HAMMER
STRENGTHENS BIOENGINEERING
by
Michael J. Schwager
A full map of the system of human genes. Better processes to make artificial tissue and organs. New techniques for imaging the body. Controlling cell behavior to treat diseases and improve human health.
Bioengineering is progressing rapidly and in many areas, which has Daniel Hammer, GCH'84, GR'87, fired up. "Explosive growth will take place in these areas over the next decade or so," says Hammer, the newly appointed chair of the Department of Bioengineering. "I took the job because this is a pretty exciting time for bioengineering and biotechnology.
"The human genome project is 12 to 18 months away from being wrapped up-perhaps sooner. There's a promise of molecular medicines based on that discovery. There's also a promise of artificial tissues and artificial organs. Those are going to be developed over the next 5 to 10 years."
Hammer, who received his master's and doctoral degrees from Penn, taught at Cornell from 1988 to 1996 and then returned here to become an associate professor in chemical engineering, with a secondary appointment in bioengineering. Last July he was promoted to full professor, and this February he assumed the bioengineering chair.
The Hammer laboratory is a nationally respected center
of study in cell properties and behavior. "My work," he says,
"is understanding how cells work. A cell is like an automobile. It's
a system. If we change parts of it, how do we change the whole?"
A key part of Hammer's work is adhesion-how cells stick to surfaces. "This," he says, "is useful in understanding how cells move throughout the body."
Cells have receptors, which help determine how and where the cells move. Hammer describes the receptors as traffic signals for motion. "Each type of cell has its own signals. Some cells, for example, are designed to move into lymph nodes and get information from them. Other cells move into the bloodstream. They do this at the rate of millions of cells per minute.
"Molecular makeup determines where cells go and what
they do. Cells often travel out of a blood vessel and into tissue. It's
like a plane landing so that passengers can get out. Which airport does
it land at? How is the cell captured to adhere to the tissue wall?"
The study of cell adhesion is "important both in normal processes and in disease," Hammer says. "Take cancer metastasis. If we understand the factors that control cell movement, we might be able to develop therapeutics. The spread of the cells, rather than the growth of cells, is what usually kills."
How do cancerous cells differ from healthy ones? "The answer to that question motivates us to understand how cells adhere," Hammer says. "One curious thing about tumor spreading is that it's organ specific. The cells form in one organ and spread to another, such as when a patient has melanoma with secondary cancer of the lung. We can do simulations of how the cells bind to surfaces."
In addition, he says, "If we can understand how viruses penetrate cell membranes, we can develop techniques to block them."
Penn's bioengineering department was one of the nation's first. It was founded in 1973, although the University has been offering courses in the field since the 1920s and graduate degrees since 1961. The department started with a handful of faculty members; today it has 21, along with 50 affiliated faculty members. Bioengineering has strong ties with other engineering departments, the life sciences, and the medical school. The Institute of Medicine and Engineering, which the engineering and medical schools established in 1996, offers a "campus-wide institute dedicated to the interface of medicine and engineering."
A sense of pride shows as Hammer speaks of bioengineering faculty members and their strengths. "Examples of people in the forefront of their fields are Leif Finkel and Kwabena Boahen, who are experts in neurocomputing. We have the best injury group in the world, with Susan Margulies, David Meaney, and Tracy Macintosh, a professor of neurology. We also have a fine group in orthopedic bioengineering: Paul Ducheyne, Sol Pollack, and Lou Soslowsky in orthopedics.
"Dan Bogen runs a wonderful project, PennToys. The idea is to understand the design of functional toys-robotics in a sense-that have unique designs. In rehabilitation, toys can elicit functional responses from children. PennToys has been quite successful in research and educating students in design."
The labs of Hammer and Dennis Discher, assistant
professor of mechanical engineering, have collaborated in using polymers
to make the first "synthetic cells." "The polymers,"
Discher says, "have, simultaneously, both an oil- and a water-like
character to them. This leads them to self-assemble in water into membranes
very similar to those of cells. But the polymer membranes prove to be
very robust compared with those of cells, opening up new possibilities
in fields ranging from drug delivery to artificial tissues.
