Aurelia Butler

Making corn salt-tolerant by engineering its microbiome. Increasing nut productivity with fungal symbiosis. Cleaning up toxic metals in the water supply with algae. Capturing soil nutrient runoff with bacterial biofilms. These were the bio-sustainability innovations designed and presented by students in the Department of Biological Engineering (BE) last May. With the sun shining brightly on an empty Killian Court, the students gathered for the final class presentations over Zoom, physically distanced due to the Covid-19-related closing of MIT’s campus this spring.
For decades, the sustainable technologies dominating public discourse have tended toward the mechanical: wind power, solar power, saltwater distillation, etc. But in recent years, biological solutions have increasingly taken the forefront. For recent BE graduate Adrianna Amaro ’20, being able to make use of “existing organisms in the natural world and improve their capabilities, instead of building whole new machines, is the most exciting aspect of biological engineering approaches to sustainability problems.”
Each semester, the BE capstone class (20.380: Biological Engineering Design) challenges students to design, in teams, biological engineering solutions to problems focused on a theme selected by the instructors. Teams are tasked with presenting their solutions in two distinct ways: as a written academic grant proposal and as a startup pitch. For Professor Christopher Voigt, one of the lead instructors, the goal of the class is to “create the climate where a half-baked concept emerges and gets transformed into a project that is both achievable and could have a real-world impact.”
A glance at the research portfolio on the MIT biological engineering homepage reveals a particular focus on human biology. But over the years, students and faculty alike have started pushing for a greater diversity in challenges to which the cutting-edge technology they were developing could be applied. Indeed, “sustainability has been one of the top areas that students raise when asked what they want to address with biological engineering,” says Sean Clarke PhD ’13, another instructor for the class.
In response to student input, the instructors chose food and water security as the theme for the spring 2020 semester. (Sustainability, broadly, was the theme the previous semester.) The topic was well-received by the 20.380 students. Recent BE graduate Cecilia Padilla ’20 appreciated how wide-reaching and impactful the issues were, while teammate Abby McGee ’20 was thrilled because she had always been interested in environmental issues — and is “not into pharma.”
Since this is the biological engineering capstone, students had to incorporate engineering principles in their biology-based solutions. This meant developing computational models of their proposed biological systems to predict the output of a system from a defined set of inputs. Team SuperSoil, for example, designed a genetic circuit that, when inserted into B. subtilis, a common soil bacteria, would allow it to change behavior based on water and nutrient levels. During heavy rain, for example, the bacteria would respond by producing a phosphate-binding protein biofilm. This would theoretically reduce phosphate runoff, thus preserving soil nutrients and reducing the pollution of waterways. By modeling natural processes such as protein production, bacterial activation, and phosphate diffusion in the soil using differential equations, they were able to predict the degree of phosphate capture and show that significant impact could be achieved with a realistic amount of engineered bacterial input.
Biological engineering Professor Forest White co-leads the class every spring with Voigt. White also teaches the prerequisite, where students learn how to construct computational models of biological systems. He points out how the models helped students develop their capstone projects: “In a couple of cases the model revealed true design challenges, where the feasibility of the project requires optimal engineering of particular aspects of the design.”
Models aside, simply thinking about the mathematical reality of proposed solutions helped teams early on in the idea selection process. Team Nutlettes initially considered using methane-consuming bacteria to capture methane gas from landfills, but back-of-the-envelope calculations revealed unfavorable kinetics. Additionally, further reading brought to light a possible toxic byproduct of bacterial methane metabolism: formaldehyde. Instead, they chose to develop an intervention for water-intensive nut producers: engineer the tree’s fungal symbionts to provide a boost of hormones that would promote flower production, which in turn increases nut yields.
