“`html
Sujit Datta‘s gaze brightens, and he beams when discussing “squishy” substances like mucus and various polymeric liquids. As a professor of chemical engineering, bioengineering, and biophysics at Caltech, he explores the movement and behavior of bacteria, fluids, and other soft, adaptable materials within the intricate settings where they are usually located—from soils and sediments to biological tissues and gels. Datta’s team, affectionately dubbed “The Squishy Lab,” employs a blend of experiments, theoretical modeling, and computational simulations to deepen our understanding of the fundamental principles that govern these systems and their myriad applications.
Datta earned his undergraduate degree in mathematics and physics at the University of Pennsylvania, where he also attained a master’s in physics. He subsequently received his PhD in physics at Harvard University, concentrating on fluid dynamics and instabilities in soft and disordered materials such as porous subterranean rocks and chemical microcapsules.
When Datta joined the faculty at Caltech in 2024, it felt like a return to his roots. Most recently, he had been at Princeton University, beginning in 2017 as an assistant professor; he was elevated to associate professor and director of graduate studies in chemical and biological engineering in 2023. Prior to that, he had been a postdoctoral researcher in chemical engineering at Caltech, investigating biophysical processes in the gut under the guidance of Rustem Ismagilov, the Ethel Wilson Bowles and Robert Bowles Professor of Chemistry and Chemical Engineering; Merkin Institute Professor; and head of the Jacobs Institute for Molecular Engineering for Medicine.
Datta’s diverse training is reflected in his current research, which integrates concepts and techniques from fields such as microscopy, materials science, chemical dynamics, and polymer physics. His team’s discoveries are pertinent across various domains, including medicine, public health, biotechnology, energy, and sustainability.
Datta was recently appointed chief editor of the journal Reviews of Modern Physics. He has also been honored with a multitude of awards, including the American Institute of Chemical Engineers’ Allan P. Colburn and 35 Under 35 Awards, multiple accolades from the American Physical Society; the American Chemical Society’s Unilever Award; and a National Science Foundation CAREER Award.
We met with Datta outside the Red Door Café on the Caltech campus to inquire about his research and what makes all this squishy material so intriguing.
Firstly, could you elaborate on the principal themes of your research and what captivates you about the physics of squishy materials?
Soft materials, or “squishy” substances, intrigue me because they are everywhere, yet they can exhibit unexpected behaviors. Take toothpaste, for instance. Generally, we categorize materials as solids, liquids, or gases. So, is toothpaste a solid or a liquid? The answer is both. It flows like a liquid when squeezed from the tube but retains its form like a solid when undisturbed. This behavior arises from the microscopic structure of toothpaste: a blend of tiny mineral particles and elongated molecules known as polymers, which are easy to deform and weakly bonded. Due to the numerous weak interactions among these microscopic elements, toothpaste occupies a gray area between conventional solids and liquids, transitioning between the two states with the slightest pressure.
What truly fuels my research is the acknowledgment that for years, the majority of investigations on squishy materials have taken place in controlled, idealized lab environments. We analyze bacteria in test tubes, test polymers in simplistic shapes, and study gels in isolation. However, in reality—be it bacterial biofilms developing within the thick mucus of our lungs or polymer solutions flowing through intricate pore networks in underground rock formations to extract trapped pollutants—these materials usually inhabit complex environments. My team aims to comprehend how external factors influence the behavior of squishy substances and how these substances, in turn, modify their surroundings.
Can you share an example of a particular problem that intrigues you?
One of our recent investigations explored the growth of bacteria in polymeric solutions such as mucus. My interest sparked from its link to cystic fibrosis, characterized by thicker, more concentrated mucus in the lungs. Patients with cystic fibrosis frequently succumb to infections originating within this denser mucus. Yet, most laboratory studies on bacteria focus on their behavior in simpler polymer-free liquid cultures. We decided to say, “Alright, let’s start examining how bacteria proliferate in that type of mucus to uncover some insights.”
Our findings revealed that within mucus, bacteria surprisingly form unusual cable-like structures, ultimately knitting themselves together to create something resembling a living gel. This is quite unlike what we observe in other liquid environments. In a typical liquid, cells proliferate, eventually dividing into two distinct cells that separate and diffuse away. This cycle repeats, resulting in a scattering of isolated cells. In mucus, while the cells still grow and divide, we discovered that they remain interconnected, end to end, instead of separating. As this process continues, they grow into long, beautiful cables that enhance their cohesion.