"The structures are biocompatible in cell culture and are just now being tested in animals. We reported initial results in a May 1999 issue of Science."
The artificial cells-called polymersomes-have the potential to deliver drugs and carry oxygen. Says Hammer, "We use porous biodegradable microspheres. We can make them of many different polymers and can load them in a drug. The idea is to target them for specific locations."
Polymersomes might also prove useful as an artificial
blood substance that could be easily stored. Hammer sees applications
in areas such as battlefields, space travel, and preventing the transmission
of disease, which can occur with the usual blood supply.
"What we're researching is passive material,"
he says. "Does the body respond to it? That remains to be tested.
Is the polymer cleared from the kidney? We don't know yet."
Nature has instances of alien tissue that the body tolerates. "There are examples of that in nondisease processes," Hammer says. "For example, E. coli in your colon is useful. It does some degradation of waste, and the body doesn't try to eliminate it."
Surrounded by two-phase contrast microscopes, laminar-flow
hoods, carbon-dioxide incubators, refrigerated centrifuges, monitors,
and a bevy of other high-precision instruments, Aaron Rabinowitz
speaks about Hammer in glowing terms. "Dan is a tremendous researcher,"
says Rabinowitz, a second-year doctoral student in chemical engineering.
"He's the authority on cell rolling and adhesion. He's built a great
career on that. And he has a great lab with great students, and grants
from prestigious funders."
Right now, Hammer is hoping to find funders for a new home for his department. "We've put together a proposal to build a new building that would house bioengineering. We would like to secure funding from a foundation to help pay for the building and the facilities within it. Our goal is to build a 50,000-square-foot, first-class teaching and research facility for bioengineering. "Our department is known for excellence in its teaching and labs. Teaching will be center stage."
Jacob Fisher, a graduate student in bioengineering, sat on the search committee that brought Hammer to the chairmanship. "Dr. Hammer and I have interacted at the departmental level, he as BE department chair and I as president of the BE graduate student body," Fisher says. "Soon after he took the position, he invited me to speak with him about graduate student concerns.
"He is developing a departmental seminar series, and he asked for our suggestions for various faculty/grad student events. He has also taken an interest in our request for a new student lounge."
Jenny Li, a bioengineering senior and president
of the Society of Bioengineering (the undergraduate student organization),
echoes Fisher. "After Dr. Hammer's official appointment as the chair
for bioengineering, I met with him to discuss the condition of the undergraduate
student body and the bioengineering curriculum. He was very eager to hear
what the students had to say regarding the department and the curriculum."
Li speaks, too, about Hammer and his work. "His research is definitely nationally recognized in the field of bioengineering. He is young and very energetic. He has a great vision of making Penn bioengineering the top department in the nation, and I believe he will achieve this vision with the support of the university."
One source of support comes from Dean Eduardo Glandt.
"Dan Hammer is one of a number of young leaders at the national level
in bioengineering," Glandt says. "He has been on a very fast
upward trajectory. He has become a force of nature: a large intellectual
presence who has brought a wonderful, large, scholarly operation."
Bioengineering is a "rapidly growing field," Glandt says. "There's
an explosion today-it's becoming an exact science, as opposed to an empirical
science. That allows the merger of science and technology. My belief is
that biology will affect every field of engineering. Materials play a
part in bioengineering. So does electrical engineering. Surprisingly,
computer science. After all, DNA is a large piece of code. Biomedical
engineering and biotech-nology constitute a major strategic direction
for the whole engineering school."
Traditionally, Hammer says, the bioengineering department
has been device oriented. "We've been strong in a program called
neuromorphic silicon-using chips for artificial vision or intelligence.
We've also done neurological computing and have a long history of medical
devices and implants. And we have a long history in injury mechanics-how
cells and tissues are changed after injury."
Consistent with the field's growth, Hammer intends to steer bioengineering
into new areas of study. His work in cell and tissue engineering broadens
the department's scope. "We haven't had a strong effort in that before.
It was supplemental to previous work, and it started when the Institute
of Medical Engineering was born [in 1996]. We will add more people in
cell and tissue engineering. We will build on the strengths we have and
add to them."
