Engineering health solutions for all

Benjamin Tien


Hundreds of women die every day due to excessive bleeding after childbirth, but this can be prevented by an injection of the hormone oxytocin, which stimulates uterine contractions that reduce bleeding. Yet oxytocin must be kept cold, and developing countries often lack the resources to transport and store the hormone. Nor do they have enough trained personnel to administer the shot.

Benjamin Tien, who graduated from Princeton in 2015 with a degree in chemical and biological engineering, has been awarded a Fulbright grant to join a research team developing an aerosolized, inhalable version of oxytocin. He’ll work at the Monash Institute of Pharmaceutical Sciences in Australia to use a technique called “spray-drying” to turn liquid oxytocin into a dry powder that can be released from an inexpensive, disposable device. This would cut out the need for special storage conditions, eliminate the risk of infection from needles, and make the treatment available even to women giving birth at home.

While at Princeton, Tien conducted senior thesis research on nanoparticles for dealing with bacterial infections such as cholera or pseudomonas with Robert Prud’homme, a professor of chemical and biological engineering and Tien’s thesis adviser. During the summer before his senior year, Tien worked at a startup company in Boston called Diagnostics for All that develops medical diagnostics for developing countries.

While doing research in Australia, Tien will also work with the Poche Center for Indigenous Health, an organization that aims to improve the health of indigenous Australians with an emphasis on forming lasting relationships with the communities. “I want to get a better sense of the challenges people are facing on the ground, which will help me know what to focus on in my career,” Tien said.

-By Takim Williams

Tiny delivery capsules for new drugs

‘Jack’ Hoang Lu researches nanoparticles for drug delivery

Graduate student ‘Jack’ Hoang Lu works on engineering nanoparticles for targeted drug delivery and diagnostics in the laboratory of Robert Prud’homme, professor of chemical and biological engineering. PHOTO BY CATHERINE ZANDONELLA

Some drugs cannot be delivered via a normal pill or injection because they cannot readily dissolve in water. About 40 percent of new pharmaceuticals have this hydrophobic (water-fearing) character, and like a globule of oil in water, they are unable to reach their targets in the body.

Robert Prud’homme, professor of chemical and biological engineering, addresses this problem by putting the drugs inside of nanoparticles, each about one-thousandth of the width of a human hair, which are then covered with a polymer called polyethylene glycol. The small size enables dissolution of the drug to increase their bioavailability.

Nanoparticles can also tackle a different delivery challenge presented by a growing class of drugs called biologics that, as the name implies, are made from cellular or genetic components. The problem is that they are all water-soluble, which make them easy prey for patrolling proteins that identify them as foreign and degrade them. The solution is similar: nanoparticles protect the biologics long enough for them to carry out their mission.

In addition to increasing the time that drugs spend flowing through the body, Prud’homme’s nanoparticles are capable of targeted delivery. This is necessary in the case of toxic drugs, including many cancer treatments, which would damage healthy cells if allowed to roam freely throughout the body. Prud’homme puts appendages, called ligands, on the outside of his nanoparticles that, due to their specific shape and chemical properties, attach to their target and only to their target. In collaboration with Patrick Sinko at Rutgers University, Prud’homme’s group discovered the optimum density of an appendage called a mannose ligand, used to target cells harboring tuberculosis microbes. The unexpected result was that attaching more appendages to a nanoparticle decreased its targeting effectiveness. This demonstration of the complex interplay between engineered nanoparticles and how the human body responds to them is a major theme of the Prud’homme research team. In addition to tuberculosis, the researchers are using these principles to attack cancer, inflammation, and bacterial infections.

The project receives funding from the National Institutes of Health, the National Science Foundation, Princeton’s IP Accelerator Fund and the School of Engineering and Applied Sciences Old Guard Grant.