Team Halo saw water filtration as the starting point for ideation, deeming it the most impactful issue to tackle. For inspiration, they looked to mangrove trees, which naturally take up salt from the water that they grow in. They applied this concept to their design of corn-associated, salt-tolerant bacteria that could enhance their plant host’s ability to grow in high salinity conditions — an increasingly common consequence of drought and industrial agricultural irrigation. Additional inspiration came from research in the Department of Civil and Environmental Engineering: In their design, the team incorporated a silk-based seed coating developed by Professor Benedetto Marelli’s group.
Many of the capstone students found themselves exploring unfamiliar fields of research. During their foray into plant-fungal symbiosis, Team Nutlettes was often frustrated by the prevalence of outdated and contradictory findings, and by the lack of quantitative results that they could use in their models. Still, Vaibhavi Shah, one of the few juniors in the class, says she found a lot of value in “diving into something you’ve no experience in.”
In addition to biological design, teams were encouraged to think about the financial feasibility of their proposed solutions. This posed a challenge for Team H2Woah and their algal-based solution for sequestering heavy metals from wastewater. Unlike traditional remediation methods, which produce toxic sludge, their system allows for the recycling of metals from the wastewater for manufacturing, and the opportunity to harvest the algae for biofuels. However, as they developed their concept, they realized that breaking into the existing market would be difficult due to the cost of all the new infrastructure that would be required.
Students read broadly over the course of the semester, which helped them enhance their understanding of food and water insecurity beyond their specific projects. Before the class, Kayla Vodehnal ’20 of Team Nutlettes had only been exposed to policy-driven solutions. Amaro, meanwhile, came to realize how close to home the issues they were researching are: all Americans may soon have to confront inadequate access to clean water due to, among other factors, pollution, climate change, and overuse.
In any other semester, the capstone students would have done their final presentations in a seminar room before peers, instructors, a panel of judges, and the indispensable pastry-laden brunch table. This semester, however, the presentations took place, like everything else this spring, on Zoom. Instructors beamed in front of digital congratulatory messages, while some students coordinated background images to present as a single cohesive team. Despite the loss of in-person engagement, the Zoom presentations did come with benefits. This year’s class had a larger group of audience members compared to past years, including at least two dozen faculty, younger students, and alumni who joined virtually to show their support.
Coordinating a group project remotely was challenging for all the teams, but Team Nutlettes found a silver lining: Because having spontaneous conversations over Zoom is harder than in person, they found that their meetings became a lot more productive.
One attendee was Renee Robins ’83, executive director of the Abdul Latif Jameel Water and Food Systems Lab, who had previously interacted with the class as a guest speaker. “Many of the students’ innovative concepts for research and commercialization,” she says, “were of the caliber we see from MIT faculty submitting proposals to J-WAFS’ various grant programs.”
Now that they have graduated, the seniors in the class are all going their separate ways, and some have sustainability careers in mind. Joseph S. Faraguna ’20 of Team Halo will be joining Ginkgo Bioworks in the fall, where he hopes to work on a bioremediation or agricultural project. His teammate, McGee, will be doing therapeutic CRISPR research at the Broad Institute of MIT and Harvard, but says that environment-focused research is definitely her end goal.
Between Covid-19 and post-graduation plans, the capstone projects will likely end with the class. Still, this experience will continue to have an influence on the student participants. Team H2Woah is open to continuing their project in the future in some way, Amaro says, since it was their “first real bioengineering experience, and will always have a special place in our hearts.”
Their instructors certainly hope that the class will prove a lasting inspiration. “Even in the face of the Covid-19 pandemic,” White says, “the problems with global warming and food and water security are still the most pressing problems we face as a species. These problems need lots of smart, motivated people thinking of different solutions. If our class ends up motivating even a couple of these students to engage on these problems in the future, then we will have been very successful.”

