Q&A/Arjun Yodh

Arjun Yodh, dirct, LRSMPhoto credit: Candace diCarlo

Arjun G. Yodh, the James M. Skinner Professor of Science, wanted to be a journalist.

But as the son of a physicist, he says his father’s work eventually attracted him to the field. Along with a few gentle paternal pushes, of course.

“I was very one-dimensional,” Yodh says, recalling his younger years. “The only advantage of being one-dimensional, looking back, is you didn’t do as many different things. But if you know what you want to do, you can actually get a lot accomplished.”

Yodh joined the Penn faculty in 1988 after a two-year postdoctoral fellowship at AT&T Bell Laboratories. Today he is the director of the Laboratory for Research on the Structure of Matter (LRSM), the center for materials research at Penn.

When announcing Yodh as the Laboratory’s 10th director in May, Penn President Amy Gutmann said his “demonstrated commitment to collaborating with colleagues from across Penn’s campus has yielded groundbreaking research advances in a number of traditionally disparate fields.”

Yodh says the quality of his colleagues has kept him at the University for more than two decades.

“I have forged great friendships and interesting science collaborations here and I have learned an enormous amount from Penn’s very talented faculty,” he says. “My students and post-docs have also been excellent; after a couple of years, they are usually telling me what to do.”

Yodh’s research focuses on fundamental and applied questions in condensed matter physics, medical and biophysics and the optical sciences. He has a primary appointment in the Department of Physics and Astronomy in the School of Arts and Sciences, with a secondary appointment in the Department of Radiation Oncology in the School of Medicine. He is also a member of the Institute of Medicine and Engineering, the Bioengineering Graduate Group and the Abramson Cancer Center.

The Current recently visited the LRSM to chat with Yodh about the lab, his research and how the lab’s work can benefit us all.

Q. What exactly is the structure of matter?
Materials are made up of atoms, molecules and sometimes even bigger classes of objects like particles and filaments. The structure of matter refers to where these constituents sit or how they are arranged in the material. This is one class of problems of interest to LRSM researchers, but there are many more. The questions we ask are often much broader than that. For example: What is the consequence of a particular arrangement? How does the resultant material respond to forces? How does it respond to light? How is electricity transported through it and does transport depend on the structure? What are the interactions between constituents and how does this affect structure? So there’s a whole set of complex interrelated problems that we work on.

Q. Can you talk a little bit about your research interests?
My research program has two parts. One part is based in condensed matter physics, and the other part is centered in biomedical optics. Originally, the biomedical research grew out of ideas and projects about multiple light scattering that we were pursuing in condensed matter, but now the biomedical program has taken on a life of its own. All of my research uses light in one way or another, so there is significant common experimental ground between the two research groups.

Q. What about your condensed matter research? What does it involve?
Tom Lubensky [a professor of condensed matter theory at Penn] perked my interest in what we call ‘soft matter.’ Soft materials deform easily when pushed. Examples of soft materials range from colloids, emulsions and surfactant suspensions to liquid crystals to cells and sand. It turns out that disorder or entropy plays a dominant role in affecting how many of these materials self-assemble, and we have been having a lot of fun measuring entropic forces, directing self-assembly, creating frustrated media and discerning the ways in which soft matter melts or transforms from one phase to another. We are also studying some hard materials such as carbon nanotubes and graphene with colleagues Jay Kikkawa and Charlie Johnson, but we approach these problems from a soft matter point of view.

Q. In layman’s terms, can you explain the difference between hard and soft material?
When you push on a soft material, it deforms easily. Your hand hurts after you hit a hard material. There are other interesting differences. The physics of thermal soft materials tends to be dominated by entropy effects, often in counter-intuitive ways. Quantum effects tend to be more important in the hard materials.