–By Takim Williams

Bioengineering: Unlocking the secrets of human health

Bioengineering cover imageBy Takim Williams

RED-HOT RIVERS OF MOLTEN COPPER and aluminum alloys streamed from one receptacle to another. As an undergraduate watching the demonstration in a materials science class, Clifford Brangwynne was reminded of cells migrating through the bloodstream. He realized at that moment that he could mold his interest in materials science and engineering into work that might ultimately have implications for human health.

Bioengineering blood vessel imageScientists like Brangwynne, now an assistant professor of chemical and biological engineering at Princeton, recognize the natural connection between engineering and the life sciences. Their research is setting the groundwork for future applications in health and medicine, including curing diseases such as Alzheimer’s, growing replacement organs and preventing developmental abnormalities. Each of these pursuits hinges on the understanding that living matter obeys the same principles as nonliving matter.

Discovering the relevant principles — and using them to manipulate biological systems to meet our needs — is the goal of the growing field of bioengineering. “The thing that we do that’s different from other scientists who are looking at states of matter and their properties is that we are doing it in the context of living cells,” Brangwynne said. “What is the state of matter inside of a cell and how does that enable biological function?”

Brangwynne gestures toward a can of Gillette shaving foam next to a cylinder of silly putty on his desk and explains that the familiar grade school schema of three states of matter — solid, liquid, gas — is not entirely accurate. There are phases in between, and combinations with their own surprising properties.

“A mound of foam is essentially a solid,” Brangwynne said. “You can push on it and it deforms, and when you take your finger away it springs back into shape. You’ve taken something that is 95 percent gas — it’s mostly air — and 5 percent liquid, and you’ve combined those in such a way that you get a solid.”

Correct biological function depends on transitions between these phases of matter. For example, your blood — typically a free-flowing liquid — clots to form a protective scab. However, these transitions can cause problems, for instance when an internal blood clot causes a stroke.

Likewise, the liquid inside each cell — the cytoplasm — regularly goes through local phase transitions, some of which are disruptive. This issue is linked to neurodegenerative diseases, including Alzheimer’s disease and amyotrophic lateral sclerosis (Lou Gehrig’s disease). In these cases, proteins aggregate and spontaneously transition from a liquid phase into a sticky, solid-like state, prohibiting normal function in the brain or nervous system. These phase transitions are also thought to be involved in controlling cell size and growth, and thus diseases such as cancer.

Nucleoli from amphibian egg cells

Researchers in the Brangwynne lab use nucleoli from amphibian egg cells to study the role of gravity in determining the size of living cells. IMAGE COURTESY OF CLIFFORD BRANGWYNNE LAB

Brangwynne’s research focuses on gaining a better understanding of these living states of matter, and how they can be manipulated. Over the past few years, his group has published several studies exploring the molecules that control intracellular phase transitions and how the living matter within a cell affects gene regulation and cell size.

In one particularly exciting study, graduate student Marina Feric discovered that liquid-phase droplets of RNA and protein are biophysically linked to cell size through the force of gravity. Brangwynne, who receives support from the National Science Foundation (NSF) and the National Institutes of Health (NIH), is optimistic that these fundamental studies will lead to medical applications. “We’re certainly hoping to use our findings to perturb these systems and keep cells in a healthier state,” he said.

Swimming upstream

Like Brangwynne, Professor Howard Stone followed the flow of ideas from an area of engineering — fluid mechanics — to biology. “The living world involves flow almost by definition,” said Stone, who is the Donald R. Dixon ’69 and Elizabeth W. Dixon Professor of Mechanical and Aerospace Engineering. “You circulate blood, you breathe streams of air in and out, you sweat to regulate temperature. If you study fluid mechanics, and if you’re somewhat open-minded, it’s easy to stumble across biological problems.”

One of the biological problems that caught Stone’s attention is how bacteria move in a fluid. Moving through water is far more difficult for bacteria than it is for a human. For single-celled creatures a millionth of a meter long, the force of friction dominates their ability to swim in a given direction. Instead, bacteria are usually just carried along for the ride.