Topics: Biological engineering, School of Engineering, Civil and environmental engineering, Broad Institute, J-WAFS, Classes and programs, Sustainability, Water, Undergraduates, Students, Alumni/ae More

The property of water that enables a bug to skim the surface of a pond or keeps a carefully placed paperclip floating on the top of a cup of water is known as surface tension. Understanding the surface tension of water is important in a wide range of applications including heat transfer, desalination, and oceanography. Although much is known about the surface tension of fresh water, very little has been known about the surface tension of seawater — until recently.
In 2012, John Lienhard, the Abdul Latif Jameel Professor of Water and Mechanical Engineering, and then-graduate student Kishor Nayar SM ’14, PhD ’19 embarked on a research project to understand how the surface tension of seawater changes with temperature and salinity. Two years later, they published their findings in the Journal of Physical and Chemical Reference Data. This spring, the International Association for the Properties of Water and Steam (IAPWS) announced that they had deemed Lienhard and Nayar’s work an international guideline.
According to the IAPWS, Lienhard and Nayar’s research “presents a correlation for the surface tension of seawater as a function of temperature and salinity.” The announcement of the guideline marked the completion of eight years of work with dozens of collaborators from MIT and across the globe.
“This project grew out of my work in desalination. In desalination, you need to know about the surface tension of water because that affects how water travels through pores in a membrane,” explains Lienhard, a world leading expert in desalination — the process by which salt water is treated to become potable freshwater.
Lienhard suggested Nayar take measurements of seawater’s surface tension and compare the results to the surface tension of pure water. As they would soon find out, getting reliable data from salt water would prove to be incredibly difficult. 
“We had thought originally that these experiments would be pretty simple to do, that we’d be done in a month or two. But as we started looking into it, we realized it was a much harder problem to tackle,” says Lienhard.
From the outset, Nayar hoped to get enough accurate data to inform a property standard. Doing so would require the uncertainty in the measurements to be less than 1 percent.
“When you talk about property measurements, you need to be as accurate as possible,” explains Nayar. The first hurdle he had to surmount to achieve this level of accuracy was finding the appropriate instrumentation to make reliable measurements — something that turned out to be no easy feat.
Measuring surface tension
To measure the surface tension of water, Lienhard and Nayar teamed up with Gareth McKinley, professor of mechanical engineering, and then-graduate student Divya Panchanathan SM ’15, PhD ’18. They began with a device known as a Wilhelmy plate, which finds the surface tension by lowering a small platinum plate into a beaker of water then measuring the force the water exerts as the plate is raised.
Nayar and Panchanathan struggled to measure the surface tension of salt water at higher temperatures. “The issue we kept finding was once the temperature was above 50 degrees Celsius, the water on the beaker evaporated faster than we could take the measurements,” Nayar says. 
No instrument would allow them to get the data they needed — so Nayar turned to the MIT Hobby Shop. Using a lathe, he built a special lid for the beaker to keep vapor in.
“The little lid Kishor built had accurately cut doors that allowed him to put a surface tension probe through the lid without letting water vapor get out,” explains Lienhard.
After making progress on obtaining data, the team suffered a massive setback. They found that barely visible salt scales, which formed on their test beaker over time, had introduced errors to their measurements. To get the most accurate values, they decided to use fresh new beakers for every single test. As a result, Nayar had to repeat nine months of work just prior to his master’s thesis being due. Fortunately, since the main problem was identified and solved, experiments could be repeated much faster.
Nayar was able to redo the experiments on time. The team measured surface tension in seawater ranging from room temperature to 90 degrees Celsius and salinity levels ranging from pure water to four times the salinity of ocean water. They found that surface tension decreases by roughly 20 percent as water goes from room temperature toward boiling. Meanwhile, as salinity increases, surface tension increases as well. The team had unlocked the mystery of seawater surface tension.
“It was literally the most technically challenging thing I had ever done,” Nayar recalls.
Their data had an average deviation of 0.19 percent, with a maximum deviation of just 0.6 percent — well within the 1 percent bound needed for a guideline.
From master’s thesis to international guideline
Three years after completing his master’s thesis, Nayar, by then a PhD student, attended an IAPWS meeting in Kyoto, Japan. The IAPWS is a nonprofit international organization responsible for releasing standards on the properties of water and steam. There, Nayar met with leaders in the field of water surface tension who had been struggling with the same issues Nayar had faced. These contacts introduced him to the long, rigorous process of declaring something an international guideline.
The IAPWS had previously published standards on the properties of steam developed by the late Joseph Henry Keenan, professor and one-time department head of mechanical engineering at MIT. To join Keenan as authors of an IAPWS standard, the team’s data needed to be verified by measurements conducted by other researchers. After three years of working with the IAPWS, the team’s work was finally adopted as an international guideline.
For Nayar, who graduated with his PhD last year and is now a senior industrial water/wastewater engineer at engineering consulting firm GHD, the guideline announcement made the long months collecting data well worth it. “It felt like something getting completed,” he recalls. 
The findings that Nayar, Panchanathan, McKinley, and Lienhard reported back in 2014 are broadly applicable to a number of industries, according to Lienhard. “It’s certainly relevant for desalination work, but also for oceanographic problems such as capillary wave dynamics,” he explains.

It also helps explain how small things — like a bug or a paperclip — can float on seawater. More

Every corner of the globe has suffered from supply chain disruptions during the coronavirus pandemic. Beginning in January with a focus on China manufacturing, the MIT Humanitarian Supply Chain Lab (HSCL) began providing evidenced-based analysis to the U.S. Federal Emergency Management Agency (FEMA) to inform strategic planning around the supply chain risks. By March, the […] More