Your research encompasses experimentation along with simulations and theory. Could you discuss how these different aspects of your work interrelate?
Typically, driven by some intuition or curiosity, we design meticulous experiments to visualize phenomena that we have not observed before. This often leads to some unexpected discoveries because nature is endlessly surprising and far more compelling than anything we could ever conceive.
When an intriguing result arises from our experiments, we strive to understand why it occurred. This is where theory and simulations come into play. We draw on concepts from a wide range of disciplines—biological physics, polymer physics, statistical physics, fluid dynamics, physical chemistry, whatever is necessary. Guided by clues from our experiments, we apply these ideas to create theoretical models that incorporate the minimal essential components to replicate the phenomena we observe. If successful, this allows us to make further predictions we can also test. It forms a feedback loop.
Often, our initial hypothesis turns out to be incorrect. So, we return to the drawing board and ask, “What did we overlook?” We incorporate that insight, test predictions, and repeat the process. Once we reach a stage where we feel we have genuinely captured the essential elements, we possess a mathematical model that may help in generalizing our findings more broadly. That is the strategy we adopt in our research.
Could you share some more “greatest hits” from your lab?
Absolutely! I can share numerous examples. I cherish everything we undertake—it’s tough to choose. However, let me give you a couple of highlights. A few years…
“““html
Previously, we posed a very straightforward inquiry: How do bacteria proliferate? Not on a 2D surface as is usually observed in laboratories, but within a 3D setting, resembling many natural bacterial environments.
Throughout the years, we constructed an experimental setup to visualize and examine bacterial behavior in 3D. We can even 3D print microbial groups and engage in all sorts of fascinating experiments with them.
We utilized the system to merely observe bacteria developing in 3D. Our findings revealed that, in contrast to growth on a 2D surface, bacterial colonies assume jagged forms that resemble broccoli. This phenomenon has been documented in various natural occurrences of bacteria, yet it has remained unexplained. Informed by our experiments, we devised a basic model to clarify the reason behind this. It illustrates a fundamental characteristic of cellular growth in 3D—when a colony of cells reaches a substantial size, the outer cells absorb nutrients from the surrounding environment, leading to nutrient scarcity for the inner cells. Since growth is restricted to a shallow surface layer, random variations in growth dominate and give rise to this peculiar broccoli-like shape. This was something we managed to capture using a basic model. With this fresh insight, we now have a method to quantitatively frame further scientific inquiries. For instance, we are continuing to investigate how these growth patterns shift among communities of differing cell types and what the physiological consequences might be.
Another illustration arises from a completely different focus in my team, which involves fluid dynamics and transport phenomena in inert systems. Individuals employ polymer solutions in a range of industrial applications, pumping them through porous materials—such as porous rocks, soil, or filters. In the 1960s, it was observed that when these solutions are pumped through a porous medium, their viscosity increases—they become thicker. Essentially, the faster you pump, the more challenging it becomes to pump, which was quite unexpected. This puzzle had persisted for an extended period.
Consequently, we designed meticulous experiments to directly observe the flow within porous materials, and we were astonished to discover that these fluids generated what appeared to be turbulence. They exhibited chaotic flows—even in conditions where turbulence would typically not be anticipated. We crafted a very straightforward model to account for that observation, tested it, and refined it. It turns out that all the agitation within the turbulence-like flow leads to significantly increased energy loss and a rise in fluid viscosity. Utilizing our final model, we devised predictions for a specific polymer solution and a particular porous medium, enabling us to quantitatively forecast the viscosity increase. Thus, in addition to uncovering something fundamental about fluid dynamics in intricate spaces, our research provided insights for professionals utilizing these types of fluids in practical scenarios.
We enjoy asking if you have any interests outside your professional life.
I certainly do! In the past, I was a competitive kickboxer. Those times may be behind me, but I remain actively engaged in running and fitness. One of my greatest pastimes is exploring Los Angeles with my 6-year-old. Additionally, I take great pleasure in cooking. Everything I do during the day is precision-oriented, so cooking is where I allow creativity and spontaneity to flourish.
“`