Image of lungs

“The living world involves flow almost by definition.” –Howard Stone, the Donald R. Dixon ’69 and Elizabeth W. Dixon Professor of Mechanical and Aerospace Engineering

The dominance of friction led to a discovery in Stone’s lab four years ago by visiting graduate student Yi Shen, who found that P. aeruginosa, a dangerous pathogen sometimes found in hospitals, can move against a current. The bacterium loses its flagellum — a long tail for swimming — when it adheres to a surface, which for many cells dictates the end of mobility. Yet P. aeruginosa can drag itself along a wall of, for example, a branched medical tube, by its small, tentacle-like pili, which are strong enough to resist the force of friction.

After observing this phenomenon, Stone and his collaborators — Professor of Molecular Biology Zemer Gitai; Albert Siryaporn, an associate research scholar in molecular biology; and Kevin Minyoun Kim, a graduate student in chemistry — began researching this behavior in systems mimicking the human body.

“Your blood vessels have branches. Your lungs are branched. We’ve made model branched systems and used a pump — like a heart — to drive fluid through it,” Stone said. “Bacteria inoculated into this flow sometimes end up in places you wouldn’t expect, and that, at this time, a simulation would never predict.” This basic research, which is supported by NSF, may allow us to better anticipate the movements of pathogens — in our bodies or our environments — in order to prevent infection and contamination.

Fluid environment

Bacteria are single-celled organisms that can form colonies, but a more sophisticated arrangement occurs in our own bodies, where huge communities of cells organize into tissues and organs. Celeste Nelson, an associate professor of chemical and biological engineering, studies the fetal development of these organs, which depends on the fluid environment in which they form.

One of the organs that forms in a fluid environment is the lung. A fetus’s lungs are filled with fluid during gestation. Nelson uses tissue cultures — parts of organs grown in laboratory dishes — and manipulates the speed and pressure of tiny streams of liquid that are directed onto the growing lung cells by small tubes.

Nelson has discovered that the higher the pressure of this fluid in the fetal lung, the more quickly the lungs develop, whereas lower pressure leads to slower development. Several congenital disorders can derail lung development, and Nelson’s work — which is supported by NIH, NSF, the David and Lucile Packard Foundation, the Camille and Henry Dreyfus Foundation, the Burroughs Wellcome Fund, the Essig Enright Family Foundation, and Princeton’s Project X, which provides seed funding for unconventional research — may improve our ability to diagnose such problems early.

The lungs, kidneys, mammary glands and other organs develop through a branched structure, which is an efficient space-filling strategy for functions that require maximum surface area. This exponential branching pattern is a highly reproducible selfassembly process, and in Nelson’s opinion, the forest of alveoli in the lungs is the most beautiful example. “The 23 generations of branches means several hundred million paths,” said Nelson. “Every one of those paths is needed for efficient diffusion of oxygen into the infant blood stream immediately after birth. “What’s amazing,” she said, “is that all of the branches in my lungs look exactly like the branches in your lungs.”

Lung image

Lung tissue extracted from a reptile embryo helps the Nelson lab study the effect of the fluid environment on lung development.

Nelson’s lab also studies a behavior in cancer cells called reversion, which — if it could be induced — would turn many cancers into benign, treatable illnesses. She collaborates with Derek Radisky, a researcher at the Mayo Clinic in Jacksonville, Florida. For Nelson, who started studying breast cancer while a postdoctoral fellow, the body’s organ systems have a mechanical elegance.

Timing is everything

Stanislav Shvartsman is as fascinated by the chemical aspects of development as Nelson is by the mechanical aspects. His research focuses on embryogenesis, the very early stages of fetal development.

“When you want to bake a cake, it’s not enough to say that you need eggs and milk and flour,” said Shvartsman, a professor of chemical and biological engineering and the Lewis-Sigler Institute for Integrative Genomics. “Knowing the ingredients, and even knowing the sequence in which you add these ingredients — which is what we know from genetics — is not enough to bake a cake that tastes good.”