Q. And the biomedical research? What are you investigating?
As you know, if you take a flashlight and you put it under your hand, some light makes it through to the other side. However, the light does not travel straight through your hand, rather, it travels along a tortuous random path. It turns out that light is scattered so much in tissue that it diffuses in a manner similar to heat flow. We use this diffusion model for light transport to quantify the absorption effects of molecules, such as hemoglobin in tissue and the scattering effects of cells and cell organelles in tissue. In practice, we make measurements of the transmitted light on a tissue surface and then work backwards to figure out things about the physiology of the underlying tissues. How much hemoglobin is in the tissue? How much of that hemoglobin is oxygenated? Is there blood flow? These are the sorts of questions we can ask and answer. These days we are using these ideas in the clinic for breast cancer imaging and stroke monitoring. A lot of the clinicians we work with are excited because the methods are non-invasive, fast, portable and suitable for continuous tissue monitoring.

Q. You mentioned that you at one time wanted to be a journalist before deciding you wanted to be a physicist. Was there a class you took or a professor you had that convinced you that physics was your calling?
I had many good professors and many interesting classes in college and graduate school. It was easy for me to become interested in physics. Physics is a deep subject, and learning physics was, and is, an amazing intellectual journey. One important event for me occurred in high school. I worked one summer at the University of Maryland on an experiment related to the potential for life to arise on Jupiter, and I placed in the Top 40 of the Westinghouse Science Talent Search in my senior year as a result. The experience boosted my confidence.

Q. You pioneered the use of diffuse optics as a tool for medical diagnostics, including the imaging of breast tumors and functional imaging and spectroscopy of the brain. Can you talk a little bit about this work?
A while back I was learning about the ways the physics community was using light to study milky materials. Then I met Britton Chance [the Eldridge Reeves Johnson University Professor Emeritus of Biophysics at Penn] and we started a dialogue about what we might do with these physics ideas in a medical context. We decided to jointly supervise some Ph.D. students on projects of mutual interest and as part of these efforts, we figured out some things about how to understand and analyze diffusing light. The approach has turned out to be very interesting clinically, more so than I had expected when we started. Brit is 96 [years old] now, and we are still collaborating.

Q. How would diffuse optics benefit someone with a breast tumor?
We’re still in a research phase with this problem, but we’re proving, I think, that we can detect and characterize mid-level breast tumors, and that we can get different kinds of information about them, mostly from their hemodynamics. The approach could be of use to patients who are young, because their breasts are fibrotic [and] X-rays are hard to use in this case. The approach could also help with breast cancer patients who are at high risk, for which a lot of screening would be important. Perhaps more interestingly, the approach could be used to routinely and repetitively monitor the responses of tumors to cancer therapies. The ease of use of optics is what may make it useful in the long run.

Q. What sort of faculty does the LRSM contain and what sorts of projects do they work on?
This LRSM is composed of approximately 50 scientists interested in materials in one way or another. Of these, there are small communities or interdisciplinary research groups interested in soft materials ranging from networks and gels to membranes, hard materials including complex oxides and nanoparticles, as well as biomaterials and bio-inspired synthetic constructs. Some of these folks make materials. Theorists work with experimentalists to understand material electronic properties and material responsiveness to environmental changes, and engineers explore new applications of these novel properties. It’s a collective effort that is interdisciplinary by design. I should also note that the LRSM has substantial education and outreach activities whose impact ranges from K-12 students and their teachers to undergraduates and faculty at other institutions locally, nationally and even internationally.

Q. What departments do you collaborate with?
The LRSM has members from practically every department in SEAS, every science department in SAS and a lot of faculty from the medical school.

Q. Is there a field where you think the LRSM’s work could have the most benefit?
There are many interesting frontiers to explore. Bio-inspired materials might find uses in problems ranging from selective stem cell differentiation to drug delivery to curing disease. Energy-inspired materials can add value to battery or solar technologies or the latest green schemes. Novel carbon-based or particle-based materials are inspiring new ideas for electronics and photonics. Novel materials responsivities will give birth to new classes of actuators, and new concepts about the responses of non-thermal media such as granular materials can teach us about how robots can be made to move in sandy environments. Even very basic observations about instabilities of soft materials will be used to control every day substances such as in cosmetics, foodstuffs, paints and pastes.

Originally published on September 3, 2009