs. Because there's no WiFi or GPS underwater, these deep-sea explorers mimic the bioluminescence of living sea creatures to communicate with one another. The next commercial project, Nagpal thinks, will be aerial swarms that can inspect crops and deliver packages. When the military adopts swarm technology, it could change the nature of conflict. "As we go forward into the future and these systems are deployed," she says, "we are going to learn lots of new lessons of what that means." —Meghan Gunn

DANIEL GIBSON - CO-FOUNDER, CTO, CODEX DNA

A few years ago, as scientists availed themselves of then-new technology for deciphering the genetic code of viruses, Gibson turned his attention to the opposite activity: how to take that code and turn it into an actual virus, the better to study it and come up with vaccines. At the time, scientists had to order short sequences of DNA from specialty firms and stitch them together to form long ones. Gibson's idea was to make that process quicker, easier and cheaper by automating it with so-called DNA printers.

Gibson's BioXp 3250, a 2-by-2-foot device, gives scientists the means to synthesize genes in the lab in eight hours, helping speed the design and fabrication of new vaccine candidates and other biological products. Last year, Pfizer used the device to help develop its COVID-19 vaccine. Today, Codex DNA, where Gibson is chief technology officer, has sold more than 160 of the printers. Together with academic research institutions and biopharma companies, Gibson is working on vaccines, precision immunotherapy for cancer, meat substitutes and other projects. His next goal is to build a vaccine printer "capable of synthesizing and delivering vaccines globally at the push of a button," he says. "This would enable a future where we stamp out viral outbreaks in real time, at a regional level, before they ever reach pandemic status." —K.R.

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