When the recipe — the proper quantities of chemicals released by the cells of the embryo at the proper times — isn’t followed exactly, there are consequences for the developing organism. For example, a large class of developmental abnormalities, known as RAS-opathies, is associated with asymmetry in the craniofacial complex, stunted height, congenital heart defects, developmental delays and other issues. Such defects are observed in one in every thousand births and are believed to be caused by mutations in genes of the Ras-MAPK pathway.

Biologists know which genes are mutated, and even where to find these genes on our DNA. What they don’t know is why these particular mutations lead to a distinct set of clinical features. To find out, researchers turn to organisms that macroscopically look very different from us — such as bacteria and worms — but are very similar at the cellular level. Shvartsman’s research group, which is supported by NIH and NSF, uses the fruit fly to study embryogenesis.

Initially, the handful of cells that make up an embryo are all identical. By the time of birth, that homogenous handful will have given rise to brain, nerve, heart, blood and every other kind of cell required for a living, breathing organism. In order to differentiate into the right kind of cell at the right time, and to arrange into the correct three-dimensional shape, the embryonic cells have to communicate. They speak to each other through a language of chemical signals.

The signals are actually protein molecules, Shvartsman said. A protein released by one cell attaches to a receptor protein embedded in the surface of a neighboring cell. That surface protein reacts by changing shape, and in turn changing the internal environment of its cell. In this way cells “hear” each other. At any given time multiple cells are releasing various proteins, and the combination of signals floating through the embryonic environment tells a cell what to become, or when to divide to make more of itself.

To crack the code, Shvartsman is looking at one signal at a time, beginning with a set of proteins that is well understood genetically thanks to the work of such Princeton biologists as Gertrud Schüpbach, the Henry Fairfield Osborn Professor of Biology. By controlling the amount of these proteins released in the fly embryo, Bomyi Lim, a former graduate student in Shvartsman’s lab and now a postdoctoral research associate at the Lewis-Sigler Institute for Integrative Genomics, has discovered the minimum dosage necessary for proper structural development. This is the first step in a long process, but it is a milestone, and Shvartsman is excited about continuing the process. “It’s very exciting to work in a field where there’s no risk of ever saying, ‘This is the end of the times-table. There is no more material to learn,’” he said.

Image of fruit fly embryo structure

The image shows thin slices of a part of fruit fly embryos where stem cells turn into mature eggs. Created by graduate students Yogesh Goyal and Bomyi Lim and postdoctoral researcher Miriam Osterfield in the laboratory of Stanislav Shvartzman, the image was selected for display in Princeton’s 2014 Art of Science competition.

Some assembly required

Brangwynne views embryogenesis as the epitome of self-assembly, the process by which small, disorganized components interact based on simple rules to form complex structures without human intervention. A classic example is the snowflake, a delicate crystalline jewel formed in midair as water molecules freeze. Engineers have been trying to take advantage of self-assembly for some time — often in Brangwynne’s field of materials science — where time and money could be saved if certain synthetic materials would form on their own in a solution, rather than being painstakingly put together atom by atom.

“The embryo of an organism like C. elegans essentially starts out as just a bag of molecules,” Brangwynne said. Once the egg is fertilized, it begins to organize, and the unstructured soup of molecules turns into a wriggling worm. “There’s absolutely nothing that human engineering can do that comes anywhere close to what I just described takes place in embryos all the time,” Brangwynne said.

While Princeton scientists are importing methods and paradigms from engineering disciplines to biology, they see a two-way street, recognizing that biology itself has methods to share.

“We would like to learn how nature, through hundreds of millions of years of evolution, has generated these systems that are just completely unbelievable in their level of sophistication,” Brangwynne said. “It’s as if we’ve been visited by an alien civilization that was millions of years more advanced than us. The first thing we would do would be to take a really close look at that spaceship. We’d try to figure out what it is made of, what are the principles that govern its flight and its control systems. That’s what we are doing with biological systems.”

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Read more about bioengineering at Princeton:

Lab on a chip is smaller than a penny.Computer chip for point-of-care diagnosis

Assistant Professor Kaushik Sengupta and his team are developing a computer chip-based diagnostic system, which is smaller than a penny but contains hundreds of different sensors for simultaneous detection of disease-causing agents.

‘Jack’ Hoang Lu researches nanoparticles for drug deliveryTiny delivery capsule for new drugs

Graduate student ‘Jack’ Hoang Lu works on engineering nanoparticles for targeted drug delivery and diagnostics in the laboratory of Robert Prud’homme, professor of chemical and biological engineering.

Benjamin TienEngineering health solutions for all

Benjamin Tien, Class of 2015, conducted senior thesis research on nanoparticles for treatment of infections. Now he is a Fulbright scholar working to develop a treatment for excessive bleeding after childbirth.

FOUR PROFESSORS Receive Presidential Science Awards

PECASE award winners

Clockwise from top left: Abigail Doyle, Yael Niv, Ramon von Handel and Rodney Priestley

Four professors received the 2013 Presidential Early Career Award for Scientists and Engineers, the highest honor bestowed by the U.S. government on science and engineering professionals in the early stages of their research careers.

Associate Professor of Chemistry Abigail Doyle, Assistant Professor of Psychology and the Princeton Neuroscience Institute Yael Niv, Assistant Professor of Chemical and Biological Engineering Rodney Priestley, and Assistant Professor of Operations Research and Financial Engineering Ramon van Handel were among the 102 researchers at American institutions selected by the Office of Science and Technology Policy within the Executive Office of the President. The winners received their awards at a White House ceremony on April 14, 2014.

“The impressive achievements of these early-stage scientists and engineers are promising indicators of even greater successes ahead,” President Barack Obama said in a release announcing the award. “We are grateful for their commitment to generating the scientific and technical advancements that will ensure America’s global leadership for many years to come.”

The annual award, established in 1996, recognizes researchers’ “pursuit of innovative research at the frontiers of science and technology and their commitment to community service as demonstrated through scientific leadership, public education or community outreach.”

–By Emily Aronson

Light-splitting crystals from inexpensive ingredients

Photonic crystals

Researchers from Princeton and Columbia universities have proposed a method for growing specialized materials called photonic crystals by ensuring that tiny particles settle into a single uniform crystal structure. Previously, the particles assumed a variety of structures, which made the resulting crystals unsuitable for high-performance uses. At left, particles form the initial two layers of a crystal, labeled A and B. With the addition of the third layer, the crystal forms one of two possible shapes, shown in side views at right. The vertical blue string to the right of each crystal shows a chemical chain that the researchers add to the mix to force one structure to form versus the other.

HIGHLY PURIFIED CRYSTALS that split light with uncanny precision are key parts of high-powered lenses, specialized optics and, potentially, computers that manipulate light instead of electricity. But producing these crystals by current techniques, such as etching them with a precise beam of electrons, is often extremely difficult and expensive.

Now, researchers at Princeton and Columbia universities have proposed a method that could allow scientists to customize and grow these specialized materials, known as photonic crystals, with relative ease.

“Our results point to a previously unexplored path for making defect-free crystals using inexpensive ingredients,” said Athanassios Panagiotopoulos, the Susan Dod Brown Professor of Chemical and Biological Engineering at Princeton. “Current methods for making such systems rely on using difficult-to-synthesize particles with narrowly tailored directional interactions.”

In an article published online July 21, 2014, in the journal Nature Communications, Panagiotopoulos and colleagues propose that photonic crystals could be created from a mixture in which particles of one type are dispersed throughout another material. Called colloidal suspensions, these mixtures include things like milk or fog. Under certain conditions, these dispersed particles can combine into crystals.

Creating solids from colloidal suspensions is not a new idea. In fact, humans have been doing it since the invention of cheese and the butter churn. But there is a big difference between making a wheel of cheddar and a crystal pure enough to split light for an optical circuit.

One of the main challenges for creating these optical crystals is finding a way to create uniform shapes from a given colloidal mixture. By definition, crystals’ internal structures are arranged in a pattern. The geometry of these patterns determines how a crystal will affect light. Unfortunately for optical engineers, a typical colloidal mixture will produce crystals with different internal structures.

In their paper, the researchers demonstrate a method for using a colloidal suspension to create crystals with the uniform structures needed for high-end technologies. Essentially, the researchers show that adding precisely sized chains of molecules — called polymers — to the colloid mixture allows them to impose order on the crystal as it forms.

“The polymers control what structures are allowed to form,” said Nathan Mahynski, a graduate student in chemical and biological engineering at Princeton and the paper’s lead author. “If you understand how the polymer interacts with the colloids in the mixture, you can use that to create a desired crystal.”

The researchers created a computer model that simulated the formation of crystals based on principles of thermodynamics, which state that any system will settle into whatever structure requires the least energy. They found that when the crystals formed, tiny amounts of polymer were trapped between the colloids as they came together. These polymer-filled spaces, called interstices, play a key role in determining the energy state of a crystal. “Changing the polymer affects which crystal form is most stable,” Mahynski said.

Besides Panagiotopoulos and Mahynski, the paper’s authors include Sanat Kumar, a professor and chair of chemical engineering, and Dong Meng, a postdoctoral researcher, both at Columbia. Support for the project was provided in part by the National Science Foundation.

–By John Sullivan

Graphene makes rockets go faster

A material known as graphene, which consists of a single layer of carbon atoms arranged in a chicken-wire pattern, can be manufactured to include ruptures studded with oxygen atoms (red balls). The resulting “functionalized graphene sheets” have been found to make rocket fuel burn faster. (Image courtesy of Annabella Selloni and Roberto Car)

A material known as graphene, which consists of a single layer of carbon atoms arranged in a chicken-wire pattern, can be manufactured to include ruptures studded with oxygen atoms (red balls). The resulting “functionalized graphene sheets” have been found to make rocket fuel burn faster. (Image courtesy of Annabella Selloni and Roberto Car)By Catherine Zandonella

Graphene, the single atom-thick carbon sheet that has garnered attention for its novel electronic properties, can also act as a catalyst in fuels to propel the super-speedy rockets of the future. Researchers at Princeton and Pennsylvania State University collaborated to explore the use of graphene additives to speed up the burn rate of nitromethane, a liquid fuel.

The researchers found that they could speed the combustion rate by about 175 times with the addition of functionalized graphene sheets, which are nearly identical to pristine graphene but have lattice vacancies and oxygen groups sprinkled throughout the layer. “You can think of graphene as a sheet of chicken wire,” said Ilhan Aksay, a key collaborator on the research and a professor of chemical and biological engineering at Princeton. “Functionalized graphene sheets are like chicken wire with ruptures or vacancies in the lattice. These vacancies can contain oxygen groups.”

The vacancies, Aksay said, greatly accelerate the combustion of nitromethane through the exchange of protons or oxygen atoms between the oxygen-containing groups and the fuel. The team made the discovery using computer models that simulate the interactions of atoms, and published the results in the Journal of the American Chemical Society. The first author on the study was Li-Min Liu, a former Princeton postdoctoral researcher now at the Beijing Computational Research Center. The research team included Penn State professor of mechanical engineering Richard Yetter and Princeton researchers Roberto Car, the Ralph W. *31 Dornte Professor in Chemistry; Annabella Selloni, the David B. Jones Professor of Chemistry; and Daniel Dabbs, a research scientist in chemical and biological engineering. The project was funded by the American Recovery and Reinvestment Act (ARRA) through the U.S. Air Force Office of Scientific Research.

-By Catherine Zandonella